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Genetics

Vegetative Compatibility Groups within Verticillium dahliae. J. E. Puhalla, Research geneticist, U.S. Department of Agriculture, Agricultural Research Service, National Cotton Pathology Research Laboratory, P.O. Drawer JF, College Station, TX 77841, Current address of senior author: Department of Genetics, University of California, Berkeley 94720; M. Hummel, biological technician, U.S. Department of Agriculture, Agricultural Research Service, National Cotton Pathology Research Laboratory, P.O. Drawer JF, College Station, TX 77841. Phytopathology 73:1305-1308. Accepted for publication 4 May 1983. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1983. DOI: 10.1094/Phyto-73-1305.

Ninety-six strains of Verticillium dahliae isolated from 38 different host-plant species in 15 countries were tested for ability to form heterokaryons with each other (vegetative compatibility). Heterokaryon formation was detected as a black line of microsclerotia that formed when albino and brown microsclerotial variants (induced by exposure to ultraviolet radiation) were paired on a complete agar medium. Of the strains tested, two had long conidia and may have been diploid. Among six other strains no heterokaryosis was detected. The remaining 86 strains were classified in 16 vegetative compatibility (v-c) groups. Strains within a v-c group formed heterokaryons with each other, but not with strains from a different group. The various v-c groups showed marked differences in frequency of occurrence and in geographical distribution. Evidence is given for genetic homogeneity within a group. Strains within a group may also be similar in virulence and host range. The v-c groups are viewed as genetically isolated populations within the species and should be taken into account in epidemiological studies.