Another Approach to Race Classification ofFusarium oxysporumf. sp.pisi

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Abstract
The validity of the races of F. oxysporum f. sp. pisi 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 were 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 pea cultivars. 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. They did not completely agree on the race designation of some of these isolates, and some isolates did not show low virulence on certain cultivars in their experiments. Five isolates from the ATCC were simultaneously tested on key differentials by this method and others. No clear evidence of low virulence was found. Little wilting occurred in some of their experiments. In the tests, plants were killed quickly with the other method, while with this one, infected plants progressed through the syndrome of disease as seen in the field. Criteria for determining races are discussed.