ENVIRONMENTAL CONDITIONS, CULTIVAR, AND PROPAGATION MATERIAL

AFFECT RHIZOME YIELD AND POSTHARVEST QUALITY OF GINGER (ZINGIBER

OFFICINALE ROSC.), GALANGAL (ALPINIA GALANGA LINN.), AND TURMERIC

(CURCUMA SPP.)

By

SOFIA JESUS FLORES VIVAR

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

2019

© 2019 Sofia J. Flores Vivar

To my parents, siblings, and plant friends

4

ACKNOWLEDGMENTS

I would like to thank Dr. Rosanna Freyre and Dr. Paul Fisher for giving me the

opportunity to work for their program initially as a Research Visiting Scholar. After that first

experience, they let me continue working and guided me through my masters’ studies. I thank

Dr. Sargent for his advice and help during my postharvest evaluations.

Special thanks to present and past students from Dr. Fisher and Dr. Freyre’s labs for their

help and support. Thanks to Victor Zayas, Erin Yafuso, Ulrich Adegbola, George Grant,

Jonathan Clavijo, Henry Kironde, and Nicholas Genna for being amazing friends. I thank Brian

Owens, Mark Kann and their teams for always being there to help me in the greenhouse and

field. I would like to thank Dr. Pearson and his team from Mid-Florida Research and Education

Center in Apopka for letting me work in their lab and providing instruction to perform the

chemical analyses of my plants. I thank Dr. Rathinasabapathi for his advice and willingness to

help me with the analysis of my rhizomes. I would like to thank Dr. Gomez for her friendship

and unwavering support. Thanks to James Colee from UF Agriculture Statistics for support with

statistical analysis.

This research project was supported by the Floriculture Research Alliance

(FloricultureAlliance.org). I thank Hawaii Clean Seed, LLC. for supplying rhizomes in 2017,

Just Ginger growers for their donation of rhizomes in 2018, and AgriStarts for donating the

micropropagated planting material.

5

TABLE OF CONTENTS

page

ACKNOWLEDGMENTS ...............................................................................................................4

LIST OF TABLES ...........................................................................................................................7

LIST OF FIGURES .........................................................................................................................9

LIST OF ABBREVIATIONS ........................................................................................................11

ABSTRACT ...................................................................................................................................12

CHAPTER

1 INTRODUCTION ..................................................................................................................14

2 ANALYSIS OF FACTORS AFFECTING SPROUTING OF GINGER (ZINGIBER

OFFICINALE) AND TURMERIC (CURCUMA SPP.) RHIZOMES ....................................17

Background .............................................................................................................................17 Material and Methods .............................................................................................................20

Results and Discussion ...........................................................................................................23 Summary .................................................................................................................................26

3 RHIZOME YIELD AND POSTHARVEST QUALITY OF GINGER (ZINGIBER

OFFICINALE) AND GALANGAL (ALPINIA GALANGA) AS AFFECTED BY

PROPAGATION MATERIAL, CULTIVAR, AND ENVIRONMENTAL

CONDITIONS DURING PRODUCTION.............................................................................30

Background .............................................................................................................................30 Materials and Methods ...........................................................................................................36

Experiment 1. Greenhouse Experiments .........................................................................36

Year 1 (2017-2018) ..................................................................................................36 Year 2 (2018-2019) ..................................................................................................38

Experiment 2. Field Experiment ......................................................................................41

Results and Discussion ...........................................................................................................43 Experiment 1. Greenhouse Experiments .........................................................................43

Year 1 (2017-2018) ..................................................................................................43

Year 2 (2018-2019) ..................................................................................................46 Postharvest Evaluations – Greenhouse Trial – Year 2 .............................................52

Experiment 2 – Field Experiment ....................................................................................54 Postharvest Evaluations – Field Experiment ............................................................59

Summary .................................................................................................................................60

6

4 INTERACTION OF PROPAGATION MATERIAL, CULTIVAR, AND

ENVIRONMENTAL FACTORS ON ORNAMENTAL PLANT PERFORMANCE,

RHIZOME YIELD, AND RHIZOME QUALITY OF TURMERIC (CURCUMA SPP.). ....79

Background .............................................................................................................................79 Materials and Methods ...........................................................................................................83

Experiment 1. Greenhouse Experiments .........................................................................83 Year 1 (2017-2018) ..................................................................................................84

Year 2 (2018-2019) ..................................................................................................85 Experiment 2. Field Experiment ......................................................................................88

Results and Discussion ...........................................................................................................90 Experiment 1. Greenhouse Experiments .........................................................................90

Year 1 (2017-2018) ..................................................................................................90

Year 2 (2018-2019) ..................................................................................................92 Postharvest Evaluations – Greenhouse Trial – Year 1 .............................................99

Experiment 2 – Field Experiment ..................................................................................101 Postharvest Evaluations – Field Experiment ..........................................................107

Summary ...............................................................................................................................109

5 CONCLUSIONS ..................................................................................................................128

LIST OF REFERENCES .............................................................................................................132

BIOGRAPHICAL SKETCH .......................................................................................................145

7

LIST OF TABLES

Table page

2-1 Mean values and Tukey grouping comparison for days to sprout, number of sprouted

buds after 4 and 8 weeks, shoot and root length and final weight of ginger and

turmeric rhizomes from different sources in Experiment 1. ..............................................27

2-2 Mean values and Tukey grouping comparison for days to sprout, number of sprouted

buds after 4 and 8 weeks, shoot and root length and final weight of ginger and

turmeric rhizomes from different sources in Experiment 2. ..............................................28

2-3 Mean values and Tukey grouping comparison for initial weight, initial number of

visible buds, initial length and diameter of rhizomes of ginger and turmeric cultivars

from different sources in Experiment 1 and 2. ..................................................................29

3-1 Mean values and Tukey grouping comparison for plant type, average new shoot

number, height increase, number of flowers, overall rating, and SPAD with varying

photoperiods in the greenhouse in year 2 (2018-2019). ....................................................62

3-2 Mean values and Tukey grouping comparison for plant type, storage period, and

color parameters of rhizomes grown under natural days in year 2, harvested and

stored for 2 weeks. .............................................................................................................63

3-3 Mean values and Tukey grouping comparison for plant type, storage period, and

color parameters of rhizomes grown under long days in year 2, harvested and stored

for 2 weeks. ........................................................................................................................64

3-4 Mean values and Tukey grouping comparison for plant type, average new shoot

number, height increase, SPAD, overall rating, and number of flowers of plants

grown in the field under full sun and 60% shade in year 2. ...............................................65

3-5 Mean values and Tukey grouping comparison for plant type, storage period storage

period, and color parameters of rhizomes harvested from the field, and stored for 2

weeks..................................................................................................................................66

4-1 Mean values and Tukey grouping comparison for plant type, average new shoot

number, height, SPAD, overall rating, and number of flowers in the greenhouse

under natural and long days in year 2. .............................................................................112

4-2 Mean values and Tukey grouping comparison for plant type, storage period, and

color parameters of rhizomes grown the greenhouse under natural days in year 2,

harvested and stored for 2 weeks. ....................................................................................113

4-3 Mean values and Tukey grouping comparison for plant type, storage period, and

color parameters of rhizomes grown the greenhouse under long days in year 2,

harvested and stored for 2 weeks .....................................................................................114

8

4-4 Mean values and Tukey grouping comparison for plant type, average new shoot

number, height, SPAD, overall rating, and number of flowers in the field under full

sun or 60% shade. ............................................................................................................115

4-5 Mean values and Tukey grouping comparison for plant type, storage period, and

color parameters of rhizomes grown in the field under full sun and 60% shade,

harvested and stored for 2 weeks .....................................................................................116

9

LIST OF FIGURES

Figure page

3-1 Rhizome, shoot and root fresh mass of ginger plants grown in the greenhouse under

natural or long days in year 1 .............................................................................................67

3-2 Rhizome fresh mass from ginger plants grown in the greenhouse in year 1. ....................68

3-3 Carbohydrate partitioning of ginger plants grown in the greenhouse under natural or

long days in year 1. ............................................................................................................69

3-4 Rhizome, shoot, root, and total fresh mass of ginger and galangal plants grown in the

greenhouse under natural and long days in year 2. ............................................................70

3-5 Visual scale from 1 to 5 to measure overall aesthetic performance of ginger plants

grown in the greenhouse in year 2. ....................................................................................71

3-6 Rhizome fresh mass from ginger and galangal plants grown in the greenhouse under

natural and long days in year 2. .........................................................................................72

3-7 Carbohydrate partitioning of ginger and galangal plants grown in the greenhouse

under natural or long days in year 2...................................................................................73

3-8 Postharvest rhizome weight loss of ginger and galangal plants grown in the

greenhouse in year 2, harvested and stored for 2 weeks. ...................................................74

3-9 Decay symptoms of rhizomes harvested in 2019 after 2 weeks of postharvest storage ....75

3-10 Rhizome, shoot, root, and total fresh mass of ginger and galangal plants grown in the

field under full sun and 60% shade in year 2. ....................................................................76

3-11 Carbohydrate partitioning of ginger and galangal plants grown in the field under full

sun and 60% shade in year 2 ..............................................................................................77

3-12 Postharvest rhizome weight loss of ginger and galangal plants grown in the field in

year 2, harvested and stored for a period of two weeks. ....................................................78

4-1 Rhizome, shoot, and root fresh mass of turmeric plants grown in the greenhouse

under natural and long days in year 1 ..............................................................................117

4-2 Carbohydrate partitioning of turmeric plants grown in the greenhouse under natural

and long days in year 1 ....................................................................................................118

