Heterokaryons of Gibberella zeae formed following hyphal anastomosis or protoplast fusion

Abstract

Heterokaryosis in Gibberella zeae varies depending upon the compatibility of the fused strains and the manner in which the strains are fused. Analysis of nutritionally complementing auxotrophic markers in pairings via hyphal anastamoses revealed a nuclear distribution in which heterokaryosis was restricted to anastamosed cells; apical cells remained auxotrophic but both types of nuclei could be recovered from multinucleate macroconidia. A comparable pairing via protoplast fusion yielded, initially, a fusion product in which apical cells were prototrophic and the conidia contained only one nuclear type. Analysis of subcultures of this fusion product, however, revealed a change. As in the heterokaryon generated by hyphal anastomoses, apical cells were auxotrophic and both types of nucleic could be found in the conidia. Heterokaryons could not be established by pairing vegetatively incompatible hyphal cells but the fusion of protoplasts from incompatible cells yielded a slow-growing, prototrophic colony in which conidia resolved only one nuclear type. This nuclear type was different from either of the parental types, and all conidia were capable of growth on minimal medium. The complementing nuclear types were not recovered. Protoplast fusion between vegetatively incompatible strains ( G. zeae Types A and B) apparently produced a heteroploid.