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ORGANIC PRODUCTION OF GRAFTED HEIRLOOM TOMATOES: NEMATODE MANAGEMENT, FRUIT QUALITY, AND ECONOMICS
By
CHARLES EDWARD BARRETT
A THESIS PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT
OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE
UNIVERSITY OF FLORIDA
2011
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© 2011 Charles Edward Barrett
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To my grandfather, one of my biggest inspirations
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ACKNOWLEDGMENTS
I thank Dr. Xin Zhao for all of her help and guidance throughout this two year
journey. I thank my committee of experts Dr. Robert McSorley, Dr. Charles Sims, and
Dr. Alan Hodges. I am very grateful for all of their excellent advice that made this project
possible. I am lucky to have a great family that was interested in my research even if at
times it was just to humor me. I thank my girlfriend Paola Ferst for sticking by me
through good or bad and for keeping me honest. My friend Joshua Adkins really pushed
me to achieve my goals and gave me tips, editorial help, and someone to enjoy a cold
beverage with. Thanks to Jorge for being someone to drink coffee with and not think
about all the things I had to do.
Thank you to: Dr. Cantliffe for allowing me this opportunity, Dr. Brecht for advice
and postharvest help, Dr. Huber for answering my random questions and being one of
the best listeners I‟ve ever met, and Dr. Stall for answering the gray wall mystery. I also
thank Desire, Wenjing, for being excellent lab mates and for all their help. My field trials
could not have been better thanks to the expertise of Buck Nelson, Timmy, and the rest
of the crew at the PSREU. Steffen and Chris were my efficiency experts and made my
field work happen even though the biodiversity of organic farming was a little unnerving
at times.
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TABLE OF CONTENTS page
ACKNOWLEDGMENTS .................................................................................................. 4
LIST OF TABLES ............................................................................................................ 6
LIST OF FIGURES .......................................................................................................... 7
ABSTRACT ..................................................................................................................... 8
CHAPTER
1 INTRODUCTION .................................................................................................... 10
2 GRAFTING FOR ROOT-KNOT NEMATODE CONTROL AND YIELD IMPROVEMENT IN ORGANIC HEIRLOOM TOMATO PRODUCTION.................. 15
Background ............................................................................................................. 15 Materials and Methods............................................................................................ 17 Results and Discussion........................................................................................... 21
3 FRUIT QUALITY AND SENSORY ATTRIBUTES OF ORGANIC HEIRLOOM TOMATOES ARE NOT INFLUENCED BY GRAFTING .......................................... 33
Background ............................................................................................................. 33
Materials and Methods............................................................................................ 34
Results and Discussion........................................................................................... 39
4 COST BENEFIT ANALYSIS OF USING GRAFTED TRANSPLANTS FOR ROOT-KNOT NEMATODE MANAGEMENT IN ORGANIC HEIRLOOM TOMATO PRODUCTION ....................................................................................... 45
Background ............................................................................................................. 45
Materials and Methods............................................................................................ 47 Results and Discussion........................................................................................... 51
5 CONCLUSION ........................................................................................................ 63
LIST OF REFERENCES ............................................................................................... 65
BIOGRAPHICAL SKETCH ............................................................................................ 69
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LIST OF TABLES
Table page 2-1 Effect of grafting treatments on root-knot nematode galling ratingsz of
heirloom tomato cultivars Brandywine and Flammey. ......................................... 28
2-2 Effect of grafting treatments on leaf area and above-ground biomass of heirloom tomato cultivars Brandywine and Flammez. ......................................... 29
3-1 Consumer demographic information. .................................................................. 42
3-2 Effect of grafting treatments on heirloom tomato fruit sensory attributesz for scion cultivars Brandywine and Flamme. ........................................................... 43
3-3 Effect of grafting treatments on heirloom tomato fruit quality attributesz for scion cultivars Brandywine and Flamme. ........................................................... 44
4-1 Sources and prices for materials used to produce grafted and nongrafted heirloom tomato transplants. .............................................................................. 57
4-2 Costs of grafted and nongrafted organic heirloom tomato transplants.z ............. 58
4-3 Estimated partialz net return per plant ($/plant) for nongrafted „Brandywine‟y plants grown organically with low root-knot nematode pressurex. ...................... 59
4-4 Estimated partialz net return per plant ($/plant) for plants of „Brandywine‟y grafted onto the rootstock „Multifort‟x grown organically with low nematode pressurew. ........................................................................................................... 60
4-5 Estimated partialz net return per plant ($/plant) for nongrafted „Brandywine‟y plants grown in a transitional organic field with high nematode pressurex. ......... 61
4-6 Estimated partialz net return per plant ($/plant) for plants of „Brandywine‟y grafted onto the rootstock „Multifort‟x grown in a transitional organic field with high nematode pressurew. .................................................................................. 62
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LIST OF FIGURES
Figure page 2-1 Cumulative marketable yield for nongrafted and grafted heirloom tomato
cultivars Flamme (A) and Brandywine (B) from the organic field trial conducted in 2010.. ............................................................................................ 30
2-2 Cumulative marketable yield for nongrafted and grafted heirloom tomato cultivars Flamme (A) and Brandywine (B) from the organic field trial conducted in 2011.. ............................................................................................ 31
2-3 Cumulative marketable yield for nongrafted and grafted heirloom tomato cultivars Flamme (A) and Brandywine (B) from the 2011 field trial designed to reflect a transition period from conventional to organic.. .................................... 32
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Abstract of Thesis Presented to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Master of Science
ORGANIC PRODUCTION OF GRAFTED HEIRLOOM TOMATOES: NEMATODE
MANAGEMENT, FRUIT QUALITY, AND ECONOMICS
By
Charles Edward Barrett
December 2011
Chair: Xin Zhao Major: Horticultural Science
Growers are looking for sustainable alternatives to methyl bromide as a soil
fumigant that are effective and economical. Increased demand for organically produced
fruits and vegetables has also contributed to the need for ecologically friendly soilborne
disease control methods. Grafting may be a valuable tool for vegetable growers but
concerns regarding the disadvantages and challenges associated with grafting must be
addressed before grafting will be widely used in the United States.
There were four objectives carried out with this two-year study. The first objective
was to determine if grafting heirloom tomatoes onto interspecific or intraspecific
rootstocks could be effective for root-knot nematode control under organic production in
Florida. The second objective was to assess the influence of grafting treatments on
yield and crop vigor. The third objective was to determine if grafting treatments affect
fruit quality attributes. The final objective was to determine if grafting to overcome root-
knot nematodes could be cost effective on an organic farm.
Three spring field trials were conducted, one in 2010 (organic) and two in 2011
(organic and transitional). Treatments included the heirloom tomato scions „Brandywine‟
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and „Flamme‟ grafted onto the rootstocks „Multifort‟ (interspecific) and „Survivor‟
(intraspecific), and nongrafted and self-grafted scion controls. In 2010, no root-knot
nematode galls were observed and total marketable yields were not significantly
different within scion treatments. In 2011, galls were observed on roots in every
treatment in both field trials. The rootstocks reduced galling by 89% on average in the
organic field trial. Under severe nematode pressure in the transitional field trial, the
scion „Brandywine‟ grafted onto „Multifort‟ produced significantly higher marketable
yields than nongrafted and self-grafted „Brandywine‟ treatments. Although it appeared
that the rootstock „Survivor‟ may have had a negative effect on sensory attributes for the
scion „Brandywine‟, this trend was not observed in the 2011 taste tests. There were no
differences in fruit nutritional contents. Grafted and nongrafted transplants were
estimated to cost $0.78 and $0.17, respectively. Sensitivity analyses conducted using
these estimated transplant production costs revealed that under severe root-knot
nematode pressure, grafting may be an economically feasible soilborne disease control
option. This study demonstrated that grafting could be successfully implemented for
root-knot nematode control in organic heirloom tomato production. The yield of grafted
tomatoes was influenced by the rootstock-scion interaction and the root-knot nematode
population. The use of nematode-resistant rootstocks did not have a significant impact
on tomato quality attributes. Grafted transplants do cost more to produce, but can
reduce the risk of economic crop losses due to root-knot nematodes.
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CHAPTER 1 INTRODUCTION
Grafting is a horticultural technique that fuses two or more different plants together
to grow as one plant. The plant (s) that provides the shoot, leaves, and fruit is (are)
referred to as the scion. The roots are provided by a plant called the rootstock.
Commercial grafting has been used in the production of fruit trees (e.g. peach, apple,
citrus) and vegetables (e.g. tomato, eggplant, melon). Records of tree grafting date
back hundreds of years, whereas early vegetable grafting records date back to only the
1920‟s (Lee, 1994). Vegetable grafting began as a method to overcome fusarium wilt
(Fusarium oxyysporum) in watermelon (Lee, 1994). In addition to improved resistance
to soilborne pathogens and diseases such as root-knot nematodes, verticillium wilt,
southern blight, and bacteria wilt; grafted vegetables often demonstrate greater vigor,
enhanced nutrient and water uptake, and improved tolerance to environmental stresses
like soil salinity, low temperature, and flooding (King et al., 2010; Lee et al., 2010;
Louws et al., 2010; Schwarz et al., 2010). Vegetable grafting is currently widely used in
greenhouses, high tunnels, and some open-field producing areas in many Asian and
Mediterranean countries (Lee et al., 2010). Japan and Korea are among the leaders in
growing grafted vegetables using an estimated 721.3 million and 766.3 million grafted
transplants a year, respectively (Lee et al., 2010).
An estimated 40 million grafted transplants are used each year in the United
States (Kubota et al., 2008). However, grafted transplants in the United States are
almost completely isolated to use in the greenhouse tomato industry (Kubota et al.,
2008). Growers in the United States are concerned with the disadvantages associated
with grafting (Lee et al., 2010). The cost of grafted transplants is a major barrier
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preventing growers from adopting this technique (King et al., 2008; Kubota et al., 2008;
Kubota, 2008; Lee et al., 2010; Rivard et al., 2010b). In a recent study, estimated prices
for nongrafted tomato transplants in the United States ranged from $0.13 to $0.51, while
price estimates for grafted tomato transplants ranged from $0.59 to $1.25 ($1.88 after
markup) (Rivard et al., 2010b). According to Lee et al. (2010), grafted vegetable
transplants were estimated to cost $0.40 to $1.20. If grafted transplants are to be used,
a grower will need to know how these higher initial costs will be recovered.
Productivity of grafted vegetables may be directly related to the economic
feasibility of the adoption of grafting technology. If yields are maintained or reduced as a
result of grafting, and all other costs are held constant, the grower never makes up the
extra cost incurred for the grafted transplants and therefore profits are reduced.
However, if a grower experiences higher yields, some or all of that cost could be
recovered. In Florida, growers fumigating with expensive pesticides for root-knot
nematodes (RKN) and other soilborne pathogens, could also reduce some production
expenses by using grafted transplants instead of fumigating (King et al., 2008).
Nematodes are a major problem in the southern United States and worldwide (Rivard et
al., 2010a; Roberts et al., 2005; Sasser, 1980). Warm temperatures, sandy soils, and
excess moisture create an ideal habitat for nematodes (Roberts et al., 2005). Conditions
in Florida in the spring and fall growing seasons are usually highly favorable for
nematode populations to cause economic crop losses on susceptible crops. While many
commercial cultivars have resistance to root-knot nematodes among other soilborne
pathogens, there is a lack of such resistance in heirloom tomatoes (Rivard and Louws,
2008).
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In contrast to the conventional production systems, organic farmers have fewer
options for soilborne disease control (Rivard and Louws, 2008). Some disease
management practices such as crop rotation may be space prohibitive due to the
smaller size of many organic farms. Crop rotation can also take many years to be
effective, which often requires more land in rotation to keep productive land available.
Crop rotation may be less effective if the pathogen has a wide range of hosts. Grafting
with resistant rootstocks can be rapidly incorporated into integrated pest management
practices for controlling soilborne diseases. Resistant rootstocks can effectively act as a
non-host plant in crop rotations with susceptible cultivars.
Organic markets in the United States have grown steadily for over a decade and
one emerging problem in the organic sector is a lack of supply (Greene et al., 2009).
Grafting could offer stability to these markets by promoting more competitive plants and
a reduced risk of crop failure (Taylor et al., 2008). Some growers in Florida and North
Carolina have begun experimenting with grafting on their farms in an attempt to
overcome soilborne pathogens for heirloom tomato production (grower pers. comm.;
Kubota, 2008; Rivard et al., 2010a). However, systematic studies on grafted heirloom
tomatoes are scarce, particularly under Florida conditions.
Heirloom tomatoes with distinct flavor and quality attributes represent a popular
niche market for local organic and small growers (Jordan, 2007). It has been suggested
that many commercial varieties of fruits and vegetables have lost much of their flavor
because modern breeding has targeted developing commodities with longer shelf lives
and better shipping capabilities (Klee, 2010). Breeders are now looking into heirloom
cultivars as sources for flavor genes (Klee, 2010). Grafting can allow for immediate use
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of disease resistant genes from rootstocks while maintaining the outstanding flavor
afforded by heirloom scions. Although Rivard et al. (2010a) showed that grafted
transplants can be used to effectively control southern blight and root-knot nematodes,
sensory attributes and nutritional content of the fruit was not mentioned. A previous
greenhouse study by Di Gioia et al. (2010) showed that soluble solid content, titratable
acidity, and sensory profiles of heirloom tomato fruit were not affected by grafting onto
interspecific rootstocks, whereas vitamin C content was reduced as a result of grafting.
