Identification of two blast resistance genes in a rice variety, Digu

Blast, caused by Magnaporthe grisea is one of most serious diseases of rice worldwide. A Chinese local rice variety, Digu, with durable blast resistance, is one of the important resources for rice breeding for resistance to blast (M. grisea) in China. The objectives of the current study were to assess the identity of the resistance genes in Digu and to determine the chromosomal location by molecular marker tagging. Two susceptible varieties to blast, Lijiangxintuanheigu (LTH) and Jiangnanxiangnuo (JNXN), a number of different varieties, each containing one blast resistance gene, Pik(s), Pia, Pik, Pi-b, Pi-k(p), Pi-ta(2), Pi-ta, Pi-z, Pi-i, Pi-k(m), Pi-z(t), Pi-t and Pi-11, and the progeny populations from the crosses between Digu and each of these varieties were analysed with Chinese blast isolates. We found that the resistance of Digu to each of the two Chinese blast isolates, ZB13 and ZB15, were controlled by two single dominant genes, separately. The two genes are different from the known blast resistance genes and, therefore, designated as Pi-d(t)1 and Pi-d(t)2. By using bulked segregation method and molecular marker analysis in corresponding F-2 populations, Pi-d(t)1 was located on chromosome 2 with a distance of 1.2 and 10.6 cM to restriction fragment length polymorphism (RFLP) markers G1314A and G45, respectively. And Pi-d(t)2 was located on chromosome 6 with a distance of 3.2 and 3.4 cM to simple sequence repeat markers RM527 and RM3, respectively. We also developed a novel strategy of resistance gene analogue (RGA) assay with uneven polymerase chain reaction (PCR) to further tag the two genes and successfully identified two RGA markers, SPO01 and SPO03, which were co-segregated toPi-d(t)1 and Pi-d(t)2, respectively, in their corresponding F-2 populations. These results provide essential information for further utilization of the Digu's blast resistance genes in rice disease resistance breeding and positional cloning of these genes.