SOME ASPECTS OF SEXUAL REPRODUCTION IN NECTRIA-HAEMATOCOCCA VAR CUCURBITAE

The processes leading up to and including plasmogamy are described in the heterothallic euascomycete N. haematococca var. cucurbitae. When conida are placed on a block of agar lying on a compatible mycelium bearing protoperithecia a series of interactions ensue that lead to the fusion of a cell(s) of the conidium with a trichogyne(s) emanating from the protoperithecium. These interactions are explainable in terms of diffusible substances that coordinate the respective behaviors of the 2 partners in the following sequence: In response to a substance(s) produced by the recipient mycelium the conidium changes in both form and function, i.e., it becomes sexually activated. Such activated conidia redistribute the protoplasm among their several cells, form papillae and secrete a substance that attracts the trichogynes which then grow towards these conidia. Plasmogamy then takes place between individual cells of a conidium and a trichogyne. Interactions in which one or both of the partners carried the c and/or m mutant genes, both of which interfere with the sexual reaction, were also examined. In mixed cultures neither mutant''s function was restored by the proximity of its normal allele. It was subsequently found that the block imposed by the m mutant allele occurred after plasmogamy and hence the intercellular complementation that the mixed cultures were designed to detect would not be expected to occur. A more intimate, intracellular action is now posited for this mutant.