Effectiveness and durability of the rice pi-ta gene in Yunnan province of China.

Rice blast is one of the most damaging diseases of rice worldwide. In the present study, we analyzed DNA sequence variation of avirulence (AVR) genes of AVR-Pita1 in field isolates of Magnaporthe oryzae in order to understand the effectiveness of the resistance gene Pi-ta in China. Genomic DNA of 366 isolates of M. oryzae collected from Yunnan province of China were used for polymerase chain reaction (PCR) amplification to examine the existence of AVR-Pita1 using gene-specific PCR markers. Results of PCR products revealed that 218 isolates of M. oryzae carry AVR-Pita1. Among of them, 62.5, 56.3, 58.5, 46.7, 72.4, and 57.4% of M. oryzae carry AVR-Pita1 from northeastern, southeast, western, northwest, southwestern, and central Yunnan province, respectively. The detection rate of AVR-Pita1 was, in order: southwestern > northeastern > western > central > southeastern > northwestern Yunnan province. Moreover, in total, 18 AVR-Pita1 haplotypes encoding 13 novel AVR-Pita1 variants were identified among 60 isolates. Most DNA sequence variation was found to occur in the exon region, resulting in amino acid substitution. Six virulent haplotypes of AVR-Pita1 to Pita were identified among 60 field isolates. The AVR-Pita1 has evolved to virulence from avirulent origins via base substitution. These findings demonstrate that AVR-Pita1 is under positive selection and mutations of AVR-Pita1 are responsible for defeating race-specific resistance in nature.