Reaction of soybean genotypes to foliar diseases with and without fungicide application

Resumo

The classical genetic improvement aims to select, mainly, cultivars with greater yield potentials; however, by associating the selection for disease resistance, it is possible to handle the management with cost reduction. The objective of this study was to evaluate the reaction of soybean genotypes to foliar diseases, and the agronomic characteristics of the soybean crop, with and without fungicide application. Two experiments were conducted concomitantly, in the same design and with the same managements, distinguishing with respect to the presence and absence of chemical treatment to control diseases. The experiments were conducted in Rio Verde, Goiás, in the 2015/2016 harvest, in a randomized complete block design with 31 soybean genotypes and three replicates. The plot consisted of 2 rows of 5 m in length, spaced 0.5 m apart. The following were evaluated: downy mildew severity, Asian rust, target spot, and end-of-cycle diseases (EOCD’s), besides agronomic characteristics such as defoliation, thousand grain weight, and grain yield. For target spot and EOCD’s, genotypes with lower susceptibil­ity to diseases were observed. Regarding downy mildew and Asian rust, the genotypes have been shown to be susceptible, and chemical control was the most effective in the management of these pathogens. There was a significant interaction for thousand grain weight and grain yield, which implies that there is a distinct behavior of the genotypes regarding the presence and absence of diseases. The presence of diseases affected all the char­acteristics significantly, however, some genotypes stood out in both experiments, not presenting a significant reduction in grain yield when predisposed to the incidence of foliar diseases, consolidating effective control through genetic resistance.