For Review Only - TSpace Repository: Home · 2018-11-27 · For Review Only Patel et al., The Value of Red Light for Increasing Basil Yield 2 ABSTRACT Patel, J.S., L. Radetsky, and

For Review Only

The Value of Red Light at Night for Increasing Basil Yield

Journal: Canadian Journal of Plant Science

Manuscript ID CJPS-2017-0343.R3

Manuscript Type: Article

Date Submitted by the Author: 15-Jun-2018

Complete List of Authors: Patel, Jaimin; Rensselaer Polytechnic Institute, Lighting Research Center Radetsky, Leora; Rensselaer Polytechnic Institute, Lighting Research Center Rea, Mark; Rensselaer Polytechnic Institute, Lighting Research Center

Keywords: Phytochrome, Downy mildew, <i>Peronospora belbahrii</i>, Organic, Red LEDs

Is the invited manuscript for consideration in a Special

Issue?: Not applicable (regular submission)

https://mc.manuscriptcentral.com/cjps-pubs

Canadian Journal of Plant Science

For Review Only

The Value of Red Light at Night for Increasing Basil Yield

Jaimin S. Patel1,2, Leora Radetsky1, Mark S. Rea1

1Lighting Research Center, Rensselaer Polytechnic Institute, Troy, NY 12180, USA.

2To whom reprint requests should be addressed. Email address: [email protected]

2Corresponding author. E-mail address: [email protected]

The Value of Red Light for Increasing Basil Yield

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Patel et al., The Value of Red Light for Increasing Basil Yield

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ABSTRACT

Patel, J.S., L. Radetsky, and M.S. Rea. 201X. The value of red light at night for increasing basil

yield. CJPS XX: XX-XX.

Sweet basil (Ocimum basilicum L.) is primarily used for culinary purposes, but it is also used in

the fragrance and medicinal industries. In the last few years, global sweet basil production has

been significantly impacted by downy mildew caused by Peronospora belbahrii. Nighttime

exposure to red light has been shown to inhibit sporulation of P. belbahrii. The objective of this

study was to determine if nighttime exposure to red light from light-emitting diodes (LEDs; λmax

= 625 nm) could increase plant growth (plant height and leaf size) and yield (number and weight

of leaves) in basil plants. In two sets of greenhouse experiments, red light was applied at a

photosynthetic photon flux density (PPFD) of 60 µmol m-2 s-1 during the otherwise dark night for

10 hours (from 20:00 to 06:00). The results demonstrate that exposure to red light at night can

increase the number of basil leaves per plant, plant height, leaf size (length and width), and leaf

fresh and dry weight, compared to plants in darkness at night. The addition of incremental red

light at night has the potential to be cost-effective for fresh organic basil production in controlled

environments.

Key words: Red LEDs; phytochrome; downy mildew; Peronospora belbahrii; organic

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Basil is a rich source of essential oil, which is used for food flavor, fragrances, dental and oral

products, traditional rituals, and medicines (Javanmardi et al. 2002; Vieira and Simon 2006;

Makri and Kintzios 2008). Among various species, sweet basil (Ocimum basilicum L.) is the

most commonly cultivated species in North America for culinary purposes. The leaves can be

used fresh or dried, stored, and processed prior to use for flavor. Thus, leaf size, quantity, and

fresh and dry weights are very important to commercial basil growers.

Basil production is compromised by downy mildew, caused by the pathogen

Peronospora belbahrii Thines (Garibaldi et al. 2004, 2005; McLeod et al. 2006; Ronco et al.

2008; Voglmayr and Piątek 2008; de la Parte et al. 2010; McGrath et al. 2010; Nagy and Horváth

2011). Few conventional fungicides are available to effectively control this disease (Wyenandt et

al. 2015). Organic basil production is even more challenging due to limited efficacy of

fungicides approved for use in organic production to control downy mildew (Allen and Saska

2013; Patel et al. 2013; McGrath and LaMarsh 2015).

