Abstract: Soybean yield depends on photosynthesis generated by leaves, so any factor that interferes with their leaf area could affect the yield. Among these, defoliating insect attacks cause significant decreases in yield by its direct reduction of the leaf area, thereby reducing the total photosynthesis of the plant. The agronomic traits of cultivars can influence the tolerance level of the plant to this kind of stress, if it is continuous. Thus, the aim of this work was to evaluate the effect of continuous defoliation in vegetative and reproductive stages in soybean cultivars with different traits. The research was carried out in an experimental randomized complete block design in a 2×5×6 factorial scheme with four replications. Factors consisted of defoliation stages (vegetative and reproductive), defoliation levels (0, 16.7, 33.3, 66.6 and 100%) and cultivars (M 7211 RR, TMG 123 RR, TMG 1176 RR, M 7908 RR, TMG 127 RR, TMG 7188 RR). The following variables were evaluated: number of pods/plant, number of seed/plant, 100-seed weight and seed yield/plant. From the obtained results, it was observed that defoliation has a negative effect on all cultivars yield components with greater decrease when it occurs in the reproductive stage. Continuous defoliation from 16% in both the vegetative and reproductive stage significantly decreases the soybean yield. Regardless of agronomic characteristics such as growth type, maturity group and leaf shape, the effect of stress by defoliation in soybean cultivars is similar.
Amilton Ferreira da Silva, Tuneo Sediyama, Francisco Charles do Santos Silva, Andre Ricardo Gomes Bezerra, Aluizio Borem, Lucas Vieira Ferreira, Daniele Piano Rosa and Joao Pedro Ambrosio Barros, 2015. Continuous Defoliation Stress in Vegetative and Reproductive Stages of Soybean Genotypes. Journal of Agronomy, 14: 279-285.