Submitted to: Rice Technical Working Group Meeting Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: 12/3/2011
Publication Date: 3/1/2012
Citation: Jia, Y., Xing, J., Crrell, J. Lee, FN. Cartwright, R., Cao, M., Yuan, L. 2012. Characterization of genetic diversity of rice blast fungus in Arkansas field isolates. Page 77. Interpretive Summary:
Technical Abstract: The rice blast resistance gene Pita has been deployed for preventing blast disease in the southern US for the past two decades. To date, at least eleven rice cultivars, Katy, Drew, Madison, Kaybonnet, Banks, Ahrent, Spring, Cybonnet, Catahoula, CL111, and Templeton carrying Pi-ta were developed by rice breeders using classical plant breeding. In an effort to examine the stability of resistance mediated by Pi-ta in deployed rice cultivars, a total of 200 Arkansas field isolates of the rice blast fungus were obtained from 1996-2009 from rice cultivars with Pi-ta and without Pi-ta and were characterized using an international rice differential system, Rep-PCR, and pathogenicity assays on the Pi-ta containing rice cultivar, Katy. The race IB49, IC17 and IB1 were found to be the three predominant races among all isolates characterized. In each race one major Rep-PCR pattern was identified. All of these races were found to contain the corresponding avirulence gene AVR-Pita1 as determined by the AVR-Pita1 gene specific primers YL149 and YL169 in polymerase chain reaction. Sequence analysis of the AVR-Pita1 alleles from avirulent isolates revealed that most of point mutations led to amino acid substitutions. These AVR-Pita1 containing races were unable to infect Katy, as would be expected, and demonstrates that Pi-ta is effective in preventing blast disease caused by the predominant races in Arkansas. However, 15 isolates from both Pi-ta and non Pi-ta containing rice cultivars were able to infect Katy and were classified to the race IC1. The AVR-Pita1 alleles were not amplified in these virulent isolates suggesting that mutations at the AVR-Pita1 locus may alter recognition specificity to Pi-ta. Our findings suggest that the AVR-Pita1 alleles in field isolates in Arkansas is under diversified selection and the impact of this finding on crop protection will be presented.