Recently, sporulation by P. belbahrii on basil leaves was shown to be inhibited by red-

light exposure from light-emitting diodes (LEDs; λmax = 625 nm) at 10 µmol m-2 s-1 to detached

leaves for 20 hours (0.72 mol m-2 day (d)-1), and at 12 µmol m-2 s-1 to whole plants for 12 hours at

night (0.52 mol m-2 night (n)-1) (Cohen et al. 2013; Patel et al. 2016).

Morphological characteristics of plants such as plant height, number of leaves, leaf area,

dry weight and plant roots are known to be affected by light, including long wavelength (red)

light (Bertazza et al. 1995; Mortensen and Strømme 1987). Thus, it is crucial to determine if the

exposure to red light at night that might be used for inhibition of downy mildew sporulation

affects basil growth and yield.

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To our knowledge, there are no studies that have systematically examined the effects of

red-light exposure (LEDs; λmax = 625 nm) at night on leaf size, leaf quantity, plant height, and

fresh and dry weights of basil leaves as well as the economic value of such treatments compared

to fungicides. It is necessary to analyze the effects of nighttime red light on basil production in

order to determine if there is an economic benefit to these unconventional treatments. Therefore,

our objective was to determine whether nighttime exposure to red light could improve basil yield

and thereby provide an economic benefit in addition to that provided by suppression of basil

downy mildew previously shown (Cohen et al. 2013; Patel et al. 2016).

MATERIALS AND METHODS

Experimental conditions and protocol

Two experiments were conducted; Experiment 1 ran from 11 November 2016 to 9 February

2017 while Experiment 2 was conducted from 28 November 2016 to 22 March 2017. In both

experiments, six to eight seeds of sweet basil cultivar Genovese were sown in each of sixteen

green plastic pots (diameter: 10 cm; height: 8.9 cm; American Educational Products, Fort

Collins, CO) filled with potting mix (Sunshine mix#1/Fafard-1p, Sun Gro Horticulture Inc.,

Agawam, MA) and 14N-4.2P—11.6K of control-release fertilizer (Osmocote, The Scotts

Miracle-Gro Company, Marysville, OH). Plants were initially grown at the Lighting Research

Center (latitude: 42.73166, longitude: -73.68695, elevation: 9.1 metres) under a 3-lamp

fluorescent light fixture (containing 3 Ecolux F32T8-SP41 fluorescent lamps, GE, Boston, MA)

operated between 08:00 and 18:00 every day. These lamps provided a photosynthetic photon flux

density (PPFD) of 44.6 µmol m-2 s-1 (daily light integral (DLI): 1.61 mol m-2 d-1) at a room

temperature of 22°C which was maintained throughout the day and night. As the seedlings

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sprouted and grew, they were thinned to maintain four plants per pot. On the twenty-third day

after sowing, the plants were moved to a greenhouse (Sage Colleges, Troy, NY; latitude:

42.727526, longitude: -73.692879, elevation: 10.9 metres) where eight pots were placed into

each of two 0.6 m × 0.6 m × 1.2 m boxes. The boxes were open on top and on one side facing

south to allow natural light and ventilation. Light and temperature loggers were placed in both

boxes throughout both experiments; light and temperature differences between the two boxes for

the entire testing periods were less than 0.5%.

In a preliminary study, basil plants were exposed to red light at night (λmax = 625 nm; 12-

hour duration) at three different irradiance levels, ranging from 21, 37 and 86 µmol m-2 s-1 (0.90

– 3.72 mol m-2 n-1) as well as darkness (Patel et al. unpublished). The lowest irradiance

suppressed P. belbahrii by 2/3 whereas the two higher levels suppressed sporulation completely.

