Resistance to Gerlachia oryzae in Rice

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Abstract
Two hundred and eighty-eight rice germ plasma accessions from six subspecific cultivars groups of Oryza sativa were tested for resistance to the leaf scald pathogen, Gerlachia oryzae. Included were indica cultivars (group I): japonica, tropical upland, and bulu cultivars (group VI); two smaller groups (groups II and V); and two satellite groups of deepwater cultivars (groups III and IV). A detached leaf method used to measure lesion growth gave results comparable to those of tests using intact plants (r2 = 0.81, P = 0.01). Rice cultivars in groups III, IV, and V and the temperate accessions of group VI had the shortest lesions and the highest proportions of resistant entries. Over all test cultivars and within groups II and VI, lesion length was positively correlated with leaf width. Cultivars Labelle and Dourado Precose inoculated with two isolates of G. oryzae showed evidence of pathogenic specialization. Such specialization may be responsible for disparities in the results of resistance tests reported from different countries.