Diversity Of Resistance Gene Pita To Blast Disease In Rice Varieties From Sichuan

Rice is one of the most important crops in the the world and nearly half of the world puulation consume rice as staple food. Rice blast disease (Magnaporthe oryzae) is one of the most devasting diseases on rice in more than85contires and regions and causes severe losss in the yield of rice grains. Breeding and deploying resistance varieties are the most efficient and safe methods to control the disease, but the breakdown of resistance of single genotypes in extensively planted rice varieties3-8years after their release has been the bootleneck of the disease control. To investigate the reasons for the majority of M. oryzae isolates in Sichuan to be virulent to resitance gene Pita,10landraces,2most popular conventional rice varieties in1970s,20parent lines of the most popular hybrid rice combinations since late1970s, IRBL lines and Tetep which were known to bear Pita genes, as well as Lijiang Xintuan Heigu (LTH) in which no resistance gene to the blast disease had been known were observed in the blast nurseries for their resitance and their genomic DNAs were PCR-amplified using Pita-specific primers before the sequencing to investigate the presence and diversity of Pita. Results of the observation and investigation were as the followed:1, Among the three IRBL lines reportedly carrying Pita, the disease indexes for leaf blast of IRBL12at Baoxing, IRBL13and IRBL29at Baoxing and Yingshan in Sichuan were lower than1.0%whereas that of the3IRBL lines at Pujiang in Sichuan well all higher than1.0%. The disease indexe for leaf blast disese of IRBL12at Yingshan was averaged at3.71%but this line was resistant at the disease nursery located in Ningqiang in Shaanxi Province. IRBL13has shown resistance in2011in Yunnan and Jiangdu while IRBL29were susceptible at the same disease nuseries.2. No segments of Pita were amplified with different primers from5Sichuan landraces. Intron sequence were failed to be amplified from Neihui182. Whole sequences of Pita were obtained from other tested varietes including LTH after amplification and sequencing.3, The aminoacid residues at918aa. in landraces10R247,10R249, once ressitance restorer lines Duohui No.1, Neihui182and Shuhui527, as well as that in IRBL13and Tetep中Pita were alanine which was nessary for the resistance to isolates carrying AVRPita. The, Pita in other varieties of hybrid or conventional rice as well as that in LTH were susceptible alleles.4. The homology of Pita in the land race10R249to that in Tetep was100%. The onceresistant restoerlines Duohui No.1, Neihui182and SH527shared Tetep as the common ancestry. But the Pita in these3resorelines derived Tetep has originated three times and the phylogeny of the two of them were close to Tetep. The homology of Pita was higher between the the majority of the varieties from Sichuan than that from other countries and some homology clades were completely or largely compsed of Sichuan varieties. The above results suggested that the extensive plantation of hybrid rice of the restorer lines carrying ressitan Pita genes and the follwed ressitance breakdown could be the reaon for the high virulence frequency of M. oryzae in Sichuan. For the same reason, Pita should not be used alone for the breeding of new resistance varieties in the areas where hyrid rice combinations carrying Pita gene such as those of Shuihui527had been planted extensively evengthough they were still resistant in the field.