The highest level, however, caused curling of the basil leaves which might compromise the

marketability of the basil plants. To avoid this potential problem, a lower level of 60 µmol m-2 s-1

was used in the present study. For this study, the “red light” box was illuminated by a custom

light fixture (LEDSupply, Randolph, VT) with red LEDs (Cree XLamp XP-E2 Red High Power

LED Star, λmax = 625 nm; full-width, half-maximum (FWHM) = 16 nm) 1.2 metres above the

benchtop, providing an average PPFD of 60 µmol m-2 s-1 on the top of each pot during the night

for 10 hours (from 20:00 to 06:00; 2.16 mol m-2 n-1). The second box was dark throughout the

night (0.0 mol m-2 n-1) and served as the control condition. Both boxes in both experiments were

exposed to natural sunlight in the greenhouse during the daytime. The temperature in the

greenhouse was maintained at 22 ± 3°C. Plants were irrigated using a misting system which was

set to automatically turn on for 5 minutes every 6 hours.

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Dependent variables

A total of four different morphological characteristics were assessed: plant height, number of

leaves per plant, leaf length and width, and fresh and dry leaf weights. The plant height, number

of leaves, and leaf length and width were measured 43 days after plants were placed in the

greenhouse. Plant height was measured from the base of the stem at the soil surface for each

plant per pot. For the total number of leaves, all fully expanded true leaves were counted for each

plant in the pot. Only the second leaf (one leaf per pair) from the base of the plant was used to

measure leaf length and width. A total of four leaves (using the second leaf from the base of the

plant) per pot were considered for measurements of leaf length and width. The leaf length was

assessed by measuring the distance between the leaf base and the leaf tip, whereas the leaf width

was assessed by measuring the distance between the widest points of both leaf blades. An

assessment of basil fresh and dry weights was undertaken following 65 days in the greenhouse to

better assess the cumulative, differential effects of the red-light treatment on growth and yield.

Two leaf pairs (the second and third pairs from the bottom of the plant) were picked and the

fresh weights of the leaves were immediately measured. These same leaves were placed in a

thermal chamber at 70°C for 24 hours, and then measured for dry weight.

Statistical analyses

Simple planned comparisons (Student’s two-sample t-test with unequal variance; Furgeson,

1966) were used to compare the two levels of the independent variable, dark versus red light at

night, on six dependent variables (plant height, number of leaves, leaf length, leaf width, fresh

leaf weight, and dry leaf weight) for two independent experiments (i.e., one repeated

experiment). The probably of a Type 1 error increases when multiple comparisons are applied to

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several dependent variables. In other words, the likelihood of falsely rejecting the null

hypothesis increases with additional comparisons. For this reason, the most conservative

Bonferroni criterion (p < 0.004) was applied to the paired comparisons to help ensure against

falsely rejecting the null hypothesis for each outcome measure (Netter and Wasserman, 1974;

McGuigan, 1997). To determine if the data from the two independent experiments could be

pooled for inferential statistics, an F-test was conducted to assess the homogeneity of variance.

Minitab version 16 (Minitab Inc., State College, PA) and Microsoft Excel version 2010 were

used for all statistical analyses.

Experimental designs and statistical analyses for greenhouse and growth chamber studies

are notoriously complicated because of unforeseen and potentially confounding variables that

might affect the outcome. With regard to the present study, it is important to avoid confounding

environmental factors that might affect plant growth in concert with the experimental light

treatment. We monitored and recorded the two most important potentially confounding

environmental factors (local temperature and natural light in the greenhouse) to ensure these did

not vary systematically with the light treatment. Assuming that these important potentially

confounding environmental factors can be shown to independent of the light treatments, it is still

possible that some other, albeit unlikely, factor might be confounded with the light treatment. It

is therefore important to replicate, as we did for this study, the entire experiment to determine if

the light treatments could produce statistically reliable results.

It is perhaps worth noting that this experimental design is not an example of

pseudoreplication. As Schank and Koehnle (2009) have discussed, there is confusion between

inferential statistics based upon multiple measurements from the same subject (e.g., a particular

leaf) versus those based upon measurements from juxtaposed (in time or space) subjects (e.g.,

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leaves from different plants) in the same environment. The former is an example of

pseudoreplication, the latter, as employed in the present experiment, is not. In fact,

pseudoreplication is a name put upon an orthodox tenet in all inferential statistics, namely that all

of the samples in a particular experimental condition must be independent of one another.