Grafted vegetable research has yielded mixed results regarding the affects of grafting
on fruit quality attributes, possibly due to the use of varying scion-rootstock
combinations, growing environments, seasons, and grafting methods (Edelstein, 2004;
Martínez-Ballesta et al., 2008; Rouphael et al., 2010).
The influence of grafting on fruit taste and fruit quality of different scion-rootstock
combinations deserves more attention as it may impact the adoption of this technique.
Conventional growers are paid based on fruit weight and may be less concerned about
taste and nutritional content than the organic or smaller market farmer. Small farmers
often have a close connection with the purchasers of their produce and therefore have
more to lose if grafting affects fruit taste or fruit quality. Organic farmers are in a unique
position to gain from grafting because consumers are willing to pay more for organic
produce, and produce with better taste (Greene et al., 2009; Klee, 2010).
Four main research objectives were explored in this two-year study. One objective
was to determine if grafting heirloom tomatoes onto different rootstocks, i.e.,
interspecific and intraspecific, can be used for root-knot nematode control in organic
production in Florida sandy soils. Another objective was to assess the influence of
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grafting on crop vigor and yield of heirloom tomato scions. A third objective was to
determine the effect of grafted treatments on fruit quality and sensory attributes. Finally,
sensitivity analyses were performed to estimate the economic feasibility of integrating
heirloom tomato grafting on an organic farm.
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CHAPTER 2 GRAFTING FOR ROOT-KNOT NEMATODE CONTROL AND YIELD IMPROVEMENT
IN ORGANIC HEIRLOOM TOMATO PRODUCTION
Background
Modern tomato breeding has led to improvements in postharvest attributes but this
has come with a noticeable decrease in fruit flavor (Klee, 2010). Educated consumers
have begun demanding heirloom tomatoes for their superior flavor and unique appeal
(Bland, 2005; Jordan, 2007; Klee, 2010). This increased interest has helped expand a
niche market for local organic growers (Jordan, 2007). However, heirloom tomatoes can
be difficult to grow in Florida due to imminent pest and disease pressure. One of the
major pest management challenges are root-knot nematodes (Meloidogyne spp.) which
thrive in warm weather and moist, sandy soils (Roberts et al., 2005; Sasser, 1980).
Root-knot nematodes (RKN) cause root galls that damage the root system and result in
stunted plant growth and significant yield loss. RKN persist in the soil for many years
and have a broad host range. These characteristics make RKN difficult to control on
organic farms. The small size of many organic farms may prevent utilization of the long
rotation times needed to ameliorate soil conditions between susceptible crops.
Organic growers often face pest and disease challenges with few effective control
methods, making organic heirloom tomato production even more difficult and potentially
less profitable than conventional production (Rivard and Louws, 2008; Rivard et al.,
2010a). With the use of appropriate rootstocks, grafting may be a useful technique for
vegetable producers to overcome soilborne pathogens including RKN. Vegetable
grafting began in Japan and Korea in the 1920‟s to manage fusarium wilt (Fusarium
oxysporum Smith) in watermelons and is currently widely used in cucurbitaceous and
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solanaceous crop production in Asian and Mediterranean countries (Lee, 1994; Lee et
al., 2010).
Recently, investigators have begun examining vegetable grafting as a tool for
United States producers. This research has focused on: grafted seedling production,
use, and economics (Kubota et al., 2008; Rivard et al., 2010b); grafting as an alternative
to methyl bromide in field production (Freeman et al., 2009); and the use of resistant
rootstocks for controlling soilborne diseases and RKN (Bausher, 2009; Lopez-Perez et
al., 2006; Rivard and Louws, 2008; Rivard et al., 2010a). With the phase out of methyl
bromide for soil fumigation and the continued rise in demand for organic produce in the
United States, the need for alternative disease control methods that do not rely on
synthetic biocides has increased (Greene et al., 2009; King et al., 2008; Louws et al.,
2010).
Intraspecific tomato hybrids (Solanum lycopersicum L.) and interspecific tomato
hybrids (S. lycopersicum xS. habrochaites S.Knapp & D.M. Spooner) have been
employed worldwide as disease resistant rootstocks in grafted tomato production (King
et al., 2010). It is unclear how the differences between intraspecific and interspecific
hybrid tomato rootstocks will affect field-grown indeterminate heirloom tomatoes.
Hence, rootstock evaluations for heirloom tomato production in open field conditions
should involve both types of rootstocks. Grafting has been used to successfully produce
heirloom tomatoes in a North Carolina organic system by effectively managing bacterial
wilt (Ralstonia solanacearum (Smith) Yabuuchi et al.) and fusarium wilt (Rivard and
Louws, 2008). Additionally, it was shown that southern blight (Sclerotium rolfsii Sacc.)
and southern RKN [M. incognita (Kofoid & White) Chitwood] could be managed by
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grafting heirloom tomatoes onto interspecific hybrid rootstocks (Rivard et al., 2010a).
Interest in tomato grafting is emerging among small and organic growers in Florida. The
results from these North Carolina studies are promising and suggest that grafting may
be applicable in Florida heirloom tomato production. However, appropriate rootstocks
for Florida conditions need to be determined.
The purpose of this study was to assess heirloom tomato grafting for RKN control
under organic production in naturally infested Florida sandy soils. It is hypothesized that
grafting onto resistant rootstocks can reduce nematode galling incidence. Intraspecific
and interspecific hybrid rootstocks were compared with respect to their influence on
nematode resistance, crop vigor, and fruit yield.
Materials and Methods
Scion and rootstock cultivars. Grafted tomato seedlings were produced using
certified organic heirloom tomato seed and commercially available non-treated rootstock
seeds. The heirloom tomato cultivars Brandywine and Flamme were used as nongrafted
controls and as scions (Tomato Fest, Little River, CA). „Brandywine‟ (BW) is a large,
red, open pollinated, indeterminate variety valued for its excellent flavor and large size.
„Flamme‟ (FL) is a golf-ball-sized, orange, open-pollinated, indeterminate variety.
„Multifort‟ (De Ruiter Seeds, Bergschenhoek, The Netherlands) and „Survivor‟ (Takii
Seeds, Salinas, CA) were used as rootstocks. „Multifort‟ (MU) is an interspecific (S.
habrochaites xS. lycopersicum) hybrid and „Survivor‟ (SU) is an intraspecific (S.
lycopersicum) hybrid. Both rootstocks were chosen for their high resistance to soilborne
pathogens, root-knot nematodes (Meloidogyne spp.) and vigorous growth habit.
Transplant production. Rootstock seeds were sown two days before scion seeds
on 16 Feb. 2010 and 11 Feb. 2011. Seedlings were grown in Fafard Organic Formula
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Custom potting mix (Apopka, FL) using 128-cell-count Speedling Flats (Sun City, FL). At
the 4-5 true leaf stage, seedlings were tube grafted. Grafting procedures were adapted
from Rivard and Louws (2006) in which young seedlings are grafted and held together
using 2.0-mm or 1.5-mm silicon clips (Hydro-Gardens, Colorado Springs, CO). Grafting
took place 34 d and 28 d after scions were sown for 2010 and 2011, respectively. The
grafted seedlings were then placed in a temperature and humidity controlled walk-in
cooler at 25 °C and ~95% RH with no light for 24 hr. Thereafter, the grafted seedlings
were gradually exposed to light, and humidity was reduced for 6 d until the seedlings
were healed. The grafted seedlings were then transported to the greenhouse to harden
off before transplanting into the field.
Field trials. Three field trials were conducted at the University of Florida Plant
Science Research and Education Unit in Citra, FL. One trial was conducted in the
spring of 2010 while two were conducted in the spring of 2011. In both years, one trial
was grown on certified organic land following the rules outlined by the National Organic
Program (U.S. Dept. Agr., 2002). The organic research land was certified by Quality
Certification Services (Gainesville, FL). Organic yellow squash (Cucurbita pepo L.) was
grown during the 2010 fall growing season to encourage a natural RKN infestation for
the 2011 organic field trial. Additionally, in the spring of 2011, a trial was conducted on a
site with a history of continuous nematode infestation that had been managed
conventionally in previous years. The plants used in this trial were produced and grown
following organic practices. This trial was designed to reflect growing conditions during
a typical three-year transition period from conventional to organic production. The soil
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type found in all three field trials is Candler sand, 0 to 5 percent slopes, hyperthermic,
uncoated Typic Quartzipsamments, with a pH of 6.0.
In all trials there were eight treatments consisting of, nongrafted and self-grafted
scion controls for „Brandywine‟ (NGBW, BW/BW) and „Flamme‟ (NGFL, FL/FL), and the
scion-rootstock combinations including „Brandywine‟ and „Flamme‟ grafted onto the
rootstocks „Multifort‟ (BW/MU, FL/MU) and „Survivor‟ (BW/SU, FL/SU). The seedlings
were transplanted on 10 Apr. 2010 and 2 Apr. 2011. A randomized complete block
design was used with five blocks (replications). In the 2010 trial there were 12 plants per
treatment in each block. In 2011, there were 15 plants per treatment in the organic field
and 8 plants per treatment in the transitional field. In all three trials the in-row plant
spacing was 0.46 m (18 inches) with 1.83 m (6 feet) between row centers. The plants
were grown in raised beds with black plastic mulch and drip irrigation. A preplant
application of Nature Safe organic fertilizer 10N-0.9P-6.6K (Cold Spring, KY) was
applied at the rate of 179 kg N/ha (200 lb N/acre). Supplemental liquid fertilizer
applications were injected into the drip system weekly at a rate of 0.45 kg N/ha
throughout the season using Neptune‟s Harvest 2N-1.3P-0.8K (Gloucester, MA).
Supplemental calcium was also supplied through injection at a rate of 0.10 kg/ha Ca
with Calplex (Botanicare, Chandler, AZ). All the nutrient inputs were approved by the
Organic Materials Review Institute (OMRI, Eugene, OR) for use in certified organic
production. The plants were staked and trellised as needed throughout the season
following the stake and weave system common to Florida tomato production (Olson et
al., 2011).
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Nematode galling. Assessments of nematode infestation on plant roots were
conducted after the final harvest. On 13 July 2010 and 30 June 2011, the roots of five
plants per treatment in each block in the organic fields and three plants per treatment in
each block in the transitional field were assessed for nematode galls. The rating
scheme proposed by Zeck (1971) that estimates nematode infestation levels on a plant
was used. This scheme is a scale from 0-10 (0 = no galling, 10 = plant and roots are
dead). Three researchers assessed each plant individually and then the ratings were
averaged to form a consensus rating for that plant. The consensus ratings were then
averaged for each treatment in each block (five plants/plot in organic field; three
plants/plot in transitional field). In addition, two nematode samples from each field were
submitted the University of Florida Nematode Assay Lab for identification of species.
Fruit yield. Tomato harvests began 58 days after transplanting (DAT) in 2010 and
63 DAT in 2011. In 2010, there were four harvests occurring on 7, 13, 17, and 25 June.
In 2011, there were 6 harvests in the organic field and 5 harvests in the transitional field
occurring on 4, 8, 13, 16, 22 (organic only), 23 (transitional only), and 28 (organic only)
June. Fruit were harvested at the breaker stage of maturity when the mature color
begins to show at the blossom end. Each harvest was graded and weighed for
marketability based on organic grower standards. Non-characteristic fruit and those
exhibiting blossom end rot, cat facing, splitting, and insect/disease damage were
counted and weighed to calculate marketable yield.
Crop vigor. One representative plant per treatment was destructively harvested in
each block following the final harvest on 25 June 2010 and 30 June 2011 in the organic
fields. Leaf area was measured using a LI-COR area meter (LI-3100; Lincoln, NE). After
21
recording leaf area, each plant was dried in a forced air drying room at 75°C for 5 days
and weighed for above-ground biomass.
Statistical analyses. Data analyses were performed for both scion varieties
separately using the GLIMMIX procedure of SAS version 9.2 (SAS Institute, Cary, NC).
All yield, crop vigor, and nematode galling data were analyzed using a one-way analysis
of variance (ANOVA), with multiple comparisons conducted using Fisher‟s LSD test at α
= 0.05.
Results and Discussion
Nematode galling. Although the 2010 organic research field was selected
because of the record of RKN infestation in previous years, no RKN galls were
observed on the tomato plants in the field trial regardless of the treatment. Grasses
were known to be the dominant crop in the field for at least two years prior to the 2010
trial. In addition to the history of grasses, the hard freezes and record low temperatures
during Jan.-Mar. 2010 may have contributed to the low RKN population in the field.
