XVI International Botanical Congess

Armillaria mellea and A. gallica are common in the interior coastal mountains of California. To determine the ecology of these two species in Northern California coastal hardwood stands, four 100-m2 plots were established and all trees were sampled. About 50% of the trees per plot supported Armillaria infections at their root collars. From 436 trees, 188 isolates were obtained and identified as A. mellea or A. gallica. Individuals were distinguished by somatic incompatibility pairings and molecular markers. Estimated sizes of individuals ranged from 3 m2 to 100 m2. Armillaria mellea was identified on all four plots, mainly from mycelial fans on living trees. Armillaria gallica was identified on three plots from epiphytic rhizomorphs on living trees or decay on dead trees. Based on our observations, both species exist mainly as saprophytes in coastal hardwood forests of California.