RESULTS

The homogeneity of variance test indicated that the width (F1,63 = 1.88; p = 0.013) and length

(F1,63 = 1.90; p = 0.012) of the leaves were significantly different in the two experiments,

whereas the number of leaves (F1,63 = 0.63; p = 0.066), plant height (F1,63 = 0.96; p = 0.858) and

fresh (F1,31 = 0.98; p = 0.353) and dry weight (F1,31 = 0.72; p = 0.375) of the leaves were not.

Since the variance for two of the six variables could not be pooled, the results of the statistical

analyses for each outcome measure in both experiments are provided in Table 1 along with

descriptive statistics (means and standard deviations). Whereas all outcome measures showed an

increase with red light relative to the dark control (e.g., Fig. 1 and 2), only dry weight had similar

variance in both experiments and showed a statistically significant difference between the red-

light treatment and the dark control in both experiments using the highly conservative Bonferroni

criterion. The pooled data for dry weight are shown in Fig. 3.

DISCUSSION

Photobiological effects

Plants use photosynthetically active radiation (PAR, wavelength range: 400 – 700 nm), to

convert carbon dioxide and water molecules into sugar and oxygen. This process is called

photosynthesis, which occurs in all green plants. There are also several other plant responses to

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the same wavelength range (400 – 700 nm) including seed germination, phototropism and de-

etiolation. In the present study, we applied red light (λmax = 625 nm) at night to basil plants that

would likely have induced several photosensitive mechanisms, perhaps most interestingly on the

long-wavelength sensitive phytochrome.

Phytochrome has two interchangeable forms; the maximum absorption peak of the

inactive (red, r) form, Pr, is at about 660 nm and the peak sensitivity of the active (far-red, fr)

form, Pfr, is at about 730 nm. Under sunlight, photons from the red and the far-red regions of the

spectrum are available for absorption by both forms of the phytochrome. This condition results

in steady-state cycling of the photopigment between the two forms, active and inactive. In the

present study, the exposure of basil plants to the narrowband red LEDs (λmax = 625 nm)

employed during the night would have led to preferential absorbance of the light by the inactive

form (Pr) of phytochrome, over the active form (Pfr) of phytochrome. We infer that preferential

absorption of the 625 nm light by Pr stimulated basil vegetative growth. This inference is

consistent with empirical findings from a variety of other studies (Flint and McAlister 1937;

Borthwick et al. 1952; Quail et al. 1983; Kasperbauer 2000). Neff and Van Volkenburgh (1994)

have indicated that Phytochrome B is required for red-light stimulated cell expansion in

Arabidopsis seedlings. This suggests that nighttime exposure to 625 nm could have stimulated a

Phytochrome response which played a role in enlarging the basil leaves.

Kim et al. (2005) examined the effect of red-light exposure from LEDs (λmax ≈ 650 – 680

nm) on lettuce photosynthetic rates. They found that maximum photosynthetic rates occurred

during the red-light exposure compared to photosynthetic rates during a combination of red (R),

green (G) and blue (B) (RGB) LED lighting. Moreover, the high photosynthesis rate was reduced

when the lettuce plants were returned to the original RGB lighting environments after 24 hours.

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Although the present experiment did not use the same spectral power distribution as that used by

Kim et al. (2005), the Pr form of the phytochrome would still preferentially absorb the red

spectrum relative to the Pfr form. In another study, basil leaf size and weight increased under

field conditions when planted with “red” polyethene mulch relative to mulch of other colors

(Loughrin and Kasperbauer 2001). Since Loughrin and Kasperbauer (2001) did not provide

sufficient information about the spectral power distribution (both amount and spectrum) of the

reflected photons from the different mulch colors in the study, valid inferences about differential

plant growth related to the light spectrum cannot be made. Notwithstanding, and consistent with

the wide range of empirical studies, differentially reflecting more red light from mulch onto basil

should have also positively affected plant growth and yield, as was demonstrated in the Loughrin

and Kasperbauer (2001) study. “Red” mulch has also been found to suppress nematode damage

in tomato plants (Adams 1997). The researchers suggest that the reflected “red” light resulted in

more plant growth and less root growth, which, in turn, reduced the amount of roots available as

a food supply for the nematodes. However, as noted previously, inferences about the differential

plant growth should not be made without additional information about the amount and spectrum

of the reflected light.

