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Industrial Crops and Products 53 (2014) 217– 227
Contents lists available at ScienceDirect
Industrial Crops and Products
journa l h om epage: www.elsev ier .com/ locate / indcrop
eveloping a castor (Ricinus communis L.) production system inlorida, U.S.: Evaluating crop phenology and response to management
avid N. Campbell a, Diane L. Rowlanda,∗, Ronnie W. Schnellb,1, Jason A. Ferrell a,nn C. Wilkiec
Agronomy Department, Institute of Food and Agricultural Sciences, University of Florida, 3105 McCarty Hall B, Gainesville, FL 32611, USAWest Florida Research and Education Center, University of Florida, 4253 Experiment Road, Highway 182, Jay, FL 32565, USASoil and Water Science Department, Institute of Food and Agricultural Sciences, University of Florida, 2181 McCarty Hall A, Gainesville, FL 32611, USA
r t i c l e i n f o
rticle history:eceived 7 September 2013eceived in revised form3 December 2013ccepted 20 December 2013
eywords:astoricinus communis L.lant growth regulatorepiquat chloridearvest aidaraquatribufos
a b s t r a c t
While castor (Ricinus communis L.) oil is an essential component in many industrial products, the U.S.currently imports all castor oil stocks due to the lack of domestic production of the crop since 1972.To reestablish U.S. production of castor, regional agronomic assessments of cultivars and managementsystems are required to assess the economic sustainability of the crop. A comparison of two castor culti-vars (Hale and Brigham) and management systems using plant growth regulators and harvest aids wasconducted at two different locations (PSREU and WFREC) within Florida during two years (2011 and2012) with the goal of assessing yield potential and phenological development of the crop in this semi-tropical climate. Yields were low in comparison to other U.S. regions where the crop has been tested withthe highest yields being 1357 kg ha−1 for Brigham at PSREU in 2011 and the lowest being 686 kg ha−1 forBrigham at PSREU in 2012. Mold observed on both cultivars and significant rates of shatter could have ledto upwards of 60% yield loss, indicating that yield potential in the region may be much higher. Oil percent-ages on average across sites and years were very consistent between the cultivars, with 45.0 and 45.4%for Brigham and Hale, respectively. Typical growth patterns of height, leaf area index (LAI), reproductivedevelopment, and root architecture were characterized for the region. The maximum height recorded
for either cultivar did not exceed 115.2 cm and the maximum seasonal LAI value was 2.87. Brigham pro-duced between 3 and 8 more racemes than Hale by the end of the season, depending on the site/year.The application of a mepiquat chloride based plant growth regulator (PGR) did not reduce plant heightat either location and had no consistent impact on photosynthetic capacity of the crop. The harvest aidparaquat led to over six times more leaf desiccation and leaf defoliation within 11 days after treatmentveral
and was more effective o. Introduction
Castor (Ricinus communis L.) is an oilseed with high commercialalue for industrial and biofuel applications (Lima et al., 2013), andecause of its specific oil properties that are particularly suited for
hese applications, the economic growth potential of the crop ismmense. In fact, global consumption driven by industry and bio-uel demand is limited only by insufficient and unreliable sourcesAbbreviations: Fv/Fm, dark adapted variable fluorescence over maximum fluo-escence; HA, harvest aid; LAI, leaf area index; PGR, plant growth regulator; PSREU,lant Science Research and Education Unit in Citra, FL; SPAD, Soil Plant Analysisivision (measure of light transmission and is related to leaf chlorophyll content);FREC, West Florida Research and Education Center in Jay, FL.∗ Corresponding author. Tel.: +1 229 869 2952.
E-mail address: [email protected] (D.L. Rowland).1 Present address: Department of Crop and Soil Sciences, Texas A&M University,
70 Olsen Boulevard, College Station, TX 77843, USA.
926-6690/$ – see front matter © 2014 Elsevier B.V. All rights reserved.ttp://dx.doi.org/10.1016/j.indcrop.2013.12.035
l than the tribufos harvest aid.© 2014 Elsevier B.V. All rights reserved.
for feedstocks (Severino et al., 2012). The United States (U.S.) gov-ernment and domestic private industries are currently dependenton foreign sources for castor oil. The U.S. maintained a stock ofcastor oil for wartime needs in the past (Roetheli et al., 1991) andprivate industries currently use castor oil in paints, coatings, inks,lubricants and a wide variety of other products (Ogunniyi, 2006;Severino et al., 2012). Although the U.S. does not produce castor oilcommercially, results from research trials indicate that the averageyield of irrigated castor grown in Texas far exceeds the global aver-age: between 2242 and 3363 kg ha−1 (Brigham, 1993) in Texas and1264 kg ha−1 internationally (FAOSTAT, 2013).
Despite the promise of high castor production levels in thesouthwestern U.S., drought conditions in Texas and throughoutmany western regions over the past decade have spurred inter-
est in finding other locations for U.S. domestic castor production.Many crops have seen a shift in production levels from the westernto the eastern U.S. because of fairly severe drought conditions inthe last decade. The southeastern U.S. presents a potential castor
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roduction area because there is typically high annual rainfall and semi-tropical climate that matches the regions of origin for therop. However, little is known about the phenology, managementequirements, yield potential, and other agronomic characteris-ics of the crop grown in different U.S. regions (Severino and Auld,013), and particularly for the agronomic conditions of the south-astern U.S.
Two semi-dwarf cultivars, Brigham and Hale, were bred in therid environment of Texas and registered in 1970 and 2003, respec-ively (Brigham, 1970; Auld et al., 2003). Hale has demonstratedotential for high yields in the U.S. and was used as a parental lineor the later-released Brigham cultivar, which was bred for reducedicin seed content (Auld et al., 2003) primarily due to the highlyoxic effects of ricin on humans. Despite being considered “semi-warf” growth types, the ample rainfall in the southeast U.S. mayesult in excessive vegetative growth that would likely need to beontrolled for successful mechanical harvest of the crop (Stafford,971). Exogenous applications of mepiquat chloride based plantrowth regulators (PGRs) have been observed to inhibit giberelliccid in cotton, thus reducing internode length (Gencsoylu, 2009).hese same compounds have the potential to reduce plant heightor castor, but giberellic acid inhibitors have shown mixed resultsn the crop in past research (Oswalt et al., 2008; Trostle et al., 2012).n addition to reducing internode length, giberellic acid inhibitorsave been shown to affect the photosynthetic capacity of cottonZhao and Oosterhuis, 2000) and a change in photosynthetic capac-ty may affect yield. Related leaf-level physiological traits that mayffect photosynthetic capacity and that may be impacted by PGRreatment include chlorophyll fluorescence, chlorophyll contentSPAD), gas exchange, leaf area, and specific leaf area. Therefore, toully assess the efficacy of PGR treatment in castor, effects of PGRpplication on both overall crop height and associated physiologicalmpacts must be evaluated.
