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Molecular Plant Pathology

Analysis of the Interaction Between Xanthomonas oryzae pv. oryzae and the Rice Cultivars IR24 and IRBB21. Mark Mazzola, Department of Plant Pathology, Kansas State University, Manhattan 66506-5502; Jan E. Leach(2), Rebecca Nelson(3), and Frank F. White(4). (2)(4)Department of Plant Pathology, Kansas State University, Manhattan 66506-5502; (3)Division of Plant Pathology, International Rice Research Institute, Manila, Philippines. Phytopathology 84:392-397. Accepted for publication 4 January 1994. Copyright 1994 The American Phytopathological Society. DOI: 10.1094/Phyto-84-392.

Xanthomonas oryzae pv. oryzae causes bacterial blight of rice, and interactions between this pathogen and its host occur in a gene-for-gene manner. In contrast to other resistance genes, the dominant locus Xa-21 confers resistance to all Indian and Philippine races of X. o. oryzae that have been examined. In this study, multiplication of X. o. oryzae and subsequent disease development were comparable in cultivar IRBB21 possessing Xa-21 and in the susceptible rice cultivar IR24 when plants were inoculated prior to 21 days postemergence. Resistance conveyed by Xa-21 was evident in 21-day-old plants, and the level of resistance increased with plant maturity. Cultivar IR24, which is used as a susceptible control in screening trials, displayed resistance to bacterial blight that was expressed only in adult plants. DNA homologous to the avirulence gene avrBs2 from Xanthomonas campestris pv. vesicatoria was present in all Philippine races of X. o. oryzae. Inactivation of the avrBs2-homologous region by transposon mutagenesis did not affect the fitness of X. o. oryzae and did not alter the response elicited by this bacterium on IRBB21, indicating that this locus does not confer avrXa21 activity.