Local population structure of the wood decay ascomycete Daldinia loculata

This paper presents a study of the local population structure of Daldinia l oculata, a xylariaceous species frequently producing conidia and sexual str omata on fire-damaged deciduous host trees. We were able to show endophytic al establishment of D. loculata by isolating mycelia from sound-looking woo d of 8 out of 14 freshly felled, nan-burned trees. Mycelia were isolated fr om all 17 burnt trees in a burned forest site of central Sweden hosting str omata of D. loculata, and the distribution of genets in the stand was deter mined by using both vegetative incompatibility tests and restriction enzyme analysis of PCR amplified nuclear gene fragments as codominant molecular m arkers. In 14 of the trees we found only one genet of D. loculata per stem, and in three of the trees we found two genets per stem. Each genet was fou nd only once in the stand, highlighting the relative importance of ascospor es instead of conidia for dispersal to new substrata. Only one allele per l ocus was found in the mycelium isolated from the wood, suggesting that D. l oculata grows vegetatively as haploid mycelia. Vegetative incompatibility a nd segregating molecular markers were observed in the progeny of single str omata, evidently a consequence of D. loculata being heterothallic. More tha n two alleles of a highly variable multiallelic locus were detected in each of two stromata when analyzing single ascospores from 14 to 16 perithecia, evenly distributed on the stromatal surface, suggesting that more than one mating event can be involved in stroma formation in D. loculata. Moreover most genotyped stromata of the same tree showed a distinct heterozygous gen otype, indicating multiple matings of the relatively large, haploid, vegeta tive mycelium in the wood by several second, very small, individual mycelia .