Submitted to: Phytopathology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 1/9/2014
Publication Date: 6/11/2014
Publication URL: http://handle.nal.usda.gov/10113/60693
Citation: Li, J., Lu, L., Jia, Y., Li, C. 2014. Effectiveness and durability of the rice Pi-ta gene in Yunnan province of China. Phytopathology. 104(7):762-768. Interpretive Summary: Rice blast is one of the most threatening diseases worldwide. The disease is managed with resistant (R) genes, fungicides, and culture practices. We collected 366 field isolates of Magnaporthe oryzae to better understand the effectiveness of the resistant gene Pi-ta in China. Using a gene specific DNA marker, we discovered that about 50% of virulent isolates did not carry AVR-Pita1 suggesting that the fungus defeated Pi-ta mediated resistance. We then analyzed the DNA sequence variation of avirulence genes of AVR-Pita1. We found 60 isolates that contained 18 AVR-Pita1 haplotypes which encode 13 novel AVR-Pita1 variants. This discovery demonstrates that AVR-Pita1 has been evolved and is responsible for defeating race-specific resistance in nature.
Technical Abstract: Rice blast is one of the most damaging diseases of rice worldwide. In the present study, we analyzed DNA sequence variation of avirulence genes of AVR-Pita1 in field isolates of M. 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 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 of Yunnan province, respectively. The detection rate of AVR-Pita1 was in order as: southwest>northeast>western>central>southeast>northwest of Yunnan province. Moreover, a total of 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.