4-3 Rhizome, shoot, root, and total fresh mass from turmeric plants grown in the

greenhouse under natural and long days in year 2. ..........................................................119

4-4 Rhizome fresh mass from one turmeric plant type grown in 14.5 L, under natural

days in the greenhouse from in year 2. ............................................................................120

10

4-5 Rhizome fresh mass from one turmeric plant type grown in 14.5 L, under long days

in the greenhouse from in year 2......................................................................................121

4-6 Visual scale from 1 to 5 to measure overall aesthetic performance of turmeric plants

grown in the greenhouse under natural and long days in year 2. .....................................122

4-7 Carbohydrate partitioning from turmeric plants grown in the greenhouse under

natural and long days from in year 2. ..............................................................................123

4-8 Postharvest rhizome weight loss from turmeric plants grown in the greenhouse under

natural and long days in year 2, harvested and stored for a period of 2 weeks. ..............124

4-9 Rhizome, shoot, root, and total fresh mass of turmeric plants grown in the field under

full sun and 60% shade in year 2.. ...................................................................................125

4-10 Carbohydrate partitioning of turmeric plants grown in the field under full sun and

60% shade in year 2. ........................................................................................................126

4-11 Postharvest rhizome weight loss of turmeric plants grown in the field under full sun

and 60% shade in year 2, harvested and stored for a period of 2 weeks .........................127

11

LIST OF ABBREVIATIONS

ANOVA Analysis of Variance

BA Benzyladenine

BAP Benzylaminopurine

CRF Controlled Release Fertilizer

DLI Daily Light Integral

h Hours

HSD

masl

Honestly Significant Difference

Meters above sea level

MAP Modified Atmosphere Packages

PAR Photosynthetically Active Radiation

PGR Plant Growth Regulator

ppm Parts Per Million

PSREU Plant Science Research and Education Unit

R:FR Red/far-red ratio

RH Relative Humidity

RLI Relative Light Intensity

s Seconds

UF University of Florida

U.S. United States

12

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

ENVIRONMENTAL CONDITIONS, CULTIVAR, AND PROPAGATION MATERIAL

AFFECT RHIZOME YIELD AND POSTHARVEST QUALITY OF GINGER (ZINGIBER

OFFICINALE ROSC.), GALANGAL (ALPINIA GALANGA LINN.), AND TURMERIC

(CURCUMA SPP.)

By

Sofia J. Flores Vivar

August 2019

Chair: Rosanna Freyre

Major: Horticultural Sciences

There is economic opportunity for growers in the United States (U.S.) to diversify their

current commercial production by introducing ginger (Zingiber officinale Roscoe), galangal

(Alpinia galanga Linn.) or turmeric (Curcuma spp.). These species are considered as high-value

crops for Florida due to the pungent spicy taste, fragrant aroma, and medicinal attributes of their

rhizomes. These species are excellent candidates as alternative “superfoods” and have gained

popularity in recent years. However, due to the lack of standard production guidelines, local

production is currently limited. The objectives of this study were to (a) evaluate plant material

sources and cultivars for greenhouse and field production of ginger, galangal, and turmeric, and

(b) identify environmental conditions that can extend the growing season of plants by avoiding

dormancy during short days and maximize high quality rhizome production.

Rhizome quality is essential for sprouting and they can be dormant at planting, thus propagation

is still a challenge for growers. Additionally, storability of rhizomes is limited, affecting their

quality. Therefore, a propagation experiment was performed two times to determine whether

rhizome quality varies over storage time and if storage affected sprouting. In both experiments,

13

rhizomes of ginger ‘Bubba baba’ sprouted earlier, had more sprouted buds and grew more than

turmeric cultivars (particularly ‘White Mango’ and ‘BKK’). This can be attributed to having the

best initial rhizome quality (highest rhizome weight and bud number), while turmeric rhizomes

had the lowest quality. When rhizomes of these cultivars and others including micropropagated

ginger (ginger “tc”) and turmeric (yellow “tc”) were grown in the greenhouse under two different

photoperiods, larger containers (50.5 L) promoted more growth and higher rhizome yield than in

smaller containers (5.7 L). The diameter of rhizomes harvested from micropropagated plants in

the first year was smaller than that obtained from rhizome-derived plants. In the second year,

plants grown under night interruption lighting (long days) had higher new shoot number and

shoot fresh mass than under natural daylength. Under natural days, ginger ‘Bubba baba’ and

turmeric ‘Black’ had significantly lower yields than those grown under long days. Under both

photoperiods, galangal “tc” had the highest rhizome yield. Ginger “tc” first and second

generation (“ownrhiz”) had similar high yields, however, the former had smaller rhizome

diameter. Turmeric white “tc” had the highest yield under long days, but there was no difference

in yield between turmeric yellow “ownrhiz” and yellow “tc” under the two photoperiods. In the

field, however, white “tc” had the lowest yield, and yellow “ownrhiz” had higher yield than

yellow “tc”. There were no differences in yields in the field for any of the genera between full

sun and 60% shade. Results suggest that micropropagation may be more effective to develop

clean stock material for seed rhizomes of ginger and turmeric than for attempting maximum

rhizome yields during the first year. Also, other shading strategies should be tested to see if

rhizome yields can be improved compared to growing in full sun. Overall, research showed that

differences in yield depend upon genotype, plant material, and environmental conditions, and an

economic analysis is needed to identify the most efficient production conditions.

14

CHAPTER 1

INTRODUCTION

In the U.S. there is increasing demand for earthy spices such as ginger, galangal, and

turmeric. These species belong to the family Zingiberaceae, were domesticated centuries ago and

are cultivated in many tropical areas of the world due to their multiple benefits besides cooking.

The rhizomes of these species are claimed to have medicinal anti-inflamatory properties (Rao et

al., 2008; Ruby et al., 1995). For instance, consumption of ginger rhizomes is recommended to

improve joint health, reduce blood sugar, and treat different types of cancer (Gregory et al.,

2008; Li et al., 2016; Srinivasan et al., 2016). Meanwhile, rhizomes of galangal are widely used

in Asian cuisines and often to replace ginger as they also have a pungent, spicy taste and a

ginger-like odor (Huang et al., 2018; Tang et al., 2018). Turmeric or Curcuma longa is by far the

most important Curcuma species, due to its worldwide use as a spice and coloring agent in

cooking (Li et al., 2011; Popuri and Pagala, 2013). Moreover, due to the presence of

curcuminoids, turmeric rhizomes also have high medicinal potential (Niranjan et al., 2013; Ruby

et al., 1995). For this reason, these three spices are highly demanded in the U.S. Consumption of

ginger per capita has increased from about 0.5 kg in 1966 to 1.7 kg in 2015 (Nguyen et al.,

2019). The import value of ginger in the U.S. in 2016 was $67.05 million (Tridge, 2019a) and for

turmeric it is $31.6 million and is gradually increasing (Tridge, 2019b; Nguyen et al., 2019).

Therefore, there is a lot of potential for increasing national production of these spices in the

country.

Ginger, galangal and turmeric plants are widely cultivated in tropical and subtropical

regions including India, China, Nigeria, Indonesia, Bangladesh, and Australia as they grow well

in warm and humid climates (Chudiwal et al., 2010; Rafie et al., 2003). In contrast, production in

the U.S. has been limited to Hawaii and very few states in the southeast, represented primarily by

15

small growers that produce conventional and organic products (Calpito et al., 2018; Hayden et

al., 2004; Hepperly et al., 2004; Huang, 2016; Hunter, 2018; Rafie et al., 2003; Snyder, 2018).

Due to the similarities in climate requirements for growth, there is an opportunity for growers in

Florida to introduce these species and commercialize them as locally-grown “superfoods”.

However, production guidelines applied to local production in Florida, including planting

material for propagation and optimal conditions for field or greenhouse cultivation, are yet

scarce. Research on propagation methods is limited by the use of seed rhizomes, and issues

related to rhizome dormancy, contamination caused by soil borne pathogens, and rhizome

storage have not been fully studied (Chung and Moon, 2011; Dohroo, 1989; Furutani, et al.,

1985; Hepperly et al., 2004; Jayakumar et al., 2001; Paull and Cheng, 2015; Sanewski, 1996). In

addition, studies under greenhouse or field environmental conditions comparing growing factors

such as container size, photoperiod treatments, use of shading, etc. done in the U.S. are rare and

limited to Hawaii (Hepperly et al., 2004; Kratky et al., 2013; Nishina et al., 1992). Considering

these limitations, plus the lack of information about the wide range of species and rhizome types

of these genera in the market, numerous opportunities exist to refine production systems of these

crops in Florida.

The overall objectives of this thesis were to (a) evaluate plant material sources and

cultivars for greenhouse and field production of ginger, galangal and turmeric, and (b) identify

environmental conditions that extend the growing season of plants by avoiding dormancy during

short days and maximizing high quality rhizome production.

In Chapter 2, various cultivars of ginger and turmeric seedrhizomes from two sources

were soaked in water or treated with plant growth regulators before planting to study their effect

on sprouting. There was also potential to evaluate the effects of initial rhizome quality, which

16

varied depending on rhizome weight and size (diameter and length), and by the duration of the

postharvest storage period.

Chapter 3 aimed to (a) evaluate the effect of different propagation material (rhizome-

derived and micropropagated transplants), container size, and photoperiod (natural and long

days) on rhizome yield of different ginger cultivars under greenhouse conditions, which was

conducted in 2017, “year 1” and (b) evaluate the effect of different propagation materials and

environmental conditions (photoperiod or shading treatments) on growth and rhizome yield of

different cultivars of ginger and galangal under greenhouse or field conditions.

