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South African Journal of Botany 76 (2010) 440 - 446
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Influence of plant growth regulators on flowering, fruiting, seed oil content,
and oil quality of Jatropha curcas
H.A. Abdelgadir a, A.K. Jäger c, S.D. Johnson b, J. Van Staden a *
a Research Centre for Plant Growth and Development, School ofBiological and Conservation Sciences, University ofKwaZulu-Natal Pietermaritzburg, Private Bag
X01, Scottsville 3209, South Africa
b School ofBiological and Conservation Sciences, University ofKwaZulu-Natal Pietermaritzburg, Private Bag X01, Scottsville 3209, South Africa c Department ofMedicinal Chemistry, Faculty ofPharmaceutical Science, 2 Universitetsparken, 2100 Copenhagen O, Denmark
Received 6 April 2009; received in revised form 15 February 2010; accepted 16 February 2010
Abstract
Field experiments were conducted to determine the effects that plant growth regulators (PGRs) have on seed production of Jatropha curcas when they are used for chemical pruning. In the subsequent year, following a single foliar application of PGRs, flowering, fruit set, fruit characteristics, seed total oil content and oil free fatty acid (FFA) content were evaluated. The number of flowers per plant, number of fruits per bunch, fruit- and seed characteristics and seed oil content were significantly affected by the different treatments. However, there were no variations in the degree of fruit set or oil FFA content. A single foliar application of N6-benzyladenine produced more flowers per plant, more fruits per bunch, heavier and bigger fruits and seeds with more oil compared to manual pruning. Treatment with 2,3,5-triiodobenzoic acid yielded more flowers per plant and heavier fruits with a higher oil content than the control and manually pruned plants. Treatment with 2,3:4,6-di-O-isopropylidene-2-keto-L-gulonic acid yielded similar results. More fruits per bunch and more seeds per fruit were also produced. Maleic hydrazide treatment yielded more flowers per plant, heavier and bigger fruits with more, heavier, oil rich seeds compared to the control and manual pruning. This study indicates that foliar application of PGRs as chemical pruners in J. curcas may have a sequential effect in boosting seed production, seed oil content and improves fruit quality. © 2010 SAAB. Published by Elsevier B.V. All rights reserved.
Keywords: Benzyladenine; Dikegulac; Maleic hydrazide; Plant growth regulators; Seed oil content; TIBA
1. Introduction
The rise in the crude oil price and the uncertainty associated with ensuring uninterrupted supplies have compelled the need to look for renewable substitutes. Biofuels are technically feasible alternatives for crude oil (Srinivasan, 2009). Biofuels offer promise, but are controversial because of the large land area required for production, potential for competition with food production, and their marginal economic viability in the absence of subsidies (Gressel, 2008). These potential negative impacts could be reduced and profitability increased if production could be made more efficient. A crop with potential for biofuel production in arid and semi-arid regions is the physic nut,
* Corresponding author. Tel.: +27 33 2605130; fax: +27 33 2605897. E-mail address: rcpgd@ukzn.ac.za (J. Van Staden).
Jatropha curcas L (Heller, 1996; Augustus et al., 2002; Azam et al., 2005; Achten et al., 2008). Interest in using J. curcas as a feedstock for the production of biodiesel is growing rapidly. The properties of the crop and its oil are sufficiently persuasive to consider it as a substitute for fossil fuels and to help reduce greenhouse gas emissions. However, J. curcas is still an undomesticated plant in which many basic agronomic properties are not yet thoroughly understood (Achten et al., 2008). Jatropha curcas oil contains about 14% free fatty acid (FFA) which is beyond the limit of 1% level which can be efficiently converted into biodiesel by trans-esterification using an alkaline catalyst (Tiwari et al., 2007). The fatty acids that were reported in a previous study of J. curcas oil are palmitic acid (11.3%), stearic acid (17%), arachidic acid (4.7%), oleic acid (12.8%), and linoleic acid (47.3%) (Adebowale and Adedire, 2006).
