Glume blight of rice in Brazil: Etiology, varietal reaction and loss estimates

The causal agent of glume blight in Brazil was determined as Phoma sorghina (Sacc.) Boerema, Dorenbosch & Van Kesteren. The pathogenicity of Brazilian isolates was proved and the characteristic symptoms described. Out of 19 rice varieties tested under artificial inoculations, two vars., Limeira and Iguape Redondo, exhibited a high degree of resistance. Quantitative relationships between glume blight and some yield components were established. The relationship between glume blight severity and filled grain percentage was linear. On the other hand, the grain weight relationship to disease severity was exponential. The disease effect was more pronounced on grain filling than on grain weight. Based on the regression equation, estimated panicle weight losses in 3 different fields of cv. IAC 25 were 41%, 29% and 45% during an epidemic year. The head yield losses in these fields ranged from 0 to 14%. Glume blight was considered to be of minor economic importance in upland rice, but attained epidemic proportions over a large geographical area in 1979-80. The evidence presented shows its potential to cause severe losses in grain weight and quality under weather conditions favorable to the disease, mainly continuous heavy rains during heading.