Entomological and physiological factors predisposing beech to infection by Neonectria ditissima and N. faginata in beech bark disease aftermath forests

            Neonectria ditissima and N. faginata are causal agents of beech bark disease (BBD) in North America.  Infection of American beech (Fagus grandifolia) by these fungal pathogens is believed to follow a single predisposing factor, infestation by beech scale (Cryptococcus fagisuga).  However, recent findings do not support this model and suggest the influence of additional or alternative predisposing factors.  Because BBD related research does not commonly operate at the species level, fundamental similarities and differences between the N. ditissima and N. faginata pathosystems are not known.  However, a fundamental understanding of these pathosystems is integral to developing effective management strategies for BBD aftermath (long-affected) forests.  Although several physiological factors differ between healthy, infested, and infected beech, the possible role of these factors in predisposing infection has not been examined.  A case-control study was conducted to investigate possible entomological and physiological factors predisposing beech to infection by Neonectria pathogens, separately and together.  Bark tissue samples and baseline measurements were collected and recorded for two-hundred uninfected beech in 2011.  The amino acid, flavonoid, and nutrient content of bark samples from trees exhibiting signs of Neonectria infection in 2012, as well as a subset of trees the remained healthy, was quantified.  Important predisposing factors were identified using generalized linear mixed models.  Distinct entomological and physiological predisposing factors were identified for N. ditissima and N. faginata.  These findings have important implications for managing forests dominated by one BBD pathogen or another.