Resistance to Grain Discoloration Disease in Iranian Local and Improved, and Some Foreign Rice Cultivars in Field Conditions

The discoloration of rice grains is a complex disease due to infection by certain microorganisms on the glumes, kernels, or both, and its extension is different according to cultivar, season and locality. To access resistance source to rice grain discoloration disease, 66 Iranian local and improved, and foreign cultivars of rice were grown at the Rice Research Institute of Iran in Rasht county. After panicle exertion, plants were kept wet to develop grain discoloration until the evaluation time by a water sprayer system, above the tested plants in the field. Assessment of cultivars was done by sampling of 15 main panicles in each cultivar, seven to 10 days before harvest. The recorded data analysis revealed a wide variability among cultivars in terms of disease index, percentage of unfilled seeds and 100 seed weight. On the bases of disease index results, the local cultivars Hassansaraei Attashgah, Ali Kazemi, Hashemi, Sadrei and Binam showed significant resistance reaction to grain discoloration disease in the field conditions. From the fungi that were isolated from discolored grain, virulence of Bipolaris oryzae, Fusarium fujikuroi, Fusarium graminearum, Curvularia sp. and Alternaria sp. were confirmed on two local and improved cultivars namely Binam and Khazar respectively, whereas no disease symptom was appeared due to Nigrospora sp. and Ulocladium sp.