ARS | Publication request: MOLECULAR MECHANISMS OF THE INSTABILITY OF AVIRULENCE GENE AVR-PITA IN RICE BLAST FUNGUS MAGNAPORTHE ORYZAE

Submitted to: Arkansas Agricultural Experiment Station Research Series
Publication Type: Experiment Station
Publication Acceptance Date: June 27, 2006
Publication Date: August 8, 2006
Citation: Zhou, E., Jia, Y., Correll, J.C., Lee, F.N. 2006. Molecular mechanisms of the instability of avirulence gene avr-pita in rice blast fungus magnaporthe oryzae. In: Norman, R.J., Meullenet, J.-F., Moldenhauer, K.A.K., editors. B.R. Wells Rice Research Studies 2005, Arkansas Agricultural Experiment Station Research Series 540. p. 160-167. Available: http://www.uark.edu/depts/agripub/Publications/researchseries/.

Technical Abstract: Rice blast, caused by Magnaporthe Oryzae, is one of the most serious diseases of rice worldwide. The Pi-ta gene in rice confers resistance to M. Oryzae isolates containing the corresponding avirulence gene AVR-Pita. In the southern U.S., rice cultivars containing Pi-ta have been widely utilized since the deployment of the first Pi-ta containing cultivar Katy in 1989. Recently, however, the efficacy of Pi-ta in controlling rice blast disease has been challenged by virulent M. Oryzae field isolates found on Banks. To better understand the molecular mechanisms of the instability of rice blast resistance in Banks, some virulent M. Oryzae field isolates were collected from Banks in Arkansas rice fields during 2004 and were analyzed for AVR-Pita variations. In this study, a series of traditional and modern molecular techniques including pathogenicity assay, rep-PCR, allele-specific PCR, Southern blot, molecular cloning, and sequencing were used to analyze allelic variation at the AVR-Pita locus in these virulent isolates. Preliminary results showed that all Banks isolates displayed point mutation, deletion, and/or transposon insertion in the coding region of the AVR-Pita gene that abolished the AVR-Pita avirulence function. This finding provided the molecular explanation for the instability of the avirulence gene AVR-Pita in rice blast fungus. Further molecular analyses of the nonfunctional AVR-Pita gene alleles are in progress.