J. curcas bears bunches of fruit at the apex of the branches. Therefore, limited branching is considered one of the major factors limiting yield in this species. Traditionally manual pruning
0254-6299/$ - see front matter © 2010 SAAB. Published by Elsevier B.V. All rights reserved. doi:10.1016/j.sajb.2010.02.088
(MP) is practiced to promote branching. This helps in producing more branches with healthy inflorescences and enhances flowering and fruit set that ultimately increases yield (Gour, 2006). However, cost, convenience and efficiency of MP in large-scale plantations still remain a major concern. A means of obtaining improved flowering, fruiting and seed oil content in J. curcas would be of enormous commercial benefit. Plant growth regulators (PGRs) may provide the means of bringing about required growth responses as there is abundant data indicating that their use can increase the yield of product per unit of time and land (Morgan, 1980). An increase in the seed hydrocarbon content in response to hormonal application to J. curcas has been reported (Augustus et al., 2002). In cottonseed, application of growth retardants increased seed protein content, oil yield, seed oil refractive index, unsaponifiable matter and total unsaturated fatty acid content (Sawan et al., 2001).
In a previous study we used N6-benzyladenine (BA); 2,3,5-triiodobenzoic acid (TIBA); 2,3:4,6-di-O-isopropylidene-2-keto-L-gulonic acid (dikegulac; DK); and 1,2-dihydro-3,6-pyridazine-dione, coline salt (maleic hydrazide; MH) as chemical pruners to increase production of lateral shoots (Abdelgadir et al., 2009). We now report on the effects of foliar applications of PGRs and MP, 1 year after application on flowering, fruit set, fruit characteristics, total seed oil content, and oil free fatty acid content of J. curcas.
2. Materials and methods
2.1. Study site and experimental design
The experiments were conducted in a monoculture plantation at the University of KwaZulu-Natal Agricultural Research Station (Ukulinga) Pietermaritzburg, South Africa, (30° 41' E, 29° 67' S and 781 m a.s.l). The plantation was established from seeds obtained from plantations at the Owen Sithole College of Agriculture, South Africa. The original seeds were imported from Malawi. The trial had an irrigation system installed to ensure survival of the plants during early establishment period. These plants were irrigated twice a week in the morning for 3 h with sprinkler system. This irrigation was only for the first three weeks with no fertigation. Shortly after planting, the trial was invaded by weeds which were controlled by a broad-spectrum herbicide Roundup (Monsanto, St. Louis, US) to clear all the unwanted vegetation. The mulch (grass cuttings) was thereafter applied to the base of the plants to reduce weed regrowth and conserve moisture. In the early stage, ten months from planting, the solution of Prev-Am (Citrus Oil Products (SA) (Pty) Ltd., Somerset West, SA) and Cyperfos 500 EC (Gouws and Scheepers Pty Ltd., Witfield, SA) insecticides in combination was sprayed onto plants to control the infestation of beetles (Aphtona species). The foliar treatments of one-year-old plants consisted of BA (3, 6, 9 and 12 mM), TIBA (0.5, 1.0,1.5 and2 mM), DK(2,4, 6and8 mM)andMH(1,2and 4 mM). Three millilitre of 0.1 M sodium hydroxide was used to solubilize the PGRs before adding water. A few drops (2 ml) of Tween® 20 (Merck) were added as a surfactant. Each plant was treated once with 200 mL of respective PGR solution using a 1 L plastic spray bottle. Early in the morning, entire plants were sprayed covering leaves, stems and meristems (Abdelgadir et al., 2009). The
adjacent plants were covered temporarily with a sheet of transparent plastic film to avoid drift of PGR. Plants sprayed with distilled water plus an equivalent amount of 0.1 M NaOH served as control. Each treatment consisted of twelve uniform plants considering a single plant as one replicate selected randomly. The spacing between the plants was 2.5 x 2.5 m. Manual pruning was done using a lopping shear on the same day as that of the foliar treatment. The cut was made about 1 cm above an active bud to prevent dieback of the stem and to encourage a new branch to develop. The minimum and maximum temperature during the experiment was 15 and 27 °C respectively. In the subsequent year (May 2008) following the foliar spray in 2007, data for the number of flowers per plant, fruit set percentage and the number of fruits per bunch were collected. In August 2008 fruits were harvested and fruit characteristics: number of fruits per plant, number of fruits per bunch, fruit weight, fruit size, number of seeds per fruit and seed weight were recorded (Fig. 1). Fruit set was considered the percentage of flowers that sets fruit per plant and was normalized by using the angular transformation. SPSS® release 15 (SPSS Inc., Chicago, USA) statistical software was used for data analysis and one-way ANOVA was performed for significant differences.