Due to castor’s indeterminate nature, mechanical harvesting inhe southeast U.S. will require both limiting plant height and usingome form of termination, or harvest aid, to ensure a standard levelf maturity. This is because there is generally a lack of regular killingreezes in many regions of the southeast U.S., thereby making har-est aids essential for a cropping system in these regions. TribufosBrecke et al., 2001) and paraquat (Brecke et al., 2001) are effec-ive harvest aids currently used in southeast cotton production, andoth show potential to affect castor growth (Weiss, 2000). Defolia-ion percentage, leaf area index (LAI) and leaf desiccation are good
etrics to assess harvest aid effectiveness in cotton (Brecke et al.,001) and are likely to be useful measurements when assessing theffectiveness of harvest aids in castor production.
When considering the production of a crop in the southeast-rn U.S., much of the agronomic, developmental, and physiologicaleatures of the crop must be studied carefully and specifically foronditions within this humid region due to the near complete lackf information currently available. Cultivar variability must also bevaluated to determine genotypic suitability to the region’s pro-uction conditions. While aboveground traits are of interest foruantifying performance of castor in this new production region,
nformation about castor root architecture and root seasonal devel-pment would be of particular interest because data on the castoroot system are particularly lacking across all production regionsSeverino and Auld, 2013). The few studies that have examinedooting responses have concentrated on analyzing root dry matterhrough destructive sampling, a technique that dramatically under-stimates root production because of loss of fine roots (Severino anduld, 2013), and does not assess root architecture by soil depth.
herefore, quantification of root system development in situ woulde particularly valuable not only to evaluate castor phenology in theoutheastern U.S., but would shed valuable light on castor rootingabit in general – data that are currently not available.nd Products 53 (2014) 217– 227
All of this phenological, physiological, and performance infor-mation can be used to determine the optimal design of a castorproduction system in Florida. Therefore, to assess the efficacy ofproducing castor in Florida, field trials were established at twolocations in north Florida to test the performance of two likelycommercial cultivars, Brigham and Hale, in production systems uti-lizing agronomic practices that would be appropriate for the region.Specifically, the study aimed to answer the following objectives forthe crop grown in a southeastern U.S. production system: (1) eval-uate the use of PGRs and harvest aids in management of the crop;(2) quantify the phenology, physiology, and maturity of the crop;(3) quantify rooting architecture in situ using minirhizotrons; and(4) evaluate the production potential of the crop through measure-ments of yield and oil composition.
2. Materials and methods
2.1. Field preparation and PGR/HA applications
Field trials in 2011 and 2012 were conducted at two locations,the Plant Science Research and Education Unit (PSREU) near Citra,FL (latitude 29.408813 N, longitude 82.173041 W, altitude 21 m)in a Sparr Fine Sand (loamy, siliceous, subactive, hyperthermicGrossarenic Paleudults); and the West Florida Research and Educa-tion Center (WFREC) near Jay, FL (latitude 30.775999 N, longitude87.1400 W, altitude 10 m) in a Red Bay sandy loam (fine-loamy,kaolinitic, thermic Rhodic Kandiudults). Data are not reported forWFREC in 2012 due to crop failure. Both sites were arranged ina completely randomized block design with a split plot arrange-ment of treatments with 3 replications and 24 plots. Treatmentsconsisted of PGR (applied, non-treated control), harvest aid (HA –tribufos, paraquat), and cultivar (Brigham, Hale), with harvest aid asmain plot, PGR as sub-plot, and cultivar as sub-sub-plot. The plots atPSREU consisted of 6 rows within each plot with two border rows,while the plots at WFREC consisted of 4 rows within each plot andone border row. Plots in both locations were 7.6 m long with 0.9 mbetween rows. Bare soil alleys, 7.3 m wide, surrounded all plots atPSREU, while at WFREC all but 4 of the alleys between plots wereplanted. Both sites were conventionally tilled and irrigated prior toplanting. Plots were planted on 5 and 1 May 2011 and 2012, respec-tively, in PSREU and on 18 May 2011 in WFREC. Seed was planted ata 4 cm depth with a two-row Monosem (Edwardsville, KS) vacuumplanter using a large edible bean plate in PSREU; and a four-rowJohn Deere (Moline, IL) vacuum planter with a peanut plate inWFREC. Sites were thinned to an intra-row density of 6 plants m−1
(for a density of 66,000 plants ha−1) at both sites in 2011. Due to lowyields in 2011, intra-row density was decreased to 3 plants m−1 (fora density of 33,000 plants ha−1) in 2012.
At PSRUE in 2011, plots were broadcast fertilized with nitrogen(N) at 112 kg N ha−1 at 25 days after planting (DAP) and again with34 kg N ha−1 at 89 DAP; in 2012, fertilizer amounts remained thesame but were side dressed: 11 kg N ha−1 at planting, 67 kg N ha−1
28 DAP, and 67 kg N ha−1 49 DAP. At WFREC in 2011, plots werebroadcast fertilized once with 112 kg N ha−1 at 16 DAP. At both sites,phosphorous, potassium, and other minor nutrients were addedbased on the general recommendations for maximal yield for mostagronomic crops in the region. For weed control, an application of561 g active ingredient (ai) ha−1 of trifluralin (DOW AgroSciences,Indianapolis, IN) was incorporated pre-plant at WFREC in 2011 andat PSREU in 2012. At both sites in both years, plots were culti-vated by tractor at least twice after planting and weeded by handapproximately every 2–3 weeks thereafter.
