Table 7.6 Estimated cost (ZAR/ha) of PGRs application, assuming 6-month-old plants of Jatropha curcas with average height of 50 cm, spray rate of 1 l of solution per 50 plants, using compressed air sprayer and plant density of 2500 plant/ha.
PGR Molecular weight (g)
Spray rate Cost
(ZAR/ha)
(g/l) (g/ha)
BA 225.5 2.7 135.1 11,356.4
TIBA 292.29 1.04 52.5 4,001.50
DK 499.81 2.37 118.5 509.00
MH 112.1 0.45 22.5 105.10
Cost was based on latest pricing of these products by Sigma-Aldrich.
(www.sigma-aldrich.com)
of exogenous cytokinins increase the number of flower buds in apple (MCLAUGHLIN and GREENE, 1991) and pear trees (ITO et al., 2000). Similar effects have been reported for jojoba Simmondsia chinensis (Link) Schneider. by PRAT, et al. (2008), who found that seventeen months after application of 100 mg l-1 of BA, a significant increase in the number of flowers per branch was observed when compared to the control treatment. He speculated that the significant increase in the number of clusters caused by BA application as being the results 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. TOMPSEET (1977) reported that BA enhanced promotion of flowering in Picea sitchensis by a mixture of gibberellins alone or in combination with NAA. In contrast, some studies reported negative effects with synthetic cytokinins as they exhibited inhibitory effects on flowering in apples (SANYL and BENGERTH, 1998) and in Chenopodium rubrum (VONDRÁKOVÁ et al., 1998). In this study BA produced heavier and bigger fruits when compared to the MP treatment. However, it was not significantly different to the controls (Figure 7.4A and B). Also no significant differences were found between treatments with respect to the number of seeds per fruit and seed weight (Figure 7.4C and D). These results agree with 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.
The results demonstrated that foliar application of TIBA produced significantly more flowers per plant and more fruit per bunch compared to the control and MP (Table 7.2). However, there were no variations in fruit set percentage (%) between treatments (Table 7.2). Further, TIBA at all concentrations produced significantly heavier fruits compared to the control and MP treatments (Figure 7.6A). Several studies reported on the promotive effect of TIBA on flowering and fruiting. A significant increase in flowering in response to TIBA application was reported in sweet cherry Prunus avium ‘Lutovoka’ 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, application of TIBA in combination with GA enhanced early flowering and higher flowering rates. Similar results on the effects of TIBA on fruiting was reported in maiden plum Prunus divaricata, sour cherry Prunus avium ‘Lutovoka’ and sweet cherry Prunus avium ‘Rivan’ trees (GROCHOWSKA et al., 2004). He found that a single foliar application of TIBA increased fruit productivity in all of these species as well as fruit masses in maiden plum Prunus divaricata. On average, the increase was about 24% higher than that of the controls. GROCHOWSKA et al. (2004) explained his 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. Therefore, he suggested that the endogenous auxin is a dominant participant in the processes of growth, flowering and fruiting of these three stone-fruit species.
The results showed that 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 produced fruits with significantly (P < 0.05) bigger size and with more seeds per fruit compared to the MP treatments (Figure 7.6B and C). TIBA was reported to decrease the number of seeds per capsule and seed weight in sesame (DAY, 1999). TIBA at 1.5 and 2 mmol l-1 produced physic nut seeds with higher oil content compared to MP (Figure 7.6E). No significant differences were found between TIBA at higher concentrations (1.5 and 2 mmol l-1) and the control treatment. However, TIBA at lower concentrations (0.5 and 1 mmol l-
1) significantly reduced the seed oil content compared to the control treatment (Figure 7.6E).
The results of this study demonstrated that DK at 2 mmol l-1 significantly increased the number of flowers per plant and the number of fruit per bunch compared to the control and MP treatments (Table 7.3). No significant differences in fruit set percentage between treatments were found (Table 7.3). Nevertheless, DK was reported to accelerate floral abscission in citrus (POZO et al., 2004). Foliar application of DK at 2, 4, and 6 mmol l-1 produced significantly more seeds per fruit
compared to MP (Figure 7.8C). However, there were no significant differences between treatments in fruit weight, fruit size and seed weight (Figure 7.8A, B and D).
These findings agree with those reported for citrus by POZO et al. (2004) that no significant differences in fruit quality were found in response to application of DK.
Also RUGINIE and PANELLI (1993) reported for olives that no significant differences were found in fruit weight between DK and the control treatments. However, DK at lower concentration (4 mmol l-1) produced significantly higher seed oil content compared with the control and MP treatments (Figure 7.8E). DK at higher concentration (8 mmol l-1), however, reduced the seed oil content significantly compared to the control (Figure 7.8E). In contrast, for olives (Olea europaea L.) RUGINIE and PANELLI (1993) reported no significant differences in oil content between DK and control treatments.
The results demonstrated that the number of flowers per plant was significantly increased by 1 mmol l-1 MH compared to the control treatment and MP (Table 7.4).
These results agree with those of ITO et al. (2000) who found that in Japanese pear foliar application of MH increased the number of laterally-borne 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 mmol l-1 produced significantly (P < 0.001) heavier fruit compared to the control, MP and MH at higher concentration (4 mmol l-1) (Figure 7.10A). Foliar application of MH at 1 and 2 mmol l-1 produced fruits significantly bigger, more seeds with heavier seed weight compared to the control, MP and MH at higher concentration (4 mmol l-1) (Figure 7.10B, C and D). MH at 2 mmol l-1 produced seeds with a significantly higher oil content (Figure 7.10E).
The results showed that only four Free Fatty Acids (FFA) were found in the study sample and the dominant FFA was linoleic acid followed by oleic acid, palmitic acid and stearic acid (Table 7.5). There was no variation detected in the FFA content between treatments (Table 7.5). These results do not agree with those of ADEBOWALE and ADEDIRE (2006) who, in addition to the four FFA detected around 4.7% of arachidic acid with a dominant component of stearic acid, which
ranked the lowest in our study sample. These discrepancies could be due to differences among cultivars of J. curcas or to the methodology used to extract and analyse fatty acids.
Quantitative data on yield increases resulting from growth regulator applications are most commonly available at the time a substance is being cleared for use (proof of efficacy). Well established products are maintained in use by grower experience rather than by newly published data. In the hands of producers, growth regulators must prove themselves as the bottom line of a financial balance sheet (MORGAN, 1980). In this respect, Figures 7.3, 7.5, 7.7 and 7.9 compare seed weight and seed oil content which are the major economic yield components for J. curcas; Table 7.6 compares the application cost (ZAR/ha) of the PGRs used in this study. The results revealed that MH was the only PGR that gave significant increase in yield component and simultaneously was the least expensive PGR. Therefore, the results from this Chapter in combination with the results from Chapter 4 suggests further thorough investigation into MH interactions in this plant in order to be registered as an efficient chemical pruning agent, yield promoter and cost effective PGR for J. curcas seed production improvement.