Yellow squash was grown during the fall of 2010 in the organic field to build a natural
RKN population for the spring 2011 season. RKN trials had been conducted in the
transitional field for >10 years and there was a well established RKN population in that
site.
In the 2011 trials, all the treatments showed RKN galling despite the use of
rootstocks. However, RKN galling index ratings were significantly lower in both fields for
tomatoes grafted onto „Survivor‟ and „Multifort‟ compared to the non- and self-grafted
„Brandywine‟ and „Flamme‟ treatments (Table 2-1). The nematode species found in both
fields was identified by the Nematode Assay lab as M. javanica (Treub) Chitwood, using
species-specific PCR primers (Dong et al., 2001). In the organic field, the hybrid
22
rootstocks performed similarly and significantly reduced root galling compared to the
nongrafted and self-grafted treatments for both scions by 89% on average. In the
transitional field, both rootstocks significantly reduced root galling for both scions in
comparison with the non- and self-grafted scion treatments. However, the rootstock
„Survivor‟ led to the lowest galling ratings for both scion cultivars (P=0.01). The self-
grafted „Brandywine‟ treatment had significantly lower galling index ratings than the
nongrafted „Brandywine‟ treatment. This reduced galling was unexpected and the cause
is unclear. It may be that for the scion „Brandywine‟, the act of grafting promoted a
defense response which resulted in reduced galling ratings, but further investigation will
be required to elucidate a cause. Intermediate levels of disease resistance and yield in
self-grafted tomatoes have been reported in previous research (Rivard, 2006).
The RKN galling ratings were generally higher in the transitional field than the
organic field, suggesting a more severe infestation (Table 2-1). This trend was observed
with the interspecific rootstock „Multifort‟ but not with the intraspecific rootstock
„Survivor‟. Under different field infestation levels, the high resistance to RKN was
consistent when the two heirloom tomato cultivars were grafted onto „Survivor‟. In
contrast, the resistance conferred by „Multifort‟ appeared to break when the soil RKN
infestation increased. In this study, „Multifort‟ performed similarly to „Beaufort‟ and
„Maxifort‟ which were assessed by Rivard et al. (2010a). These three interspecific
tomato rootstocks are from similar breeding lines and tend to exhibit tolerance to RKN
rather than resistance when soil RKN population levels are high. RKN resistance is
conferred by the Mi-1 gene that was introduced into commercial tomato rootstocks and
cultivars from the wild tomato relative Solanum peruvianum L. (López-Pérez et al.,
23
2006; Medina-Filho and Stevens, 1980). López-Pérez et al. (2006) showed that
„Beaufort‟ carried the Mi-gene and exhibited tolerance to RKN (M. incognita) since RKN
populations were able to reproduce and increase on the „Beaufort‟ rootstock. It was also
revealed that „Hypeel45‟, a processing tomato with Mi-gene resistance, retained yields
and had lower galling ratings than „Beaufort‟ (López-Pérez et al., 2006). Our relatively
high galling ratings for the interspecific rootstock „Multifort‟ and lower galling ratings for
the intraspecific rootstock „Survivor‟ were consistent with the study by López-Pérez et
al. (2006). In the transitional field a significant reduction in root galling was also
observed with the BW/BW treatment. The effect of self-grafting on RKN resistance
deserves further research. Nevertheless, there were generally lower root galling ratings
with self-grafted than nongrafted treatments for both scion cultivars in the organic and
transitional fields.
Fruit yield. For the cultivar Flamme in 2010, the grafted plants produced
significantly lower marketable yields than the nongrafted control for the first two
harvests. However, there were no significant differences in total marketable yield for the
„Flamme‟ treatments 2010 and 2011 (Figures 2-1 A, 2-2 A, and 2-3 A). Reduced early
yields may be an effect of the grafting process. Khah et al. (2006) reported greater early
yields for nongrafted plants and hypothesized that the stress associated with grafting
and healing delayed flowering in grafted plants. There were no significant differences in
marketable yield at any harvest for the scion „Brandywine‟ in 2010 (Figure 2-1 B). In
2011, there was variability in marketable yields for the „Brandywine‟ treatments between
the organic and transitional fields. In the organic field, the NGBW and BW/SU
treatments produced significantly higher total marketable yields than the BW/BW and
24
BW/MU treatments (Figure 2-2 B). However in the transitional field, BW/MU
demonstrated significantly higher total marketable yields than the BW/BW and NGBW
treatments (Figure 2-3 B). The BW/SU treatment resulted in statistically similar yields to
all other „Brandywine‟ treatments in the transitional field. Overall, total fruit yields
showed trends similar to marketable fruit yields (data not shown).
Some of these yield differences in 2011 may be attributed to the presence of RKN.
With no RKN pressure in the 2010 trial, there were no differences in total marketable
yield with either scion cultivar. However, with high RKN pressure in the 2011 transitional
field, the highest marketable yield for the scion „Brandywine‟ was achieved when grafted
onto „Multifort‟. Our results were consistent with the study by López-Pérez et al. (2006),
in which significantly higher tomato fruit yield was observed with resistant rootstocks at
high RKN (M. incognita) densities. According to Rivard et al. (2010a), total and
marketable tomato fruit yields were higher on interspecific hybrid rootstocks under
severe RKN and southern blight disease pressure. In contrast, grafting did not exhibit
any significant effect on heirloom tomato yield under low disease pressure and it was
unclear if grafting onto interspecific hybrid rootstocks would be beneficial in such
circumstances (Rivard et al., 2008).
López-Pérez et al. (2006) did not detect a yield response with plants grafted onto
resistant rootstocks at intermediate populations of RKN. In our study, NGBW and
BW/SU preformed similarly at intermediate levels of RKN infestation in the 2011 organic
field trial while, BW/BW and BW/MU yielded significantly less marketable fruit. It is
unclear why tomato yield was reduced for BW/MU since it showed significantly lower
root galling ratings compared to NGBW and BW/BW, and did not differ significantly from
25
BW/SU in terms of RKN resistance. This response could be related to the genetic
background of „Multifort‟. This rootstock was developed from a breeding line of
greenhouse rootstocks aimed at enhanced crop vigor and extended growing seasons in
addition to disease resistance. It could be that the increased vigor and vegetative
growth that is useful in greenhouse conditions had a deleterious effect on „Brandywine‟
fruit yield in the shorter field-grown season. More studies are warranted to examine the
influence of vigorous interspecific hybrid rootstocks on the yield of indeterminate
cultivars grown in field production systems. New rootstocks developed for open-field
production would help establish more integrated pest management techniques for
growers not using greenhouses or high tunnels (Kubota et al., 2008).
Scion-rootstock influences were observed in this study. Although „Flamme‟ was
susceptible to RKN, marketable fruit yields were not significantly affected by grafting
with resistant rootstocks. This indicates that other factors, in addition to RKN infestation,
may be involved in determining tomato yield. It was noted that the size of „Flamme‟ fruit
was much smaller than „Brandywine‟ fruit. One effect that occurred in 2011 but not in
2010 was the presence of „Brandywine‟ cull-fruit diagnosed with the abiotic disorder
graywall (W.M. Stall, pers. comm.). No „Flamme‟ fruit displayed graywall symptoms.
Graywall incidence was greater in the transitional field than in the organic field, which
may have contributed to the overall reduction in marketable yield per plant observed in
the transitional field trial in contrast to the organic field trial (Figures 2-2 and 2-3).
Graywall is a physiological disorder and its cause is unclear, but it can be reduced by
adequate K (Olson, 2004). It was most severe in the field with the highest nematode
26
pressure, and it is unclear whether its increased incidence there could be attributed to
adverse effects of RKN on nutrient and water uptake.
Crop Vigor. Rootstock effects were also observed in leaf area and above-ground
biomass evaluations. When grafted to the rootstock „Multifort‟, the scion „Brandywine‟
produced significantly more above-ground biomass than NGBW, BW/BW, and BW/SU
in both years (Table 2-2). Furthermore, BW/MU produced significantly greater leaf area
than the other „Brandywine‟ treatments in 2010. In the 2011 trial, the leaf area of
BW/MU was greater than that of BW/BW and BW/SU, but there was no significant
difference between BW/MU and NGBW. The scion „Flamme‟ treatment combinations
performed similarly to the „Brandywine‟ treatment combinations. For both years, FL/MU
produced significantly greater leaf area than NGFL, FL/FL, and FL/SU. In 2011, above-
ground biomass was significantly greater for FL/MU than all other „Flamme‟ treatments
(Table 2-2).
The interspecific rootstocks „Beaufort‟ and „Maxifort‟ have been shown to increase
biomass and leaf area for the heirloom tomato „Cuore di Bue‟ when grown in a
greenhouse (Di Gioia et al., 2010). The effect of the rootstock should be carefully
examined when grafting is used for a specific growing condition. The interspecific hybrid
rootstock „Multifort‟ used in this experiment is similar to „Maxifort‟ in terms of vigorous
growth. This is advantageous for greenhouse tomato production where season
extension is strongly emphasized. However when used in the open-field, this increase in
vegetative growth may not be beneficial. This is due to the shorter field production cycle
in Florida where early yields are important to achieve the greatest profit. On the other
27
hand, the increased vigor provided by „Multifort‟ might be related to the tolerance
exhibited by this rootstock to high populations of RKN.
Despite the presence of RKN in 2011, both yield and crop vigor for all treatments
were greater in 2011 than those from 2010 (Figures 2-1, 2-2, and 2-3, Tables 2-1 and 2-
2). The 2010 and 2011 growing seasons were different with regard to average
temperature and rainfall. The 2010 growing season was 8.74 °C cooler and there was
27.6 cm more rain on average. The drier, more mild 2011 season may have been more
favorable for growing irrigated tomatoes.
Interest in vegetable grafting is growing in the United States, therefore more
research is needed to determine the rootstock effects on crop performance under site-
specific conditions and different production systems. With respect to controlling RKN,
our studies indicated the interspecific hybrid rootstock tended to exhibit tolerance under
severe RKN pressure to help improve the heirloom tomato yield. In fields with
intermediate levels of RKN infestation, the intraspecific hybrid rootstock was more
effective in reducing root galls and maintaining fruit yield. Interestingly, there was a lack
of a clear relationship between root galling and tomato yields. Scion-rootstock
interactions were revealed as reflected by the differential response of the two heirloom
tomato scions to the two rootstocks used. When assessing whether or not to use
grafted tomato plants for RKN management, growers need to consider the severity of
the RKN infestation, the growing system, and the scion and rootstock cultivars to be
used.
28
Table 2-1. Effect of grafting treatments on root-knot nematode galling ratingsz of heirloom tomato cultivars Brandywine and Flammey.
Treatmentx Organic field Transitional field
Brandywine
NGBW 7.18 a 9.30 a
BW/BW 5.86 a 7.30 b
BW/MU 1.72 b 3.88 c
BW/SU 0.28 b 0.54 d
Flamme
NGFL 6.02 a 8.06 a
FL/FL 5.28 a 6.12 a
FL/MU 0.52 b 3.48 b
FL/SU 0.16 b 0.00 c z Root-knot nematode galling index proposed by Zeck (1971), ratings for spring 2011. y Means separated with Fisher‟s LSD test at α=0.05, same letter in each column indicates no significant difference; scion cultivars were analyzed separately. x NGBW and NGFL: Nongrafted „Brandywine‟ and „Flamme‟; BW/BW and FL/FL: Self-grafted „Brandywine‟ and „Flamme‟; BW/MU and FL/MU: „Brandywine‟ and „Flamme‟ grafted onto the interspecific rootstock „Multifort‟; BW/SU and FL/SU: „Brandywine‟ and „Flamme‟ grafted onto the intraspecific rootstock „Survivor‟.
29
Table 2-2. Effect of grafting treatments on leaf area and above-ground biomass of heirloom tomato cultivars Brandywine and Flammez.
2010
2011
Leaf areay Biomassx
Leaf areay Biomassx
Treatmentw (cm²) (g/plant)
(cm²) (g/plant)
Brandywine
NGBW 3145 b 177 b
13137 ab 349 ab
BW/BW 2926 b 171 b
11343 b 316 b
BW/MU 5549 a 239 a
18300 a 478 a
BW/SU 2649 b 159 b
9618 b 281 b
Flamme
NGFL 2420 b 172 a
6875 b 248 b
FL/FL 2358 b 168 a
8000 b 278 b
FL/MU 3833 a 204 a
10460 a 383 a
FL/SU 1729 b 165 a
6928 b 271 b z Means separated with Fisher‟s LSD test α=0.05, same letter in each column indicates no significant difference; scion cultivars were analyzed separately. y Mean total leaf area per plant. x Mean total above-ground dry weight per plant. w NGBW and NGFL: Nongrafted „Brandywine‟ and „Flamme‟; BW/BW and FL/FL: Self-grafted „Brandywine‟ and „Flamme‟; BW/MU and FL/MU: „Brandywine‟ and „Flamme‟ grafted onto the interspecific rootstock „Multifort‟; BW/SU and FL/SU: „Brandywine‟ and „Flamme‟ grafted onto the intraspecific rootstock „Survivor‟.
