Frequencies and Variations of Avirulence Genes in Hunan Province, China.

Rice blast caused by poses significant threaten to rice production. For breeding and deploying resistant rice varieties, it is essential to understand the frequencies and genetic variations of avirulence () genes in the pathogen populations. In this study, 444 isolates were collected from Hunan Province, China in 2012, 2015, and 2016, and their pathogenicity was evaluated by testing them on monogenic rice lines carrying resistance genes , , , , or . The frequencies of corresponding genes , , , , and were characterized by amplification and sequencing these genes in the isolates. Both and conferred resistance to >75% of the tested isolates, while , , and were effective against 55.63, 15.31, and 3.15% of the isolates, respectively. and were detected in 90% of the isolates and , , and were present in 26.12, 66.22, and 79% of the isolates, respectively. Sequencing of genes showed that most mutations were single nucleotide polymorphisms, transposon insertions, and insertion mutations. The variable sites of and were mainly located in the coding sequence regions (CDS), and most were synonymous mutations. A 494-bp Pot2 transposon sequence insertion was found at the 87 bp position upstream of the start codon in . Noteworthy, although no mutations were found in CDS of , a GC-rich inserted sequence of ∼200 bp was found at the 1,272 bp position upstream of the start codon in three virulent isolates. As and were widely distributed with low genetic variation in the pathogen population, and should be promising genes for breeding rice cultivars with blast resistance in Hunan.