The mode of action chosen for the PGR was a giberellic acidinhibitor with the active ingredient, mepiquat chloride. The PGRwas foliarly applied at both PSREU and WFREC. Pix (BASF, Lud-wigshafen, Germany) was applied at PSREU, while StanceTM (Bayer
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D.N. Campbell et al. / Industrial C
ropScience, Monheim am Rhein, Germany) was applied at WFREC.n 2011, PGR applications were initiated when 50% of the crop wast the second raceme growth stage; while in 2012, the first appli-ation was applied when 50% of the crop had one flower. In 2011 atSREU, 105.7 and 35.2 g ai ha−1 of mepiquat chloride was applied 49nd 83 DAP, respectively; while at WFREC, 98.8 and 37.0 g ai ha−1
epiquat chloride was applied 41 and 70 DAP, respectively. In 2012t PSREU, 23.5, 58.7, 58.7 g ai ha−1 of mepiquat chloride was appliedt 41, 51, and 62 DAP, respectively.
Because mechanical harvest of castor in Florida will requirearvest aid application due to the lack of a killing frost, crop defo-
iation and termination were accomplished with two harvest aidsHA): Def 6®, ai tribufos (Bayer CropScience, Monheim am Rhein,ermany) and Gramoxone® Extra, ai paraquat (Syngenta, US). In011, plots were sprayed 126 and 143 DAP in PSREU and WFREC,espectively with tribufos (rate of 1509.7 g ai ha−1) and paraquatrate of 671.0 g ai ha−1). In both years, leaf area index (LAI) was
easured with the LiCor 2200 instrument (LI-COR Environmental,incoln, NE) 4 times after application of the HA. In addition, percenteaf desiccation and leaf defoliation were assessed 2, 4, 7, and 11ays after HA application at the PSRUE location only.
.2. Yield, 100-seed weight and oil percentage
In 2011, PSRUE plots were harvested 105 and 138 DAP andFREC plots were harvested 109 and 155 DAP. Due to high shatter
osses noted before the first harvest in 2011, seed production overhe season was followed more closely in 2012 at PSREU, with therst yield collection at 86 DAP and additional harvests conductedeekly thereafter until the final collection at 157 DAP. Yield sam-les were collected by hand from the two inner rows at both
ocations (and in both years at PSREU); samples collected peri-dically during the growing season consisted of mature brownapsules, while the last harvest of the season also included greenapsules that were enlarged. In both years, capsules were first ovenried at 60 ◦C for a minimum of 72 h (resulting in seeds approxi-ately 6–7% water content), followed by complete hand threshing
nd removal of a random sub sample of approximately 20 g toetermine a husk/seed weight proportion. This proportion washen applied to total weights (husk and seed) to determine final00-seed weight and yield for each plot.
In 2011, seed oil percentage was determined by Advanced Pre-ision Laboratories, LLC in Sumner, GA where the samples wereround and analyzed in triplicate. The laboratory followed theOAC Official Method 948.22 “Fat (crude) in Nuts & Nut Products”sing a Soxtec 2050 Automated Extractor by Foss. The extractionups were heated in a 100 ◦C oven for approximately 1 h and thenooled in a desiccator to assure the cups are completely dry prioro extraction. The extracted oil samples were dried at 100 ◦C for0 min to fully evaporate the petroleum ether from the samplend then cooled in a desiccator prior to weighing the final sample.t was noted that the soluble starch concentration in the sample
as minimal, thus avoiding a second extraction by water. In 2012,he seed oil percentage was determined by the Bioenergy and Sus-ainable Technology lab at the University of Florida, Gainesville,L, with time-domain nuclear magnetic resonance (TD-NMR). TD-MR quantification of oil in castor seed samples was carried outsing a MQC-23 NMR analyzer (Oxford Instruments, UK), equippedith a 26 mm diameter probe operating at a resonance frequency of
3.4 MHz and maintained at 40 ◦C. Data were acquired using Mul-iQuant calibration and analysis software (Oxford Instruments, UK)nder operating parameters in accordance with ISO 10565 (1998).
ecause a solvent extraction based method for comparison requireslarge baseline of samples to calibrate the machine, a four-pointMR calibration (r2 = 0.999) correlating oil weight and NMR sig-al was calculated with three different castor oils (two commercial
nd Products 53 (2014) 217– 227 219
pure castor oils and an extracted and filtered random sample fromthis study) at four different quantities. Castor oil was extracted froma seed sample and filtered (0.45 �m) to remove any impurities. Cas-tor seeds were hand threshed from fruit pods leaving seed coatsintact and dried at 105 ◦C. All samples were conditioned at 40 ◦C for90 min prior to NMR analysis. Samples were run in triplicate; eachtriplicate analyzed 20 seeds selected at random (approximately3–5 g).
2.3. Phenology and root architecture
In both 2011 and 2012, LAI was measured from late May throughmid- to late-September approximately every two weeks for bothHale and Brigham using the non-destructive LiCor 2200 instrument(LI-COR Environmental, Lincoln, NE). LAI measurements began 42,21 and 35 DAP and concluded on 119, 143 and 88 DAP in PSREU2011, PSREU 2012, and WFREC 2011, respectively. One LAI mea-surement consisted of regularly spaced measurements underneaththe canopy spanning the distance between rows with the sensorhead held both parallel (4 readings) and perpendicular (4 readings)to the crop row with each orientation paired with one reading abovethe canopy.
To determine changes in total height, number of racemes,and nodes to the first raceme, ten randomly selected plants perplot were tagged and reassessed throughout the growing sea-son. Total height was measured to the nearest 1 cm of the tallestplant structure. The number of racemes included structures at ini-tial flower formation and all intermediate developmental stagesthrough mature racemes. In 2011, racemes were omitted from thecount if whole raceme failure (failure to produce a harvestablecapsule) was observed to better relate reproductive structure toyield; while in 2012, all racemes were counted regardless ofraceme failure to better understand the total number of racemespossible. Nodes below the first raceme included a count of allnodes above the soil surface and below the insertion point of thefirst raceme. The days until flowering were calculated by assum-ing a linear relationship between raceme number and days afterplanting. Leaf initiation rate (LIR) was calculated as the numberof nodes below the first raceme divided by the days to flowerinitiation.
Root architecture and growth was assessed by regularlyrecording root images through the season within the row toapproximately 80 cm below the soil surface for both Hale andBrigham in 2011 and 2012 at PSREU. Clear plastic minirhizotrontubes (183 cm in length) were inserted in-row and parallel to thecrop at a 45◦ angle with the soil surface. Roots were imaged alongthe entire length of the tube using a minirhizotron camera system(Bartz, Carpinteria, CA). Images were taken 4–6 times throughoutthe growing season and analyzed using the WinRHIZO TRON soft-ware (Regent Technology, Canada) which calculates root lengthfor each image. Measurements of total root length were summedwithin 10 cm increments along the installation depth of each tubeand analyzed according to these 7 soil depth zones in 2011, and dueto a deeper tube depth, 8 total depth zones in 2012.
