Marker-assisted Selection And Application For Rice Blast Resistant Gene Pib

Blast is the world's most serious rice disease and annually causes great losses.Breeding disease-resistant varieties is the main approach for rice blast control. With theemergence and rapid development With DNA molecular markers, Marker-assistedselection (MAS) technology has become an effective approach for the correct choice ofresistance genes. However, as resistance gene and the molecular marker differ greatly indifferent groups, while the groups used to construct molecular marker are not usually thebreeding material itself, the practical application is limited. In addition, as the establishedmolecular marker is not the gene itself, breeding in large groups may cause the target genenot linked to the molecular marker, resulting in the choice failure of the resistance gene.Therefore, the best approach is to use disease-resistant gene itself to establish thecorresponding molecular markers. Resistance gene cloning makes it possible to establishsuch markers.Pib, a cloned major gene with blast resistance, is located on the region near the endof he long arm of Chromosome 2 of rice and belongs to a small gene family (Pib, PibH8,HPibH8-1, HPibH8-2). Pib gene codes the protein with 1251 amino acid residuecomposing a nucleotide binding site (NBS) and leucine-rich repeat (LRR) proteins.The physiological races identification of 36 rice blast stains found that there were 7groups, 23 races. ZC and ZA group was the dominant group and ZG1, ZC15 and ZE3raced were the most dominant. Meanwhile, 8 strains were utilized to identify the resistanceof the 106 hybrid rice. The results showed that the resistance frequency on average is25.15%. Parental restorer had higher level of resistance than the parental maintainer ingeneral. It was also found that the four races of C15, B13, D7 and B15 had higherpathogenic frequency of 84.9%, 83%, 80.9% and 80%respectively. Then these 36 strainswere utilized to identify the resistance of two Pib gene containing materials (IRBLb-B andF-145-2). The results showed that the 36 strains tested. IRBLb-B and F-145-2 wereresistant to the infection of 26 and 31 strains of the total 36 tested strain. The resistancefrequency was 72.2% and 86.1%, respectively, suggesting that the two Pib gene containingmaterial had high resistance. However, the difference between the resistance frequencywas big (13.9%).With the established the susceptible allele Pib dominant molecular marker, combinedwith the previously reported resistance alleles Pib dominant molecular marker, a set of Pibgene molecular marker was utilized to molecularly identify 109 hybrid parental rice or materials. Meanwhile, in the greenhouse, rice blast strains of 05-12 (ZB13) and 05-30(ZC15) was selected for the pathogenic test of the above 109 hybrid rice parents, with thestandard spray inoculation protocol. The results show that the 5 hybrid rice parent of 94-4,HA303, 05H38 and so on, carrying the Pib gene, were all resistant to 05-12 and 05-30,providing the theoretical evidence for Resistance-assisted selection (RAS) provide atheoretical basis. Meanwhile, this rice blast resistance gene Pib dominant molecularmarker set was utilized to select among 600 F₂ plants in the early stage and 185 Pibresistance gene homozygous plants were obtained. Field resistance investigation resultswere in accordance with the results of molecular detection of the resistance gene.Therefore this set of dominant molecular markers could be applied to rice blast resistancegene Pib molecular marker-assisted breeding.In conclusion, this study had established novel DNA molecular markers with thecloned Pib functional gene sequence itself, and had successfully applied to the research ofassisted breeding and disease-resistant mechanism. The markers overcome the drawbacksof the conventional molecular markers, providing powerful technical safeguard for MAS,and opened new path for the application of the cloned Pib gene in breeding.