Novel Variation and Evolution of of in Field Isolates.

The product of the avirulence () gene of can be detected by the product of the corresponding resistance () gene of rice and activates immunity to rice mediated by the gene. The high degree of variability of isolates in pathogenicity makes the control of rice blast difficult. That resistance of the gene in rice has been lost has been ascribed to the instability of the gene in . Further study on the variation of the genes in field isolates may yield valuable information on the durable and effective deployment of genes in rice production areas. and are a pair of valuable genes in the Rice- pathosystem. is detectable by and determines the effectiveness of . To effectively deploy the gene , the distribution, variation, and evolution of the corresponding gene were found among 312 isolates collected from Yunnan rice production areas of China. PCR amplification and pathogenicity assays of showed that 202 isolates (64.7%) held alleles and were avirulent to IRBLzt-T (holding ). There were 42.3-83.3% avirulent isolates containing among seven regions in Yunnan Province. Meanwhile, 11 haplotypes of encoding three novel variants were identified among 100 isolates. A 198 bps insertion homologous to solo-LTR of the retrotransposon inago2 in the promoter region of in one isolate and a frameshift mutation of CDS in another isolate were identified among 100 isolates, and those two isolates had evolved to virulent from avirulent. Synonymous mutation and non-AUG-initiated N-terminal extensions keeps the gene avirulence function in field isolates in Yunnan. A haplotype network showed that H3 was an ancestral haplotype. Structure variance for absence (28.2%) or partial fragment loss (71.8%) of was found among 39 virulent isolates and may cause the avirulence function to be lost. Overall, evolved to virulent from avirulent forms via point mutation, retrotransposon, shift mutation, and structure variance under field conditions.