Variation in virulence among isolates of Armillaria ostoyae

Abstract

The virulence of Armillaria ostoyae isolates from coastal (16) and interior (33) British Columbia, elsewhere in North America (eight) and Europe (six) was assessed on 2-year-old Douglas-®r seedlings in pots during a 3-year trial. Isolates from most geographical locations infected similar proportions of seedlings, had similar average damage scores and killed a similar percentage of diseased seedlings. Isolates from the coastal region had a signi®cantly higher probability than interior isolates that a diseased seedling received a damage score > 3 on a 1±5 scale, and coastal isolates killed a higher proportion of diseased seedlings than interior isolates. The mean damage score for isolates that had been in culture for 20±25 years was about 25% lower than that for recently collected isolates. The results indicate that the higher incidence and longer duration of mortality in the southern interior of British Columbia compared to the coast can not be attributed to greater virulence of interior isolates of A. ostoyae.

Survival time analysis of Pinus pinaster inoculated with Armillaria ostoyae: genetic variation and relevance of seed and root traits

“…Although no previous work has considered as many tree families as in the current study, further strains could have been tested. We feel confident about the unique strain used as observed mortality due to A. ostoyae, starting 3 months after inoculation and reaching up to 80%, was much higher than mortalities reported in other A. ostoyae greenhouse pot experiments (<52%), involving 2-or 3-year-old conifer seedlings (Mugala et al 1989;Omdal et al 1995;Morrison and Pellow 2002;Prospero et al 2004). Our strain produced vigorous rhizomorphs within weeks, in contrast to other studies reporting rhizomorph production of A. ostoyae 18 months after inoculation (Prospero et al 2006).…”

“…A number of inoculation trials involving isolates of A. ostoyae have been conducted on several pine species, and sometimes the pathogen was found to exhibit considerable variation in virulence among the isolates and among the host genetics (Mugala et al 1989;Omdal et al 1995;Morrison and Pellow 2002;Prospero et al 2004). Although no previous work has considered as many tree families as in the current study, further strains could have been tested.…”

“…The strain was selected because of its outstanding capacity of producing vigorous rhizomorphs (Fig. 1b), and the fact that the most virulent isolates of A. ostoyae are usually the best rhizomorph producers (Omdal et al 1995;Morrison and Pellow 2002;Prospero et al 2004). A preliminary test performed in 1-year-old P. pinaster seedlings with additional strains (C1 and C18 among others (Prospero et al 2004, kindly provided by Daniel Rigling, Swiss Federal Research Institute) confirmed the superior virulence of EFA 1048/07 (results not included).…”

“…have been conducted on several conifer species (Mugala et al 1989;Omdal et al 1995;Morrison and Pellow 2002;Prospero et al 2004;Hood et al 2009;Cruickshank et al 2010). The incidence and mortality reported in those studies were calculated only for trees that were symptomatic or asymptomatic during the study period, whereas a number of infected trees had not show any symptoms at the time when the final disease incidence assessment was performed.…”

Phylogeographic patterns of Armillariaostoyae in the western United States

“…The advanced age of this individual shows an ability to survive several forest generations that likely included diverse species compositions. Other studies have shown that A. ostoyae genets can exhibit a range in pathogenicity (Omdal et al 1995), virulence (Omdal et al 1995;Morrison and Pellow 2002) and ecological behaviour (McDonald et al 1998). While A. ostoyae is generally considered highly pathogenic, one study reported most isolates of A. ostoyae behaved primarily as saprophytes, with only occasional mild pathogenicity on declining trees (Bé rubé and Dessureault 1988).…”