Genetic Analysis of Field Resistance to Leaf Blast in Rice

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Abstract

Resistance to rice blast can be classified into true resistance (qualitative resistance) and field resistance (quantitative resistance). True resistance is unstable and controlled by major genes that react specifically to different races of blast fungus. The breakdown of true resistance has often occurred and shocked rice breeders. On the other hand, field resistance is a quantitative difference between varieties in a field where true resistance is ineffective. A variety with high field resistance shows a slow disease progress even if it is infected by blast and susceptible lesions are formed. Field resistance is usually stable to changes in pathogenicity of blast fungus. The breakdown of field resistance had not been observed in actual rice cultivation and rice breeders are trying to improve field resistance of varieties in Japan.