It is important to point out, however, that the effects shown in the present study may have

simply resulted from the application of more photosynthetic energy at night. It is therefore

important to design future experiments to determine if, in fact, similar increases in yield can be

accomplished with other wavelengths and in addition, to compare the effectiveness of these

wavelengths on the suppression of downy mildew sporulation. In general, however, we infer

from the present study that illumination by narrowband, red LEDs during the night, previously

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shown to successfully inhibit basil downy mildew sporulation, can also increase leaf size,

number of leaves, plant height, and fresh and dry weight of basil.

Economic comparisons

Value is defined as the ratio of benefits to costs. In a perfect world, the benefits and costs would

be well defined, and the grower would simply compute the value ratio when deciding to grow or

not grow basil. The value of growing basil is becoming more and more uncertain with the ever-

widening threat of basil downy mildew wiping out an entire crop (Wyenandt et al. 2015). If the

grower wants to continue to produce basil, it is becoming increasingly clear that some

preventative measures will need to be taken to mitigate the risk of complete crop failure. Thus,

the cost of growing basil will have to increase, decreasing the value of the crop to the grower

unless there is an associated price increase to offset the added cost. If, however, the preventative

measure also increases yield, the numerator as well as the denominator will change and the

necessary price increase due to the disease would be less.

The present study showed that nighttime red-light exposure increased growth and yield

by every outcome measure, albeit to different amounts (Table 1). Average dry weight for the

pooled data from two experiments increased by 68% (Fig. 3) and, although not statistically

significant, average fresh weight for pooled data from two experiments increased by 17% due to

the nighttime application of red light. Previous research (Patel et al. 2016) also showed that

nighttime applications of red light minimized the spread of basil downy mildew. Naturally, there

is a cost associated with the application of red light at night. Therefore, the value of the basil

crop after treatments of nighttime red light, considering both benefits and costs, needs to be

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examined and, moreover, compared to the value of the basil crop using conventional fungicide

application.

The following revenue table (Table 2) provides a value comparison for a basil grower

with a 200 m2 facility. For this case study, it is assumed that the grower would have already

installed an LED system that delivers red light at approximately 660 nm. Typical commercially

available LED lighting systems for growing basil may provide a PPFD of 200 µmol m-2 s-1 for 16

hours per day (DLI: 11.5 µmol m-2 d-1), much more than is required to suppress downy mildew

sporulation. For a 200 m2 facility the estimated installed cost would be $65,000 – $171,000 (total

luminaire quantity: 88-132, depending on the model). At the present time, the capital cost of an

LED lighting system would be prohibitive for just disease control, so it was assumed that such a

system had already been installed to promote growth. It was further assumed for this case study

that basil stems will be harvested every 14 days, either for high-price fresh leaves or for low-

price dry leaves. Basil may be harvested for both, but for this analysis, the value of fresh basil

and dry basil are treated separately. After 65 days, the plants would be removed from the facility

and a new crop planted. These and the other assumptions used for the revenue table are

documented in Appendix 1. An Excel spreadsheet is publicly available on our website

(http://www.lrc.rpi.edu/programs/plants/plants_home.html) where growers and other interested

parties can substitute different assumptions for a new revenue table.

As can be seen from Table 2, fresh organic basil will command the highest price. If there

is no downy mildew and the grower does nothing and the entire crop is harvested, revenue is

maximized ($6397). If the grower does nothing and there is downy mildew, however, there can

be complete crop failure and the grower receives no revenue ($0). If the grower decides to

mitigate the risk of complete crop failure, the grower has two decisions to make. First, they need

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to decide if they want to remain organic or not and, second, the grower needs to decide whether

to take preventative action or not. Red light, as applied at night in the present study, is a

potentially effective method of enhancing plant growth and yield and, as demonstrated in

previous studies (Cohen et al. 2013; Patel et al. 2016), can limit sporulation of P. belbahrii.

