Study On Genetic Diversity Of Magnaporthe Oryzae In South-West Hubei Province Between 2016-2017

Rice blast is the most devastating fungal disease in the world.Rice at different stages and tissues can be infected,and yields reduced.One of the most effective and environmental friendly way to avoid rice yield loss is to plant resistant rice varieties.However,the population structure of Magnaporthe oryzae is complex,and these often make resistant varieties unable to be planted for a long time.The laboratory has studied diversity of rice blast fungus population in southwestern Hubei for a long time.In this project,rice blast fungi from susceptible straws of specific varieties planted in the southwest of Hubei from 2016 to 2017 were isolated,and the colony morphology,pathogenicity,genetic structure and avirulence gene composition of the fungi were studied.The results are as following:1.There were 217 single spores of Magnaporthe oryzae isolated from 52 susceptible straws in 6 regions in 2016,and 353 isolated from 261 susceptible straws in 8 regions in 2017.According to colony morphology,they can be divided into 8 types(A-H).There were 6 types(C-H)in 2016,and the main types were E(46.3%)and G(25.5%).There were 7 types(A-E,G,H)in 2017,and the main types were D(44.4%)and E(31.4%).The strains in Lichuan Zhonglu area contain all types,and the H type only exists in here.Strains isolated from Hefeng all belong to the E type.2.The pathogenicity of 376 strains preserved in the past two years was identified by using 7 Chinese identified varieties of blast fungi and 18 single resistance gene identification varieties.There were 305 strains with pathogenicity.According to the reaction for the 7 Chinese identification varieties,187 strains were divided into 5 groups which include 12 subordinated physiological races in 2016.ZC was the dominant population(43.9%)and the dominant physiological race was ZC13(37.4%).Using 18 single resistance gene identification varieties,the strains from 2016 are divided into 92 lineages,which had strong pathogenicity to Pit,Pita,Pib and Pid(pathogenicity rate of more than 80%)and weak pathogenicity to Pizt and Pikh(less than 10% pathogenicity rate).Strains from 2017 are divided into 85 lineages,which had strong pathogenicity to Pish and Pik9(pathogenicity rate of more than 80%)and weak pathogenicity to Pita(pathogenicity rate 6.8%).The pathogenicity to different resistant genes changed in the two years,and the pathogenicity rate of Pita decreased from 90.9 to 6.8%,while the pathogenicity rate of Pish and Pi11 increased.3.A total of 20 pairs of primers of RAPD,REMAP and rep-PCR were used to form a molecular marker system,and 409 strains were divided into 11 types at 0.775 similar levels,each containing only one year’s strain.Of these,3 types strains are from 2016 and 8 types strains are from 2017.These indicated that the genetic structure of the population in 2017 was significantly more complex than that of the 2016.4.The analysis of 7 avirulence genes ACE1,Avr1-CO39,Avr-Pik,Avr-Pia,Avr-Pita,Avr-Pizt and Avr-Pi9 in the fungus showed that the frequency of ACE1,Avr1-CO39,Avr-Pik,Avr-Pita and Avr-Pizt was high in 2016,while in 2017 the frequency of 7 avirulence genes all is high(more than 60%).The frequency of ACE1,Avr1-CO39 and Avr-Pizt does not change during the two years,and Avr-Pita and Avr-Pik decreases,while Avr-Pita and Avr-Pi9 increases obviously.According to the source of the strains,in 2016,with the exception of Badong without Avr-Pita,Lichuan Zhonglu and Xianfeng contain all avirulence genes.And in 2017,except Hefeng only contains Avr1-CO39,Avr-Pizt and Avr-Pi9,Xuanen,Lichuan Boyang,Changyang,Jiangshi,Lichuan Zhonglu and Zigui contains all avirulence genes.The analysis for mating type showed that the mating type in 2016 was mainly MAT1-2(80.5%)and in 2017 MAT1-1 was dominant(70.18%).With the exception of Xianfeng in 2016,where the frequency of the two mating types was about equally,there was only a single mating type in other locations areas.