PHYSIOLOGY AND BIOCHEMISTRY OF ASCOCARP INDUCTION AND DEVELOPMENT

Recent investigations of environmental factors influencing ascocarp induction, morphogenesis, and associated biochemical changes are considered in this review article. Nutritional studies confirm that specific nutrient sources and concentrations favour ascocarp production, and that the fungi vary in their response to particular nutrients. Ascocarp formation by many fungi is favoured by maltose or starch as a carbon source, and amino acids as the nitrogen source. It generally occurs over a narrow temperature range, most often near 20-24-degrees-C. Comparatively few critical studies have been made of the effects of pH or moisture on ascocarp production. The qualitative and quantitative effects of light on ascocarp production and ascospore discharge have received much more attention, and the response of several fungi to light has been evaluated. Recent evidence indicates that a flavin compound serves as the photoreceptor for near-uv and blue light and is probably involved in an initial redox reaction involving cytochrome b. The effect of volatiles of various origins in the atmosphere has also-been determined to affect ascocarp development of some fungi. Mycologists would like to learn how the environmental factors regulate the morphogenesis of ascocarps. Investigators addressing this question have studied the possible role of sterols, hydrolysis and mobilization of glucan reserves, respiratory pathway, tyrosine metabolism, cyclic AMP, and mycosporins on ascocarp induction. Some of the complex biochemical changes occurring during maturation of the ascocarp can be detected and localised by cytochemical and immunofluorescent techniques.