Effect of soybean leaf position on the antixenosis expression to Anticarsia gemmatalis and the relation with nutrients and trichomes

This study aimed to assay the effect of soybean leaf position on the antixenosis expression to Anticarsia gemmatalis and its relation with nutrients and trichomes. Discs from leaves of resistant and susceptible genotypes excised from the upper or lower part of 30 day-old plants were put into Petri dishes, where larval feeding preference was evaluated in free-choice and non-choice tests. Quantification of the nutrients N, P and K and trichome density were performed. In the free-choice test, there were no differences between the genotypes or leaf positions, whereas in the no-choice test, the larval consumption was higher on the upper part leaves from the susceptible genotype. The feeding preference may be related to the greater amount of N and P in the leaves, but trichome density seems not to influence the antixenosis expression. The use of the upper part leaves is more appropriate to assay the antixenosis against A. gemmatalis.