Genetic diversity and colonization patterns of Onnia tomentosa and Phellinus tremulae (Hymenochaetaceae, Aphyllophorales) in the boreal forest near Thunder Bay, northwestern Ontario

Abstract

Forest health is impacted greatly by fungi, particularly those that cause disease in living trees. By examining genetic diversity within populations of pathogenic fungi and their patterns of colonization it is possible to gain a greater understanding of host-pathogen interactions. Two common pathogens in the boreal forest are Onnia tomentosa, causal agent of a root-rot disease in spruce known as stand opening disease, and Phellinus tremulae, causal agent of white heart rot in stems of trembling aspen. Both fungi are members of the Hymenochaetaceae in the Basidiomycota. Two black spruce (Picea mariana) plantations located north of Nipigon were examined for Onnia tomentosa. Spatial coordinates of 124 basidiomata were taken, and the basidiomata collected from plots that had received different commercial thinning treatments. Using extracted DNA from each of the basidiomata, it was possible to measure genetic diversity and consequently genet size. One hundred and sixteen genetically distinct individuals were found suggesting that the majority of the basidiomata represented unique genets. The distribution pattern was mapped. Stand thinning appears to negatively impact colonization of spruce by O. tomentosa compared with that observed in unthinned control stands. In an ancillary study, a stand of trembling aspen (Populus tremuloides) located at Silver Mountain (74 km SW of Thunder Bay) was examined for Phellinus tremulae. Four infected trees were harvested and each stem cut into 50 cm sections with the top 5 cm from each section removed as a cookie. From each cookie, isolations of P. tremulae were made onto agar media and somatic compatibility techniques were utilized to determine size and distribution of genets in each tree. Two trees contained two genets of P. tremulae, one tree contained a single genet, while the remaining tree failed to yield any isolations of P. tremulae at all.