The biological consequences of somatic incompatibility in wood decaying Basidiomycetes and other fungi.

Abstract

Certain aspects of the biological consequences of somatic incompatibility in Basidiomycetes and other fungi were investigated. Somatic incompatibility was shown to operate in woody substrata by delimiting discrete individuals within local populations of the wood decaying fungal species Xylaria hypoxylon (Ascomycete) and the Basidiomycetes Pleurotus cornucopiae (Agaricales) and Stereum hirsutum (Aphyllophorales). Patterns of colonisation and community development within cut beech logs differed according to the type of inoculum arriving at the resource and its ecological behaviour. Aerial establishment was via spores, with non-decay, ruderal and wood decaying Ascomycetes being replaced by Basidiomycetes. Basidiomycete expansion and the formation of numerous somatically incompatible individuals, was associated with the transition from homokaryons to heterokaryons. Establishment from the soil was via the mycelia of cord forming species. These species actively replaced the aerial combative community. The high numbers of decay individuals reduced fruiting and decay rate of wood. The role of somatic incompatibility in the generation of an individual was investigated in the species Stereum hirsutum. This species was shown to have a heterothallic (diaphoromictic) mating system, controlled by a single locus (C-Factor) with multiple alleles. Somatic incompatibility was regularly observed between sexually incompatible homokaryons, as well as between both sib-related and non sib-related heterokaryons. Somatic incompatibility aided the preferential selection of unrelated nuclei following the pairing of homokaryons of differing lineage. The movement of nuclei across somatic incompatibility barriers was dependent on their genetic background and lineage, but not nucleus migration rate per se, which was determined by the accepting homokaryon. The selection pressure on genetically unrelated homokaryons was enhanced with age. A close relationship between sexual and somatic incompatibility was demonstrated. Pairings between sibling basidiospore progeny from field isolates showed reduced levels of sexual compatibility, compared with non sib-related pairings. Inbreeding reduced the observed levels of somatic incompatibility and increased the apparent levels of sexual compatibility. The presence of an unlinked, multiallelic, heterogenic incompatibility locus was found, which produced a lytic interaction between a proportion of sexually incompatible homokaryons. This reaction often showed interisolate replacement, with further progress being halted by the late expression of somatic incompatibility between isolates.

Date of Award	1984
Original language	English
Awarding Institution	University of Bath