Based on the disease severity data mentioned by Patel et al. (2016), we estimate that suppressing

sporulation with nighttime red-light treatments can reduce basil marketable yield by 50% rather

than 100% without nighttime red-light treatments. With nighttime red-light treatments and no

disease, the yield is increased slightly (17%) but the revenue is reduced ($5475), due to the

incremental electric lighting energy costs ($2010, see Appendix 1). The risk of complete crop

failure due to disease is reduced by 50% using nighttime red-light treatments; however, this

approach still provides positive revenue to growers, even with disease ($1733).

If the grower abandons the organic approach and applies conventional fungicides, the

47% premium value for organic basil in the marketplace disappears, but the grower is assured of

revenue for fresh basil, with or without disease (Table 2). Taking into account the loss of the

organic premium and the cost of applying pesticides, revenue for the grower is assured ($4241).

This revenue can be compared to the organic red-light treatment; if there is no disease, the

revenue is 23% less, whereas revenue is 245% more if disease occurs. If there is disease in the

non-organic facility, using nighttime red light treatments will still result in moderate positive

revenues ($536).

Growing basil for dry consumption always generates less revenue, even if the crop is

organic (64% lower revenue). For an organic basil crop treated with red light at night, moderate

revenues are possible if there is no disease ($607) but disease in the facility will result in

economic losses (-$701). Using nighttime red light treatments for non-organic basil grown for

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dry consumption may not be cost effective, whereas modest revenue can be achieved if the

grower uses fungicide treatments ($948). If there is no disease, using nighttime red light

treatments results in an economic loss (-$230) even though greater yields are produced. Indeed,

if the non-organic basil facility contracts the disease, the red-light treatments will lead to an even

larger economic loss (-$1120).

The revenues presented for this case study are based on a nighttime red-light treatment

using 625 nm LEDs for 10 hours at 60 µmol m-2 s-1. More research is needed to determine the

optimum red-light treatment for yield and for minimizing basil downy mildew sporulation.

Although red light can certainly increase growth and yield and minimize downy mildew

sporulation, red LEDs with a longer peak wavelength (e.g., 660 nm) may be more effective than

the 625 nm LEDs for increasing growth and yield, reducing downy mildew sporulation, or both.

It is also not known whether the 10-hour duration of red-light exposure is necessary. Perhaps

red-light exposure provided intermittently throughout the night might be equally effective for

suppressing sporulation of basil downy mildew. Finally, 60 µmol m-2 s-1 may be more than

necessary for suppressing basil downy mildew while growth and yield would be unaffected by a

lower irradiance level. As we, and of course, other interested laboratories, complete research on

this topic, it will be possible to more accurately assess the optimum wavelength, duration, and

amount of nighttime red-light treatment, and thereby to recalculate the revenue values in Table 2.

Today, there is no economic panacea for basil growers. Each basil grower must

continuously reevaluate the risk and then decide the best way to mitigate that risk. Hopefully the

research results presented here and those previously published (Patel et al. 2016) provide

growers with some preliminary insights into how the evolving research into the impact of red

light on basil growth and yield, and on its primary disease, may affect the value (benefit/cost) of

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this crop. Obviously, these findings should be extended to much larger field trials to gain better

insights into the economics of red-light treatments at night, both for suppression of basil downy

mildew sporulation and increasing basil yield.

ACKNOWLEDGEMENTS

Thanks are given to Professor Mary Rea, PhD, Chair of the Department of Biology & Health

Sciences at The Sage Colleges, for granting access to the greenhouse and to Janice Bonaccorso

for assistance with the greenhouse facility. From the Lighting Research Center (LRC), Tim

Plummer is acknowledged for assistance in growing and maintaining the basil and for building

the test apparatus, John Bullough for assisting with the statistical analyses, Andrew Bierman for

equipment calibration, and Rebekah Mullaney for editing the manuscript. Funding for the project

was supported by the LRC Partners Program and the Organic Agriculture Research and

Extension Initiative Program (grant number # 2015-51300-24135).

