Temporal progression of wheat blast as a function of primary inoculum, fungicide application and genotype resistance

Delineide Pereira Gomes Valterley Soares Rocha João Romero Amaral Santos de Carvalho Rocha Moacil Alves de Souza Olinto Liparini Pereira About the authors

ABSTRACT

In Brazil, there are few studies on the epidemiology of wheat blast; consequently, little information has been generated about the disease progress. This study evaluated the temporal progression of wheat blast in four genotypes subjected to chemical control and to different amounts of primary inoculum of Pyricularia graminis-tritici in the field. The genotypes BRS 264, VI 98053, CD 116 and CD 104 were inoculated with five volumes of fungal suspension (concentration of 1.5 x 105 spores.mL-1), in order to obtain, respectively, five percentages (0, 5, 10 , 20 and 30%) of plants inoculated in the experimental unit. The intensity of blast was quantified based on the incidence and the severity of this disease in spikes and flag leaves. Evaluations were performed at 1, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50 days after inoculation (DAI). The obtained regression equations were significant and adjusted to the logistic model. Application of the fungicide (pyraclostrobin plus epoxiconazole) delayed the onset of blast symptoms in the genotypes and, when combined with the moderately resistant cultivar (CD 116), had better efficiency in reducing the disease. The cultivars BRS 264 and CD 104 presented higher incidence and severity in the spikes according to time. In general, the genotypes present low severity of blast in flag leaves (<0.45 %) and a low temporal progression in the different amounts of inoculum of P. graminis-tritici. In the region of Viçosa-MG, Brazil, under the studied conditions of artificial inoculum, the cultivar CD 116 is confirmed as moderately resistant to blast and the genotypes BRS 264, VI 98053 and CD 104 are susceptible.

Keywords
Triticum aestivum; Pyricularia graminis-tritici; incidence; severity; epidemiology

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