Reaction of commercial corn hybrids and comparison of methods for evaluation of maize White Spot and Gray Leaf Spot

With the objective of evaluating the resistance level of commercial corn hybrids and comparing the efficiency of the estimates of the area under the disease progress curve (AUDPC) and that of the phenotypical stability parameters in the evaluation of resistance maize white spot and gray leaf spot, three experiments were carried out in the agricultural year of 2007/2008 in three environments. Twelve commercial maize hybrids were used, in a randomized block experimental design with three replications. Five evaluations of disease severity (maize white spot and gray leaf spot) based on visual symptoms were performed at seven-day intervals from the 80th day after maize emergence, ranging from 1 (highly resistant) to 9 (highly susceptible). The area under the disease progress curve (AUDPC) was estimated, as were the phenotypical stability parameters, i.e., the linear regression coefficient (b i) between the independent variable evaluation time (x), and the dependent variable, disease severity (y) and the determination coefficient (R²). It was found that in the case of maize white spot and maize gray leaf spot, both methodologies used proved to be effective in the discrimination of the resistance level of the hybrids, enabling them to be ranked in a similar way. The most resistant hybrids to maize white spot and maize gray leaf spot were AG7088, AG 7010 and 2B707, and the most susceptible were 30F44, 30F53 and AG8021. The 30K64, DKB177, DKB390 and Impacto hybrids showed variable levels of resistance with the environment.

Cercospora zeae-maydis; Pantoea ananatis; fungal disease; phenotypical stability