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Relationship Between Vegetative Compatibility and Pathogenicity of Isolates of Fusarium oxysporum f. sp. tuberosi from Potato. Sonja L. Venter, Research Centre for Plant Biotechnology, Private Bag X293, Pretoria, 0001; D. J. Theron(2), P. J. Steyn(3), D. I. Ferreira(4), and A. Eicker(5). (2)(3)Vegetable and Ornamental Plant Research Institute, Private Bag X293, Pretoria, 0001; (4)Research Centre for Plant Biotechnology, Private Bag X293, Pretoria, 0001; (5)University of Pretoria, Pretoria, 0001. Phytopathology 82:858-862. Accepted for publication 28 February 1992. Copyright 1992 The American Phytopathological Society. DOI: 10.1094/Phyto-82-858.

Thirty-five South African isolates of Fusarium oxysporum f. sp. tuberosi, which cause dry rot, stem-end rot, and wilt of potatoes (Solanum tuberosum), were characterized by pathogenicity and vegetative compatibility. The isolates were assigned to six vegetative compatibility groups (VCGs) according to pairings of complementary nitrate-nonutilizing (nit) mutants induced on chlorate-containing media. A complex pattern of association between disease symptoms caused in potatoes, VCG, and geographic distribution was found. For instance, 14 of the 16 isolates assigned to VCGs A and B were originally isolated from stem-end rot. Only one stem-end rot isolate was assigned to a different VCG. F. o. tuberosi isolates that were originally isolated from dry rot tubers were assigned to VCGs E and F. Isolates causing dry rot that were collected in the Transvaal Highveld, South Africa, belonged to VCG E, whereas isolates from the eastern Orange Free State, South Africa, were assigned to VCG F. Eight of the 10 isolates that were isolated from wilted potato plants were assigned to VCGs C and D. These isolates originated from several geographical locations. The remaining two isolates obtained from wilted potato plants were assigned to VCG A. Pathogenicity and vegetative compatibility reactions in VCGs A and C suggest that a relationship between isolates that cause stem-end rot and those that cause wilt of potatoes might exist.