2.4. Physiological responses to PGR application
To assess the impact of PGR application on leaf level physio-logical responses, measurements were conducted on the Brighamcultivar 1, 8, and 15 days after PGR treatment (DAT) at the PSREUsite in 2011 and 2012. At each of these time points, field physiolog-ical measurements were taken between 0900 and 1100 EDT on the
first fully expanded leaf from two different plants within each plot.Just prior to gas exchange measurements, leaves were dark adaptedfor at least 30 min and the ratio of variable to maximal fluorescence(Fv/Fm) was measured using an OS-1 fluorometer (OptiSciences
220 D.N. Campbell et al. / Industrial Crops and Products 53 (2014) 217– 227
Table 1ANOVA of yield, 100-seed weight and seed oil percentage for two castor cultivarsmeasured at the research site PSREU in 2011 and 2012. Factors include: cultivar(Brigham and Hale), PGR (treated and control), harvest aid (tribufos and paraquat),year (2011 and 2012), and all possible interactions. Shown are p-values (in bolddenoting significance of p < 0.05) for the factors in the model.
Effect Yield 100-Seed weight Oil percentage
df p-Value df p-Value df p-Value
Cultivar (C) 1 0.172 1 0.001 1 0.399PGR (P) 1 0.691 1 0.654 1 0.988Harvest aid (H) 1 0.466 1 0.970 1 0.354Year (Y) 1 <0.001 1 0.002 1 <0.001C × P 1 0.664 1 0.385 1 0.307C × H 1 0.684 1 0.602 1 0.122P × H 1 0.712 1 0.897 1 0.956C × P × H 1 0.421 1 0.353 1 0.498C × Y 1 0.073 1 0.527 1 <0.001P × Y 1 0.457 1 0.254 1 0.839H × Y 1 0.708 1 0.202 1 0.311
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Table 2ANOVA of yield, 100-seed weight and seed oil percentage for two castor cultivarsmeasured at the research site WFREC in 2011. Factors include: cultivar (Brighamand Hale), PGR (treated and control), harvest aid (tribufos and paraquat), and allpossible interactions. Shown are p-values (in bold denoting significance of p < 0.05)for the factors in the model.
Effect Yield 100-Seed weight Oil percentage
df p-Value df p-Value df p-Value
Cultivar (C) 1 0.0082 1 0.0337 1 0.5770PGR (P) 1 0.0166 1 0.2952 1 0.0072Harvest aid (H) 1 0.9814 1 0.2077 1 0.4159C × P 1 0.8537 1 0.5235 1 0.0123
TMMd
2
C × P × Y 1 0.493 1 0.260 1 0.823C × H × Y 1 0.893 1 0.446 1 0.038P × H × Y 1 0.663 1 0.762 1 0.136C × P × H × Y 1 0.545 1 0.807 1 0.536
nc., Hudson, NH). Relative chlorophyll content was then measuredn these same leaves using a SPAD meter (Spectrum Technolo-ies Inc., Plainfield, IL). These same leaves were again used in gasxchange measurements while the leaves were still attached to thelants. Gas exchange was measured using a LI6400-XT infra-redas analyzer (LiCor Environmental Sciences, Lincoln, NE); leaf con-itions were kept constant within the cuvette at 1800 �mol PAR,60 ppm CO2, and ambient temperature and atmospheric humid-
ty. After measurement, the leaves were collected, kept cool in annsulated container, and transported back to the lab for further
easurements.At the lab, a leaf section of approximately 1 cm2 was cut while
voiding the midrib for further fluorescence analysis (results nothown). The petiole was removed from the remainder of the leafnd leaf area was determined using the LiCor model 3100 leaf areaeter (LiCor Environmental Sciences, Lincoln, NE). The leaf was
ried at 60 ◦C for at least 72 h and weighed again to determine dryeight. Specific leaf area (SLA) was calculated as the ratio of leaf
rea to dry weight.
.5. Statistical analysis
Because PGR products were different between locations, eachite was analyzed separately. In addition, PSREU had a year factor in
he statistical model, while WFREC did not because measurementsere taken in 2011 only. Multivariate and univariate repeatedeasures along with ANOVA were used to analyze each of the yield,henological, and physiological characteristics measured (JMP Pro
able 3ean values and standard errors for yield, 100-seed weight and seed oil percentage for
easurements were taken in 2011 and 2012 at PSREU and 2011 only at WFREC. Meansifferences among PGR and non-PGR treatments for yield and oil percentage.
Site Year Cultivar PGR Yield (kg h
Mean
PSREU2011
Brigham Combined 1357
Hale Combined 1311
2012Brigham Combined 686
Hale Combined 1018
WFREC 2011
Brigham No 960
Brigham Yes 746
Hale No 1236
Hale Yes 990
a Mold on capsules was noted at in all years at both research sites, but may have been011.
C × H 1 0.4297 1 0.1252 1 0.2012P × H 1 0.8898 1 0.8017 1 0.2467C × P × H 1 0.5739 1 0.7818 1 0.1900
9 software, SAS Institute Inc., Cary, NC). Depending on the typeof measurement, the following fixed factors and interactions wereanalyzed: year (Y), plant growth regulator (PGR), cultivar (C), dateafter treatment (DAT), days after planting (DAP), and date (D). A pre-liminary multivariate repeat measures MANOVA test was run, andwhen the data passed the test of sphericity (SAS Institute, 2010),the data were rearranged and a univariate repeated measures anal-ysis was conducted identifying statistically significant findings withfurther separation using Tukey’s multiple comparison test.