30
0
100
200
300
400
500
600
700
58 64 68 76
Ma
rke
tab
le y
ield
(g
/pla
nt)
NGFL
FL/FL
FL/MU
FL/SU
LSD
0
100
200
300
400
500
600
700
58 64 68 76
Ma
rke
tab
le y
ield
(g
/pla
nt)
Days after transplanting
NGBW
BW/BW
BW/MU
BW/SU
LSD
Figure 2-1. Cumulative marketable yield for nongrafted and grafted heirloom tomato cultivars Flamme (A) and Brandywine (B) from the organic field trial conducted in 2010. Each harvest was analyzed using a one-way analysis of variance and means were separated by Fisher‟s LSD test. LSD bars represent the least significant difference at α = 0.05. NGBW and NGFL: Nongrafted „Brandywine‟ and „Flamme‟; BW/BW and FL/FL: Self-grafted „Brandywine‟ and „Flamme‟; BW/MU and FL/MU: „Brandywine‟ and „Flamme‟ grafted onto the interspecific rootstock „Multifort‟; BW/SU and FL/SU: „Brandywine‟ and „Flamme‟ grafted onto the intraspecific rootstock „Survivor‟.
A
B
31
0
200
400
600
800
1000
1200
1400
1600
1800
63 67 72 75 81 88
Ma
rke
tab
le y
ield
(g
/pla
nt) NGFL
FL/FL
FL/MU
FL/SU
LSD
0
200
400
600
800
1000
1200
1400
1600
63 67 72 75 81 88
Ma
rke
tab
le y
ield
(g
/pla
nt)
Days after transplanting
NGBW
BW/BW
BW/MU
BW/SU
LSD
Figure 2-2. Cumulative marketable yield for nongrafted and grafted heirloom tomato cultivars Flamme (A) and Brandywine (B) from the organic field trial conducted in 2011. Each harvest was analyzed using a one-way analysis of variance and means were separated by Fisher‟s LSD test. LSD bars represent the least significant difference at α = 0.05. NGBW and NGFL: Nongrafted „Brandywine‟ and „Flamme‟; BW/BW and FL/FL: Self-grafted „Brandywine‟ and „Flamme‟; BW/MU and FL/MU: „Brandywine‟ and „Flamme‟ grafted onto the interspecific rootstock „Multifort‟; BW/SU and FL/SU: „Brandywine‟ and „Flamme‟ grafted onto the intraspecific rootstock „Survivor‟.
A
B
32
0
200
400
600
800
1000
1200
1400
63 67 72 75 82
Ma
rke
tab
le y
ield
(g
/pla
nt)
NGFL
FL/FL
FL/Mu
FL/Su
LSD
0
100
200
300
400
500
600
700
800
63 67 72 75 82
Ma
rke
tab
le y
ield
(g
/pla
nt)
Days after transplanting
NGBw
Bw/Bw
Bw/Mu
Bw/Su
LSD
Figure 2-3. Cumulative marketable yield for nongrafted and grafted heirloom tomato cultivars Flamme (A) and Brandywine (B) from the 2011 field trial designed to reflect growing conditions during a typical three-year transition period from conventional to organic. Each harvest was analyzed using a one-way analysis of variance and means were separated by Fisher‟s LSD test. LSD bars represent the least significant difference at α = 0.05. NGBW and NGFL: Nongrafted „Brandywine‟ and „Flamme‟; BW/BW and FL/FL: Self-grafted „Brandywine‟ and „Flamme‟; BW/MU and FL/MU: „Brandywine‟ and „Flamme‟ grafted onto the interspecific rootstock „Multifort‟; BW/SU and FL/SU: „Brandywine‟ and „Flamme‟ grafted onto the intraspecific rootstock „Survivor‟.
A
B
33
CHAPTER 3 FRUIT QUALITY AND SENSORY ATTRIBUTES OF ORGANIC HEIRLOOM
TOMATOES ARE NOT INFLUENCED BY GRAFTING
Background
Grafting is a horticultural technique primarily used to control soilborne pathogens,
provide relief from abiotic stressors, and improve crop productivity in Cucurbitaceous
and Solanaceous vegetables. This technique may be especially intriguing for organic
producers because it can be used to overcome soilborne pathogens for which they may
have limited control options. Many recent studies have demonstrated the effectiveness
of grafting for controlling root-knot nematodes, bacterial wilt, fusarium wilt, and southern
blight in the United States (Bausher, 2009; Kubota et al., 2008; Lopez-Perez et al.,
2006; Rivard and Louws, 2008; Rivard et al., 2010a). Grafting research and breeding
efforts for both tomatoes and tomato rootstocks have traditionally focused on improving
disease resistances and increasing yield, rather than fruit quality (Lee, 1994; King et al.,
2010; Klee, 2010; Rouphael et al., 2010). According to Klee (2010), consumers have
noticed a decrease in fruit and vegetable flavors as breeding efforts have resulted in
enhanced postharvest attributes and they are willing to pay more for produce with
improved taste. With this increase in consumer interest for fruits and vegetables with
superior flavor, more recent studies have examined grafting effects on fruit quality (Di
Gioia et al., 2010; Fernandez-Garcia et al., 2004; Mišković et al., 2009; Pogonyi et al.,
2005).
Many studies concerning grafting effects on fruit quality have reported varying
results (Edelstein, 2004; Martínez-Ballesta et al., 2008; Rouphael et al., 2010).
Increased concentrations of lycopene, β-carotene, glucose, fructose, and soluble solids
in tomato fruit as a result of grafting have been demonstrated (Fernandez-Garcia et al.,
34
2004; Oda et al., 1996). Meanwhile, some previous reports showed no differences in
soluble solids, pH, lycopene, and titratable acidity in fruit from grafted and nongrafted
plants (Di Gioia et al., 2010; Khah et al., 2006; Romano and Paratore, 2001).
Furthermore, reduced fruit concentrations of vitamin C, soluble solids, total sugars, and
lycopene due to grafting or rootstock influence were demonstrated (Di Gioia et al., 2010;
Lee et al., 1999; Mišković et al., 2009; Pogonyi et al., 2005).
To date, few studies have examined the effect of rootstocks on fruit quality and
sensory attributes of heirloom tomatoes (Di Gioia et al., 2010). Without a clear
understanding of how grafting influences fruit nutritional content and sensory attributes,
growers may be less likely to invest the extra cost associated with grafted transplants.
This cost, as reported by Rivard et al. (2010b) could be 64% to 354% higher for grafted
plants produced in the United States. Uncertainties regarding the effect of grafting on
fruit quality and sensory attributes may be especially discouraging for heirloom tomato
growers who market their fruit as having exceptional flavor and eating quality.
Grafting may provide an effective management tool for growers to control
soilborne pathogens and cope with environmental stressors. However, if fruit quality is
adversely affected as a result of grafting, growers may be less likely to adopt this
technique. The purpose of this study was to examine fruit quality and sensory attributes
of two distinctly different heirloom tomato cultivars grafted onto intra- and inter-specific
hybrid rootstocks. These plants were grown on certified organic land in order to
evaluate grafting as a viable tool for organic producers in Florida.
Materials and Methods
Grafted transplants. Certified organic heirloom tomato seeds and non-treated
rootstock seeds were used to produce grafted tomato seedlings. „Brandywine‟ and
35
„Flamme‟ (Tomato Fest, Little River, CA) were used as scions with „Multifort‟ (De Ruiter
Seeds, Bergschenhoek, The Netherlands) and „Survivor‟ (Takii Seeds, Salinas, CA)
rootstocks. „Flamme‟ (FL) is an orange, plum type, open pollinated, indeterminate
heirloom cultivar popular among chefs. „Brandywine‟ (BW) is a red colored, beefsteak
style, open pollinated, indeterminate heirloom cultivar known for outstanding flavor.
„Multifort‟ (MU) is an interspecific (S. lycopersicum xS. habrochaites) hybrid rootstock
whereas; „Survivor‟ (SU) is an intraspecific (S. lycopersicum) hybrid rootstock. Both
rootstocks have vigorous growth habit and resistance to root-knot nematodes
(Meloidogyne spp.). The rootstock seeds were sown on 16 February 2010 and 11
February 2011, two days before scion seeds, as recommended by both rootstock seed
companies.
Speedling (Sun City, FL) 128-cell-count flats and Fafard Organic Formula Custom
potting mix (Apopka, FL) were used to grow the seedlings. Seedlings were tube grafted
at the 4-5 true leaf stage. Grafting took place 34 d (2010) and 28 d (2011) after scions
were sown. The grafting and healing protocol was adapted from Rivard and Louws
(2006). The newly grafted seedlings were held together with 1.5-mm or 2.0-mm silicon
clips (Hydro-Gardens, Colorado Springs, CO). After grafting, the seedlings were placed
in a climate controlled walk-in cooler at 25 °C and ~95% RH without light for 24 hr. The
seedlings were progressively exposed to increased light durations and reduced humidity
for 6 d, until the graft unions had healed. Healed grafted seedlings were relocated to a
greenhouse to harden off for 5 d before transplanting.
Field experiments. Tomato seedlings were transplanted on 10 April 2010 and 2
April 2011. Both field experiments were arranged in a randomized complete block
36
design with five blocks. There were 12 plants per treatment in each block in 2010 and
15 plants per treatment in 2011. Both trials consisted of eight treatments: non-grafted
(NGBW, NGFL) and self-grafted (BW/BW, FL/FL) controls, and the grafted
combinations (BW/MU, BW/SU, FL/MU, FL/SU). The plants were grown on raised beds
with black plastic mulch and drip irrigation. Nature Safe 10N-0.9P-6.6K (Cold Spring,
KY) Organic Materials Review Institute (OMRI) approved granular fertilizer was applied
preplant at a rate of 179 kg N/ha (200 lb N/acre). Neptune‟s Harvest 2N-1.3P-0.8K
(Gloucester, MA) OMRI approved fish and seaweed based, liquid fertilizer was injected
into the drip system throughout the season to provide supplemental fertilization. The
stake and weave system common to Florida fresh market tomato production was
utilized and plants were trellised to provide vertical support (Olson et al., 2011).
Both field trials took place at the University of Florida Plant Science Research and
Education Unit in Citra, FL., in the spring of 2010 and 2011. The tomato plants were
grown on certified organic land in compliance with the National Organic Program (U.S.
Dept. Agr., 2002). The soil type in both fields was Candler sand, 0 to 5 percent slopes,
hyperthermic, uncoated Typic Quartzipsamments, with a pH of 6.0. There were four
harvests in 2010 and six harvests in 2011.
Consumer sensory analyses. Consumer taste tests were conducted in 2010 and
2011 at the University of Florida sensory lab in Gainesville, FL. Fruit were harvested at
the breaker stage and allowed to ripen to maturity before analysis. In the 2010 study,
tomato fruit from NGBW, BW/BW, BW/MU, and BW/SU were harvested on June 13 and
stored at ambient temperature for 3 days prior to the sensory evaluation. Fruit from both
„Brandywine‟ and „Flamme‟ treatments were tested in 2011. Tomatoes from NGFL,
37
FL/FL, FL/MU, and FL/SU were harvested on 8 June and analyzed on 14 June, while
tomatoes from NGBW, BW/BW, BW/MU, and BW/FL were harvested on 13 June and
assessed on 17 June. Fruit from the five field blocks were pooled for each treatment to
provide enough ripe fruit for >100 sensory analysis samples. Tomatoes were cut into
cubes about 2.5-cm thick. Each serving sample consisted of 2-cubes of tomato fruit.
There were 75 consumer panelists for the 2010 „Brandywine‟ taste test. The 2011
studies included 75 consumer panelists for the „Flamme‟ taste test and 69 panelists for
„Brandywine‟ taste test. The sensory lab houses 10 private booths, each containing a
computer monitor, keyboard, and sliding window for presenting the sample to be tested.
Sensory test ballot presentation and data collection is completed on the computers
which are equipped with Compusense® Five (Compusense, Guelph, Canada). All
procedures used were approved by the University of Florida Institutional Review Board.
Passersby were recruited to serve as consumer panelists with signs placed near
the sensory lab. Each panelist first checked in at the front desk, signed a voluntary
consent form, and was directed to a booth. The panelist then received instruction from
the computer monitor to begin the sensory test. The sensory tests began with three
demographic questions; gender, age, frequency of tomato consumption (Table 3-1).
Then, each panelist was asked to “indicate how much you like or dislike the following
attributes” using a hedonic scale. The attributes assessed were overall appearance,
overall acceptability, firmness, tomato flavor, and sweetness. The hedonic scale ranged
from 1-9 (1 = dislike extremely, 2 = dislike very much, 3 = dislike moderately, 4 = dislike
slightly, 5 = neither like nor dislike, 6 = like slightly, 7 = like moderately, 8 = like very
much, 9 = like extremely). Between each of the four tomato samples, the panelists were
38
asked to “take a bite of cracker and a sip of water to rinse your mouth”. After completing
the taste test, each panelist was compensated with their choice of a free soda or a
coupon for food on campus.
