Among the factors that may cause decreases in soybean yield there are the foliar diseases that despite control it can limit grain yield. The Asian soybean rust (Phakopsora pachyrhizi) is considered the most important disease of soybean in Brazil. The aim of this work was to simulate the progress of Asian rust in Brazilian soybean cultivars by removal of trifoliate leaves from the bottom to the top. The experimental design was a randomized complete block, in a 3x3x5 factorial scheme, with four replications. It was observed that there was significant interaction between cultivars and defoliation for all yield components and consequently in seed yield. Increase in the defoliation intensity towards the bottom to the top during the reproductive stages studied (R3, R5, R6) there is a linear decrease in grain productivity, reaching in the highest defoliation level, loss of 79.6, 77.7 and 38.6% in R3, R5 and R6 stages, respectively. The simulation of damage by soybean rust through defoliation cultivars showed severity in leaf area reduction and its consequent effect in grain seed yield.
Key words: Yield components, leaf area, reproductive stage, biotic stress.
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