In Chapter 4, rhizome-derived and micropropagated transplants of different turmeric

species and cultivars were compared. Rhizome yield from turmeric plants grown in different

container sizes and photoperiods were evaluated under greenhouse conditions in 2017, “year 1”.

The effect of different propagation materials and environmental conditions (photoperiod or

shading treatments) on growth and rhizome yield of turmeric plants was evaluated in the

greenhouse or field.

For both Chapters 3 and 4, the “year 2” greenhouse experiment was conducted from 2018

to 2019. The photoperiod treatments evaluated were “natural days” and “long days” via night

interruption . In the field, the experiment also took place from 2018 to 2019 and the shading

conditions were 0% shade (“full sun”) and 60% shade. Plant growth, overall plant performance,

and rhizome yield were compared for three types of ginger and one micropropagated galangal.

Separately, these variables were also compared for four rhizome-grown turmerics two

micropropagated transplants (white and yellow turmeric), and one second generation yellow

turmeric originally obtained from micropropagation.

17

CHAPTER 2

ANALYSIS OF FACTORS AFFECTING SPROUTING OF GINGER (ZINGIBER

OFFICINALE) AND TURMERIC (CURCUMA SPP.) RHIZOMES

Background

Ginger (Zingiber officinale) and turmeric (Curcuma spp.) are usually propagated through

vegetative rhizome pieces, with adventitious roots and lateral shoots emerging from their nodes

(Hayden et al., 2004). Rhizomes are underground storage organs that remain dormant in the soil

and allow ginger and turmeric plants to survive during adverse periods (Abelenda and Prat,

2013). Along with other compounds, starch is one of the main metabolic products stored in this

organ, which serves as an energy store for germination and rooting (Ravindran and Babu, 2005).

In ginger, starch can constitute up to 60% of total mass (Talele et al., 2015), while for turmeric

species starch levels (dry weight basis) range from 45.2% to 48.5% (Sajitha and Sasikumar,

2014)

After harvest, undamaged and well-developed rhizomes are selected and sanitized for

preserving as seed (Ravindran et al., 2007). Ginger and turmeric rhizomes are usually stored in

well-ventilated containers at 12 to 14 °C with 60% to 70% relative humidity (RH). For ginger,

temperature should not be lower than 12 °C as rhizomes are chilling sensitive (Paull and Cheng,

2015). Overall, rhizomes can be stored for 90 and up to 105 days in ventilated polythene bags

(Ravindran and Babu, 2005). A high percentage of healthy rhizomes was recovered, and high

sprouting (99%) was observed in the field (Ravindran et al., 2007). However, storability of

rhizomes is limited, and if they are stored for long periods they encounter issues related to

weight loss and decreased starch content (Chung and Moon, 2011). Paull et al. (1988) observed

that shriveling becomes evident after a 10% of weight loss in ginger rhizomes. Furthermore,

ginger rhizomes stored at 10 and 15 °C for five months had a weight loss of about 23% and a

rapid reduction in starch content after the two first months of storage (Shukor et al., 1986). In

18

contrast, optimum and uniform germination was observed when seed rhizomes were stored for

30 and 45 days before planting in the field (Kerala Agricultural University, 1993). It is important

to consider these issues related to long-term storage of fresh rhizomes because they lose quality

over time, and preservation of seed rhizomes is one of the most important aspects for rhizome

successful propagation.

The size of rhizomes pieces in ginger and turmeric used for propagation can vary

between growing locations and cultivars, and larger rhizomes produce higher yield

(Hailemichael and Tesfaye, 2008; Kandiannan et al., 2010; Whiley, 1990). Turmeric seed

rhizome size of 30 g or above results in greater plant growth and yield (Hossain et al., 2005), and

Asian commercial producers use ginger seed rhizomes between 15 and 75 g (Ravindran and

Babu, 2005). An alternative approach to rapidly multiply turmeric plant number is via a mini-set

technique, where rhizome pieces of about 7 g are used (Aswathy and Jessykutty, 2016).

However, a reduction in rhizome size is often associated with seedling mortality due to infection

through the cut rhizome surfaces (Ravindran et al., 2007). Ginger rhizomes are usually cut into

one or two sections so that each seed piece has two to four well-developed buds (Rafie and

Mullins, nd). Rhizomes can be cured by drying them in a clean and disease-free area for three

days or more at ambient temperature and 60% RH (Hepperly et al., 2004; Gupta and Verma,

2011; Jayashree et al., 2015; Kaushal et al., 2017). Instead of treatment with fungicides,

rhizomes can also be treated with hot water (50 °C) to help control fungal attack and to ensure

optimum germination (Nair, 2013). After storage, rhizome pieces are usually planted in moist

sawdust in plastic seedling trays at 25 ± 2 °C (Labrooy and Abdullah, 2016), because

temperatures above 30 °C reportedly lead to quick germination but weak sprouts (Ravindran and

Babu, 2005). The germination process takes about 50 days for ginger (Ravindran and Babu,

19

2005). However, since ginger rhizome buds undergo dormancy, sprouting is poor and erratic and

take even more time for younger seed pieces (Sanewski, 1996). For turmeric, germination

usually starts about two weeks after planting and lasts for up to four weeks (Ravindran et al.,

2007).

Other crops such as potato (Solanum tuberosum) or yam (Dioscorea spp.) also have

underground organs that undergo dormancy. Research in these crops has shown that proteins and

nucleic acids regulate dormancy and sprouting, and dormancy has a genetic component because

the time required for sprouting varies between potato cultivars (Visse-Mansiaux et al., 2017).

Studies in turmeric (C. longa) indicate that the stable dormant period is only 30 days. However,

sprouting takes place 75 days after harvest and proteins are synthesized at the end the dormancy

period, similar to potato tubers (Jayakumar et al., 2001).

Growth regulators can induce even and rapid sprouting in plant storage organs.

Cytokinins play an important function in the control of cell proliferation and bud break in many

plants (Abelenda and Prat, 2013; Criley, 1988). Benzyladenine (BA) or benzylaminopurine

(BAP) and kinetin are cytokinins that can be synthetically produced, but also occur naturally at

low levels in some plant species (Kieber and Schaller, 2014). Ethylene is also responsible for

many processes and responses to biotic and abiotic stresses (Corbineau et al., 2014). Studies

have demonstrated the effects of ethylene on breaking dormancy of seeds and sprouting of

various bulbous plants via a series of complex signaling networks (Esashi and Leopold, 1969).

Within Zingiberaceae, the efficacy of plant growth regulators on rhizome sprouting has been

tested under research conditions. Curcuma alismatifolia had rapid and increased shoot

emergence when treated with 100 ppm of BAP or 750 ppm of Ethephon (an ethylene-releasing

compound) for 30 minutes (Thohirah, et al., 2010). Similar results were obtained on Kaempferia

20

parviflora with a combination of 750 ppm Ethephon and 150 ppm BAP (Labrooy and Abdullah,

2016). In ginger, highest sprouting (95.6%) was recorded when rhizomes were treated with 100

ppm BAP for 24 h, and 25 and 50 ppm promoted high sprouting (>80%) compared with the

control (54%) (Aswathy and Jessykutty, 2016). In the same experiment, treatments with

ethephon at 125 ppm and 250 ppm for 30 min resulted in lower sprouting (

21

baba’) and turmeric (‘Hawaiian Red’, ‘White Mango’ and ‘BKK’) were obtained from two

different sources: “Commercial” rhizomes were supplied by Just Ginger (Zolfo Springs, FL), and

“UF” material was harvested from the same cultivars planted in the field or greenhouse at UF in

June 2017 and harvested in January or February, 2018 (Gainesville, FL). Rhizomes from UF

were stored in a cool chamber at 14.6 ± 1.3 °C (mean ± standard deviation) and 66.0 ± 18.8%

RH until the beginning of each experiment (127 and 161 days for experiments 1 and 2,

respectively). Commercial rhizomes were freshly harvested and obtained in 17 Apr. 2018 and

were stored at 13.6 ± 0.5 °C and 63.3 ± 19.7% RH until the beginning of each experiment (73

and 107 days, respectively).

Rhizomes were treated either with 50 or 150 ppm of BAP (6-BA; PhytoTechnology

Laboratories, Shawnee Mission, Kansas) by soaking for 30 minutes; 250 or 750 ppm of ethephon

(Florel; Lawn and Garden Products, Inc., Fresno, CA) by soaking for 30 min; hot water (at 50

°C) for 10 min; room temperature (22°C) water for 30 min or for 24 h; or were not treated

(control). A total of 64 labeled seed pieces (8 forcing treatments x 8 cultivars) were randomly

placed on moistened paper towels, spaced 5 cm apart and distributed in four black plastic flat

trays (T.O. Plastics, Inc. Clearwater, MN, USA.). The experimental design was a randomized

complete block design with 12 replicates per forcing treatment, cultivar, and source. Each

replicate rhizome per forcing treatment, cultivar and source combination was randomly located

on each of the 12 shelf sections (blocks) in the growth chamber. A fogger (Vevor Machinery

Equipment Co., City, State, USA) was placed in the center of the chamber to keep optimum

moisture levels, and the paper towels were moistened with approximately 100 ml of tap water

every day. Rhizomes were weighed, initial rhizome length and diameter were measured with a

caliper (Fowler, Ultra-Call Mark III, Switzerland), and number of visible buds were counted.

22

Twice a week for eight weeks, the first bud sprouting was recorded for each seed piece. Rhizome

final weight and primary root and shoot length were measured at the end of eight weeks.