3. Results
3.1. Yield, 100-seed weight and oil percentage
At PSREU, there were differences in yield, 100-seed weight,and oil percentage between years and 100-seed weight betweencultivars; PGR treatment and HA type had no effect on these char-acteristics (Table 1). At WFREC, cultivar differences were presentfor yield and 100-seed weight while PGR treatment had an effecton yield and oil percentage; HA type had no effect on any of thesecharacteristics (Table 2). Average yield values at PSREU were higherin 2011 and average 100-seed weight and percent oil were higherin 2012 (Table 3). At both PSREU and WFREC, Hale had a higheraverage 100-seed weight (20.6 and 23.0 g at PSREU and WFREC,respectively) than Brigham (18.7 and 21.5 g at PSREU and WFREC,respectively) (Table 3). Hale out-yielded Brigham at WFREC with anaverage yield of 1113 and 853 kg ha−1 for Hale and Brigham, respec-tively. PGR application did decrease yields (868 vs. 1098 kg ha−1)and oil percentage (45.2 vs. 46.2%) at WFREC (Table 3). Numeri-cally over both sites, the highest yields were seen at PSREU in 2011
for the Brigham cultivar (1357 kg ha−1) and the lowest at PSREU in2012 for the Brigham cultivar (686 kg ha−1); in contrast, the highest100-seed weights were found at WFREC in 2011 for the Hale cul-tivar (23 g) and the lowest at PSREU in 2011 again for the Brighamtwo castor cultivars (Brigham and Hale) at two research sites, PSREU and WFREC. are reported by PGR application within each cultivar at WFREC due to significant
a−1a) 100-Seed weight (g) % Oil
SE Mean SE Mean SE
105 17.9 0.5 43.3 0.4124 19.5 0.6 42.9 0.3
52 19.4 0.5 45.0 0.569 21.7 0.5 47.6 0.4
80 21.6 0.5 45.8 0.491 21.3 0.3 45.8 0.496 23.5 0.9 46.5 0.336 22.4 0.8 44.7 0.3
severe enough to have contributed to yield losses at PSREU in 2012 and WFREC in
D.N. Campbell et al. / Industrial Crops and Products 53 (2014) 217– 227 221
Fc(
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Fig. 3. Sample of castor root images obtained through the minirhizotron system on
Fa
ig. 1. Weekly harvest yield values at the research site PSREU in 2012 for two castorultivars, Brigham and Hale. Harvests are indicated according to days after plantingDAP).
ultivar (18 g). The highest numerical oil percent was measured forale at PSREU in 2012, with values over sites and years ranging
rom 42.9 to 47.6 (Table 3).In 2011, high rates of shatter were visually noted at the
rst harvest (105 and 109 DAP in PSREU and WFREC, respec-ively) caused by natural seed loss processes as well as highinds from a tropical storm; loss estimates were approximately
0–60% of the total number of seeds. By examining weeklyield collections in 2012 at PSREU, Hale yielded more thanrigham on a weekly basis until the end of the season when lesshan 40 kg ha−1 was collected at each harvest time, with yieldeaking at 107 and 100 DAP for Hale and Brigham, respectivelyFig. 1).
.2. Phenology and root architecture
Most phenological measurements, regardless of PGR treatment,howed increasing seasonal growth trends with some interesting
ig. 2. Number of racemes, leaf area index (LAI), and plant height for two castor cultivarscross two years: PSREU 2011 and 2012, and WFREC 2011. Time of measurement is indic
24 June (top panel) and 5 August (bottom panel) in 2011 at the PSREU research site.Note the presence of root hairs on 24 June that are not present on 5 August once theroot segment has aged and become more suberized.
cultivar differences. Hale consistently had between 1.6 and 5.2more nodes below the first raceme than Brigham (Table 4). Brighamflowered 11–18 days before Hale and LIR values ranged from 0.16to 0.26 across all sites and years combinations. The first racemes
, Brigham and Hale, assessed throughout the growing season at two research sitesated according to days after planting (DAP).
222 D.N. Campbell et al. / Industrial Crops and Products 53 (2014) 217– 227
Table 4Mean values for nodes below first raceme, days to flower, and leaf initiation rate(LIR) at the research sites PSREU in 2011 and 2012, and WFREC in 2011 for twocastor cultivars, Brigham and Hale.
Site Year Cultivar Nodes Days to flower LIR
PSREUa2011
Brigham 6.9 35 0.2Hale 12.1 46 0.3
2012Brigham 6.6 38 0.2Hale 8.2 51 0.2
WFREC 2011Brigham 7.3 35 0.2
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Table 6ANOVA of castor root length as measured across the season in images taken inminirhizotron tubes at the PSREU research site in 2011 and 2012. Factors include:plant growth regulator (PGR), cultivar (Brigham and Hale), date across the sea-son, soil depth zone (in 10 cm increments), and all possible interactions. Shownare p-values (in bold denoting significance of p < 0.05) for the factors in the model.
Effect Length 2011a Length 2012
df p-Value df p-Value
PGR (P) 1 0.320 1 0.336Cultivar (C) 1 0.991 1 0.477Date (D) 3 <0.001 4 <0.001Zone (Z) 6 <0.001 7 <0.001P × C 1 0.231 1 0.409P × D 3 0.643 4 0.082P × C × D 3 0.932 4 0.145C × D 3 0.725 4 0.031P × Z 6 0.001 7 <0.001C × Z 6 0.404 7 <0.001D × Z 18 0.285 28 0.008P × C × Z 18 0.307 7 <0.001P × D × Z 6 1.000 28 0.754P × C × D × Z 18 1.000 28 0.917
TAab
Hale 11.6 53 0.2
a Locations and years were analyzed separately due to different cultural practices.
ere observed as early as 35 DAP in WFREC and around 41 DAP inSREU (Fig. 2) with PGR having no effect on total number of racemesTable 5). Brigham produced between 3 and 8 more racemes thanale by the end of the season, depending on site/year (Table 5 andig. 2). Cultivars differed in LAI only at PSREU 2012 with Hale hav-ng a greater LAI than Brigham (Table 5 and Fig. 2). LAI was also notffected by PGR (Table 5) but differences across dates reflected anverall increase in canopy development as the season progressed.eak LAI values in PSREU 2011 and WFREC 2011 were observedpproximately 76 DAP with values of 2.01 and 2.87, respectivelyFig. 2); while at PSREU 2012, LAI reached a maximum of 2.10 at 143AP. Contrary to expectations, PGR did not have any effect on planteight at PSREU in either year (Table 5), while PGR applied plantsere actually taller at WFREC 2011 (data not shown). The two cul-
ivars differed in height only at WFREC 2011, with Hale being tallerhan Brigham.
