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Genetics

Classification of Isolates of Verticillium dahliae Based on Heterokaryon Incompatibility. J. E. Puhalla, Research Geneticist, Science and Education Administration, U. S. Department of Agriculture, National Cotton Pathology Research Laboratory, P. O. Drawer JF, College Station, TX 77840; Phytopathology 69:1186-1189. Accepted for publication 14 May 1979. 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, 1979. DOI: 10.1094/Phyto-69-1186.

Nineteen isolates of Verticillium dahliae from various hosts and geographical areas were tested for ability to form heterokaryons with each other. Two methods of heterokaryon formation were used. In one, doubly auxotrophic mutants were induced with ultraviolet light (UV) and paired on minimal agar medium. Prototrophic growth arising from such pairings was heterokaryotic. In the second method, UV-induced mutants with albino (alm) and brown (brm) microsclerotia were paired on complete agar medium. In some alm × alm and alm × brm pairings, black microsclerotia developed along the line of contact. The isolates involved in such pairings were the same ones that produced prototrophic growth from auxotroph pairings. Thus, the black microsclerotia also indicated heterokaryosis. Among the 19 isolates tested, four subgroups were defined. Isolates within a subgroup formed heterokaryons with each other, but isolates from different subgroups did not. Because heterokaryosis and the subsequent parasexual cycle are the only known means of gene exchange in this asexual fungus, the subgroups may be viewed as genetically isolated populations. The recognition of genetically isolated populations within V. dahliae may permit a determination of the origin of new pathotypes or the spread of known pathotypes.