Durable Resistance to Rice Blast Mediated by Race-nonspecific Genes in Rice: A Mini Review
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Abstract
Rice blast is a major biotic constraint of rice worldwide, that causes a serious threat to rice production. Genetic improvement of blast resistance is one of important objectives in rice breeding programs. Race-specific resistance genes (R-genes) confer complete resistance to rice blast fungus, but a breakdown of resistance mediated by R-genes has been frequently caused by new races of blast pathogen. To avoid the risk of genetic vulnerability, the use of race-nonspecific resistance has been concentrated in Japanese upland rice varieties whose resistance has been maintained for a long time. However, linkage drag between genes underlying race-nonspecific resistance and undesired traits has hindered its use. Among QTLs detected, a single recessive resistance gene, pi21 was identified by map-based cloning and characterized. The use of pi21 has improved durable resistance in rice breeding programs in Japan. Three QTLs conferring race-nonspecific resistance to rice blast were detected on chromosomes 4 and 12. Among them, a single recessive gene, pi21 was isolated by positional cloning and characterized. This allele has been used for genetic improvement of durable blast resistance through DNA marker-assisted selection in rice breeding programs in Japan and Africa Rice Center.