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Table 1. Means and [standard deviations] of the basil morphological characteristics and yield for

the nighttime red-light treatment and the dark control condition

Experiment 1

Experiment 2

Time in

greenhouse

(days)

Dependent

variables

Dark Red

LEDs

Dark Red

LEDs

43

Plant height (cm) 9.73

[2.43] ***

13.80 [5.14]

12.57 [4.20]

15.24 [4.63]

Number of leaves 5.44

[1.46]

5.75 [1.59]

6.31 [2.03]

***7.63

[1.56]

Leaf length (cm) 5.74

[1.13] ***

7.19 [1.61]

6.20 [0.98]

6.78

[1.22]

Leaf width (cm) 4.84

[0.92] ***

6.53 [1.53]

5.07 [0.92]

***6.13

[1.02]

65

Fresh leaf weight (g)

1.77 [0.54]

2.24

[0.65]

1.98 [0.69]

2.15

[0.60]

Dry leaf weight (g)

0.12 [0.03]

***0.22

[0.66]

0.17 [0.06]

***0.26

[0.08]

*** Indicates a statistically greater outcome measure for the nighttime red-light treatment

relative to the dark control condition (p < 0.004); a Bonferroni criterion was used for the

Student’s t-test to account for multiple paired comparisons between the red-light treatment and

the dark control among the different outcome measures. Thus, the probability of a family-wise

Type 1 error was set at p < 0.004 to reach statistical significance.

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Table 2. A case study revenue table for different basil grower decisions; see text and Appendix 1

for complete details

No preventative

treatment

Preventative treatment

Organic

red light

Non-

organic

fungicide

Fresh

Organic

No disease

$6397a

$5475b,d -

Disease $0g $1733b,d,f -

Non-organic

No disease

$4352

$3082b,d $4241c

Disease $0g $536b,d,f $4241c

Dry

Organic

No disease

$1557a

$607b,e -

Disease $0g ($701)b,e,f -

Non-organic

No disease

$1059

($230)b,e $948c

Disease $0g ($1120)b,e,f $948c a47% premium for organic

bCost of energy = -$2010 (60 µmol m-2 s-1 for 10 hours per night for 65 days for a 200 m2

facility)

cCost of fungicide = -$111 (9 applications over 65 days for a 200 m2 facility)

d+17% for greater yield (fresh); It should be noted that this value is based upon the results of the

present study and this amount could be different for growers.

e+68% for greater yield (dry); It should be noted that this value is based upon the results of the

present study and this amount could be different for growers.

f-50% for loss of yield (due to sporulation inhibition)

gIt should be noted that this value depends upon disease pressure and may not be $0 in all cases.

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Fig. 1. Representative leaves from the basil plants kept under dark conditions at night (left) and

under red-light exposure at night (right). The nighttime red-light exposure increased leaf size.

Fig. 2. Representative pots showing the difference in height of the basil plants kept under dark

conditions at night (left) and under red-light exposure at night (right). The red-light exposure

increased plant height.

Fig. 3. Relative increase in dry weight for basil grown under nighttime red-light relative to the

dark control. The asterisks (***) indicates a statistical significance at p < 0.0001 for the pooled

data from both experiments.

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Fig. 1

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Fig. 2

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Fig. 3

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Appendix 1

This appendix reports the assumptions and costs associated with the revenue comparisons in

Table 2.