2.2. Extraction of oil
The same seed samples used to determine the fruit characteristics were ground using an A11 BASIC analytical mill. Distilled n-hexane was used as solvent to extract the oil, using a Soxhlet apparatus (Araújo and Sandi, 2006). Three samples (3 g each) of the seed meal from each treatment were placed in Whatman single-thickness cellulose extraction thimbles. Empty round-base glass flasks were weighed for initial mass. Hexane (150 mL) was transferred to each flask and these placed on the Soxhlet plate. The Soxhlet system was connected firmly to a cooling system and ran for 2 h. The solvent was then removed from the extract using a Rotary Evaporator (Büchi).
2.3. Oil analysis
Oil was analysed (Martínez-Herrera et al., 2006; Jäger et al., 2008; Halim et al., 2009) as follows: oil (5 ^L), 1000 ^L MeOH (HPLC-grade), 200 ^L (trimethylsilyl) diazomethane (Aldrich); were mixed and shaken for 15 min. Glacial acetic acid (250 ^L), 2.5 mL heptane (HPLC-grade), 3 mL saturated NaCl solution; were added, shaken for 30 min, and 1 mL of the heptane fraction was transferred into a GC-MS vial. The sample (1 ^L) was injected into the GC-MS. An Agilent 6890N Network GC system coupled to a 5973 Network Mass Selective Detector was used. GC conditions: injector temperature: 250 °C; temperature programme: start 70 °C hold for 4 min, 40 °C/min to 160 °C, 3 °C/min to 270 °C; column: HP5MS; and carrier gas: He.
3. Results
3.1. N-benzyladenine
Foliar application of BA at 3 mM significantly (P<0.05) increased the number of flowers per plant compared to the control
Fig. 1. Jatropha curcas fruits and seeds. (A) Variation in fruit maturity; (B) variation in fruit size; (C) variation in number of seeds per fruit. Bar scale = 1 cm for (A-B), 0.5 cm for (C).
and MP (Table 1). BA at 12 mM produced significantly (P< 0.05) more fruits per bunch compared to the control and MP. However, there were no significant differences in fruit set percentage (Table 1). BA at 9 mM produced significantly (P<0.05) heavier and bigger fruits compared to MP (Fig. 2A and B). No significant differences were detected between treatments with respect to the number of seeds per fruit and seed weight (Fig. 2C and D). However, BA at 9 mM had a significantly (P< 0.05) higher seed oil content compared to MP plants (Fig. 2E).
3.2. 2,3,5-Triiodobenzoic acid
TIBA at 1.5 mM produced significantly more flowers per plant and more fruit per bunch respectively, compared to the control and MP (Table 1). However, no significant variations in fruit set percentage were found between treatments (Table 1). Foliar application of TIBA at all concentrations produced significantly (P<0.007) heavier fruits compared to the control
Table 1
Effect of benzyladenine (BA), 2,3,5-triiodobenzoic acid (TIBA), dikegulac (DK), maleic hydrazide (MH) and manual pruning (MP) on the number of flowers/plant, fruit set (%) and the number of fruit per bunch in J. curcas plants. Data were collected 1 year after PGR application.
Plant growth regulator application No. of flowers/ Fruit No. of f
(mM) plant set (%) ruit/bunch
0.0 53.7±7.3b 86.7±2.8a 4.6±0.7b
3.0 72.8±4.7a 88.8±5.4 2.7±0.3c
6.0 30.0±7.0c 81.6±4.1 2.8±0.4c
9.0 38.6±6.3c 80.9±2.9 4.0±0.4bc
12.0 45.0±9.2bc 80.5±2.9 5.2±0.7a
MP 38.8±8.5b 84.6±4.6 3.3±2.7b
0.0 53.7±7.3b 86.7±2.8a 4.6±0.7b
0.5 42.1±6.3bc 77.4±3.4 3.3±0.7b
1.0 46.1 ± 5.3b 78.3±3.2 3.3±0.6b
1.5 69.6±9.3a 78.2±3.1 3.7±0.5b
2.0 60.9±5.1ab 77.9±2.7 5.5±0.9a
MP 38.8±8.5b 84.6±4.6 3.3±2.7b
0.0 53.7±7.3b 86.7±2.8a 4.6±0.7b
2.0 71.25±6.6a 76.4±3.1 5.4±0.6a
4.0 58.7±4.9b 79.4 ±4.6 3.1 ±0.5b
6.0 51.4±5.3b 71.3±3.1 3.7±0.9b
8.0 53.7±8.2b 74.5 ±7.6 4.0±0.3b
MP 38.8±8.5b 84.6±4.6 3.3±2.7b
0.0 53.7±7.3b 86.7±2.8a 4.6±0.7b
1.0 59.9± 10.2a 80.5 ±3.5 2.9±0.4
2.0 44.6±4.9b 81.3 ±4.2 3.6±0.5
4.0 34.5±3.9b 83.5 ±3.9 4.8±1.0
MP 38.8±8.5b 84.6±4.6 3.3±2.7b
Means±(S.E) with different letter(s) are significantly different according to Tukey's test (P<0.05). a No significant difference at P < 0.05, according to F test.
