Distribution And Variability Of Avirulene Gene AvrPi9 Of Magnaporthe Oryzae Isolates From The Two Rice Blast Nurseries In Yunnan Province

Blast is the severest disease on rice. The pathogen, Magnaporthe oryzae, varies so fast that resistant cultivars lost resistance. For the allocation of rice cultivar, the avirulence gene, AvrPi9, of the pathogen was monitored by inoculation of 369 isolates from Lijiangxintuanheigu, a susceptible cultivar in the two blast nurseries located in Louping and Tengchong counties, Yunnan Province, onto a set of near-isogenic lines and the frequency of the avirulence gene was detected by PCR amplification based on the primers of the coding sequence. AvrPi9 variation was studied preminarily according to the inoculation and amplification. The results are the followings.The gene, AvrPi9 had very high frequencies, 94.17% and 91.14% for Tengchong and Luoping based on the isolates sampled from the nurseries in 2012-2014. Except for the resistance genes, Pi9, Pi12, Pi7 and Pizt, the isolates had very high virulence to other genes of rice. The virulence frequency of Piz, Pib and Pish in Luoping was higher than that in Tengchong, but that of other resistance genes in Tengchong was higher that in Luoping according to location sites. The virulence frequency in the both of counties increased as years moved on.The majority of blast resistance genes are not useful in Yunnan even one single or association application. Only the genes combinations of Pi9 with Pizt, Pi7 and Pi12 had high resistance association coefficients(RAC), 0.81, 0.81 and 0.82, showing the genes had a good application value. Besides, the combination of Pizt and Pi12 had 0.8 RAC, indicating the both genes have still had some application potential.AvrPi9 frequency decreased annually in the two nurseries and the gene has been changing though its coding region did not vary. The 16 bp of sequence lacked in the upstream of 246 bp, which might be related to pathogencity variation.