Root architecture was not different between Hale and Brighamnd was not affected by PGR, but showed differences among datesnd soil depth zones (Table 6). Fig. 3 shows an example of the typef images obtained and the changes in the root segments that coulde seen over time, including the development of root hairs. Withinhe measured soil profile, cumulative root length (Fig. 4) was lowert the first date compared with all other dates, indicating that thereatest period of root establishment was within the first 60–70ays of crop development with no other significant increase in rootrowth past that period. Castor roots grew downward at the ratef 14 mm day−1 at 50 DAP in 2011 and 20 mm day−1 at 21 DAP in012. Roots were not well developed in the top layer at soil depthone 1 (approximately 0–10 cm below the soil surface) with valuesor root length being lower in this zone compared to all other zones.owever beyond this depth, the root system was fairly uniform and
eached the maximum limits of the measuring tubes at a depth of
3.4 and 83.9 cm below the soil surface in 2011 and 2012, respec-ively (Fig. 4). The lower density planting in 2012 resulted in lowerverall cumulative root growth, but growth patterns were similarith a peak around 70 DAP in both years. Measurements in 2012able 5NOVA of the number of racemes, leaf area index (LAI), and plant height for two castor cnd WFREC in 2011. Factors include: plant growth regulator (PGR), cultivar (Brigham andold denoting significance of p < 0.05) for the factors in the model.
Effect PSREU 2011a PSREU 2012
Racemes LAI Height Racemes LA
df p-Value df p-Value df p-Value df p-Value df
PGR 1 0.591 1 0.526 1 0.533 1 0.243 1
Cultivar (C) 1 <0.001 1 0.894 1 0.508 1 <0.001 1
Date (D) 5 <0.001 8 <0.001 5 <0.001 5 <0.001 5
PGR × C 1 0.308 1 0.839 1 0.467 1 0.834 1
PGR × D 5 0.993 8 0.733 5 0.838 5 0.165 5
PGR × C × D 5 0.714 8 0.938 5 0.615 5 0.999 5
C × D 5 <0.001 8 0.619 5 0.016 5 <0.001 5
a Site/years were analyzed separately due to different cultural practices.
C × D × Z 18 1.000 28 0.826
a Site/years were analyzed separately due to different cultural practices.
were conducted longer than 2011 and, as a result, root senescencewas observed at 142 DAP in 2012.
3.3. Physiological responses to PGR application
As with plant height and root length, the applications of PGRhad a limited effect on most of the physiological processes mea-sured for the cultivar Brigham measured at PSREU, but did increasePn in 2011 (Table 7) with rates of 24.7 and 22.7 �mol CO2 m−2 s−1
for PGR treated and non-treated plants (Table 8). All other mea-surements (Ci, transpiration, SPAD, and Fv/Fm) were not affectedby PGR in this year (Table 7). The effects on photosynthesis werenot present in 2012 but PGR lowered SPAD and Fv/Fm (Table 7). In2012, SPAD for PGR treated and non-treated plants was 39.8 and41.1, respectively (Table 8). Days after treatment (DAT) showedstatistical differences in both years on various physiologicalparameters, but because there was a lack of any increasing ordecreasing trends, the effect of DAT appears to be due to thevariability among environmental conditions during the differentmeasurement days.
3.4. Effectiveness of harvest aid treatment
In both years, the type of harvest aid and DAT did affect LAI, leafdefoliation and leaf desiccation, but prior PGR application and cul-tivar did not influence the response to HA type (Table 9). Paraquat
ultivars measured across the season at the research sites PSREU in 2011 and 2012 Hale), date across the season, and all possible interactions. Shown are p-values (in
WFREC 2011
I Height Racemes LAI Height
p-Value df p-Value df p-Value df p-Value df p-Value
0.432 1 0.992 1 0.144 1 0.444 1 0.0220.001 1 0.836 1 0.001 1 0.595 1 0.005
<0.001 7 <0.001 4 <0.001 2 <0.001 4 <0.0010.140 1 0.523 1 0.237 1 0.307 1 0.7670.937 7 1.000 4 0.183 2 0.522 4 0.5830.741 7 1.000 4 0.018 2 0.401 4 0.9900.008 7 0.890 4 <0.001 2 0.404 4 0.001
D.N. Campbell et al. / Industrial Crops and Products 53 (2014) 217– 227 223
F ermin2 indica
wcsat
ig. 4. Castor root length (mm) by soil depth zone (shown in 10 cm increments) det011 and 2012 for two castor cultivars, Brigham and Hale. Time of measurement is
as more effective than tribufos in desiccating and defoliating the
rop during both years as indicated by greater decreases in LAI andubstantially higher leaf desiccation and leaf defoliation percent-ges. By 7 DAT, paraquat decreased LAI 1.3 and 1.7 times more thanribufos when compared to the pre-treatment value during 2011ed by sequential root imaging in minirhizotrons at the PSREU research site in bothted according to days after planting (DAP).
and 2012, respectively (Fig. 5). The slight increase in LAI at 11 DAT
is likely due to leaf regrowth that was visually noted in the field.Regardless of HA product, leaf browning was observed at 2 DAT,whereas leaf defoliation lagged and was observed starting at 4DAT. By the end of the season, paraquat had substantially increased
224 D.N. Campbell et al. / Industrial Crops and Products 53 (2014) 217– 227
Table 7ANOVA of leaf level physiological and morphological traits for the castor cultivar, Brigham, following treatment with a plant growth regulator (PGR) at the research sitePSREU in 2011 and 2012. Shown are p-values (in bold denoting significance of p < 0.05) for the factors in the model: PGR, days after treatment (DAT), and their interaction.
Year Effect df Pn Ci Transpiration SPAD Fv/Fm Leaf area SLA
2011aPGR (P) 1 0.013 0.233 0.653 0.061 0.768 0.735 0.907DAT (D) 2 0.022 0.271 0.202 0.016 0.871 0.073 0.208P × D 2 0.983 0.933 0.805 0.894 0.309 0.309 0.407
2012PGR (P) 1 0.203 0.456 0.290 0.010 0.014 0.606 0.681DAT (D) 2 0.528 0.275 0.001 0.012 0.001 0.460 0.001P × D 2 0.392 0.387 0.233 0.756 0.889 0.954 0.463
a Site/years were analyzed separately due to different cultural practices.
Table 8Average values for leaf level physiological characteristics measured in the castor cultivar Brigham for plants that were not treated with PGR after PGR treatment at theresearch site PSREU in 2011 and 2012. Values were averaged across DAT.
