Effect of gibberellic acid on pod set in soybean

Abstract

Field-grown soybean plants (Glycine max (L .) Merr. cv. Evans) were treated with gibberellic acid (GA 3 ; 10g1-') and/or (2-chloroethyl)-trimethylammonium chloride (CCC ; 0 .8g1-')in 1983 and 1984, and subsequent anthesis, pod set, seed size, seed number, and seed yield were determined at one node . The treatments were applied to five leaves in the center of each plant (typically leaves 7-11) and reproductive development at the node in the center of those leaves was monitored . Gibberellin A3 applied "Early" (about 3 d before anthesis of the first flower at the monitored node) had no effect on the number of flowers produced, but decreased the fraction of flowers that set pods in both experimental years (by 32% in 1983 and 76% in 1984) . Seed size was slightly decreased by the GA 3 treatment in 1983 but not in 1984 . The "Middle" GA3 treatment (applied about 3 days after the "Early" treatment) slightly decreased the number of pods set; and "Late" treatments (9 days after) had no effect . None of the monitored parameters were affected by CCC .The "Early" experiments were repeated with two additional genotypes, Lincoln and T210 . Genotype T210 is a single-gene, dwarf mutant of Lincoln whose stem elongation and leaf expansion are insensitive to GA, Gibberellin A 3 affected the reproductive parameters in Lincoln very similarly to Evans but those in T210 were unaffected . This indicates that GA 3 exerts its effect by increasing the mass of vegetative tissue and thus diverting assimilates away from the pods . However, since the mutation in T210 might affect a receptor that is in flowers as well as shoots, it is possible that GA 3 exerted its effect on the normal genotypes directly on the developing pods, rather than indirectly by diverting photoassimilates .

Effects of growth regulators on reproductive abscission in faba bean (Vicia fabacv. Troy)

“…In contrast, gibberellins probably have little more than a modulating role through an involvement in pod set since increased pod numbers occurred only when GA 3 was applied directly to the reproductive structures (cf. Birnberg & Brenner 1987). Promotive effects of GA 3 sprays on pod set have been reported in other grain legumes (Clifford 1981;Pereto & Beltran 1987) and in faba bean there is a report that GA 3 enhances cytokinin promotion of pod set (Chapman & Sadjadi 1981).…”

Gibberellin and cytokinin effects on soybean growth

“…Since GA translocation occurs mainly through the symplast (Castro & Melotto, 1989), it could be the cause for the difference between responses, because when GA 3 is utilized via foliar application, an increase in hypocotyl length and in the length of the two nodes immediately above it can be verified and, consequently, affect the height of plants at that stage (Mislevy et al, 1989).…”

“…When applied at the pre-blooming stage, GAs decrease the number of flowers and fruit set, probably by increasing vegetative mass which, in turn, shares the photoassimilates with the fruit (Birnberg & Brenner, 1987). This hypothesis is also sustained by King et al (2000), who reported greater stem growth in Fuschia hibrida and Pharbitis nil, resulting in the inhibition of flowering.…”

Application of abscisic acid promotes yield in field-cultured soybean by enhancing production of carbohydrates and their allocation in seed

“…Regarding yield in soybean, it has been shown that applications of GA 3 diminished harvest by 8-11% by reducing seed weight (Mislevy et al 1989). The effect of GA 3 may, however, vary according to the time of application: when it was applied 3 days before flowering it did not affect the number of flowers, but reduced their viability and hence the pod number; when the application was during flowering, it slightly reduced the number of pods; during post-flowering there were no effects (Birnberg and Brenner 1987). In addition, it has been reported that foliar applications of Uniconazole (an inhibitor of GA synthesis) at the beginning of flowering promoted biomass accumulation and yield by favouring assimilate translocation (Zhang et al 2007).…”