Pyramiding Three Genes With Resistance To Blast In Rice By Marker-assisted Selection

Rice blast, caused by Magnaporthe grisea, is the most serious disease in rice (Oryza sativa L). Most of rice varieties planted in China only carried a little number of resistance genes and were susceptible to blast. Consequently, the damage by blast in rice presented an increasing trend in recent years. Developing resistant varieties to blast is one of the most economical and effective methods. Jin 23B is an excellent CMS maintain-line with good qualities and combining ability except for blast resistance. This study was mainly to pyramid three blast resistant genes into Jin 23B by marker-assisted selection.The donors, carried different resistance genes, were C101LAC (carried Pi-1 and Pi-33 resistance genes) and C101A51 (carried Pi-2 gene), respectively. In process of pyramiding Pi-1, Pi-2 and Pi-33, two methods, inoculation identification and marker assisted selection, were carried out. The main results were as follows:1) Four specific rice blast isolations (PH14, CH131, CH43 and ZJ42), were screened out on the base of identification results, Of which PH14 and CH43 could not infect C104LAC (carried Pi-1) and Bei-jing-nuo (carried Pi-33) respectively, while two isolations, CH131 and ZJ42, could not infect C101A51 (carried Pi-2). These selected isolations were used to inoculation identification for distinguishing three resistance genes, Pi-1, Pi-2 and Pi-33.2) Based on the markers information of rice and the fine mapping results of resistant genes, Pi-1, Pi-2 and Pi-33, three SSR markers (RM224, RM527 and RM3215) flanked to these genes, were used in the process of marker-assisted selection (MAS), respectively. 3) The correct ration was 94.4% with molecular marker RM224 for selecting Pi-1 gene on segregating generation, while the correct ration was only 87.86% when PH14 isolation was used to select this gene. However, if combined the two methods, RM224 and PH14, the correct ration could up to 99.32%. The similar results were found in the other two genes, Pi-2 and Pi-33, which indicated the method of molecular marker was better than that of inoculation identification in selecting target gene.4) Applying both SSR markers and specific isolates in multiple F1 generation, the 35 plants were acquired with heterozygous genotype of 3 blast resistant genes, and four of them with much more similar to Jin 23 were selected. In progeny of the selected four plants, five plants with homozygous genotype of Pi-1, Pi-2 and Pi-33 were selected.5) With 30 isolates, we identified four lines, W1 carried Pi-1 and Pi-2, W2 carried Pi-2 and Pi-33, W3 carried Pi-1 and Pi-33, and W4 pyramiding 3 genes Pi-1, Pi-2 and Pi-33. The results indicated that the spectrum of lines pyramiding 2 blast resistant genes ranged 73.3% to 86.7%, which was broader than that of lines carried only one gene, C104LAC, C101A51 and Bei-jing-nuo. However, the spectrum of W4 was close to 100% (96.7%) for pyramiding 3 genes, and just one isolate used in this study could infect this line.