Gross retail basil prices without nighttime red-light treatment costs or fungicide costs

Organic

(fresh)a,b,d

Non-

organic

(fresh)

Organic

(dry)c,d

Non-

organic

(dry)

Price per bunch ($ US) $2.00 $1.36 1.46 $0.99

Basil stems per bunch 5e 5e 15f 15f

Price per stem ($ US) $0.40 $0.27 $0.10 $0.07

Basil plant density (plants m-2) 10

Basil stems harvested per plant every 14 weeks 2

Stem harvesting density every 14 days (stems m-2) 20

Average growing area (m2/grower) 200

Stem harvesting density every 14 days (stems/total area) 4000

Number of harvests over 65-day growing period 4

Stems harvested over 65 days 16000

Gross price over 65 days ($ US), no red light at night, no

fungicide $6397 $4352 $1557 $1059

aOrganic fruits and vegetables are 47% more expensive on average than non-organic products (Consumer Reports 2015)

https://www.consumerreports.org/cro/news/2015/03/cost-of-organic-food/index.htm

bOrganic price per bunch from grower in Argyle, NY

cOrganic dry basil prices based on volume pricing (Pacific Botanicals, OR)

dNet weight per bunch: 2.5 ounces (http://www.nproduce.com/serving-fresh-herbs)

eFive stems per bunch (per grower in Argyle, NY)

fBased on a 3-to-1 ratio of stems to yield 2.5 ounces of dry basil leaves (based on percentages in Danso-Boateng 2013 and Lynch

2010)

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Fungicide costs over 65 days (non-organic treatment)

Fungicide cost (ProPhyt 2.5 gallon container) $70

Dose for basil plants (pints product/acre) 5

Growing area (m-2 per acre) 4047

Pints per growing container (pints per 2.5 gallons) 20

Fungicide cost per acre $17.50

Fungicide cost for 200 m2 growing area $0.86

Labor cost for one fungicide treatment (200 m2) $11.45a

Number of fungicide treatments over 65 days 9

Total fungicide treatment cost 65 days ($ US) $111

aAverage hourly labor cost (Bureau of Labor Statistics 2016)

The use of trade names (ProPhyt) does not imply endorsement by the authors, nor criticism of similar products not mentioned.

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Nighttime red light treatment costs over 65 days

Number of nights red light is on 65

Number of hours red light is on per night 10

Power demand in watts for red light (λmax=625 nm, 60 umol.m-2.s-1), per 0.6 × 0.6 m 55.65

Average energy cost per kWh $0.10

Average energy cost for 65 days per 0.6 × 0.6 m $3.62

Energy cost for 60 µmol m-2 s-1 for 10.5 hours per night for 65 days ($ US m-2) $10.05

Energy cost for 200 m2 for 10.5 hours per night for 65 days $2010

Increase in fresh weight due to red light treatment, compared to no treatment 1.17

Increase in dry weight due to red light treatment, compared to no treatment 1.68

Gross price over 65 days, including markup for increase in fresh weight ($) with red light at night, no

fungicide applications $5475

Gross price over 65 days, including markup for increase in dry weight ($) with red light at night, no

fungicide applications $607

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Cost comparisons

Organic

(fresh)a

Non-

organic

(fresh)

Organic

(dry)a

Non-

organic

(dry)

Gross price over 65 days ($)

No red light at night, no fungicide applications $6397 $4352 $1557 $1059

Energy costs for nighttime red light ($) $2010 - $2010 -

Conventional fungicide costs ($) - $111 - $111

Net price after preventative costs ($) $5475b $4241 $607c $948

Net price if 50% of crop is lost to downy mildew disease

under nighttime red light treatment (assuming fungicide

treatments are 100% effective)

$1733b $4241 ($701)c $948

Difference in price due to nighttime red light, no loss due to

downy mildew ($5475/ $4241) 1.29

Difference in price due to nighttime red light, 50% loss due

to downy mildew ($1733/$4241) 0.41

aOrganic fruits and vegetables are 47% more expensive on average than non-organic products (Consumer Reports 2015)

https://www.consumerreports.org/cro/news/2015/03/cost-of-organic-food/index.htm

bIncludes 17% increase in price due to increase in fresh weight with red light treatment

cIncludes 68% increase in price due to increase in dry weight with red light treatment

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For Review Only - TSpace Repository: Home · 2018-11-27 · For Review Only Patel et al., The Value of Red Light for Increasing Basil Yield 2 ABSTRACT Patel, J.S., L. Radetsky, and