The order the tomato samples were presented to each panelist was randomized.
To reduce bias caused by the order in which the samples were presented, all possible
orders were presented approximately an equal number of times. Following each
sensory panel the data were collected from all computers and compiled.
Fruit quality attributes. Vitamin C, soluble solids content (SSC), pH, and total
titratable acidity (TTA) were determined for tomato fruit from all 8 treatments harvested
13 June 2010 and 8 June 2011. Five ripe and representative fruit were blended for 30 s
to form a homogenate for each treatment. This was replicated three times in both years.
The homogenate was centrifuged for 20 min at 15,000 rpm and 5 °C. Then the
supernatant was filtered through 8-layer cheese cloth to obtain a clarified extract.
Vitamin C was measured using a PowerWave XS2 microplate spectrophotometer
(BioTek, Winooski, VT) with absorbance at 540 nm (Terada et al., 1978). SSC was
measured with an Abbe Mark II, digital refractometer (Reichert Technologies, Depew,
NY). Initial pH was recorded and TTA was determined by potentiometric titration of 6 mL
of tomato extract to an end point of pH = 8.2 with 0.1 N NaOH using a 719 S Titrino
automatic titrator (Metrohm, Herisau, Switzerland).
Statistical analyses. All data were analyzed using a one-way analysis of variance
with Tukey‟s HSD test for multiple comparisons among treatments. The consumer
sensory test data were collected and analyzed using the Compusense® Five software
used for data collection and analysis by the University of Florida Sensory lab. The fruit
39
quality data were analyzed using the GLM procedure of SAS version 9.2 (SAS Institute,
Cary, NC).
Results and Discussion
Consumer sensory analyses. In 2010 the consumers perceived taste differences
between „Brandywine‟ fruit harvested from the different grafting treatments. There were
significant differences regarding overall appearance, overall acceptability, and tomato
flavor. For the overall appearance and tomato flavor attributes, NGBW was rated
significantly higher than BW/SU (Table 3-2). NGBW was rated significantly higher than
BW/MU and BW/SU for the overall acceptability attribute. BW/BW was rated similarly to
all other treatments for all taste attributes. In 2010 it appeared that the rootstock
„Survivor‟ might have had a consistent negative effect on taste however, this trend did
not persist in 2011. Both „Brandywine‟ and „Flamme‟ were evaluated in 2011 and no
significant differences were observed for the measured sensory analysis attributes.
These results are consistent with those of Di Gioia et al. (2010) where it was
demonstrated that grafting did not influence the sensory attributes sweetness, sourness,
and tomato-like taste for the heirloom tomato cultivar Cuore di Bue. In their study „Cuore
di Bue‟ was grafted onto interspecific hybrid rootstock cultivars Beaufort and Maxifort
which were produced from a similar breeding line as the rootstock „Mulifort‟ used in this
study.
Tomato flavor is a complex balance of sugar and acid contents with aroma
volatiles (Krumbein and Auerswald, 1998). Cultural practices and environmental
conditions during fruit development can affect the ratios of flavor compounds in the fruit.
Harvest maturity also has a major influence on flavor in climacteric fruits like tomatoes
(Mattheis and Fellman, 1999). Environmental conditions were more amicable and yields
40
were much greater in 2011 compared to 2010 (data not shown). As a result, more fruit
were available at similar stages of maturity in the 2011 study and no differences in
sensory attributes were observed. One possible explanation for the differences detected
in 2010 may be that with fewer fruit to choose from, there was more variability in fruit
maturity. When a tomato is picked before reaching maturity and ripened off the vine,
they tend to have less „tomato-like‟ intensity, are less sweet and have more off-flavor
than tomatoes ripened on the vine (Kader et al., 1977).
Grafting may also affect the maturity of fruit at harvest. Grafted plants can delay
early harvests compared to nongrafted plants because they may be less
developmentally mature due to the grafting and healing processes (Khah et al., 2006;
Lee et al., 2010). Khah et al. (2006) showed that there were no significant differences in
the number of flowers per plant later in the growing season. In our studies fruits from the
second and third harvests were used in order to reduce the variability of fruit maturity
between grafted and nongrafted treatments.
Fruit quality. Vitamin C, SSC, pH, and TTA were measured in 2010 and 2011. No
significant differences between treatments were found in either year for „Brandywine‟ or
„Flamme‟ (Table 3-3). This was expected as previous studies reported few consistent
effects of grafting or rootstock on nutritional quality attributes of tomatoes. Khah et al.
(2006) demonstrated that pH, Brix, lycopene content, and firmness were unaffected
when the commercial tomato cultivar Big Red was grafted onto „Primavera‟ and „Heman‟
tomato rootstocks. Similarly, Di Gioia et al. (2010) showed that total soluble solids and
total titratable acidity were not significantly influenced by grafting heirloom tomatoes
onto interspecific hybrid rootstocks. Rouphael et al. (2010) pointed out that grafted fruit
41
quality attributes may be dependent on the selection of scion, rootstock, and growing
environment.
It has been suggested that grafting can have a positive impact on tomato fruit
quality (Martínez-Ballesta et al., 2008). Meanwhile, it has also been indicated that
grafting could affect tomato fruit quality negatively (Edelstein, 2004). Scion and
rootstock combinations can even perform differently in consecutive years (Mišković et
al., 2009). There are many possible scion-rootstock combinations and growing
environments. Clearly, more of these scenarios will need to be examined before
researchers fully understand the impact of grafting with different rootstocks on fruit
quality attributes. These studies will need to assess specific rootstocks for specific
growing conditions in a variety of regions.
Heirloom tomato fruit are desired for their exceptional flavors, colors, and unique
shapes. Overall, neither grafting nor rootstock demonstrated a prominent effect on
sensory attributes and other fruit quality measurements of „Brandywine‟ and „Flamme‟
tomato fruit in the present study. Nevertheless, growers interested in using grafted
plants need to be aware that scion-rootstock interactions are still not fully understood. It
is suggested that different grafting combinations be evaluated under site-specific
conditions before selecting appropriate rootstocks and incorporating this technique on a
large scale.
42
Table 3-1. Consumer demographic information.
Percent of Percent of Percent of
Characteristic Category 75
consumersz 75
consumersy 69 consumersx
Gender Male 51 52 54
Female 49 48 46
Age
Under 18 0 1 3
18-29 80 79 74
30-44 15 13 14
45-65 4 7 9
Over 65 1 0 0
Tomato consumption
frequency
More than once a week
52 32 49
Once a week 26 25 20
More than once a month
17 27 16
Once a month 5 13 10
Never 0 3 5 z 75 consumers participated in the taste test on „Brandywine‟ treatments in 2010. y 75 consumers participated in the taste test on „Flamme‟ treatments in 2011. x 69 consumers participated in the taste test on „Brandywine‟ treatments in 2011.
43
Table 3-2. Effect of grafting treatments on heirloom tomato fruit sensory attributesz for scion cultivars Brandywine and Flamme.
Treatment Appearance Acceptability Firmness Tomato flavor
Sweetness
„Brandywine‟ 2010y
NGBW 6.39 a 6.76 a 6.45 6.61 a 6.19 BW/BW 6.31 ab 6.23 ab 6.05 6.23 ab 5.91 BW/MU 6.05 ab 6.20 b 6.49 5.97 ab 5.77 BW/SU 5.76 b 6.11 b 6.21 5.96 b 5.80
P-valuew 0.02 0.01 0.21 0.03 0.25
„Brandywine‟ 2011x NGBW 6.30 6.16 6.26 6.12 5.59 BW/BW 6.12 6.35 6.41 6.29 6.07 BW/MU 6.39 6.01 6.10 5.88 5.71 BW/SU 6.48 6.29 6.17 6.36 6.10
P-valuew 0.50 0.42 0.57 0.20 0.09
„Flamme‟ 2011y NGFL 6.11 6.19 5.93 6.27 a 5.80 FL/FL 6.01 5.69 5.99 5.67 ab 5.29 FL/MU 5.79 5.72 5.61 5.73 ab 5.52 FL/SU 5.91 5.83 5.87 5.63 b 5.49
P-valuew 0.54 0.09 0.38 0.03 0.20 z Sensory attribute ratings from hedonic scale with values 1-9 (1 = dislike extremely, 9 = like extremely), means separated with Tukey‟s HSD test α = 0.05, same letter in each column indicates no significant difference; scion cultivars were analyzed separately and by year. y 75 participants. x 69 participants. w P-values calculated at α= 0.05 confidence level.
44
Table 3-3. Effect of grafting treatments on heirloom tomato fruit quality attributesz for scion cultivars Brandywine and Flamme.
Treatment Vitamin Cy
(mg AA/100 g fw) Soluble solids content
(°Brix) pH Total titratable
acidity (% Citric acid)
2010
„Brandywine‟
NGBW 26.78 3.47 4.33 0.32
BW/BW 25.27 3.20 4.29 0.38
BW/MU 24.85 2.40 4.31 0.34
BW/SU 25.75 3.37 4.26 0.43
P-valuex 0.19 0.10 0.22 0.60
„Flamme‟
NGFL 28.20 3.87 4.33 0.46
FL/FL 27.59 3.67 4.34 0.52
FL/MU 25.96 3.73 4.31 0.51
FL/SU 29.07 3.97 4.35 0.47
P-valuex 0.26 0.84 0.09 0.06
2011
„Brandywine‟
NGBW 32.33 4.93 4.45 0.32
BW/BW 31.47 4.93 4.47 0.33
BW/MU 30.79 4.97 4.44 0.31
BW/SU 30.06 4.80 4.47 0.29
P-valuex 0.33 0.45 0.74 0.13
„Flamme‟
NGFL 35.90 4.97 4.32 0.35
FL/FL 35.15 4.90 4.30 0.37
FL/MU 35.29 4.83 4.34 0.34
FL/SU 34.83 4.93 4.33 0.36
P-valuex 0.11 0.61 0.50 0.10 z Quality attributes measured from five randomly selected fruit per treatment with three replications, scion cultivars were analyzed separately and by year. y Vitamin C content reported as mg of ascorbic acid per 100 g fresh weight. x P-values calculated at α= 0.05 confidence level.
45
CHAPTER 4 COST BENEFIT ANALYSIS OF USING GRAFTED TRANSPLANTS FOR ROOT-KNOT
NEMATODE MANAGEMENT IN ORGANIC HEIRLOOM TOMATO PRODUCTION
Background
Vegetable grafting is popular in Asian and European countries where continuous
cropping and intensive production is practiced. This technique offers
resistance/tolerance to biotic and abiotic stressors in a variety of cucurbitaceous and
solanaceous crops (Kubota et al., 2008; Lee et al., 2010; López-Pérez et al., 2006;
Louws et al., 2010; Rivard et al., 2010a; Venema et al., 2008). In the United States,
vegetable grafting is gaining in importance because of the phase out of soil fumigation
with methyl bromide (King et al., 2008; Rivard et al., 2010b). King et al. (2008) pointed
out that because the price of methyl bromide is increasing and the price of grafted
plants is decreasing, grafting may be an economically viable method of disease control
in the United States.
The continued increase in demand for foods produced organically may also have
helped fuel the interest in vegetable grafting in the United States (Greene et al., 2009;
Kubota et al., 2008; Lee et al., 2010; Rivard et al., 2010b). For instance, organic
growers have tried grafting to control root-knot nematodes (RKN) (Kubota et al., 2008)
which are a major problem in the sandy soils common to Florida (Roberts et al., 2005).
RKN-resistant tomato rootstocks have been shown to reduce RKN galling and maintain
yields both in the United States (Bausher, 2009; Rivard et al., 2010b) and elsewhere
(Louws et al., 2010; Verdejo-Lucas and Sorribas, 2008). However, grafting in the United
States has not yet reached its full potential as a control for soilborne pathogens.
It has been estimated that 40 million grafted vegetable transplants are currently
used in the U.S. every year. Most of these plants are produced in Canada and are used
46
by major greenhouse tomato producers for season extension and increased crop vigor
(Kubota et al., 2008). In contrast, it has been estimated that over 200 million grafted
tomato transplants are used annually in Japan and Korea combined for improved crop
production and relief from soilborne pathogens, temperature extremes, and excess salts
(Lee et al., 2010). Grafting in the United States is expected to expand greatly in the
coming years as more uses are realized, high quality transplants become more
available, and prices for grafted transplants are reduced (King et al., 2008; Kubota,
2008; Lee et al., 2010).
High labor costs and low return per plant have been suggested as barriers to
adoption of grafted vegetable production in the United States (Rivard et al., 2010b). Lee
et al. (2010) reported prices of grafted transplants between $0.40 and $1.20 for various
crops. Grafted tomato transplants can cost between $0.60 and $0.90 per transplant
without factoring in seed costs (Kubota et al., 2008). Although interest in this technique
is on the rise, there has been little reported on the price of grafted transplants for
vegetable production in the United States (Rivard et al., 2010b). The price of domestic
grafted tomato plants has been estimated by Rivard et al. (2010b) as between $0.59
(on-farm, organic) and $1.88 (retail, twin leader) in two different transplant production
facilities. However to our knowledge, there have been few studies examining both the
cost of grafted tomato transplants and their expected return. This information could help
growers in the United States decide if the extra cost of grafted transplants could be
justified by increased output or by the reduction of production inputs when using grafting
to overcome soilborne diseases.
