Longping Branch Institute, Postgraduate School, Central South University, Changsha, Hunan 410125, China; State Key Laboratory of Hybrid Rice, National Hybrid Rice Research and Development Center, Changsha, Hunan 410125, China
United States Department of Agriculture–Agricultural Research Service, Dale Bumpers National Rice Research Center, Stuttgart, AR 72160
Department of Plant Pathology, University of Arkansas, Fayetteville 72701
Rice Research and Extension Center, University of Arkansas, Stuttgart
Department of Plant Pathology, University of Arkansas, Fayetteville
State Key Laboratory of Hybrid Rice, National Hybrid Rice Research and Development Center, Changsha, Hunan 410125, China
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Accepted for publication 18 October 2012.
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-Pita1. 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-Pita1. These isolates belong to the races IA1, IB1, 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-Pita1 was not amplified from 28 virulent isolates. One AVR-Pita1 allele was amplified by AVR-Pita1-specific primers in 78 avirulent isolates. Interestingly, different AVR-Pita1 alleles were found in each of the 12 avirulent isolates, as determined by DNA sequencing. Sequence analysis of 90 PCR products revealed 10 AVR-Pita1 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-Pita1 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.
This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 2013.