TAXONOMY, SEXUALITY AND MATING TYPES OF DIAPORTHE ADUNCA

The perithecial stage of the pathogenic fungus Diaporthe adunca, found for the first time since 1851 in natural populations of its host Plan tago lanceolata, is described. Analysis of artificial reciprocal cross es and progeny from naturally occurring perithecia indicated that D. a dunca is heterothallic with two mating types. Both mating types were e qually frequent in natural populations, but have variable female ferti lity. The alpha-conidia performed consistently as fertilizing agents. They also serve as infective agents and so are subject to strong natur al selection. The number of sporulating pycnidia was negatively relate d to the number of perithecia formed later on the same Plantago scapes , indicating a trade-off between sexual and asexual reproduction. Envi ronments which favour asexual forms might therefore accelerate a loss of female fertility. Fertilization in natural populations of D. adunca probably occurs during late summer and autumn, when the epidemic is a t its maximum and many alpha-conidia can be splashed between neighbour ing infected scapes.