Colonization and confrontation of four Armillaria sinapina isolates to Armillaria ostoyae within inoculated wood blocks and stumps

Roots represent a third of terrestrial biomass. After logging, fungal pathogens use stump roots as a food base to survive and this may result in negative impact on aboveground plant production. Mycelial spread determines the fungal volume in the stump, which in turn dictates inoculum potential and spread distance; hence, it is a key disease factor. The current study focuses on the spread and confrontation of two sympatric species of Armillaria with differing virulence. Living cut blocks of Douglas-fir stem were inoculated at opposite ends with a virulent Armillaria ostoyae isolate, or four A. sinapina isolates with low virulence from two biogeoclimatic zones. The inoculum blocks were buried in moist sand, and then the surface area and volume occupied by each was determined. The drier zone A. sinapina isolates colonized 80% of the block surface areas, while the moister zone isolates were about equal with A. ostoyae (42% colonized). Additionally, inoculum blocks of each species were buried against a root and root collar of two living trees, the trees were cut, and the stumps became colonized. One stump had greater A. ostoyae colonization over A. sinapina by 12%, and the other larger stump by 74% because of thicker root collar bark that hindered A. sinapina. All interspecific encounters produced a stalemate. Increased growth potential of A. sinapina in drier zones might enable root colonization before drying. Southern Canada is forecast to become drier and warmer, favouring A. ostoyae over A. sinapina in the currently more productive areas, with an increasing negative impact on aboveground productivity.