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Genetics of Stem Rot Resistance in Rice and Virulence in Sclerotium oryzae. S. A. Ferreira, Department of Plant Pathology, University of California, Davis 95616, Current address of senior author: Department of Botany and Plant Pathology, Colorado State University, Ft. Collins 80523; R. K. Webster, Department of Plant Pathology, University of California, Davis 95616. Phytopathology 65:968-971. Accepted for publication 28 March 1975. DOI: 10.1094/Phyto-65-968.

Comparison of 10 rice cultivars revealed different levels of resistance to stem rot disease. Progeny from crosses between cultivars differing in disease reaction were evaluated. Stem rot resistance was quantitatively inherited and transferable to a less resistant cultivar. Heritability of resistance in a Bluebelle × Colusa cross was 43%. A large potential for variation in virulence among isolates of S. oryzae was observed. Single ascospore progeny of crosses of isolates differing in virulence were evaluated. Virulence in S. oryzae was quantitatively inherited and transgressive segregation of factors controlling virulence in the progeny was evident. In populations, there is a tendency for virulence to be stabilized at an intermediate level. Since the perfect stage of S. oryzae (Magnaporthe salvinii) can be found on diseased rice stems, this mechanism may be operable, with the effect that highly virulent isolates may not predominate in nature.

Additional keywords: disease resistance, virulence, Magnaporthe salvinii.