and MP treatments (Fig. 2F). TIBA at all concentrations produced significantly (P<0.05) bigger fruits with more seeds per fruit compared to MP (Fig. 2G and H). However, individual seed weight was not influenced by the different treatments (Fig. 2I). TIBA at 1.5 and 2 mM produced seeds with significantly higher oil content compared to those from 0.5 and 1 mM and MP treatment, but not compared to the control (Fig. 2J). No significant differences in seed oil content were found when applying TIBA at concentrations higher than 1.5 mM. However, at lower concentrations (0.5 and 1 mM) TIBA reduced the seed oil content significantly when compared with the control treatment (Fig. 2J).
3.3. Dikegulac
DK at 2 mM significantly increased the number of flowers per plant and the number of fruit per bunch compared to the control and MP treatments. However, there were no differences between treatments in fruit set percentage (Table 1). Foliar application of DK at 2,4, and 6 mM produced significantly more seeds per fruit compared to MP (Fig. 2M). However, there were no significant differences between treatments in fruit weight, size and seed
Fig. 2. Effects of BA, TIBA, DK, MH, and MP (manual pruning) 1 year after treatment, on fruit characteristics of two-year-old plants of J.curcas. A, F, K andP = fruit weight; B, G, L and Q = fruit size; C, H, M and R = number of seeds per fruit; D, I, N and S = seed weight; and E, J, O and T = seed total oil content (%). Standard error bars with same letter(s) are not significantly different according to Tukey's test (P<0.05).
weight (Fig. 2K, L and N). DK at a lower concentration (4 mM) produced significantly more seed oil compared to the MP and DK
palmitic acid (18.2%), linoleic acid (41.7%), oleic acid (33.9%) and stearic acid (6.1%). The highest FAA content detected were
at 8 mM (Fig. 2O). Concentrations higher than 4mM are not palmitic acid (21.3%) recorded for DK at 2 mM, linoleic acid
recommended.
3.4. Maleic hydrazide
(48%) recorded for TIBA at 0.5 mM, oleic acid (36.1%) recorded for BA at 3 mM and stearic acid (8.1 %) recorded for MH at 2 mM (Table 2).
The number of flowers per plant was significantly increased by 1 mM MH compared to the control treatment and MP (Table 1). MH at 2 mM produced heavier fruit compared to the control, MP and a higher concentration of MH (4 mM) (Fig. 2P). Foliar application of MH at 1 and 2 mM produced fruits that were significantly bigger and heavier and that contained more seeds per fruit than the control, MP and MH at 4 mM (Fig. 2Q, R and S). MH at 2 mM produced seeds with a significantly higher oil content (Fig. 2T).
3.5. Oil analysis
There were no variations in the free fatty acid (FFA) composition between the PGRs, MP and control treatments (Table 2). The average FAA content for the bulk sample were
4. Discussion
Crop yields are often increased indirectly by preventing losses, hastening the production cycle, or facilitating mechanical harvesting operations. Knowledge of the influence of PGR application on flowering is of interest for understanding both internal mechanisms regulating flowering and practical usefulness of controlling the time and degree of flowering (Tompseet, 1977; Bonnet-Masimbert and Zaerr, 2004). It was suggested that the application of PGRs is often more consistently successful in enhancing flowering than agricultural treatments (Philipson, 1990). However, it is important to define the age of plants used in PGR experiments, since the results can be influenced strongly by the stage of plant development at the time of treatment (Ross, 1976). In a few crops, PGRs increase plant growth or divert
Table 2
Effects of PGRs on seed free fatty acid content (%) of two-year-old plants of J curcas. Seeds were collected 1 year after PGR treatment.