47
Florida growers and transplant producers interested in vegetable grafting need
information based on local production systems. The purpose of this study was to
determine the cost of producing grafted heirloom tomato transplants on-farm and
estimate the economic return with expected yields for organic growers interested in
implementing this technique. Sensitivity analyses were performed to assess the
economic feasibility of growing grafted heirloom tomatoes. These analyses were
created using fruit yield information from field trials of heirloom tomatoes grown under
different levels of RKN infestation.
Materials and Methods
Transplant production. Certified organic scion seeds and untreated rootstock
seeds were used to produce transplants in accordance to the rules outlined by the
National Organic Program (U.S. Dept. Agr., 2002). The heirloom tomato cultivar
Brandywine (Tomato Fest, Little River, CA) was used for the scion and nongrafted
transplants. „Brandywine‟ (BW) is popular with local growers and consumers. The
interspecific hybrid rootstock cultivar Multifort (De Ruiter Seeds, Bergschenhoek, The
Netherlands) was used for the rootstock of the grafted transplants. „Multifort‟ (MU) was
chosen for its vigor and resistance to soilborne pathogens including RKN.
To provide seedlings with similar stem diameter for grafting, rootstock seeds were
sowed 2 d prior to sowing the scion seeds. Grafting occurred 34 d (2010) and 28 d
(2011) after the scion seeds were sowed. Seedlings were splice grafted at the 3-5 leaf
stage. A 1.5-mm or 2.0-mm silicon grafting clip (Hydro-Gardens, Colorado Springs, CO)
was used to hold the grafted scion and rootstock together. Grafted seedlings were
healed in a climate controlled walk-in cooler at 95% relative humidity, 25 °C, and without
light for 24 hr. Relative humidity was reduced and light exposure was increased for 6 d
48
following grafting until the grafted transplants were healed. The transplants were then
hardened off in the greenhouse for 3 d before transplanting into the field. Grafting and
healing procedures were adapted from Rivard and Louws (2006). Nongrafted
transplants were grown in the greenhouse until transplanting into the field.
Transplanting took place on 10 April 2010 and 2 April 2011.
Field trials. An organic field trial was conducted in 2010 and repeated in 2011. A
transitional organic field trial was also conducted in 2011 at a site with a history of
nematode infestation. This trial was designed to resemble a field in the 3-year transition
to organic. A randomized completed block design with 5 replications (blocks) was used
for all three field trials. Each trial consisted of three treatments: nongrafted BW (NGBW),
self-grafted BW (BW/BW), and BW grafted onto MU (BW/MU). All field trials were
conducted at the University of Florida Plant Science Research and Education Unit
(PSREU) in Citra, FL. The soil type was Candler sand, 0 to 5 percent slopes,
hyperthermic, uncoated Typic Quartzipsamments, and had a pH of 6.0. Tomato
harvests for the organic fields took place on 7, 13, 17, and 25 June 2010, and 4, 8, 13,
16, 22, and 28 June 2011. The transitional field was harvested on 4, 8, 13, 16, and 23
June 2011. All tomatoes were graded using grower standards for marketability. Fruit
that were not marketable were culled according to their defect (e.g., blossom end rot,
cat facing, splitting, etc.). After grading, all fruit were counted and weighed. At the
completion of each trial, the roots of five plants per treatment in each block in the
organic fields and three plants per treatment in each block in the transitional field were
assessed for nematode galls. Both years, the root gall rating scheme proposed by Zeck
(1971) was used to estimate nematode infestation levels on plant root systems. This
49
scale is organized from 0-10 (0 = no galling, 10 = plant and roots are dead). Three
researchers assessed each plant individually and then the ratings were averaged for
each plant. The plant ratings were then averaged for each treatment in each block (five
plants per plot in the organic fields; three plants per plot in the transitional field).
Economic analyses. Sources and prices for materials and labor used to perform
the partial budget analysis were identified for estimating the cost of producing grafted
heirloom tomato transplants (Table 4-1). A detailed partial budget analysis was
conducted using data acquired during this grafted heirloom tomato study. All phases of
grafted and nongrafted transplant production were recorded to provide accurate
estimates for labor, materials, and total transplant production costs. Production costs
were based on a target of 1,000 grafted and nongrafted transplants. The 2011 average
wage for an entry level agricultural worker in the state of Florida was $8.45/h (State of
Florida, Agency for workforce innovation, 2011). This wage was used for all labor
calculations. The cost of BW seed for the nongrafted transplants reflected the over-
seeded rate of 10% (1,100 seeds) to account for 90% germination. Scion and rootstock
seed costs for the grafted transplants reflected the over-seeded rate of 25% (1,250
seeds each) to account for 90% germination and 90% grafting success. The cost of one
grafted vs. nongrafted transplant was then calculated from the total cost of production
for 1,000 transplants.
Healing chamber labor and material estimates were based on experience gained
at the University of Florida, and reflected the most practical option for local growers and
grafters. Because the walk-in cooler used in this study for healing the grafted
transplants may be conveniently substituted by a simpler structure, the healing chamber
50
cost was estimated based on a modified system that could be easily constructed.
Hence, this economic analysis did not include the price of grafted transplants produced
using a commercial walk-in cooler as healing chamber.
Sensitivity analyses were conducted to compare partial net returns for grafted and
nongrafted plants grown under organic and transitioning to organic growing conditions.
These partial net returns per plant were calculated by subtracting the cost of the
transplant from the estimated return and do not account for other production costs (e.g.,
transplanting labor, field preparation, mulch, fertilizer, etc.). Sensitivity analyses were
carried out using the mean yield per plant ± 3 standard errors and a range of average
price per pound received for organic heirloom tomato fruit. The mean yield per plant and
standard error for nongrafted and grafted plants were estimated from the analyses of
yield data from the 2010 and 2011 field trials using the GLIMMIX procedure in SAS 9.2
(SAS institute, Cary, NC).
According to the data provided by the UF/IFAS - Florida Automated Weather
Network (F.A.W.N.) for Citra, FL, the spring 2010 growing season (February-July) was
15.7 °F (8.74 °C) colder and had 10.9 inches (27.6 cm) more rainfall compared to the
spring of 2011. Overall, the 2011 spring season was a much more mild and dry growing
season and was more favorable for growing tomatoes. The tomato yield data used to
construct the grafted and nongrafted analyses for the organic field were pooled from
2010 and 2011 to form a more representative data set. The range of prices per pound
used for the sensitivity analyses were derived from the monthly average price of a 10 lb
carton of organic heirloom tomatoes, as published by the United States Department of
Agriculture from 2008 (U.S. Dept. Agr., 2009).
51
Results and Discussion
Transplant cost analyses. Sources and prices for materials used in production of
grafted and nongrafted heirloom tomato transplants are shown in Table 4-1. Grafted
transplants required more materials, seeds, and labor and were more expensive to
produce than nongrafted plants. In this study, grafted transplants cost $0.78 per plant
while nongrafted transplants cost $0.17 per plant (Table 4-2). Our results are consistent
with the report by Rivard et al. (2010b) that estimated $0.59 per grafted plant and $0.13
per nongrafted plant for organically produced tomato transplants. The reason grafted
transplant prices were higher than nongrafted in the present study was similar to that
stated by Rivard et al. (2010b). The bulk of this price difference is associated with the
price of the rootstock seeds. In the present study, the rootstock seed cost accounted for
36% of the total cost of the grafted transplants and 46% of the cost difference between
grafted and nongrafted transplants. It has been suggested that high labor costs could be
a major barrier to adoption of grafted vegetable production (Kubota et al., 2008; Rivard
et al., 2010b). However, labor costs were not considered a major contributor to grafted
transplant cost and accounted for 15% of the cost difference between grafted and
nongrafted transplants.
Overall, grafting added $0.61 per transplant to the cost of production. This is
similar to the $0.60 to $0.90 (excluding seed cost) per grafted transplant price reported
by Kubota et al. (2008). Our results were also consistent with the per transplant price
increase of $0.46 in North Carolina and $0.74 in Pennsylvania for grafted tomato
production as reported by Rivard et al. (2010b). The cost of building an inexpensive but
effective healing chamber was considered in the cost estimation of grafted transplants
instead of the walk-in cooler that was actually used since a walk-in cooler may not be
52
available to some growers. However, it should be noted that using a walk-in cooler as a
healing chamber may help reduce the cost of producing grafted transplants on-farm
when one is available. The reduction in cost would be accomplished by avoiding the
cost of building a healing chamber. Many growers have walk-in coolers and grafted
vegetable production typically takes place prior to the start of the season during what
may be considered a down-time for walk-in cooler use.
Lowering the cost of grafted transplants and rootstock seeds could increase
adoption by growers in the United States. The price reduction of grafted transplants may
be more important for commercial producers who rely on propagators to supply large
quantities of high quality transplants. Meanwhile, a decrease in rootstock seed cost may
be more important for small-scale growers who may be more interested in producing
grafted seedlings on-site.
Sensitivity analyses. Sensitivity analyses are useful for systematically estimating
changes in variables in an economic model. In the present study, we used sensitivity
analyses to estimate the return per plant of grafted and nongrafted plants with varying
yields and prices per pound of tomatoes. Sensitivity analyses were developed to
compare grafted transplant cost and economic returns associated with expected yields.
Excluding the extra cost of grafted transplants, overall production costs would be similar
whether grafted or nongrafted transplants were used. Comparisons were made between
plants grown in a field with relatively low RKN infestations and plants grown in a field
with high RKN infestations to assess the economic feasibility of using grafted
transplants for RKN control.
53
This study focused on organic heirloom tomato production because of the unique
opportunity for vegetable grafting to be adopted by these typically smaller growers.
Heirloom tomatoes often command a higher market price than regular fresh market
tomatoes. Organic produce also commands a higher price at market therefore; organic
heirloom tomatoes offer a niche market with price premiums that afford more
opportunity for growers to experiment with grafted transplants. This is especially true
when using grafted transplants with high resistance/tolerance to soilborne diseases for
yield improvement in fields with a history of soilborne disease.
Root-knot nematode galling was not observed during the organic field trial
conducted in 2010. There was root galling in the 2011 organic field trial but the lower
galling ratings for grafted plants did not result in increased yield as compared to
nongrafted plants. The 2010 and 2011 growing seasons were also very different with
respect to climatic conditions. The 2010 growing season was 8.74 °C cooler and had
27.6 cm more rain on average. Yield data from the organic fields were pooled from the
two seasons to provide a representative estimate for an average year.
The results of the sensitivity analyses presented in Tables 4-3 and 4-4 were
representative of expected yields for grafted and nongrafted heirloom tomato plants
grown in an organic field with relatively low RKN pressure. NGBW plants produced a
mean marketable yield of 1.8 lbs per plant and at that yield for the lowest tomato price
per pound ($1.80) the estimated partial net return was $3.07 per plant. This was $1.49
more than the estimated partial net return for the mean marketable yield of BW/MU at
1.31 lbs per plant at the same price of $1.80 per pound. This comparison demonstrates
that grafting may not be economically feasible when applied to fields with low RKN
54
pressure and insignificant yield improvement as a result of grafting. Taylor et al. (2008)
came to a similar conclusion that farmers growing seedless watermelons should not
consider using grafted plants if fusarium wilt (Fusarium oxysporum) is not an issue. On
the other hand, grafting may be a cost effective practice under high disease pressure.
O‟Connell et al. (2009) reported consecutive crop failures on a farm in North Carolina as
a result of soilborne diseases (as cited in Rivard et al., 2010b). In this case,
implementation of grafted plants allowed the grower to maintain organic tomato fruit
yields and remain profitable where it was previously not possible.
Tables 4-5 and 4-6 showed the sensitivity analysis results based on expected
yields for nongrafted and grafted plants grown in a research plot representing a field
under transition to organic with high RKN pressure. The NGBW plants in this transitional
field trial had a mean marketable yield of 0.35 lbs per plant with an expected partial net
return of $0.46 per plant when paid $1.80 per pound of heirloom tomato fruit. The mean
marketable yield of BW/MU plants was 1.44 lbs per plant which was 76% higher than
that of NGBW. The expected partial net return per plant for BW/MU was $1.82 when
paid $1.80 per pound. This represents a $1.36 per plant difference between the grafted
and nongrafted estimated partial net return in the transitional field. The $1.82 expected
partial return per plant for BW/MU was lower than the $3.07 for nongrafted plants under
low disease pressure. However, when high levels of RKN infestation occurred, the
grafted plants demonstrated great potential for maintaining fruit yield and reducing
economic crop losses.
