Quantification of damages and reaction of resistance of commercial mayze hybrids to Cercospora zeae-maydis / QuantificaÃÃo de Danos e ReaÃÃo de resistÃncia de Hibridos Comerciais de Milho a Cercospora Zeae-maydis

AUTOR(ES)
DATA DE PUBLICAÇÃO

2007

RESUMO

With the objective of quantifying the damages caused by mayze gray leaf spot, establish the existing relationship between these damages and the severity of the disease, the resistance of commercial maize hybrids to Cercospora zeae-maydis and determining which is the best timing of evaluation of the disease, four experiments were conducted in two sowing seasons in experimental area of the Lavras Federal University, in Lavras/MG, in the agricultural year of 2005/2006. The two first experiments were set up on 11/11/2005 and the two last ones on 23/12/2005. In one of the experiments of each sowing seasons, the disease was controlled with the use of fungicide epoxiconazole + pyraclostrobin - Opera BASF S.A. (0.75 L ha-1) and the other was conducted without the control of the disease. Twelve commercial hybrids of maize were utilized. The randomized block design with three replications was used. Eight evaluations of the severity of the disease were performed visually in seven day intervals from the 60 days after the emergence, by means of a score scale ranging of 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. From the data obtained the percentage of damages, the correlations between the grain yield and the percentage of damages with the estimates of the AUDPC and the estimates of correlation between severity of the disease in each evaluation season and the estimates of the AUDPC were estimated. It was discovered that the damage level varied among the sowing seasons and evaluated hybrids, their being on average 13.3%; gray leaf spot of maize is an disease that reduces the maize grain yield, mainly for the late sowing; the fungicide epoxiconazole + piraclostrobina - Opera BASF S.A. is efficient in the control of gray leaf spot of maize and the use of resistant hybrids excuses the chemical control of the disease. Considering the data of the AUDPC, it was observed that the hybrids most resistant to Cercospora zeae-maydis were P 30K75, P 30F87, AG 7000 and DKB 350 the most susceptible ones were AG 9020, DKB 214 and P 30F44. For the susceptible and moderately resistant hybrids, the late sowing provided increased severity of the disease. The evaluation of the severity of the disease between 90 and 110 DAE is efficient to discriminate the level of resistance of the hybrids and supplies resulte similar to those obtained by the AUDPC.

ASSUNTO(S)

zea-mays zea mays; gray leaf spot; fungal disease doenÃa fÃngica cercosporiose fitotecnia

ACESSO AO ARTIGO

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