Treatment Free fatty acid contenta (%)
Palmitic acid Linoleic acid Oleic acid Stearic acid
Control 18.8 40.0 34.5 6.4
MP 17.3 43.3 32.9 6.4
BA (mM)
3.0 19.5 37.7 36.1 6.8
6.0 12.3 43.9 33.7 6.9
9.0 18.1 40.1 34.3 6.7
12.0 17.5 43.6 33.1 5.8
TIBA (mM)
0.5 16.8 48.1 30.0 5.2
1.0 20.8 39.0 32.7 7.5
1.5 17.7 44.2 32.8 5.4
2.0 17.8 43.3 32.9 6.1
DK (mM)
2.0 21.3 40.4 37.3 1.05
4.0 19.4 39.2 34.8 6.6
6.0 20.1 37.7 35.3 6.9
8.0 19.7 38.6 35.0 6.7
MH (mM)
1.0 16.8 45.9 32.3 5.0
2.0 19.6 37.0 35.3 8.1
4.0 17.3 44.1 33.1 5.6
a No significant differences were observed.
photosynthate to the harvested product so that the actual productivity is increased. There are a variety of reasons to anticipate a significant increase in the commercial use of PGRs and many approaches to discovering and developing these uses (Morgan, 1980). The effect of PGRs in promoting branching of J. curcas was discussed earlier (Abdelgadir et al., 2009). The objective of this study was to evaluate the subsequent effect following foliar application of PGRs and MP on the flowering, fruit set, fruit characteristics and seed total oil content in two-year-old plants of J. curcas.
The results showed an increase in the number of flowers per plant and the number of fruits per bunch by foliar application of BA compared to the untreated control and MP (Table 1). Endogenous cytokinin levels have been observed to fluctuate during floral induction (Bernier et al., 1993). Several studies have shown that application of exogenous cytokinins increase the number of flower buds in apple (McLaughlin and Greene, 1991) and pear trees (Ito et al., 2001). Similar effects have been reported for jojoba (Prat et al., 2008), with a significant increase in the number of flowers per branch, seventeen months after the application of BA. It was speculated that the significant increase in the number of clusters caused by BA application was the result of cytokinin action on the axillary meristems, reflected in an enlargement of the axillary meristematic zone. This growth would allow the differentiation of more than one flower per axillary bud, resulting in an increase in total number of flowers produced. Also Werner et al. (2001) found that cytokinins had an important regulatory effect on Nicotiana tabacum meristem
morphogenesis, enlarging the meristem, which gave a greater probability for the development of flower meristems. However, Tompseet (1977) reported that BA enhanced promotion of flowering in Picea sitchensis when mixed with gibberellins alone or in combination with NAA. In contrast, some studies reported negative effects with synthetic cytokinins as they exhibit inhibitory effects on flowering in apples (Sanyl and Bangerth, 1998) and in Chenopodium rubrum (Vondrâkovâ et al., 1998). BA concentration of 3 mM increased flowering of J. curcas plants, but at higher concentrations it was decreased. A similar response was observed for in vitro flowering of Kniphofia leucocephala when the concentration of BA was increased (Taylor et al., 2005). Cytokinins are reported to act with sucrose for floral initiation (Bernier et al., 2002; Bernier and Périlleux, 2005). It is possible that lower concentrations of BA are more effective in mobilizing the sugars than the higher concentrations. In the case of J. curcas BA may have increased the activity of sugar mobilization up to the flowering and fruiting stages, however a subsequent decline in sugar levels reduced the formation of fruits. In J. curcas BA produced heavier and bigger fruits when compared with MP. However, it was not significantly different to the controls (Fig. 2A and B). Also no significant differences were found between treatments with respect to the number of seeds per fruit and seed weight (Fig. 2C and D). The present results are in agreement with those of Prat et al. (2008) who reported no significant differences in the total weight of seeds per plant between the BA treatments and the control in jojoba.
Foliar application of TIBA produced significantly more flowers per plant and more fruits per bunch compared to the control and MP (Table 1). However, there were no variations in fruit set percentage between treatments (Table 1). Further, TIBA at all concentrations yielded significantly heavier fruits compared to the control and MP treatments (Fig. 2F). Several studies reported a promotive effect of TIBA on flowering and fruiting. A significant increase in flowering in response to TIBA application was reported in sweet cherry by Grochowska et al. (2004). In another study with soybean, Noodén and Noodén, (1985) found that foliar application of TIBA increased the number of pods per node. Geng et al. (2005) found that in tulip bulbs an application of TIBA in combination with gibberellin enhanced early flowering and brought about higher flowering rates. Similar results on the effects of TIBA on fruiting were reported in maiden plum, sour cherry and sweet cherry trees (Grochowska et al., 2004). A single-collar application of TIBA increased fruit productivity in all of these species as well as fruit masses in maiden plum. On average the increase was about 24% higher than that of the controls. Grochowska et al. (2004) explained these results by the fact that the most characteristic action of TIBA is the inhibition of the polar transport of auxin and, thus, it is categorized as a growth retardant contributing to reduced auxin levels. The results led to the suggestion that endogenous auxin is a dominant participant in the processes of growth, flowering and fruiting of these three stone-fruits.
