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Dominance Reversal of a Bacterial Blight Resistance Gene in Some Rice Cultivars. G. S. Sidhu, Postdoctoral Fellow, International Rice Research Institute, Los Baños, Philippines; Gurdev S. Khush, Plant Breeder, International Rice Research Institute, Los Baños, Philippines. Phytopathology 68:461-463. Accepted for publication 21 September 1977. Copyright © 1978 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-68-461.

The inheritance of resistance to Xanthomonas oryzae isolate PXO61 (from the Philippines) in five rice cultivars was studied. The same gene confers resistance in the five cultivars. The pattern of segregation indicates a monogenic recessive factor when the plants are inoculated at the booting stage, but it is monogenic dominant when the plants are inoculated during flowering. The dosage effect of the resistance gene causes this reversal of dominance because the heterozygous plants are susceptible at booting and resistant during flowering. This gene, designated Xa6, is linked to Xa4, another dominant gene for resistance, with a crossover value of 26%.

Additional keywords: Oryza sativa L., Xanthomonas oryzae, allelic relationships, dominant, recessive, monogenic.