Reação de híbridos comerciais de milho às ferrugens polissora e tropical

The goals of this work were to evaluate the resistance level of eight commercial corn hybrids to the pathogens Puccinia polysora Underw and Physopella zeae (Mains) Cummins & Ramachar and to compare the efficiency of the methods of the area under the disease progress curve (AUDPC) and of the phenotypical stability parameters in the evaluation of this resistance. Experiments were conducted in four environments in the Southeast and Center-West regions of Brazil. Five evaluations for the severity of the diseases were performed at ten-day intervals from the 60th day after sowing, by employing a diagrammatic scale. The area under the disease progress curve (AUDPC) and also phenotypical stability parameters, i. e., the linear regression coefficient (b) between the evaluation time (x) and the disease severity (y) and the determination coefficient (R2) were evaluated. It was found that in the case of P. polysora, both methods utilized proved to be effective to discriminate the resistance level of the hybrids, enabling ranking them in a similar way. To P. zeae, there was not good agreement between both methods, mainly because the discrimination of resistance level was not outstanding. The most resistant hybrids to P. polysora were Z 8392, C 909 and C 333, and the most susceptible were P 3069, AG 9012 and C 956. The most outstanding ones in terms of resistance to P. zeae were C 909 and C 333 and the most susceptible were P 3069 and AG 9012.