Observations on perithecium production and spore discharge in Pleurage setosa

Abstract

In Pleurage setosa , light is usually required for the initiation but not for the subsequent development of perithecia. The distribution and abundance of perithecia in Petri dish cultures are closely linked with light intensity. Observations on colonies grown initially in the dark and then transferred to light show that the youngest dark-grown regions respond most quickly and completely to light, whereas the older regions take longer to produce their more scattered perithecia. Fruiting of Petri dish cultures in the absence of light is induced by spread-out multipoint inoculation (using a blended mycelium or many spores), or by flooding a dark-grown culture with water. Violet and blue light are most effective in inducing fruiting, and in the positive phototropism of perithecial necks, whereas green and orange have little or no effect. Spore discharge can occur both in light and in darkness, but is markedly stimulated by light. Regular alternation of 12 hr. light and 12 hr. dark induces a diurnal periodicity of discharge which does not, however, persist in subsequent continuous darkness. Analysis of the distribution of horizontally discharged spore-clusters shows that the larger missiles (each with more than 100 spores) are usually thrown to a distance of 25–35 cm.