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Vegetative Compatibility and Self-Incompatibility within Fusarium oxysporum f. sp. melonis. D. J. Jacobson, Graduate research assistant, Department of Plant Pathology, University of California, Berkeley 94720; T. R. Gordon, Assistant professor, Department of Plant Pathology, University of California, Berkeley 94720. Phytopathology 78:668-672. Accepted for publication 24 November 1987. Copyright 1988 The American Phytopathological Society. DOI: 10.1094/Phyto-78-668.

A worldwide collection of Fusarium oxysporum f. sp. melonis isolates was characterized by virulence and vegetative compatibility. Sixty-five isolates comprised five distinct vegetative compatibility groups (VCGs). There is a complex pattern of association between race, VCG, and geographic distribution; a VCG contained either one or several races, while a race was either unique to one VCG or divided among multiple VCGs. California isolates were placed in two VCGs, one unique to the San Joaquin Valley (0130) and the other distributed over North America (0131). In one case, isolates from both VCG 0130 and 0131 were recovered from the same field. Seven isolates were identified as vegetatively self-incompatible based on their inability to form heterokaryons between complementary nitrate nonutilizing mutants and between nitrate nonutilizing and sulfate nonutilizing mutants. The partial or complete absence of intra-isolate fusion cells, as determined microscopically, was also characteristic of vegetatively self-incompatible isolates. Four of these isolates were unable to form heterokaryons with other isolates; however, the other three isolates were able to form heterokaryons with tester strains and were included in VCG 0134. VCG analysis combined with race determination provides a more complete description of sub-forma specialis groups within F. o. f. sp. melonis. Vegetative self-incompatibility must be taken into account in such classifications.