At the time of harvest, rhizome quality affects storability of rhizome seeds. Thus, if

rhizomes are stored for longer periods, they will encounter issues related to weight loss and

decreased starch content (Chung and Moon, 2011; Shukor et al., 1986) which affects quality, and

ultimately affects sprouting, growth and yield (Ravindran et al., 2007). Therefore, two identical

experiments were performed to understand how rhizome quality varies over storage time and

whether it affected sprouting. Experiment 1 was conducted from 12 June to 7 Aug. 2018.

Rhizomes averaged 4.1 ± 0.5 cm (mean ± standard deviation) in length and 1.7 ± 0.39 cm in

diameter, contained 2.8 ± 0.9 visible buds, and weighed 9.5 ± 4.9 g. Air temperature averaged

25.5 ± 0.3 °C, RH was 89 ± 4.3%, light intensity was 19.9 µmol·m2·s-1 of photosynthetically

active radiation (PAR), and the average daily light integral (DLI) was 1.14 mol·m-2·d-1. Final data

were collected after 56 days. Experiment 2 was conducted 36 days later, from July 17 to

September 13, 2018. Rhizomes were approximately 3.8 ± 0.7 cm, contained 0.3 ± 0.4 visible

buds, and weighed 7.8 ± 5.8 g. This difference in initial bud number and weight from experiment

1 is most likely caused by the extended storage period (36 days). The growth chamber was

maintained at 25.5 ± 0.4 °C and 88.5 ± 4.3% RH, with the same light conditions as above. Final

data were recorded after 58 days.

Data from experiment 1 and 2 were analyzed separately using PROC GLM in SAS (SAS

Version 9.4; SAS Institute, Cary, NC), with Tukey’s Honestly Significant Difference (HSD) at P

= 0.05 for mean separation. Multiple linear regression model and Pearson correlations were also

done using SAS.

23

Results and Discussion

Overall, rhizomes had an average of 83.3% sprouting in experiment 1 and 61% in

experiment 2. Sprouting took place after an average of 29.4 (experiment 1) and 31.7 days

(experiment 2). Rhizomes of turmeric and ginger have been reported to typically sprout after

four weeks, although the majority of the sprouts emerge after 6-8 weeks (Evenson et al., 1978;

Sanewski and Fukai, 1996). Similarly, in our study there was an increase in bud number over

time for most of the cultivars, from week four to week eight. There are inherent differences in

shoot emergence between planting pieces from different parts of the rhizome (Sanewski and

Fukai, 1996), which may explain the variability in our data.

Forcing treatments did not have an effect on the sprouting process of ginger and turmeric

rhizomes (Tables 2-1 and 2-2). There were no significant effects of the chemical and water

forcing treatments on days to sprout, sprouting percentage, bud number on weeks four or eight,

final rhizome weight or shoot and root length. In contrast to our study, Curcuma alismatifolia

showed rapid and increased shoot emergence when treated with 100 ppm of BAP or 750 ppm of

ethephon (Thohirah, et al., 2010) and in Zingiber officinale up to 95.6% sprouting was recorded

when rhizomes were treated with 100 ppm BAP and even lower concentrations (25 and 50 ppm)

promoted high sprouting (>80%) compared with untreated rhizomes (54%) (Aswathy and

Jessykutty, 2016). This indicates that the plant growth regulator (PGR) concentration is not the

only factor that influences the sprouting process. Additionally, in other crops the response is

sometimes negative. In corms of gladiolus for example, BAP delayed the sprouting process, but

induced multiple shoots (Sajjad et al., 2015). In yam results of sprouting were inconsistent,

indicating that PGRs do not necessarily break dormancy, but they can hasten or delay the rate of

shoot apical development (Ile et al., 2006; Jaleel et al., 2007). PGRs are synthetic compounds

and the majority of them are labeled as pesticides so disposal of residual solutions can be

24

problematic (Latimer and Whipker, 2012; Sajjad et al., 2017). Since our results indicated that

PGRs do not necessarily improve sprouting of ginger or turmeric seed rhizomes, growers would

not need to spend extra money on chemical products or extra time and labor to treat their

rhizomes before planting. Moreover, although water soaking treatments were not necessarily

advantageous for accelerating sprouting either, soaking rhizomes in hot water is recommended as

a safe sanitation procedure (Nair, 2013).

Cultivar and source and their interaction had a significant effect on sprouting and growth

(Tables 2-1 and 2-2). In both experiments, rhizomes of ginger ‘Bubba baba’ sprouted earlier

(after about 22 days), had more sprouted buds (on average 1.6), and accumulated more fresh

mass after 8 weeks (on average 14.9 g) than the turmeric cultivars. Since ginger and turmeric are

two different genera it is not surprising that sprouting varied considerably among cultivars.

Overall, there is a wide variability among ginger and turmeric cultivars with respect of yield

attributes, and quality characters which are affected by both genetics and environmental

conditions (Anandaraj et al., 2014; Ravindran and Babu, 2005). For most of the evaluated

parameters there was an effect of source. The main difference between sources was that

rhizomes from “UF” were stored for longer (127 and 161 days for experiments 1 and 2,

respectively) than the “Commercial” rhizomes (73 and 107 days for experiments 1 and 2,

respectively). Rhizomes stored for longer periods, encounter issues related to weight loss,

shriveling, and reduced starch content (Chung and Moon, 2011; Paull, 1988).

The effects of cultivar and source on sprouting in part resulted from significant

differences in the initial quality (bud number and weight) of rhizomes, shown in Table 2-3. In

both experiments, rhizomes of ginger ‘Bubba baba’ had the highest initial weight (ranging from

16.3 to 17.9 g) and the highest initial bud number (ranging from 0.87 in experiment 2 to 4.4 in

25

experiment 1). In contrast, rhizomes of turmeric ‘BKK’ had the lowest initial weight (ranging

from 2.1 to 4.9 g) and the lowest initial bud number (ranging from 0.03 to 2.9) along with

turmeric ‘White Mango’ (ranging from 0.06 to 2.6). Since rhizomes of ginger ‘Bubba baba’ from

both Commercial and UF sources weighed more at the start of each experiment they also had the

highest final rhizome weight (13.9 to 15.5 g, Tables 2-1 and 2-2). This cultivar sprouted earlier

and thus, produced longer shoots and roots than the other cultivars. Turmeric ‘BKK’ had a low

initial weight and also the lowest final weight (1.8 to 4.1 g). In both experiments a positive

correlation was found across all propagative material on initial rhizome weight and initial bud

number with days to sprout (P < 0.001), bud number at week 4 (P < 0.001), bud number at week

8 (P < 0.001), and a very high correlation with final weight (P < 0.001; r = 0.92 and 0.94 for

experiments 1 and 2, respectively). The formation of shoot and root meristems requires energy

from the rhizome (Panneerselvam et al., 2007). Because the nutrition for germination and rooting

also derives from the reserves stored in the rhizome bud, the size and nutrition of the seed

rhizome have a great influence on the subsequent stages after sprouting (Ravindran and Babu,

2005). While size of rhizomes pieces used for propagation varies upon location and cultivar, the

criteria is often based on yield as larger rhizomes produce higher yields (Hossain et al., 2005;

Kandiannan et al., 2010).

Higher rhizome weights are correlated with increased number of shoots per plant

(Furutani et al.,1985). For this reason, ginger growers generally use planting pieces within the 40

– 70 g size range as they produce similar high shoot numbers (Sanewski and Fukai, 1996).

Carbohydrate content plays an important role in rhizome growth. In potato, after the onset of

sprouting, sugar content declines in the tubers as they are being consumed until the sprout

reaches approximately 1 g of dry matter (Viola et al., 2007). Studies in ginger have demonstrated

26

that longer periods of storage reduce shoot growth due to a decreased of starch and sugar levels

as a consequence of excessive respiration (Sanewski, 1996). In turmeric, larger rhizome seeds

are less susceptible to weight loss and have enough stored food to ensure reliable germination

(Ravi et al., 2016). Studies have also shown that there is a gradual decrease of starch content in

the rhizomes from the moment of harvest up to 42 days after harvest, followed by a rapid decline

until sprouting (Panneerselvam et al., 2007). The same pattern has been reported in potato tubers,

where the shoots control the food reserves of the tuber (Davies and Ross, 1984). However, there

is limited research concerning the carbohydrate metabolism during dormancy and sprouting in

turmeric rhizomes (Jaleel et al., 2007).

Summary

Propagation is one of the most important stages for optimum crop productivity. Planting

material and any treatment applied will affect the vigor of the plant and, ultimately, rhizome

yield. Forcing treatments did not have an effect on sprouting, but cultivar and plant source

affected the uniformity and speed of sprouting of ginger and turmeric rhizomes during

propagation. Rhizomes of ginger ‘Bubba baba’ sprouted as early as 19 days after planting,

however, for turmeric cultivars, particularly ‘BKK’ and ‘White Mango’ sprouting was delayed

up to 39 or 52 days respectively (experiment 2). Initial bud number and rhizome weight were

significantly correlated with all evaluated parameters. Rhizomes in experiment 1 had better

sprouting than in experiment 2, which were stored for longer (over 120 days). This suggests that

initial rhizome quality has a great impact on sprouting and overall growth. Therefore, in order to

enhance a uniform and rapid sprouting, high-quality (healthy, larger than 15 g, and clean)

rhizomes should be carefully selected after harvest and stored under optimum conditions (12 to

14 °C with 60 - 70% RH), ideally for no longer than 100 days.