These findings suggest that grafting could be an economically feasible approach
to controlling RKN in heirloom tomato production in organic and transitional organic
55
systems with severe RKN pressure. Grafting could be critical for growers in the
transition process from conventional to organic farming systems with high populations of
soilborne pathogens such as nematodes. Many of the pest control strategies employed
in organic or alternative cropping systems can take multiple seasons to have a
beneficial effect (McSorley, 2002) whereas, grafting effects are immediate. Resistant
rootstocks can also reduce field infestation levels for following crops and provide a non-
host root system in a crop rotation. Grafting may also reduce the need for expensive
fumigants in conventional farming systems thereby reducing input costs. This study
focused on the use of grafting to control RKN, in addition, grafting has been used
successfully in the United States for managing bacterial wilt, fusarium wilt (Rivard and
Louws, 2008), as well as southern blight (Rivard et al., 2010a).
As the demand for organically produced fruits and vegetables continues to rise,
more organic farmers will need effective soilborne disease control methods. Grafting is
an effective tool for soilborne disease management that carries economic
considerations with it. A grower must understand the benefits and limitations associated
with grafting and only use this technique when appropriate. Our findings suggest the
use of grafted plants in fields with a history of high soilborne disease pressure. This
research focused on organic heirloom tomato production to demonstrate a scenario in
which grafting could provide the most benefit. Actual production costs for individual
farmers will vary and for that reason only transplant costs were included in our cost-
benefit analyses. This study was designed to provide a base line reference for growers
interested in producing and using grafted transplants on-farm. Yields and production
costs can be estimated from grower experience and used in conjunction with the
56
analyses presented in this study to make a decision of whether or not to implement
grafting on their farms. Further work should examine local production methods and
costs to provide accurate information for growers in diverse environments. Grafting
shows many promising applications and a better understanding of the economic risks
involved might help promote adoption of this useful technique. More rootstocks should
be developed for open-field production which in Florida is typically associated with
short, wet, and hot seasons. The season extension capability of many greenhouse
rootstock varieties may be restrictive for field production. Early harvests may be more
important to open-field tomato growers to capture highest market prices.
It is expected that more growers in the United States will consider using grafted
transplants for soilborne disease control in the near future (King et al., 2008; Kubota,
2008; Lee et al., 2010). Researchers, extension agents, and growers will need to work
together to ensure that rootstocks suited for open-field conditions and the appropriate
scion-rootstock combinations are used to optimize the benefits of this technique. The
economic viability of grafted vegetable production will ultimately depend on farmers to
know their soilborne disease incidence on site and choose the right rootstock and scion
to meet their needs. Heirloom vegetables do not yield as much as hybrid vegetables
(Bland, 2005). Organic farmers may get a higher return per plant through the use of
hybrids rather than heirlooms and this must be weighed against the loss of the heirloom
premium market price.
57
Table 4-1. Sources and prices for materials used to produce grafted and nongrafted heirloom tomato transplants.
Pricez Lifespany Item Description Unit ($/unit) (years) Source
Seedling materials „Brandywine‟ Nongrafted /scion 30 seeds 1.18 TomatoFest, Little River,
CA „Multifort‟ Rootstock 250 seeds 57.00 Paramount Seeds, Palm
City, Florida Fafard custom organic mix
Potting soil 40 quart bag
9.50 BWI, Apopka, FL
Speedling 128-cell planter flats
Styrofoam seedling tray
5 flats 34.70 5 Speedling, Inc., Sun City, FL
Neptune‟s Harvest Liquid organic fertilizer
1 gallon 45.50 Neptune‟s Harvest, Gloucester, MA
Grafting Supplies 2.0-mm clips Silicone grafting
clips 1000 clips 42.00 Hydro-Gardens,
Colorado Springs, CO Razor blades, hand sanitizer, paper towels, etc.
Tools for grafting Per 1250 grafted plants
8.00 Local/regional department store
Healing Chamber Supplies
Cool-mist humidifier Maintains humidity Per chamber
25.00 5 Local/regional department store
Air conditioner Window unit Per chamber
159.00 5 Local/regional hardware store
Wood, PVC pipe, plastic sheeting, etc.
Frame and covering for chamber
Per chamber
26.86 5 Local/regional hardware store
z Based on fall 2011 prices. y Expected years of use, a straight-line depreciation was applied for the number of years indicated.
58
Table 4-2. Costs of grafted and nongrafted organic heirloom tomato transplants.z
Graftedy Nongraftedx
Laborw Material Labor Material
Item $/1000 plants $/1000 plants
Seeds Scion („Brandywine‟)v 49.56 43.66 Rootstock („Multifort‟)u 285.00 Seedling Potting soil 19.00 9.50 production Flatst 27.76 12.49 Seed sowing and care 92.95 59.15 Liquid fertilizer 91.00 45.50 Grafted transplant Graftings 52.81 production Silicon clips 56.70 Miscellaneous supplies 8.00 Post-graft care 21.13 Healing chamberr Humidifier 5.49 Air conditioner 31.80 Building supplies 26.86 Assembly 16.90 Subtotal 183.79 601.17 59.15 111.15 Total 784.96 170.30 Cost/plant 0.78 0.17 z Estimate of costs based on fall 2011 prices for a target 1,000 grafted transplants. y Seeds over sowed by 25% to account for 90% graft success and 90% germination. x Seeds over sowed by 10% to account for 90% germination. w $8.45/hr pay wage for all labor. v Indeterminate heirloom tomato cultivar, certified organic seed. u Interspecific hybrid rootstock. t 128-cell count transplant flats, straight line depreciated for 5-years estimated use. s 200 plants/grafter/h graft rate. r Straight-line depreciated for 5-years estimated use.
59
Table 4-3. Estimated partialz net return per plant ($/plant) for nongrafted „Brandywine‟y plants grown organically with low root-knot nematode pressurex.
z Matrix values represent [(yield*$/lb) – transplant cost]. Other production, harvest, and packing costs (e.g. land preparation, drip tape, mulch, fertilizer, pest control, labor, etc.) must be factored in to achieve a full net return per plant. y „Brandywine‟ is a popular, indeterminate, heirloom, beefsteak tomato cultivar that is susceptible to root-knot nematodes. x Root-knot nematode pressure was assessed by root galling ratings (Zeck, 1971). w Yields presented were the estimated mean yield ± 3 standard errors, the estimated mean yield was based on pooled data from the 2010 and 2011 organic field trials. v Prices per pound were calculated from published 2008 monthly averages for 10 lb cartons of organic heirloom tomato fruit (USDA, 2009), 1 lb = 0.454 kg.
Standard error
Yieldw (lbs/plant)
Tomato pricev
($/lb)
1.80 2.00 2.20 2.40 2.60 2.80 3.00 3.20 -3 1.39 2.33 2.61 2.89 3.17 3.45 3.72 4.00 4.28 -2 1.53 2.58 2.88 3.19 3.49 3.80 4.10 4.41 4.72
-1 1.66 2.82 3.16 3.49 3.82 4.15 4.49 4.82 5.15 Mean 1.80 3.07 3.43 3.79 4.15 4.51 4.87 5.23 5.59
+1 1.93 3.31 3.70 4.09 4.47 4.86 5.25 5.63 6.02 +2 2.07 3.56 3.97 4.39 4.80 5.21 5.63 6.04 6.46 +3 2.21 3.80 4.24 4.68 5.13 5.57 6.01 6.45 6.89
60
Table 4-4. Estimated partialz net return per plant ($/plant) for plants of „Brandywine‟y grafted onto the rootstock „Multifort‟x grown organically with low nematode pressurew.
Standard error
Yieldv (lbs/plant)
Tomato priceu
($/lb)
1.80 2.00 2.20 2.40 2.60 2.80 3.00 3.20 -3 0.90 0.85 1.03 1.21 1.39 1.57 1.75 1.93 2.11 -2 1.04 1.09 1.30 1.51 1.71 1.92 2.13 2.34 2.54 -1 1.17 1.33 1.57 1.80 2.04 2.27 2.51 2.74 2.98
Mean 1.31 1.58 1.84 2.10 2.37 2.63 2.89 3.15 3.41 +1 1.45 1.82 2.11 2.40 2.69 2.98 3.27 3.56 3.85 +2 1.58 2.07 2.39 2.70 3.02 3.34 3.65 3.97 4.29 +3 1.72 2.31 2.66 3.00 3.35 3.69 4.03 4.38 4.72
z Matrix values represent [(yield*$/lb) – transplant cost]. Other production, harvest, and packing costs (e.g. land preparation, drip tape, mulch, fertilizer, pest control, labor, etc.) must be factored in to achieve a full net return per plant. y „Brandywine‟ is a popular, indeterminate, heirloom, beefsteak tomato cultivar. x „Multifort‟ is an interspecific hybrid tomato rootstock with resistance to root-knot nematodes and vigorous habit. w Root-knot nematode pressure was assessed by root galling ratings (Zeck, 1971). v Yields presented were the estimated mean yield ± 3 standard errors, the estimated mean yield was based on pooled data from the 2010 and 2011 organic field trials. u Prices per pound were calculated from published 2008 monthly averages for 10 lb cartons of organic heirloom tomato fruit (USDA, 2009), 1 lb = 0.454 kg.
61
Table 4-5. Estimated partialz net return per plant ($/plant) for nongrafted „Brandywine‟y plants grown in a transitional organic field with high nematode pressurex.
Standard error
Yieldw (lbs/plant)
Tomato pricev
($/lb)
1.80 2.00 2.20 2.40 2.60 2.80 3.00 3.20 -3 -0.25 -0.63 -0.68 -0.73 -0.78 -0.83 -0.88 -0.93 -0.98 -2 -0.05 -0.27 -0.28 -0.29 -0.30 -0.31 -0.32 -0.33 -0.34 -1 0.15 0.10 0.13 0.15 0.18 0.21 0.24 0.27 0.30
Mean 0.35 0.46 0.53 0.60 0.67 0.74 0.81 0.87 0.94 +1 0.55 0.82 0.93 1.04 1.15 1.26 1.37 1.48 1.59 +2 0.75 1.18 1.33 1.48 1.63 1.78 1.93 2.08 2.23 +3 0.95 1.54 1.73 1.92 2.11 2.30 2.49 2.68 2.87
z Matrix values represent [(yield*$/lb) – transplant cost]. Other production, harvest, and packing costs (e.g. land preparation, drip tape, mulch, fertilizer, pest control, labor, etc.) must be factored in to achieve a full net return per plant. y „Brandywine‟ is a popular, indeterminate, heirloom, beefsteak tomato cultivar that is susceptible to root-knot nematodes. x Root-knot nematode pressure was assessed by root galling ratings (Zeck, 1971), high root galling ratings in the transitional organic field indicated a severe nematode infestation. w Yields presented were the estimated mean yield ± 3 standard errors, the estimated mean yield was based on data from the 2011 transitional organic field trial. v Prices per pound were calculated from published 2008 monthly averages for 10 lb cartons of organic heirloom tomato fruit (USDA, 2009), 1 lb = 0.454 kg.
62
Table 4-6. Estimated partialz net return per plant ($/plant) for plants of „Brandywine‟y grafted onto the rootstock „Multifort‟x grown in a transitional organic field with high nematode pressurew.
Standard error
Yieldv (lbs/plant)
Tomato priceu
($/lb)
1.80 2.00 2.20 2.40 2.60 2.80 3.00 3.20 -3 0.84 0.73 0.90 1.07 1.24 1.41 1.58 1.74 1.91 -2 1.04 1.10 1.30 1.51 1.72 1.93 2.14 2.35 2.56 -1 1.24 1.46 1.71 1.96 2.20 2.45 2.70 2.95 3.20
Mean 1.44 1.82 2.11 2.40 2.69 2.97 3.26 3.55 3.84 +1 1.64 2.18 2.51 2.84 3.17 3.50 3.83 4.15 4.48 +2 1.85 2.54 2.91 3.28 3.65 4.02 4.39 4.76 5.13 +3 2.05 2.90 3.31 3.72 4.13 4.54 4.95 5.36 5.77
z Matrix values represent [(yield*$/lb) – transplant cost]. Other production, harvest, and packing costs (e.g. land preparation, drip tape, mulch, fertilizer, pest control, labor, etc.) must be factored in to achieve a full net return per plant. y „Brandywine‟ is a popular, indeterminate, heirloom, beefsteak tomato cultivar. x „Multifort‟ is an interspecific hybrid tomato rootstock with resistance to root-knot nematodes and vigorous habit. w Root-knot nematode pressure was assessed by root galling ratings (Zeck, 1971), high root galling ratings in the transitional organic field indicated a severe nematode infestation. v Yields presented were the estimated mean yield ± 3 standard errors, the estimated mean yield was based on data from the 2011 transitional organic field trial. u Prices per pound were calculated from published 2008 monthly averages for 10 lb cartons of organic heirloom tomato fruit (USDA, 2009), 1 lb = 0.454 kg.
63
CHAPTER 5 CONCLUSION
Vegetable grafting is used successfully in intensive agricultural production systems
throughout the world. With the phase-out of methyl bromide for soil fumigation, growers
in the United States are searching for sustainable alternatives for pest management.
