Analysis of Genetic and Molecular Identity Among Field Isolates of the Rice Blast Fungus with an International Differential System, Rep-PCR, and DNA Sequencing

摘要

Xing, J., Jia, Y., Correll, J. C., Lee, F. N., Cartwright, R., Cao, M., and Yuan, L. 2013. Analysis of genetic and molecular identity among field isolates of the rice blast fungus with an international differential system, Rep-PCR, and DNA sequencing. Plant Dis. 97:491-495. The Pi-ta gene deployed in southern U.S. rice germplasm is effective in preventing the infection by strains of Magnaporthe oryzae isolates that carry the avirulence (AVR) gene AVR-Pital. In the present study, 169 isolates from rice (Oryza sativa) cultivars, with and without Pi-ta, were analyzed for their genetic identity using an international differential system, repetitive element-based polymerase chain reaction (Rep-PCR), and sequence analysis of PCR products of AVR-Pital. These isolates belong to the races IA1, IB17, IB17, IC1, and IC17 of M. oryzae. These isolates were further classified into 15 distinct groups by Rep-PCR. There was a predominant group within each race. Pathogenicity assays on 'Katy' (Pi-ta) and 'M202' (pi-ta) rice determined that IC1 was virulent to Katy and M202; IB17, IC17, and most of IA1 and IB1 were avirulent to Katy and virulent to M202, suggesting that the Pi-ta gene in Katy is responsible for preventing infection by these isolates. Consistently, AVR-Pital was not amplified from 28 virulent isolates. One AVR-Pital allele was amplified by AVR-Pita1-specific primers in 78 avirulent isolates. Interestingly, different AVR-Pital alleles were found in each of the 12 avirulent isolates, as determined by DNA sequencing. Sequence analysis of 90 PCR products revealed 10 AVR-Pital haplotypes, 4 of which were new. In total, 12 amino acid changes were identified in the new variants when compared with the first described AVR -Pita sequence (AF207841). The finding of isolates with altered AVR-Pital from rice cultivars with and without Pi-ta suggests that these virulent isolates were adapted to the field environments in the southern United States. Further research will be needed to verify this prediction.