Water‐soluble mycelial antigens from two physiological races (2 and 3) of Fusarium oxysporum L. sp. lupini were compared by tandem‐crossed immunoelectrophoresis. When antiserum against race 3 was tested some 50 antigens were detected. The two races had apparently almost identical antigenic patterns differing only in one antigen specific to race 3. This specific antigen might be related to the virulence of this fungus.

Extracts from Fusarium oxysporum (F.o.) and F. oxysporum var. redolens (F.o.r.) isolates were compared by means of electrophoresis and crossed immunoelectrophoresis. The polymorphism of five isozyme systems allowed a distinction between F.o. and F.o.r. isolates. The isozyme patterns of three other isozyme systems did not allow this distinction between F.o. and F.o.r. to be made. Both fungi appeared almost identical serologically. Relative amounts of their corresponding proteins differed but the qualitative patterns of the proteins were nearly the same with the anti‐F.o.r. serum, only one specific antigen was detected in the extracts from F.o.r., isolates. Although the results obtained indicate a strong similarity between F.o. and F.o.r., they are not sufficient for an unequivocal statement that the fungi belong to the same species.

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