Taxonomy, sexuality and mating types of Diaporthe adunca

Abstract

The perithecial stage of the pathogenic fungus Diaporthe adunca, found for the first time since 1851 in natural populations of its host Plantago lanceolata, is described. Analysis of artificial reciprocal crosses and progeny from naturally occurring perithecia indicated that D. adunca is heterothallic with two mating types. Both mating types were equally frequent in natural populations, but have variable female fertility. The alpha-conidia performed consistently as fertilizing agents. They also serve as infective agents and so are subject to strong natural selection. The number of sporulating pycnidia was negatively related to the number of perithecia formed later on the same Plantago scapes, indicating a trade-off between sexual and asexual reproduction. Environments 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 at its maximum and many alpha- conidia can be splashed between neighbouring infected scapes. [KEYWORDS: Fungus cochliobolus-heterostrophus; light leaf-spot; phomopsis-subordinaria; plantago-lanceolata; vegetative incompatibility; pyrenopeziza-brassicae; magnaporthe-grisea; populations; pathogenicity; fertility]