The occurrence of a parasexual cycle in Fusarium oxysporum Fr. f. pisi (Linf.) Snyder and Hansen was investigated. 2. Diauxotrophic strains were used to produce heterocaryons; one to four diploid spores were found when approximately 1 x 106 spores from four of five heterocaryons were plated on minimal medium. 3. Colonies of the heterocaryons did not resemble those of the component strains in morphology or color; the diploids also differed from the "parental" heterocaryons and from the component strains in colonial characteristics. 4. Three of four heterocaryons yielded conidia with nuclei from one of the two component strains; diploids produced haploid spores which had either nuclei identical to those in spores from the parental heterocaryon or nuclei with one of the two nutritional requirements of spores from the parental heterocaryon. 5. Recombinant nuclei were identified in spores from three of four diploids. 6. Failure to detect all possible recombinant nuclei from diploids was attributed to strong selective forces favoring the inclusion of nuclei with certain genotypes in spores from the heterocaryons and diploids.
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Tuveson et al. (1959) studied this question.