Effect of different concentrations of Figaron on production and abscission of reproductive organs, growth, and yield in soybean (Glycine max L.)

Figaron (ethyl-5-chloro-3(1H)-indazolyl-acetate), a synthetic auxin, has been used in the past to abort surplus flowers in soybean. We examined the effects of Figaron on chlorophyll levels, photosynthetic rate, stomatal conductance, growth, flowering pattern, flower production, reproductive abscission and yield of soybeans grown in pots in 1999 and 2000. Concentrations of Figaron were 2 in 1999 and 3 in 2000. Plant height and leaf area in plants treated with 100 or 150 mg l−1 Figaron were statistically not different from those of controls. However, in both cultivars these parameters were significantly smaller in plants given 200 mg l−1 Figaron than in controls. Total chlorophyll content, rate of photosynthesis, and stomatal conductance in plants treated with 100 or 150 mg l−1 decreased initially, but after 12 days of Figaron application these parameters became higher than in controls. In both cultivars level of these parameters remained low in plants given 200 mg l−1. In the later stages of growth, total chlorophyll content, photosynthesis rate, and stomatal conductance decreased slightly in plants of both cultivars treated with 150 or 200 mg l−1 Figaron to levels below those of plants treated with 100 mg l−1 or control plants. Different concentrations of Figaron reduced flower production, however, 150 or 200 mg l−1 Figaron had the greatest effect in both cultivars. The percentage reduction in flower production increased with increasing concentrations of Figaron, leading to a decrease in the rate of reproductive abscission. On the other hand, in both cultivars the total number of pods was higher in plants treated with 150 or 200 mg l−1 Figaron than in those treated with 100 mg l−1 or the controls; this led to an increased percentage of unfilled pods and decreased the seed weight. Ultimately, the higher concentrations of Figaron (150 and 200 mg l−1) decreased soybean yield compared to plants in 100 mg l−1 and control.