Factors influencing ascospore germination in three species of Sporormiella

Ascospore germination of Sporormiella intermedia, S. isomera, and S. minima requires sodium acetate as an exogenous source of energy. Maximum ascospore germination occurs at a concentration of 5.0 g/ℓ of sodium acetate in the medium. Among the physical factors studied, the pH of the medium was found to be crucial: germination occurred within a very narrow pH range (5.0–7.0) and reached an optimal level at pH 5.5. The ascospores of S. intermedia and S. isomera germinated between 10 and 30 °C while those of S. minima germinated between 10 and 40 °C. The optimal temperature varied for each species (10–20 °C for S. intermedia; 20–25 °C for S. isomera; 30–35 °C for S. minima). At 30 °C and above, a globose vesicle formed in all three species before the formation of the germ tube. Light had no influence on ascospore germination, nor were external supplies of nitrogen or vitamins necessary for spore germination.