27

Table 2-1. Mean values and Tukey grouping comparison for days to sprout, number of sprouted buds after 4 and 8 weeks, shoot and

root length and final weight of ginger and turmeric rhizomes (‘Bubba baba’, ‘Hawaiian Red’, ‘White Mango’, and ‘BKK’),

from different sources (Experiment 1). Data represent the least squared means derived from a three-way ANOVA using the

general linear model procedure in SAS. Different letters next to value within each column indicate significant differences

according to Tukey’s honestly significant difference (HSD) test (P < 0.05).

Factors Days to sprout

No. sprouted

buds after 4

weeks

No. sprouted buds

after 8 weeks

Final shoot length

(cm) after 8 weeks

Root length (cm)

after 8 weeks

Final weight

(g)

Interaction effects

Cultivar Source

Ginger ‘Bubba baba’ Commercial 19.6 e 1.6 a 2.3 NS 2.1 a 1.5 a 15.5 a

Ginger ‘Bubba baba’ UF 24.0 de 1.5 a 2.3 NS 1.7 ab 0.8 b 14.3 b

Turmeric ‘Hawaiian Red’ Commercial 28.7 bcd 0.5 bc 1.5 NS 1.5 ab 0.4 c 7.3 c

Turmeric ‘Hawaiian Red’ UF 31.1 bc 0.5 bc 1.6 NS 1.3 bc 0.3 c 8.4 c

Turmeric ‘White Mango’ Commercial 33.0 ab 0.4 bc 1.3 NS 1.3 bcc 0.3 c 5.4 d

Turmeric ‘White Mango’ UF 34.0 ab 0.4 c 1.4 NS 0.8 c 0.2 c 5.1 de

Turmeric ‘BKK’ Commercial 27.1 cd 0.8 b 1.3 NS 1.9 ab 0.5 b 4.3 de

Turmeric ‘BKK’ UF 37.9 a 0.2 c 1.1 NS 0.7 c 0.2 c 4.1 e

Main effects

Cultivar

Ginger ‘Bubba baba’ 21.7 c 1.5 a 2.3 a 1.9 a 1.2 a 14.9 a

Turmeric ‘Hawaiian Red’ 29.9 b 0.5 b 1.5 b 1.4 b 0.4 b 7.9 b

Turmeric ‘White Mango’ 33.5 a 0.4 b 1.4 bc 1.1 b 0.3 b 5.2 c

Turmeric ‘BKK’ 32.3 ab 0.5 b 1.2 c 1.3 b 0.3 b 4.2 d

Source

Commercial 27.1 bz 0.8 a 1.6 NS 1.7 a 0.7 a 8.1 a

UF 31.8 a 0.7 b 1.6 NS 1.1 b 0.4 b 8.0 a

ANOVA Summary

Cultivar * * * * * *

Forcing treatment NS NS NS NS NS NS

Cultivar*Forcing treatment NS NS NS NS NS NS

Source * * NS * * NS

Cultivar*source * * NS * * *

Forcing treatment *source NS NS NS NS NS NS

Cultivar*forcing treat.*source NS NS NS NS NS NS zMeans separation in columns by Tukey’s multiple range test at P ≤ 0.05.

NS, *, Nonsignificant or significant at P < 0.05, respectively.

28

Table 2-2. Mean values and Tukey grouping comparison for days to sprout, number of sprouted buds after 4 and 8 weeks, shoot and

root length and final weight of ginger and turmeric rhizomes (‘Bubba baba’, ‘Hawaiian Red’, ‘White Mango’, and ‘BKK’),

from different sources (Experiment 2). Data represent the least squared means derived from a three-way ANOVA using the

general linear model procedure in SAS. Different letters next to value within each column indicate significant differences

according to Tukey’s honestly significant difference (HSD) test (P < 0.05).

Factors Days to

Sprout

No. of sprouted buds

after 4 weeks

No. sprouted

buds after 8

weeks

Final shoot length

(cm) after 8 weeks

Root length (cm)

after 8 weeks

Final weight

(g)

Interaction effects

Cultivar Source

Ginger ‘Bubba baba’ Commercial 18.8 d 1.8 a 1.5 abc 2.1 a 1.8 NS 15.0 a

Ginger ‘Bubba baba’ UF 26.5 cd 1.9 a 1.6 ab 1.4 ab 1.2 NS 13.9 a

Turmeric ‘Hawaiian Red’ Commercial 24.0 cd 1.5 a 1.9 a 1.1 b 0.7 NS 6.5 b

Turmeric ‘Hawaiian Red’ UF 27.4 c 1.1 bc 1.6 ab 1.6 ab 0.6 NS 5.1 c

Turmeric ‘White Mango’ Commercial 36.4 b 0.9 bc 1.0 bcd 0.8 bc 0.3 NS 3.8 cd

Turmeric ‘White Mango’ UF 52.4 a 0.1 d 0.3 d 0.2 c 0.1 NS 3.4 d

Turmeric ‘BKK’ Commercial 35.2 b 0.7 cd 0.9 cd 0.9 bc 0.3 NS 1.8 e

Turmeric ‘BKK’ UF 38.7 b 0.6 cd 1.3 abc 0.7 bc 0.2 NS 2.7 de

Main effects

Cultivar

Ginger ‘Bubba baba’ 22.3 c 1.8 a 1.6 a 1.8 a 1.52 a 14.4 a

Turmeric ‘Hawaiian Red’ 25.8 c 1.3 b 1.7 a 1.4 a 0.65 b 5.8 b

Turmeric ‘White Mango’ 44.2 a 0.5 c 0.6 c 0.5 b 0.18 c 3.6 c

Turmeric ‘BKK’ 37.0 b 0.7 c 1.1 b 0.8 b 0.27 bc 2.3 d

Source

Commercial 28.0 bz 1.2 a 1.3 a 1.2 a 0.8 a 6.8 a

Source 35.4 a 0.9 b 1.2 a 1.0 a 0.5 b 6.3 b

ANOVA Summary

Cultivar * * * * * *

Forcing treatment NS NS NS NS NS NS

Cultivar*Forcing treatment NS NS NS NS NS NS

Source * * NS * * *

Cultivar*source * * * * NS *

Forcing treatment *source * NS NS NS NS NS

Cultivar*forcing treat.*source NS NS NS NS NS NS zMeans separation in columns by Tukey’s multiple range test at P ≤ 0.05.

NS, *, Nonsignificant or significant at P < 0.05, respectively.

29

Table 2-3. Mean values and Tukey grouping comparison for initial weight, initial number of visible buds, initial length and diameter

of rhizomes of ginger and turmeric cultivars (‘Bubba baba’, ‘Hawaiian Red’, ‘White Mango’, and ‘BKK’), from different

sources (Experiment 1 and 2). Data represent the least squared means derived from a three-way ANOVA using the general

linear model procedure in SAS. Different letters next to value within each column indicate significant differences

according to Tukey’s honestly significant difference (HSD) test (P < 0.05).

Factors Initial weight (g) Initial bud number Initial length (cm) Initial diameter (cm)

Exp.1 Exp.2 Exp.1 Exp.2 Exp.1 Exp.2 Exp.1 Exp.2

Interaction effects

Cultivar Source

Ginger ‘Bubba baba’ Commercial 17.9 a 16.9 a 3.2 bc 0.9 NS 4.8 b 4.7 a 2.1 a 2.1 a

Ginger ‘Bubba baba’ UF 16.8 a 16.3 a 4.4 a 0.9 NS 5.1 a 4.9 a 2.0 b 2.0 a

Turmeric ‘Hawaiian Red’ Commercial 8.8 b 7.7 b 1.8 d 0.2 NS 3.7 e 3.8 b 1.8 c 1.7 b

Turmeric ‘Hawaiian Red’ UF 9.7 b 5.7 c 3.6 b 0.2 NS 4.4 c 4.0 b 1.8 c 1.4 c

Turmeric ‘White Mango’ Commercial 7.4 c 4.6 cd 2.6 c 0.1 NS 3.9 de 3.3 c 1.6 d 1.4 c

Turmeric ‘White Mango’ UF 6.1 d 4.3 de 1.8 d 0.0 NS 3.5 f 3.2 cd 1.6 d 1.4 c

Turmeric ‘BKK’ Commercial 4.6 e 2.1 ef 2.9 c 0.0 NS 3.9 d 2.9 d 1.3 e 0.9 e

Turmeric ‘BKK’ UF 4.9 de 3.0 f 2.6 c 0.0 NS 3.7 ef 3.3 c 1.3 e 1.2 d

Main effects

Cultivar

Ginger ‘Bubba baba’ 17.4 az 16.6 a 3.8 a 0.9 a 4.9 a 4.8 a 2.1 a 2.0 a

Turmeric ‘Hawaiian Red’ 9.3 b 6.7 b 2.7 b 0.2 b 4.1 b 3.9 b 1.8 b 1.5 b

Turmeric ‘White Mango’ 6.7 c 4.4 c 2.2 c 0.1 b 3.8 c 3.2 c 1.6 c 1.4 c

Turmeric ‘BKK’ 4.7 d 2.5 d 2.8 b 0.0 b 3.7 c 3.1 c 1.3 d 1.0 d

Source

Commercial 9.7 NS 7.9 a 2.6 b 0.3 NS 4.1 b 3.7 a 1.7 NS 1.5 a

Source 9.4 NS 7.3 b 3.1 a 0.3 NS 4.2 a 3.8 b 1.7 NS 0.5 b

ANOVA Summary

Cultivar * * * * * * * *

Source NS * * NS NS * * NS

Cultivar*source * * * NS * * * * zMeans separation in columns by Tukey’s multiple range test at P ≤ 0.05.

