The rare oak polypore Piptoporus quercinus: Population structure, spore germination and growth

Abstract

Piptoporus quercinus, the rare oak polypore, is one of only four non-lichenised fungi listed on Schedule 8 of the Wildlife and Countryside Act 1981, in the UK. It is thereby accorded the highest level of legal protection in the UK. It fruits exclusively on oak (Quercus spp.), primarily veteran trees in old growth wood pasture and parkland in the midlands and southern England. Beyond information on fruit body occurrence, little is known of the ecology of this species. Germination of chlamydospores and basidiospores was investigated under a range of conditions (temperature, pH, different media). The mating system was ascertained by pairing single spore derived isolates, and somatic compatibility investigated by pairing fruit body isolates. Germination of basidiospores was consistently below 1 % with most success occurring on 2 % malt extract agar adjusted to pH 4 at 20 °C. Chlamydospores had a much higher average percentage of germination (47 % ± 22), and germinated even after prolonged exposure to extreme conditions (desiccation or exposure to −20 °C or 40 °C for 48 h, 7 d or 14 d). The mating system was unifactorial (bipolar), although only four mating alleles were discovered in the six populations sampled, two alleles being unique to one fruit body. There were no signs of somatic incompatibility between the majority of isolates, exceptions being an isolate from Wentwood, South Wales, and an isolate from Germany collected in 1975, both of which displayed apparent signs of somatic incompatibility in all experimental pairings. The lack of somatic incompatibility between the majority of UK isolates, together with the low number of mating alleles, may point to inbreeding within the UK population. Apparently compatible isolates were not, however, clonal, as shown by variation in their mycelial extension rates on agar at various temperatures.