Análise dialélica de linhagens de milho para rendimento de grãos e resistência à cercosporiose e mancha de phaeosphaeria

Abstract

Obtaining disease resistant genotypes with high grain yield are priority in maize breeding. Thus, it is important to identify parents and estimate genetic parameters and gene effects to lead the procedures that will be used to obtain new hybrids. The aims of this study were: (i) to evaluate the genetic resistance of inbred lines to Cercospora zeina and Phaeosphaeria maydis, the causal agents of diseases known as gray leaf spot and Phaeosphaeria leaf spot, in order to apport information for maize breeding; (ii) to evaluate the grain yield of the lines and identify parents those that, when crossed, form resistant hybrids to disease andsatisfactory grain yield. Toachieve the objectives, two experiments were carried out. The first experiment (experiment I) was carried out in order to obtain the yield and assess the severity of the genotypes in natural infestation of Cercospora zeina and Phaeosphaeria maydis. The second (experiment II) was carried out in order to assess the resistance of genotypes, comparing three different methods of evaluation, when inoculated with Cercospora zeina. Both experiments were carried out in the field and assessments of disease severity were performed. Data were examined by analysis of variance and diallel analysis. General and specific combining abilities were significant (pmenor0.01) for gray leaf spot resistance, Phaeosphaeria leaf spot resistance and grain yield. Specific combining ability was predominant, indicating that non-additive genes were more important, and some inbred lines are recommended to new hybrids formation. Inbred lines F1, F3, D2 and D4 were the ones that contributed most to the grain yield. Inbred lines F2, F4, D2, D3 and D6 were the ones that contributed most to resistance to gray leaf spot. The inbred lines F3, D3 and D4 are the most suitable for resistance to Phaeosphaeria leaf spot. The method 2 of evaluation was more efficient to select inbred lines and differentiate them significantly from the others. The results of the experiment I and II are in agreement with the identification of inbred lines for resistance to C. zeina.