Mining Of Rice Blast-Resistant Genes And Its Application For Rice Breeding

Rice (Oryza sativa L.), one of the world’s most important food crops, feeds half of the world’s people, and more than 65% of people in our country use it as the staple food. The crop disease is one of the main factors limiting the improvement of crop yield and quality. Plants have evolved a variety of defense mechanisms against the pathogenic microorganisms in the process of their long-term interactions, in which resistance gene (R gene) is one of the main defense means. Rice blast, caused by the ascomycete Magnaporthe oryzae, can reduce 10%-30% of the global rice production and even more than 50%, leading to huge economic losses. It has been proved that breeding and cultivation of the disease-resistant varieties is considered as the most effective and economical strategy to solve this problem. Moreover, discovery and cloning of more resistance genes in rice germplasm is the basis of the breeding for disease resistance. Up to now, it has been reported that about 100 rice blast resistance genes are discovered on all rice chromosomes except for chromosome 3, and 28 genes have been cloned. Based on the conserved sequence structure and the functional characteristics of the cloned rice blast resistance gene combined with resistance spectrum analysis, we investigated the resistance background of Oochikara using allele mining approach and cloned several resistance genes. In addition, we carried out the breeding program to improve the rice blast resistance by introducing the blast resistance gene Pbl and pi21 into some elite rice cultivars. The main results are as follows:1. By innoculation testing with 34 Magnaporthe oryzae strains collected from different regions, Oochikara confers broad spectrum resistance to most M. grisea isolates with 88.2% of the resistance spectrum.2. By allele mining approach, four rice blast resistance genes, Pish、Pia、Pi-ta and Pikm were cloned from Oochikara. It is confirmed that Oochikara does not contain the rice blast resistance genes Pit, Pi35, Pib, Pi2/Pi9,pi21, Pi5, Pi-d3 and Pi37.3. According to the gene-for-gene hypothesis, avirulent gene AvrPik-E was isolated form Magnaporthe oryzae isolate 08-7-3. By genetic analysis of the rice blast resistance, Oochikara is also demonstrated to possess some unknown resistance gene other than the four cloned resistance genes.4. Some elite lines were selected in the BC2F7 population derived from a backcross of Nanjing46 introgessed with Pb1 by MAS approach with the developed marker Pbl-1 as well as agronomic trait evaluation. A functional marker Pi21-1 for detection of rice blast resistance gene pi21 was used to introduce pi21 into some elite cultivars by MAS.