Physiology of production of perithecia and microconidia in Hypomyces solani f. sp. Cucurbitae

Abstract

Production of perithecial primordia or microconidia by Hypomyces solani f. sp. cucurbitae, race 1 was stimulated either by exposure of cultures to 4 °C, or by the addition of commercial tyrosinase to 10-day cultures growing in potato dextrose agar. These processes in H. solani f. sp. cucurbitae, race 2 and H. solani f. sp. pisi were not affected by either treatment. A strain of race 1, in which production of microconidia but not of perithecial primordia was increased by cold treatment was crossed with a strain with the converse response (primordia but not microconidia increased by cold). No recombinants for these character differences were found among 98 ascospores. It is concluded that a gene controlling cold stimulation exists as two alleles which determine the response. This gene showed no linkage to mating type. Active tyrosinase was produced in all race 1 strains after the cold treatment, while the race 2 strains showed no activity. H. solani f. sp. pisi had extracellular tyrosinase activity in cultures without cold treatment. These results suggest that tyrosinase can be a limiting factor in the initiation of reproductive morphogenesis.