Year PGR treatment Pn (�mol CO2 m−2 s−1) Ci (�mol CO2 mol air−1) Transpiration (mmol H2O m−2 s−1) SPAD Fv/Fm
2011No 22.7 283 14.0 38.7 0.82Yes 24.6 277 13.6 41.6 0.81
lwt
4
dasavCccttylsFce
TA2(
2012No 26.6 263
Yes 26.0 262
evels of visually rated leaf desiccation and defoliation over tribufosith 26.7 and 6.6 times more leaf desiccation and 117.1 and 9.3
imes more leaf defoliation in 2011 and 2012, respectively (Fig. 5).
. Discussion
The main goal of this study was to evaluate phenological cropevelopment and performance and the effect of different man-gement techniques that could be employed in a castor croppingystem for the southeastern U.S. region. The maximum yieldschieved in the current study were higher than the single pre-ious study of castor yields available from Florida (Domingo androoks, 1945) and are comparable with current yields from otherountries (FAOSTAT, 2013). In addition, due to the weekly yieldollection in 2012, the yield reported for this year represents theotal possible yield achievable and may not reflect actual produc-ion levels. However even with the added collection periods, theseield levels are low when compared to the maximum productionevels achievable domestically in Texas (Brigham, 1993). Several
eed characteristics may have contributed to the low yield levels inlorida including relatively low 100-seed weights and low oil per-entages when compared to the USDA castor germplasm (Wangt al., 2010). One contributing environmental factor to the lowable 9NOVA of leaf are index (LAI), and canopy defoliation and desiccation for two castor cult012. Shown are p-values (bold denoting significance of p < 0.05) for the factors in the mDAT), harvest aid (tribufos and paraquat), and all possible interactions.
Effect df 2011a
LAI Defoliation
p-Value p-Value
PGR (P) 1 0.372 0.191
Cultivar (C) 1 0.978 0.927
DAT 3 <0.001 <0.001
Harvest aid (H) 1 <0.001 <0.001
P × H 1 0.272 0.374
C × DAT 3 0.731 0.498
P × H × C 1 0.144 0.927
P × C 1 0.068 0.927
P × DAT 3 0.551 0.776
H × C 1 0.390 0.927
H × DAT 3 0.424 <0.001
P × DAT 3 0.604 0.066
H × C × DAT 3 0.215 0.453
a Site/years were analyzed separately due to different cultural practices.
10.5 41.1 0.8210.2 39.8 0.82
yields was likely the presence of mold on the racemes. Gray moldwas previously reported as one of the main limiting factors for suc-cessful castor cultivation in the southeast (Domingo and Crooks,1945; Weiss, 1971; Godfrey, 1919) and the presence of an uniden-tified mold was detected in the current study, with the greatestproblems noted at WFREC 2011 and PSREU 2012. However, no dif-ference in cultivar susceptibility to mold was noted. Whole racemefailure and individual capsule failure – presumably due to mold –was observed in both locations and likely reduced yield. In fact,over 70% of the total harvest in WFREC 2011 was gathered at thefirst harvest, and subsequent periods of heavy rain promoted moldgrowth and ultimately raceme failure. It is possible that commer-cial fungicide applications may help alleviate this yield-reducingproblem in the future. The combination of early maturing habits,raceme size, and a propensity to shatter also likely played an inte-gral role in producing low yields in this study. Given an estimatedloss due to mold and shatter of up to 60% at the two locations, itis possible that Hale and Brigham could theoretically have yieldedupwards of 2101 and 1632 kg ha−1, respectively at WFREC; while
at PSREU, the theoretical optimal yields for both cultivars couldhave been a little over 2200 kg ha−1. Because Brigham flowers werefirst observed in WFREC around 12 days earlier than the aver-age castor flowering times reported for the U.S. (Weiss, 2000), theivars following treatment with harvest aids at the research site PSREU in 2011 andodel: PGR (treated and control), cultivar (Brigham and Hale), days after treatment
2012
Desiccation LAI Defoliation Desiccation
p-Value p-Value p-Value p-Value
0.749 0.283 0.398 0.9400.411 0.157 0.297 0.128
<0.001 <0.001 <0.001 <0.0010.002 0.005 0.001 <0.0010.872 0.021 0.256 0.8230.150 0.067 0.315 0.0410.320 0.936 0.411 0.6470.463 0.561 0.720 0.4030.539 0.520 0.428 0.0160.281 0.213 0.552 0.477
<0.001 0.007 <0.001 <0.0010.727 0.646 0.974 0.5610.116 0.493 0.428 0.084
D.N. Campbell et al. / Industrial Crops and Products 53 (2014) 217– 227 225
F (a), pc
pwler(fi
ig. 5. Effects of the harvest aids tribufos and paraquat on percent leaf desiccationultivars, Brigham and Hale, at the PSREU research site in both 2011 and 2012.
lants at this location may not have had enough vegetative growthhen flowering started, thus reducing photosynthetic capacity and
owering photoassimilate reserves for the growing racemes. The
arly flowering could explain why the primary and secondaryacemes were typically smaller than those produced in TexasWeiss, 2000) or for Israeli cultivars that were examined in growerelds in south Florida (personal observation). The LIR values forercent leaf defoliation (b), and leaf area index (LAI – c) averaged across two castor
these cultivars in Florida were similar to extra-early maturing geno-types with LIR values ranging from 0.21 to 0.27 leaf day−1 (Anjani,2010).
Quantification and characterization of seasonal growth habits –height, number of nodes below the first raceme, days till flower-ing, LIR, LAI, and rooting architecture – of castor grown in Floridaare necessary to evaluate any cropping system for this area. These
2 rops a
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26 D.N. Campbell et al. / Industrial C
easonal growth habits are important because data on height andodes below the first raceme will affect mechanical harvesting;AI will characterize canopy growth and development; and rootingrchitecture will affect cultivation and propensity for deep miningf nutrients and water in the soil. Overall canopy growth in thistudy showed a typical increasing pattern throughout the season,ut the peak LAI measurements are somewhat low in comparison tother crops, including 7–8 for sorghum (Muchow and Davis, 1988),–6 for soybean (Shibles and Weber, 1965) and 5–7 for cottonAshley et al., 1965). Castor leaf area has been correlated with leafength (Wendt, 1967), and LAI has been computed (Vijaya Kumart al., 1996), but seasonal LAI development has not been reportedreviously for the crop. Given the lack of published data for castorpecifically, it is not possible to confirm the representative naturef the maximum LAI values reported in this study.
