EVALUATION OF SEVERITY OF GRAY LEAF SPOT AND GRAIN YIELD IN COMMERCIAL MAIZE HYBRIDS

With the objective of evaluating the severity of Gray Leaf Spot and grain yield in commercial maize hybrids and determining the best time to evaluate the disease, two experiments were carried out in two sowing seasons (two planted on 11/11/2005, and other two planted on 12/23/2005) at Lavras Federal University - UFLA, Lavras, MG, Brazil. Twelve commercial maize hybrids were used, in a randomized block experimental design with three replications. Eight evaluations of disease severity based on visual symptoms were performed at seven-days intervals from the 60th day after maize emergence (DAE), ranging from 1 (highly resistant) to 9 (highly susceptible). The area under the disease progress curve (AUDPC) was estimated and grain yield per plot was also obtained and so the correlation between severity of the disease in each evaluation season and the estimates of the AUDPC were supported by the data. Considering the data of the AUDPC, it was observed that the most resistant hybrids to Cercospora zeae-maydis were P 30K75, P 30F87, AG 7000, and DKB 350, while the most susceptible were AG 9020, DKB 214, and P 30F44. The most susceptible hybrids to Gray Leaf Spot are not necessarily those with lowest grain yield. The disease severity evaluation between 88 and 109 DAE is efficient to discriminate the level of resistance of the hybrids and the results are similar to those obtained by the AUDPC.