NS, *, Nonsignificant or significant at P < 0.05, respectively.

30

CHAPTER 3

RHIZOME YIELD AND POSTHARVEST QUALITY OF GINGER (ZINGIBER

OFFICINALE) AND GALANGAL (ALPINIA GALANGA) AS AFFECTED BY

PROPAGATION MATERIAL, CULTIVAR, AND ENVIRONMENTAL CONDITIONS

DURING PRODUCTION

Background

The use and demand of spices in the United States (U.S.) is increasing. Per capita spice

consumption increased from ~0.5 kg in 1966 to 1.7 kg in 2015, and import values reached

$1,801 million in 2016 (Nguyen et al., 2019; Tridge, 2019). Among the most commonly

consumed spices in the country, ginger (Zingiber officinale) rhizomes are high-value, sought-

after products that have gained popularity in recent years. Ginger rhizomes are commonly used

as a fresh, dried, or processed products and are claimed to have medicinal anti-inflammatory

properties. Therefore, consumption of ginger rhizomes has been recommended to improve joint

health, reduce blood sugar, and treat different types of cancer (Gregory et al., 2008; Li et al.,

2016; Srinivasan et al., 2016).

Galangal (Alpinia galanga), known also as “greater galangal” or “Thai ginger”, is another

edible within the Zingiberaceae family, mainly cultivated in Asia (Ecocrop-FAO, 1997).

Galangal rhizomes have similar medicinal properties as ginger. In addition, due to their

similarities in taste and odor, galangal is often used to replace ginger in Asian cuisines

(Chudiwal et al., 2010; Huang et al., 2018; Tang et al., 2018).

Ginger and galangal are commonly propagated by seed rhizomes (Chudiwal et al., 2010;

Ravindran and Babu, 2005). For ginger propagation, rhizome size can vary between 15 and 75 g

depending upon the growing location and cultivar (Ravindran and Babu, 2005; Whiley, 1990).

For galangal, rhizomes with at least one developed shoot are recommended to maximize yield

(Peter, 2004). Careful disinfection is an important consideration when using seed rhizomes, as

they are highly susceptible to Fusarium, Pythium, Ralstonia, and other soil-borne diseases that

31

can lead to yield losses (Dohroo, 1989; Hepperly et al., 2004). An alternative to seed rhizome

propagation is to use tissue culture-derived transplants, which can ensure pathogen-free, uniform

starting material. However, transplants are more expensive than seed rhizomes and tend to result

in lower yield (i.e., smaller rhizomes) during the first production cycle (Smith and Hamill, 1996;

Ravindran and Babu, 2005).

Ginger and galangal are widely cultivated in tropical and subtropical regions of the world

(Rafie et al., 2003). However, production in the U.S. has been limited to Hawaii and a very few

states in the southeast. It is grown primarily by small growers that produce conventional and

organic ginger products (Hayden et al., 2004; Hepperly et al., 2004; Hunter, 2018; Rafie et al.,

2003). Ginger grows well in warm, humid climates and can be cultivated in altitudes ranging

from 0 to 1,500 m above sea level (Sasikumar et al., 2008). Optimum growing temperatures for

ginger range between 20 to 25 °C, and lower temperatures (

32

allowing for year-round production and offering opportunities to increase productivity and

maximize profit for the grower (Majsztrik et al., 2017; Suhaimi et al., 2012).

To develop successful ginger and galangal production systems in Florida, however,

considerations about environmental limitations that affect plant growth and development must be

considered. Ginger plants enter dormancy in early winter, when natural photoperiods decrease

below a critical night length of 12 hours (Adaniya et al., 1989; Pandey et al., 1996). When they

are grown in the field, rhizomes have to be harvested during this period, limiting the rhizome

production to specific seasons during the year. However, some studies have demonstrated that

the crop does not experience dormancy under long photoperiod (~16 h) whereas rhizome

production is promoted by photoperiods of ~10 h (Adaniya et al., 1989; Pandey et al., 1996).

Day-extension or night-interruption with electric lamps are strategies commonly used by the

horticulture industry to control the seasonality of flowering plants by manipulating the critical

night length of photoperiodic-sensitive crops. Most photoperiodic research has focused on

flowering rather than on vegetative-growth responses. However, few studies have shown the

significant effect that photoperiodic control has on ginger (Adaniya et al., 1989; Pandey et al.,

1996). Therefore, by manipulating the photoperiod under controlled conditions, growth and

rhizome yield could be maximized. In contrast, galangal does not seem to be sensitive to

photoperiod-induced dormancy. Tang et al. (2018) reported that galangal flowers during the

summer in the subtropics, but it can produce flowers and rhizomes all year in tropical areas

regardless of the photoperiod. Information regarding cultivation of galangal is scarce.

Excess solar radiation is another environmental aspect that could affect ginger and

galangal production in Florida. Under natural conditions, ginger and galangal have been reported

to grow well under shade as excess irradiance under full sun promotes tip burn on the leaves

33

(Babu and Jayachandran, 1997; Chudiwal et al., 2010; Stephens, 2015). In contrast, galangal is

reported to grow well both in shade and full sun conditions (Ochatt and Jain, 2007). Some

studies in ginger have shown that when plants are grown in the field under shade, plant

photosynthetic rate is increased due to the higher leaf area produced, high plant nutrient content

which ultimately could led to high yields (Kumar et al., 2005; Ravindran and Babu, 2005).

Higher rhizome yield in ginger was found when plants were grown under low to medium levels

of shade, including 20%, 25%, 40% compared to higher levels such as 60% or 75% (Ajithkumar

and Jayachandran, 2003; Babu and Jayachandran, 1997). While some studies found that high

levels of shade reduced ginger yield compared to no shade, plant wilting was reduced during the

hottest time of the day (Kratky et al., 2013). Then, under shade, leaf temperature can be reduced,

decreasing transpiration rates and enhancing overall plant growth (Kratky et al., 2013; Tew,

1962).

Regardless of the growing conditions, identifying the right maturity at the point of

harvest is important for optimum color and aroma, which ultimately affects rhizome quality

(Ravindran, et al., 2007). Depending on the market, ginger can be sold as a fresh product or in a

peeled, split, and dried form (FAO, 2004). For fresh market there are two kinds of ginger

rhizomes, the “young” and “mature”. The young ginger is bright yellow to brown with greenish-

yellow vegetative buds, but no sprouts. It is mostly offered by Asian markets and does not need

to be peeled. The commonly available is the mature ginger and has a tough skin that, which

makes peeling required (Masabni and King, n.d; Paull and Cheng, 2015). The marketable size of

a clump of rhizomes (“hands”) varies from 150 g to 300 g (FAO, 1999). To meet the minimum

standard requirements for high quality fresh ginger, whole rhizomes from similar varietal

characteristics must be selected. These rhizomes have to be clean and free of any visible foreign

34

matter. Additionally, they must be free of deterioration and rotting, with dried cut surfaces, free

of pests and any damage caused by pests affecting flesh quality, as well as free of abnormal

external moisture at the skin (Hawaii Department of Agriculture, 1992). According to the

CODEX standards (FAO, 1999), ginger fresh rhizomes are classified as “Extra”, “Class I”, and

“Class II”. Rhizomes from the “Extra” Class must be of superior quality. They must be cleaned,

well-shaped and free of defects, with the exception of very slight superficial defects. Rhizomes

from “Class I” must be of good quality, firm and without evidence of shriveling and sprouting.

The keeping quality for this kind of rhizomes tolerates light skin defects due to rubbing as long

as they are healed and dry, with total surface area affected not exceeding 10%. In contrast,

rhizomes classified as “Class II” do not qualify for inclusion in the higher classes, but satisfy the

minimum requirements mentioned above. Rhizomes should be reasonably firm and skin defects

due to rubbing (healed and dry) cannot exceed an affected total surface area of 15%; although

early signs of sprouting, slight markings caused by pests, and bruises are allowed.

For ginger, the optimum time of harvest mostly depends on the end use. For instance,

between five to six months after planting (before full maturity) ginger rhizomes are harvested for

fresh products and preserves due to their low pungency and fiber content (Nishina et al., 1992).

At about nine months after planting, rhizomes reach their maximum pungency and fiber content.

For planting material harvest can be further delayed (~9 months) until the leaves of ginger are

completely dried (FAO, 2004). Rhizomes of ginger intended for storage need to be first cured

(held at 22 – 26 oC and 70% RH) for several days to allow the skin to thicken and the cut

surfaces to dry. Curing helps reduce postharvest weight loss and decay (Paull et al., 1988). After

curing, ginger rhizomes should be stored in well ventilated containers at 12 – 14 °C with 60% -

70% RH and temperature cannot be lower than 12 °C as they are chilling sensitive. Galangal is

35

also sold fresh, in slices as preserves, or dried in powder form. In the U.S. galangal products are

usually found in Southeast Asian markets (Loha-unchit, 2000). Galangal rhizomes are paler and

woodier than ginger, and the flesh is creamy white. Similar to ginger, galangal rhizomes are

likely to have cut ends, then these have to be healed and dry, but should not be soft or moldy

(Smith, 2017). Rhizomes of galangal develop quickly and should be harvested approximately

three months after planting, otherwise they become very fibrous. However, for essential oil

extraction, rhizomes are harvested after around seven months of growth (Ochatt and Jain, 2007).