The steadily increasing demand for organic fruits and vegetables has also helped drive
the need for new methods of controlling soilborne diseases that do not rely on synthetic
chemicals. Interest in grafting is emerging in the United States but adoption has
remained low. Growers are concerned that grafting will have a negative impact on crop
performance and fruit quality. More importantly, the higher cost of grafted transplants
has presented a major barrier that has prevented a more wide-spread adoption of this
technique. Growers need to know how the extra costs associated with using grafted
plants will be recovered and what effects grafting will have on fruit attributes before they
consider it economically feasible.
This research demonstrated that through the use of appropriate rootstocks,
grafting can be used to successfully overcome the root-knot nematode species
Meloidogyne javanica in organic production of heirloom tomatoes in the open-field. Yield
was generally unaffected by grafting treatments under low nematode pressure.
However, tomato yields were maintained by using a nematode-resistant interspecific
hybrid rootstock under severe nematode pressure as compared to nongrafted plants.
Given that nematode infestations can be particularly severe during the transition to
organic production, grafting may play an effective role in pest management in the
transition process. To address concerns with regard to a possible rootstock effect on
fruit quality and sensory attributes, fruit assessments and consumer taste tests were
64
conducted. The rootstocks used in this study showed no consistent effect on fruit quality
attributes including fruit taste. A partial budget analysis was performed to determine the
cost of producing grafted tomato transplants on-farm. The major contributor to the cost
of grafted transplants in this study was the price of rootstock seeds. In time, the price of
rootstock seeds should drop as more rootstocks are developed for United States
producers, making grafting more affordable. Finally, sensitivity analyses were performed
to estimate expected partial returns for grafted and nongrafted plants grown under high
and low root-knot nematode pressure conditions. The use of grafted plants was
demonstrated to be economically feasible when specific scion-rootstock combination
was used in a field with a severe root-knot nematode infestation.
Growers using grafted transplants will need to choose appropriate rootstocks for
their site-specific growing conditions. Future research should be conducted in major
production regions with multiple rootstocks, including both intraspecific and interspecific
hybrids, in order to fully elucidate the scion-rootstock interactions. This will help growers
select the most suitable rootstock for their production systems and reduce the risk of
economic losses.
65
LIST OF REFERENCES
Bausher, M.G. 2009. Commercial tomato rootstock performance when exposed to natural populations of root-knot nematodes in Florida. HortScience 44:1021-1021 (abstr.).
Bland, S.E. 2005. Consumer acceptability of heirloom tomatoes. MS thesis. University of Georgia, Athens, GA.
Davis, A.R., P. Perkins-Veazie, R. Hassel, A. Levi, S.R. King, and X. Zhang. 2008. Grafting effects on vegetable quality. HortScience 43:1670-1672.
Di Gioia, F., F. Serio, D. Buttaro, O. Ayala, and P. Santamaria. 2010. Influence of rootstock on vegetative growth, fruit yield, and quality in „Cuore di Bue‟, an heirloom tomato. J. Hort. Sci. Biotechnol. 85:477-482.
Dong, K., R.A. Dean, B.A. Fortnum, and S.A. Lewis. 2001. Development of PCR primers to identify species of root-knot nematodes: Meloidogyne arenaria, M. hapla, M. incognita and M. javanica. Nematropica 31:273-282.
Edelstein, M. 2004. Grafting vegetable-crop plants: pros and cons. Acta Hort. 659:235-238.
Fernandez-Garcia, N., V. Martinez, and M. Carvajal. 2004. Fruit quality of grafted tomato plants grown under saline conditions. J. Hort. Sci. Biotechnol. 79:995-1001.
Freeman, J., S. Rideout, and A. Wimer. 2009. Performance of grafted tomato seedlings in open-field production. p. 045-1 to 045-2. In: G.L. Obenaf (ed.). 2009 Annual international research conference on methyl bromide alternatives and emissions reductions. Methyl Bromide Alternatives Outreach, Fresno, CA. 20 September 2011. <http://mbao.org/2009/Proceedings/045FreemanJGrafted%20tomato%20MBAO.pdf>.
Greene, C., C. Dimitri, B.-H. Lin, W. McBride, L. Oberholtzer, and T. Smith. 2009. Emerging issues in the U.S. organic industry. EIB-55, U. S. Dept. Agr. Econ. Res. Serv., Washington, DC.
Jordan, J.A. 2007. The heirloom tomato as cultural object: investigating taste and space. Sociologia Ruralis 47:20-41.
Khah, E.H., E. Kakava, A. Mavromatis, D. Chachalis, and C. Goulas. 2006. Effect of grafting on growth and yield of tomato (Lycopersicon esculentum Mill.) in greenhouse and open-field. J. Appl. Hort. 8:3-7.
King, S.R., A.R. Davis, W. Liu, and A. Levi. 2008. Grafting for disease resistance. HortScience 43:1673-1676.
66
King, S.R., A.R. Davis, X. Zhang, and K. Crosby. 2010. Genetics, breeding and selection of rootstocks for Solanaceae and Cucurbitaceae. Scientia Hort. 127:106-111.
Klee, H.J. 2010. Improving the flavor of fresh fruits: genomics, biochemistry, and biotechnology. New Phytologist 187:44-56.
Krumbein, A. and H. Auerswald. 1998. Characterization of aroma volatiles in tomatoes by sensory analyses. Nahrung 42:395-399.
Kubota, C. 2008. Use of grafted seedlings for vegetable production in North America. Acta Hort. 770:21-28.
Kubota, C., M.A. McClure, N. Kokalis-Burelle, M.G. Bausher, and E.N. Rosskopf. 2008. Vegetable grafting: History, use, and current technology status in North America. HortScience 43:1664-1669.
Lee, J.M.1994. Cultivation of grafted vegetables I. current status, grafting methods, and benefits. HortScience 29:235-239.
Lee, J.M., H.J. Bang, and H.S. Ham. 1999. Quality of cucumber fruit as affected by rootstock. Acta Hort. 483:117-123.
Lee, J.M., C. Kubota, S.J. Tsao, Z. Bie, P. Hoyos Echevarria, L. Morra, and M. Oda. 2010. Current status of vegetable grafting: Diffusion, grafting techniques, automation. Scientia Hort. 127:93-105.
López-Pérez, J.A., M. Le Strange, I. Kaloshian, and A.T. Ploeg. 2006. Differential response of Mi gene-resistant tomato rootstocks to root-knot nematodes (Meloidogyne incognita). Crop Protection 25:382-288.
Louws, F.J., C. Rivard, and C. Kubota. 2010. Grafting fruiting vegetables to manage soilborne pathogens, foliar pathogens, arthropods and weeds. Scientia Hort. 127:127-146.
Martínez-Ballesta, M., L. López-Pérez, M. Hernández, C. López-Berenguer, N. Fernández-García, and M. Carvajal. 2008. Agricultural practices for enhanced human health. Phytochem. Rev. 7:251-260.
Mattheis, J.P. and J.K. Fellman. 1999. Preharvest factors influencing flavor of fresh fruit and vegetables. Postharvest Bio. and Technol. 15:227-232.
McSorley, R. 2002. Nematode and insect management in transitional agricultural systems. HortTechnology 12:597-600.
Medina-Filho, H.P. and M.A. Stevens. 1980. Tomato breeding for nematode resistance: survey of resistant varieties for horticultural characteristics and genotype of acid phosphates. Acta Hort. 100:383-393.
67
Mišković, A., Ž. Ilin, and V. Marković. 2009. Effect of different rootstock type on quality and yield of tomato fruits. Acta Hort. 807:619-624.
O‟Connell, S., S. Hartmann, C.L. Rivard, M.M. Peet, and F.J. Louws. 2009. Grafting tomatoes on disease resistant rootstocks for small-scale organic production. 20 September 2011. <http://ofrf.org/funded/highlights/oconnell_07f30.html>.
Oda, M., M. Nagata, K. Tsuji, and H. Sasaki. 1996. Effects of scarlet eggplant rootstock on growth, yield, and sugar content of grafted tomato fruits. J. Japan. Soc. Hort. Sci. 65:531-536.
Olson, S.M. 2004. Physiological, nutritional, and other disorders of tomato fruit. Florida Coop. Ext. Serv. Bul. HS-954, University of Florida, Gainesville, FL.
Olson, S.M., W.M. Stall, G.E. Vallad, S.E. Webb, S.A. Smith, E.H. Simonne, E.J. McAvoy, B.M. Santos, and M. Ozores-Hampton. 2011. Tomato production in Florida, p. 309-332. In: S.M. Olson and B.M. Santos (eds.). Vegetable production handbook for Florida. Vance Publishing Corporation, Lincolnshire, IL.
Pogonyi, Á., Z. Pék, L. Helyes, and A. Lugasi. 2005. Effect of grafting on the tomato‟s yield, quality and main fruit components in spring forcing. Acta Aliment. 34:453-462.
Rivard, C.L. 2006. Grafting tomato to manage soilborne diseases and improve yield in organic production systems. MS thesis, North Carolina State University, Raleigh, NC.
Rivard, C.L. and F.J. Louws. 2006. Grafting for disease resistance in heirloom tomatoes. North Carolina Coop. Ext. Serv. Bul. Ag-675, North Carolina State University, Raleigh, NC.
Rivard, C.L. and F.J. Louws. 2008. Grafting to manage soilborne diseases in heirloom tomato production. HortScience 43:2104-2111.
Rivard, C.L., S. O‟Connell, M.M. Peet, and F.J. Louws. 2010a. Grafting tomato with interspecific rootstock to manage diseases caused by Sclerotium rolfsii and southern root-knot nematode. Plant Dis. 94:1015-1021.
Rivard, C.L., O. Sydorovych, S. O‟Connell, M.M. Peet, and F.J. Louws. 2010b. An economic analysis of two grafted tomato transplant production systems in the United States. HortTechnology 20:794-803.
Roberts, P.A., W.C. Matthews, Jr., and J.D. Ehlers. 2005. Root-knot nematode resistant cowpea cover crops in tomato production systems. Agron. J. 97:1626-1635.
Romano, D. and A. Paratore. 2001. Effects of grafting on tomato and eggplant. Acta Hort. 559:149-153.
68
Rouphael, Y., D. Schwarz, A. Krumbein, and G. Colla. 2010. Impact of grafting on product quality of fruits and vegetables. Scientia Hort. 127:172-179.
Sasser, J.N. 1980. Root-knot nematodes: A global menace to agriculture. Plant Dis. 64:36-41.
Schwarz, D., Y. Rouphael, G. Colla, and J.H. Venema. 2010. Grafting as a tool to improve tolerance of vegetables to abiotic stresses: thermal stress, water stress, and organic pollutants. Scientia Hort. 127:162-171.
State of Florida, Agency for workforce innovation. 2011. Occupational employment statistics and wages, 2011 wage estimates. Department of Economic Opportunity, Tallahassee, FL. 20 September 2011. <http://www.labormarketinfo.com/library/oes.htm>.
Taylor, M., B. Burton, W. Fish, and W. Roberts. 2008. Cost benefit analysis of using grafted watermelon transplants for fusarium wilt disease control. Acta Hort. 782:343-350.
Terada, M., Y. Watanabe, M. Kunitomo, and E. Hayashi.1978. Differential rapid analysis of ascorbic acid 2-sulfate by dinitrophenylhydrazine method. Ann. Biochem. 84:604–608.
U.S. Department of Agriculture, Agricultural Marketing Service. 2002. Code of Federal Regulations, Title 7, Part 205. National Organic Program. 08 August 2011. <http://www.ams.usda.gov/AMSv1.0/getfile?dDocName=STELDEV3004452>.
U.S. Department of Agriculture, Economic Research Service. 2009. Wholesale vegetable prices, Boston and San Francisco, 2008. 20 September 2011. http://www.ers.usda.gov/Data/OrganicPrices/.
Venema, J.H., B.E. Dijk, J.M. Bax, P.R. van Hasselt, J. Theo, and M. Elzenga. 2008. Grafting tomato (Solanum lycopersicum) onto the rootstock of a high-altitude accession of Solanum habrochaites improves suboptimal-temperature tolerance. Environ. Expt. Bot. 63:359-367.
Verdejo-Lucas, S. and F.J. Sorribas. 2008. Resistance response of the tomato rootstock SC 6301 to Meloidogyne javanica in a plastic house. Eur. J. Plant Pathol. 121:103-107.
Zeck, W. 1971. A rating scheme for field evaluation of root-knot nematode infestations. Pflanzenschutz-Nachrichten Bayer 24:141-144.
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BIOGRAPHICAL SKETCH
Charles Edward Barrett was born in Amsterdam, NY. When he was 5 years old his
family moved to Edgewater, FL. Charles grew up loving the ocean, the springs and all of
Florida‟s natural beauty. He graduated from New Smyrna Beach High School in May of
2002 and decided to work before going to college. Charles earned his A.A. from
Daytona Beach Community College in December of 2007 and began at the University of
Florida in January 2008. Charles felt inspired in Gainesville and after receiving his B.S.
in botany, he was accepted into the UF graduate school for an opportunity to earn a
M.S. in horticultural science.
Upon completion of his M.S. program Charles will decide to either continue his
education or seek employment.
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