The root data collected in this study are novel and representn situ seasonal quantification of castor root architecture that hasot been previously available. Several root characteristics found
n this study have important implications for management of therop. For example, the relatively low root lengths in the 0–10 cmone below the soil surface are important because farm managersave been advised to be mindful of the shallow spreading root sys-em of castor plants when cultivating (Weiss, 2000). Based on theurrent results, the minimal root development in this cultivatableone indicates that mid-season cultivation may be possible withoutignificant root system damage for castor grown in Florida, whichrovides an important weed control measure in an environmenthere in season weed pressure can be high. The castor root sys-
em extended below 80 cm depth by 70 DAP and it is likely that theoots continued deeper in the soil, thus allowing for a greater dis-ribution within the soil profile and indicating the crop has a highotential for mining minerals and water. Rooting habit has beenoted in previous literature, but data of this type have never beeneported for castor and represent important botanical informationor the crop that could be applied to various U.S. and possibly globalroduction regions of similar climate.
One of the most important and perhaps surprising results of theurrent study is the lack of effect of PGR on overall plant height inither castor cultivar. Because plant height was not affected in 2011,GR application was initiated earlier in an effort to optimize itsffect in 2012. The lower concentration, but higher frequency ratespplied in 2012 were more similar to the recommendations for cot-on crop management (Brecke et al., 2001). However, even with aifferent application scheme, there was no impact on plant height
n either year at PSREU; with an actual increase in height withGR application at WFREC in 2011. Despite the lack of response,GR application may not be required for these cultivars becausehe tallest average height of 115.2 cm noted in the current studyas within the upper limit of the suggested range (30–125 cm) forechanical cultivation (Auld et al., 2003) and is similar to the semi-
warf cultivars (100–200 cm) grown in the Texas High Plains andrans-Pecos region (Brigham, 1993).
Although PGRs did not affect height to any great extent, theyid affect some physiological parameters, including having aariable effect on photosynthetic capacity in 2011 compared to012. In 2011, the PGR-applied plots had significantly higher pho-osynthetic rates, while this effect was absent in 2012 when loweralues were recorded for SPAD and Fv/Fm. Giberellic acid inhibitorsave been shown to both decrease (Reddy et al., 1996) and increaseZhao and Oosterhuis, 2000) the photosynthetic rate of cotton andhe results from this study show similar gas exchange results forastor. Although there were statistically significant impacts on
ome of the measured physiological parameters, the small mag-itude of these differences were likely to have relatively littleiological importance or impact on final yield. Overall gas exchangeates measured in this study, regardless of PGR treatment, matchnd Products 53 (2014) 217– 227
previously measured photosynthesis and transpiration rates forcastor (Pinheiro et al., 2008; Dai et al., 1992).
Due to the irregularity of a killing freeze in Florida, the useof a harvest aid will be a necessary cropping system component,and the results of this study reveal that paraquat is a much moreeffective harvest aid than tribufos. The goal of the harvest aid is todecrease the amount of vegetative material so that a mechanicalharvester can more efficiently gather and separate seed from vege-tative material. Leaf browning (leaf desiccation) will aid in harvestefficiency, but leaf drop (leaf defoliation) will maximize harvestefficiency due to the prevention of vegetative material entering thecombine. Visual observations of leaf desiccation and leaf defolia-tion were quantified using non-destructive measures of LAI whichshowed significant decreases in canopy architecture following har-vest aid treatment. The effects of paraquat as a harvest aid arecomparable with past studies in cotton, but tribufos defoliationpercentages are much lower. In one cotton study, the least effec-tive harvest aid defoliated 51.2% of the leaves after 7 DAT (Anon.,1999); while in the current study, tribufos defoliated only 3.1% ofthe leaves after 7 DAT. It is interesting that the hormone-relatedleaf abscission inducing mechanism of tribufos was not effective asa harvest aid given that previous literature states castor is severelydamaged by hormone-type herbicides (Weiss, 2000). Paraquat didnot terminate all the plants at the 2.1 L ha−1 rate, but the fact that itterminated the majority of plants may prevent it from being a har-vest aid if rattooning the crop becomes a viable production optionin the southeastern U.S. Due to the presence of regrowth at 11 DATfor paraquat, the recommendation to harvest within 10 days is inagreement with previous literature (Brigham, 1993). By harvestingwithin 10 days or less, a farmer would achieve the full effect of theharvest aid, avoid shatter, and avoid regrowth that would reducethe harvest efficiency.
5. Conclusion
While yields were lower than those reported for TX, the over-all castor canopy and root growth measured in this study showpromise for cropping systems in FL. Ultimately, yields need to beincreased to be competitive with other U.S. production regionsand the potentially increased yield may become realized with areduction of disease pressure, particularly for mold development inracemes. Future research is needed to further evaluate the poten-tial to grow castor in Florida, especially by incorporating fungicidesand other disease management strategies. The growth patterns ofheight, LAI, reproductive development and root architecture showpromise that castor may be capable of producing higher yields in FL.This study reports new data on rooting architecture indicating thatthe crop in FL may be more deeply rooted than anecdotal reportsof the crop elsewhere in the world. Mepiquat chloride, as a plantgrowth regulator, did not affect plant height and had conflictingeffects on the photosynthetic capacity of the crop. Tribufos did noteffectively terminate the crop in this system, but paraquat workedwell and would be effective as long as the crop is not managedin a rattooning system. This project focused on a cropping systemwith a single harvest, but the results of this study combined withthe potential to grow castor in a rattooning system in the south-eastern climate (data not shown) may suggest rattooning is a moreeconomically sustainable cropping system for castor in Florida.
Acknowledgements
The authors thank UF/IFAS for providing support for thisresearch as well as the staff at PSREU and WFREC for assistancein plot establishment and management. The authors are gratefulto Dr. D.L. Auld from the Texas Tech University for providing the
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eed and crop consultation, Dr. Catherine Campbell for copy editingssistance, and Dr. Arnold Saxton for statistical assistance. Valuableupport was also provided by B. Colvin, B. Poudel, J. Thompson, S.yrd, A. Cook, C. Smith and especially A. Schreffler during seasonaleasurements and data analysis.
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