In galangal, the shelf life of rhizomes is limited by browning of the cut surface, therefore they

are usually treated with anti-browning solutions prior to marketing (Chinwang et al., 2015). In

addition, it is reported that for a high-quality product, fresh harvested rhizomes of ginger and

galangal should be washed and sanitized with hypochlorous acid (Nair, 2013; Sasikumar et al.,

2008). For both ginger and galangal adequate postharvest handling of rhizomes is required as

they are sensitive to weight loss and highly susceptible to various pathogens such as Penicillium

spp., Fusarium spp., and Pythium spp. (Kaushal et al., 2017; Nepali et al., 2000; Trujillo, 1963).

Numerous opportunities exist to refine ginger and galangal production systems in

Florida. Practices related to planting material for propagation, photoperiodic control, and

radiation (light and temperature) stress tolerance must be developed. Therefore, the objectives of

this study were 1) to evaluate the growth and yield of ginger and galangal propagules (rhizome-

derived and micropropagated transplants) grown in different container sizes and under varying

photoperiods in a greenhouse environment; and 2) to measure the effect of shading conditions on

plant growth and rhizome yield and quality of ginger and galangal plants grown in the field.

36

Materials and Methods

Experiment 1. Greenhouse Experiments

Different experiments were independently conducted over a two-year period. The

experiment in year 1 was conducted at the University of Florida (UF) Environmental

Horticulture Research Greenhouse Complex in Gainesville, FL. The experiment in year 2 was

conducted in the greenhouses at the Plant Science Research and Education Unit (PSREU) in

Citra, FL. In year 1, propagules used were micropropagated or tissue cultured transplants “tc” of

unknown ginger obtained from Agri-Starts™ Inc. (Apopka, FL, USA) and Hawaiian-grown

rhizomes of cultivar ‘Bubba baba’ (“rhiz”) obtained from Hawaii Clean Seed LLC (Pahoa, HI,

USA). In year 2, the same materials were used, and in addition, rhizomes harvested from the “tc”

material (“ownrhiz”: second generation “tc”, harvested after about one year of growth) and

galangal “tc” (Alpinia galanga, cultivar unknown) were also included.

Year 1 (2017-2018)

This experiment was conducted from 19 Apr. 2017 to 29 Jan. 2018 and aimed to evaluate

growth and yield of ginger propagules grown in two container sizes and under two photoperiods

in a greenhouse environment. Propagules of ginger included micropropagated transplants (“tc”)

[planted in two different dates: “tc early” (planted on 3 Oct. 2016) and “tc late” (planted on 27

Apr. 2017)] and Hawaiian-grown rhizomes (“rhiz”) planted on 19 Apr. 2017. Both “tc” ginger

transplants were initially planted individually in 380 mL containers (Pöppelmann TEKU®,

Claremont, NC) filled with sphagnum peat substrate (Klasmann-Deilman, Miami, FL, USA),

while “rhiz” plants were planted in 2.78 L containers (Nursery Supplies Inc, Kissimmee, FL,

USA) filled with a substrate consisting of sphagnum peat and perlite (Fafard®2P, Sun Gro

Horticulture Distribution Inc, 770 Silver Street Agawam, MA, USA). The “tc early” transplants

37

were subsequently potted into 5.7 L containers (Nursery Supplies Inc) on 9 Dec. 2016 and

mounded with 5 cm of additional substrate on 17 Jan. 2017.

All plants were subsequently repotted on 17 July 2017 either into 5.7 L or 50.5 L

containers (Nursery Supplies Inc) with a 1:1 (v/v) mix of coarse coconut husk chips and fine

coconut fiber (Envelor Inc, Old Bridge, NJ, USA). Containers were placed in two polycarbonate-

covered greenhouse compartments in Gainesville, FL with automated heating and pad-and-fan

evaporative cooling. Within each compartment, containers were arranged in a RCBD with eight

replicate containers per plant material type and container size, where two replicate containers per

plant material type and container size combination were randomly located on each of the four

benches (blocks) inside the greenhouse.

One compartment received “natural days”, and the second received “long days” provided

by night interruption lighting from 10 pm to 2 am with incandescent lamps at 3.2 µmol·m2·s-1 of

PAR In the natural days greenhouse, average temperature was 23.2 ± 2.2 oC and light was 11.8 ±

5.8 moles·m-2·d-1 DLI. The long days greenhouse averaged 22.0 ± 1.0 oC, with 6.7 ± 4.5

moles·m-2·d-1 DLI and 74.1% RH. In both greenhouses, plants were hand-irrigated with 17-1.8-

14.1 blended water-soluble fertilizer (Greencare Fertilizers, Kankakee, Michigan) at 200 mg/L N

with each irrigation.

Between 17 – 21 Aug. 2017 all plants in 5.7 L and 50.5 L containers were mounded with

5 cm and 10 cm of additional substrate, respectively. Plants were harvested between 22 - 29 Jan.

2018. Fresh mass of rhizomes, shoots, and roots, and percent rhizome moisture [rhizome fresh

mass – (dry mass of rhizomes oven dried in a 50 oC oven for three days) / rhizome fresh mass]

were measured. Postharvest evaluations were not carried out. Effects of container size and plant

material were analyzed separately between the two greenhouse compartments (light treatments)

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with analysis of variance (ANOVA), using RStudio version 3.3.2 (RStudio, Inc., Boston,

Massachusetts, USA), agricolae, stats, and lsmeans packages. Least-square treatment means

were compared using Tukey’s honestly significant difference with P = 0.05.

Year 2 (2018-2019)

In year 1, we observed that plants grown under long days remained dark green and

actively grew in the winter, whereas under natural days plants showed considerable yellowing

and initiation of dormancy when harvested in late January. Thus, in year 2 we wanted to evaluate

whether the growing season for ginger could be extended by keeping plants green and actively

growing under long days (night interruption) during the winter.

This experiment was conducted from 18 Apr. 2018 to 9 Mar. 2019 and aimed to evaluate

yield of ginger and galangal propagules produced under two photoperiods in a greenhouse

environment. Propagules of ginger included micropropagated transplants (“tc”), second

generation “tc” rhizomes (“ownrhiz”), or Hawaiian-grown rhizomes (“rhiz”), plus a “tc”

galangal. Rhizomes were initially planted individually on 18 Apr. 2018 in black plastic flat trays

(T.O. Plastics, Inc. Clearwater, MN, USA.) filled with sphagnum peat substrate (Klasmann-

Deilman) under growth chamber conditions (25 ± 0.5 °C and 84.3 ± 4.5% RH). Micropropagated

ginger and galangal were transplanted into 2.78 L containers (Nursery Supplies Inc) filled with a

substrate consisting of sphagnum peat and perlite (Fafard®2P) on 4 May 2018. Sprouting of

rhizomes took place between 22 May and 5 June 2018. Sprouted rhizomes were then planted into

2.78 L containers with the same substrate and grown in a polycarbonate-covered greenhouse in

Gainesville. The greenhouse had a day and night temperature of 25.6 ± 1.9 °C and 24.7 ± 1.8 °C

respectively. All plants were subsequently repotted on 27 June 2018 into 14.5 L pots with a mix

of pine bark, sphagnum peat, perlite, and vermiculite (Fafard®52 Mix, Sun Gro Horticulture

Distribution Inc). Pots were then placed in two polycarbonate-covered greenhouse compartments

39

in Citra, FL with automated heating and pad-and-fan evaporative cooling. The experimental

design was a split-plot design with photoperiod as the main plot and plant type as the subplot.

Within each compartment, containers were arranged in a RCBD with six replicate pots per

cultivar and propagation material, where two replicate pots per cultivar and propagation material

combination were randomly located on each of three benches (blocks).

One compartment received “natural days”, with day and night temperatures of 26.6 ± 3.1

°C and 21.3 ± 2.6 °C, respectively, and 9.1 ± 3.6 moles·m-2·d-1 DLI. The second greenhouse had

“long days” provided by night interruption lighting from 10 pm to 2 am with incandescent lamps

at 1.32 µmol·m-2·s-1 PAR from 6 July onwards. It had 26.8 ± 3.9 °C and 21.4 ± 2.1 °C day and

night temperatures respectively, and 8.4 ± 3.8 moles·m-2·d-1 DLI. Plants were drip-irrigated with

tap water and fertilized using an 8 - 9 month release 15-3.9-10 Osmocote Plus™ (ICL Specialty

Fertilizer Customer, 4950 Blazer Memorial Parkway, Dublin, Ohio) controlled release fertilizer

(CRF) at a rate of 114 g.pot-1. Plants were mounded once with new substrate in 29 Aug. 2018 to

approximately a 10 cm depth.

In order to assess plant growth, number of new shoots and plant height were measured

every two weeks, as well as chlorophyll index using a chlorophyll meter (SPAD-502DL, Konica

Minolta Sensing, Osaka, Japan). To evaluate the overall aesthetic performance, a scale from 1 to

5 was used, where 1 = very poor quality, not acceptable, severe leaf necrosis, tip burn or

chlorosis, poor form, 2 = poor quality, not acceptable, large areas of necrosis, tip burn or

chlorosis, poor form, 3 = acceptable quality, few leaves with tip burn, somewhat desirable form

and color, 4 = very good quality, very acceptable and desirable color and form, 5 = excellent

quality, perfect condition, premium color and form. In ginger and galangal, excellent form was

40

considered when plants were well branched and full, not lodged, without tip burn or chlorotic

leaves, and had stems of relatively uniform length.