For Jatropha, no significant differences in fruit size, the number of seeds per fruit and seed weight between TIBA and the control treatments were recorded. However, TIBA at all
concentrations yielded bigger fruits with more seeds per fruit compared to the MP treatments (Fig. 2G and H). For sesame, TIBA decreased the number of seeds per capsule and seed weight (Day, 1999). In the present study, TIBA at 1.5 and 2mM produced seeds with higher oil content compared to MP (Fig. 2J).
Dikegulac at 2 mM increased the number of flowers per plant and the number of fruits per bunch compared to the control and MP treatments (Table 1). No differences in fruit set percentage between treatments were found (Table 1). Foliar application of DK at 2, 4, and 6 mM produced significantly more seeds per fruit compared to MP (Fig. 2M). There were no significant differences between treatments in fruit weight, size and seed weight (Fig. 2K, L and N). These findings are comparable with those reported for citrus (Pozo et al., 2004) in that no significant differences in fruit quality were found in response to application of DK, although DK was reported to accelerate floral abscission. Rugini and Panelli (1993) reported that no significant differences were found in the fruit weight of olives between DK and the control treatments. DK at lower concentration (4 mM) produced a significantly higher seed oil content compared to the control and MP treatments (Fig. 2O). DK at higher concentration (8 mM), however, reduced the seed oil content significantly compared to the control (Fig. 2O). In contrast in olives, Rugini and Panelli (1993) reported no significant differences in oil content between DK and control treatments.
The number of flowers per plant was significantly increased by 1 mM MH application compared to the control treatment and MP as well as its higher concentrations (2.0 and 2 mM) (Table 1). These results are comparable with those of Ito et al. (2001) who found that in Japanese pear foliar application of MH increased the number of laterally born flower buds on the shoots. They suggested that MH may increase cytokinin levels in lateral buds and thus as a result increase the number of flower buds. In this study MH at 2 mM yielded heavier fruit compared to the control, MP and MH at higher concentration (4 mM) (Fig. 2P). Foliar application of MH at 1 and 2 mM yielded bigger fruits with heavier seeds compared to the control, MP and MH at higher concentration (4 mM) (Fig. 2Q, R and S). MH at 2 mM produced seeds with a significantly higher oil content compared to MP (Fig. 2T).
Only four free fatty acids (FFA) were found in our study samples. The FFA were linoleic, oleic, palmitic and stearic acids (Table 2). There was no variation detected in the FFA content between treatments (Table 2). These results differ from those of Adebowale and Adedire (2006) who also reported around 4.7% arachidic acid with the dominant component being stearic acid. We did not detect arachidic acid and stearic acid which was consistently the lowest FFA in our samples. This could be due to cultivar differences or to the methodology used to extract and analyse the fatty acids.
5. Conclusions
In this study BA, TIBA and DK tested exhibited better results than MP. However, these PGRs were not much more effective as compared to control plants. Investigations of these regulators under different climatic zones and levels of soil nutrient and moisture will improve the knowledge of application. Quantitative data on yield increases resulting from growth regulator applica-
tions are most commonly available at the time a substance is being approved for agricultural use. In the hands of producers, PGRs must prove themselves as the bottom line of a financial balance sheet (Morgan, 1980). In this respect, Fig. 2(D, I, N, S) and (E, J, O, T) compares seed weight and seed oil content which are the major economic yield components for J. curcas. Based on the present results it appears that MH is the most likely PGR candidate to provide a significant increase in the yield component. It is also the least expensive PGR used. Therefore, the results from this study in combination with those from an earlier study regarding branch promotion (Abdelgadir et al., 2009) suggest further thorough investigation into MH interactions in this plant as it may provide an efficient chemical pruning agent, yield promoter and cost effective PGR for increased J. curcas seed production.
Acknowledgements
We thank Verus Farming Ltd., South Africa and the University of KwaZulu-Natal, Pietermaritzburg for financial support. Professor Colin Everson generously made available the plants used in the field trials.
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Edited by NJ Taylor
