Distribution, hosts, and site relationships of Armillaria spp. in central and southern Ontario

This study investigated the species, geographic distribution, host range, site relationships, and impacts of Armillaria in central and southern Ontario. Rhizomorphs and infected wood samples were collected at 110 of 111 sites. Six species were identified by polymerase chain reaction or diploid-haploid pairings. Armillaria gallica Marxmuller & Romagn. was most commonly isolated and had the broadest host range. It was seldom isolated from conifers but often from oaks. It was the species most often found on moist sites and showed strong preference for calcareous soils. Armillaria calvescens Bérubé & Dessureault was rarely isolated from conifers but often from maples, where it commonly caused butt rot. It was found most often on coarse loamy or fine, well-drained, fresh sites. Armillaria ostoyae (Romagn.) Herink. had the second broadest host range. It was seldom found on sugar maple (Acer saccharum Marsh.) but dominated on conifers, especially on dry-fresh, rapidly drained sandy to coarse loamy sites. It was not found on sites with finer soils. Armillaria sinapina Bérubé & Dessureault and Armillaria gemina Bérubé & Dessureault were found in more northerly parts of the study area on noncalcareous sites. Armillaria sinapina often caused butt rot and was often found on poorly drained sites. Armillaria gemina was found only on hardwoods. Armillaria mellea (Vahl:Fr.) Kummer s.st. was found on dead hardwoods at four locations.