Plants from the natural days treatment were harvested on 22 Jan. 2019, whereas plants

from long days were harvested one month later, on 21 Feb. 2019 (after about seven and eight

months of growth in the finishing pots, respectively). After harvest, fresh and dry mass of

rhizomes, shoots, and roots as well as percent rhizome moisture [rhizome fresh mass – (dry mass

of rhizomes oven dried in a 40 oC oven until constant weight) / rhizome fresh mass] were

determined (Li et al., 2016). Additionally, rhizomes from each treatment (natural and long days)

were evaluated under postharvest storage conditions. Rhizomes were cleaned, disinfected with

10% bleach and cured (held at 22 – 26 oC and 70% RH) for four days. Rhizomes from natural

days were then stored in a cool room at 12.8 ± 0.6 °C and 89.6 ± 6.6% RH for 16 days, while

rhizomes from long days were stored at 12.9 ± 0.1 °C and 65.1 ± 4.4% RH for 15 days. In this

case the RH was adjusted with a dehumidifier. Traits evaluated were number of

infected/damaged rhizomes, and percentage of weight loss [(initial - final weight / initial weight)

× 100]. Rhizome skin and flesh color were determined using a chroma meter (model CR-400,

Konica Minolta Inc., Tokyo, Japan). After curing and after the storage period, the external skin

color was measured and then one representative rhizome piece for each type was cut in half to

display and measure the internal flesh color. The color system (lightness-L*, chroma-C*, and hue

angle-h⁰) of this meter uses values calculated from the L*a*b* system, where L* indicates the

lightness, which ranges from black (0) to white (100), C* indicates chroma or saturation, and

describes the vividness or dullness of a color regardless of its luminance, and h⁰ indicates hue,

and is the angle that defines the actual color of the object in the color space (McGuire, 1992;

Minolta, 1994).

41

Growth, yield, and postharvest data from galangal and ginger plants grown in the

greenhouse under natural and long days were analyzed together, where blocks were considered

as random effects and photoperiod, plant type, and its interactions were considered as fixed

effects. The analysis was performed using RStudio version 3.3.2 for analysis of variance

(ANOVA), with Tukey’s Honestly Significant Difference (HSD) at P = 0.05 for mean

separation.

Experiment 2. Field Experiment

This experiment was conducted at the University of Florida (UF) Environmental

Horticulture Research Greenhouse Complex in Gainesville, FL and aimed to measure the effect

of two factors (propagule type and light environment) on plant growth, ornamental performance,

and yield under shading conditions. Rhizomes were initially planted on 18 Apr. 2018 in black

plastic flat trays (T.O. Plastics, Inc.) filled with sphagnum peat substrate (Klasmann-Deilman)

under growth chamber conditions (25 ± 0.5 °C and 84.3 ± 4.5% RH). Micropropagated

transplants were initially planted in 380 mL containers (Pöppelmann TEKU®) filled with peat

substrate (Klasmann-Deilman) and then repotted on 4 May 2018 into 2.78 L pots filled with a

substrate consisting of sphagnum peat and perlite (Fafard®2P, Sun Gro Horticulture Distribution

Inc). Sprouted rhizomes were potted on 15 May 2018 (using the same container size and

substrate) and grown in the same greenhouse in Gainesville. Then all plants were planted in the

field on 21 June 2018 under full sun or shade. Six shade structures were randomly set up in four

field rows with aluminum poles and 60% shade cloth. Plants under shade received an average

day and night temperature of 25.3 ± 7.3 °C and 19.3 ± 7.4 °C, respectively, with 10.3 ± 3.6

moles·m-2·d-1 DLI. The full sun environment had an average day and night temperature of 23.3 ±

7.0 oC and 16.4 ± 6.8 °C respectively, with 21.1 ± 10.6 moles·m-2·d-1 DLI. Plants were drip-

irrigated with tap water and fertilized by using an 8 - 9 month release 15-3.9-10 Osmocote

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Plus™ (ICL Specialty Fertilizer Customer) CRF at a rate of 114 g·plant-1. Plants were arranged

in a split-plot design, with environment (sun and 60% shade) as the main plot, and propagules as

subplots. Micropropagated “tc” transplants of unknown ginger and galangal cultivars, originally

obtained from Agri-Starts™ Inc were used, as well as the harvested “tc” ginger rhizomes from

year 1 (“ownrhiz”), and Hawaiian ‘Bubba baba’ rhizomes. Two environment replicates were

randomly located on each of three blocks and there were a total six propagule replicates per

environment. Plants were harvested on 4 Feb. 2019, after about 9 months of growth.

In order to assess plant growth, number of shoots, height, and chlorophyll index were

measured every two weeks. The overall aesthetic performance was determined using the same

scale used for the greenhouse experiment (year 2). Similarly, fresh mass of rhizomes, shoots, and

roots, percent rhizome moisture [rhizome fresh mass – (dry mass of rhizomes oven dried in a 40

oC oven until constant weight) / rhizome fresh mass] and rhizome skin and flesh color were

measured after harvest. Rhizomes harvested in year 2 were also evaluated in postharvest storage

conditions. Rhizomes were cleaned and treated as described above and stored at 12.8 ± 0.3 °C

and 70.9 ± 12.4% RH for 16 days. The same traits as described for the greenhouse postharvest

experiments were evaluated.

Data from plants grown in the field either under full sun or shade (environment factor)

were analyzed together. Blocks were considered as random effects and environment, plant type,

and its interaction were considered as fixed effects and were analyzed by ANOVA with Tukey’s

HSD at P = 0.05 (RStudio version 3.3.2).

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Results and Discussion

Experiment 1. Greenhouse Experiments

Year 1 (2017-2018)

Regardless of the photoperiod, container size affected rhizome fresh mass (P < 0.001),

which is the important harvestable yield. When plants where grown in larger containers (50.5 L),

they had average rhizome yields of 913 g·plant-1 and 815 g·plant-1 under natural and long days,

respectively. In contrast, when grown in smaller containers (5.7 L), average rhizome yields were

370 g·plant-1 under natural days and 438 g·plant-1 under long days (Figures 3-1A and B).

Additionally, when plants were grown under natural days, there was interaction between plant

type and container size as all plants increased yield under larger containers compared to smaller

containers (P < 0.001, Figure 3-2A). However, there was no interaction between plant type and

container size when plants were grown under long days (P > 0.05, Figure 3-1B). Container size

is considered an important variable influencing plant and root morphology, as it is directly

related to water holding capacity and root zone humidity and porosity (Chen and Wei, 2018;

Judd et al., 2015). Most geophytes grown in large containers produce multiple, fleshy, and thick

roots or rhizomes (Landis et al., 2014). Research in tuber crops like potato (Solanum tuberosum)

and sweet potato (Ipomoea batatas) has also shown that production in large containers increases

tuber yield (Bandara et al., 1998).

Rhizome diameter was not measured in our study, however we observed that rhizomes

harvested from micropropagated ginger (tc early or tc late) had smaller diameters than those

derived from rhizomes, which would most likely affect their marketability as a fresh product

(Figure 3-2). Ginger tc early were grown for approximately seven more months than tc late, but

the diameter of its rhizomes was still small. Commercially, ginger plants started from rhizomes

are typically grown for six months before harvest (FAO, 2004; Jayashree et al., 2015).

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Regardless of the photoperiod, when grown in large containers ginger plants propagated from

rhizomes produced ~960 g of fresh rhizomes, while micropropagated gingers averaged ~818 g.

Both plant types were grown for over nine months, indicating that micropropagated transplants

may require longer periods of growth to achieve yields comparable to that of rhizome-derived

plants. At the moment of planting, micropropagated transplants are in their first stage of growth.

They are usually very small, weigh less than 1 g, and lack the rhizome structure (Smith and

Hamill, 1996). Rhizomes are the main source of food and reserves for the ginger plant at the

beginning of the crop cycle, thus a lack of this structure in micropropagated transplants may have

limited plant growth and rhizome production. In addition, in a study by Ravindran and Babu

(2005), tissue-cultured ginger transplants had similar characteristics to seedling plugs, resulting

in smaller yield than that of second-generation plants derived from the harvested rhizomes.

Moreover, in some field studies, the size of ginger rhizomes increased over time and reached

normal size (comparable to that of mother plants) in the third year (Ravindran and Babu, 2005).

These studies support our conclusion that differences in rhizome-derived and micropropagated

plants will have significantly different yield capabilities in the first year of production.

Large containers resulted in more shoot fresh mass under long days (average of 1,473 g)

than under natural days (average of 949 g). There was no interaction between plant type and

container size under natural days, and there was more shoot growth in the tc late plants (~913 g)

compared with tc early (~507 g) or ginger rhiz (~387 g,) (Figure 3-1C). Meanwhile, under long

days there was interaction between container size and plant type. In the small containers tc early

had more shoot fresh mass (~1,796 g) than tc late (~552 g) and ‘Bubba baba’ (~500 g), while in

large containers tc late and ‘Bubba baba’ had comparable shoot fresh mass (2,092 and ~1,500 g,

respectively) and tc early was lower (~829 g), Smith and Hamill (1996) also found several small

45

(up to a total of ~32) shoots in micropropagated ginger. Rhizomes are modified stems that also

allow plants to naturally propagate and grow. During the early stages of ginger growth, the

sprouted apical bud becomes the main tiller (shoot) and as it grows, its base enlarges into a

rhizome developing the primary and secondary rhizomes, commonly known as fingers. As

growth continues, buds on the secondary fingers can develop into tertiary shoots and tertiary

fingers (Ravindran and Babu, 2005). Therefore, there is a close relationship between shoots and

rhizomes. Due to this rhizome – shoot interaction and the fact that large containers promoted

high rhizome yield on all plants including tc under both photoperiods, we can infer that the high

number of shoots was favored by the high number of rhizome pieces pr