Research On The Genetic Diversity Of Rice Blast Fungus Population In Guidong County,Hunan Province

Rice blast,caused by the Magnaporthe oryzae,is a destructive fungal disease which threatens rice production safety.At present,breeding and cultivation of resistant varieties is the most economical and environmental way to control rice blast disease.Understand of fungal population structure and distribution of avirulence genes(AVR genes)in rice field is important for rice blast prevention and control.The high variability of rice blast fungus causes that the composition or variation of fungal population will affect the occurrence of disease.In this study,100 rice blast isolates were collected from Guidong County,Hunan Province,in 2016 and 2018.And the pathogenicity,physiological race,genomic structure,distribution and variation of AVR genes were studied,the main research results of this study are as follows:The pathogenicity was analyzed on 24 rice Monogenic Lines(MLs),we found that the fungal pathogenicity frequency on 24 MLs in 2018 was higher than 2016;meanwhile,Pikm showed high resistance frequency to rice blast isolates in both years.The results showed that Pikm could be used in rice blast resistance breeding in Guidong County.The races of all blast isolates were determined based on the Chinese differential cultivars,the results showed that ZC group was the most dominant and ZB group was second in 2016;ZA group was the most dominant and ZB group was second in 2018;the dominant race changed from ZC15 in 2016 to ZA5 in 2018.The genome patterns of all isolates were determined by Rep-PCR,there were 9 patterns(A,B,D,E,F,G,K,L,and M)in 2016,and 8 patterns(A,C,F,H,I,J,N,and O)in 2018.and only A and F were found in both years,these results showed that the genome structure ware different between two years.The diversity indexes of population were calculated.The group diversity index of fungal population in 2016 and 2018 were 0.618 and 0.514,respectively;the race diversity indexes were 0.838 and 0.800,respectively;the genome patterns diversity indexes were 0.895 and0.539,respectively.These results indicated that fungal population diversity in 2016 was richer than those in 2018.Four AVR genes(AVR-Pi9,AVR-Pikm,AVR-Pib,and AVR-Pizt)were screened in all isolates and results showed that its frequencies in 2016 were 100.00%,96.30%,62.96%,and70.37%,respectively;and were 97.26%,97.26%,95.89%,and 89.04%,respectively,in 2018.The results showed that these AVR genes widely exist in rice blast fungus in Guidong county,the frequencies of AVR-Pib and AVR-Pizt increased.Sequence analysis of AVR genes was performed,and a 2 bp deletion was found in CDS region of AVR-Pib in some isolates.No mutations were found in other AVR genes.