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Another Approach to Race Classification of Fusarium oxysporum f. sp. pisi. G. M. Armstrong, Department of Plant Pathology, University of Georgia College of Agriculture Experiment Stations, Georgia Station, Experiment, GA 30212; Joanne K. Armstrong, Department of Plant Pathology, University of Georgia College of Agriculture Experiment Stations, Georgia Station, Experiment, GA 30212. Phytopathology 71:474-478. Accepted for publication 2 May 1980. Copyright 1981 The American Phytopathological Society. DOI: 10.1094/Phyto-71-474.

The validity of the races of Fusarium oxysporum f. sp. pisi that we differentiated has been challenged. Kraft and Haglund stated that differentiation was due chiefly to low virulence of the isolates and the method of inoculation. They obtained the isolates that we deposited with the American Type Culture Collection (ATCC) and tested them on a limited number of cultivars with their methods. They accepted as valid at that time races 1, 2, and 5, based on isolates from fields in the northwestern USA and the reactions of a few cultivars. We maintain that the small number of isolates and cultivars used by them was too limited to test the validity of all races. It was only after using a large number of cultivars and isolates from widely separated localities that the full potentialities of F. oxysporum f. sp. pisi became evident. Moreover, they did not completely agree with each other on the race designation of some of our isolates, and some isolates did not show low virulence on certain cultivars in their experiments. We obtained five isolates from the ATCC and simultaneously tested them on key differentials by our method and theirs. No clear evidence of low virulence was found, and we do not understand why they obtained so little wilting in some of their experiments. In our tests, plants were killed quickly with their method, while, with ours, infected plants progressed through the syndrome of disease as seen in the field. Criteria for determining races are discussed.