Title:

Influence of Temperature and Nutrient Availability on Beech Bark Disease fungal pathogen growth

Since the introduction of beech bark disease (BBD) in 1890, American beech (Fagus grandifolia) populations throughout the United States have experienced widespread mortality. BBD is a disease complex that consists of a scale insect, Cryptococcus fagisuga, and two species of Neonectria fungi, N. faginata and N. ditissima. While both fungi occur throughout the range of BBD, recent evidence suggests that stand-level prevalence is structured by broad geographic gradients in environmental variation (e.g., temperature). However, we currently lack an understanding of what regulates the prevalence of the two fungal species and how they respond to environmental variation. Therefore, the overall objective of our study is to examine growth rates, perithecia production and competitive hierarchies of the two BBD fungal species under controlled laboratory conditions, while systematically manipulating environmental factors, including temperature, nitrogen and phosphorous concentrations. Four Neonectria isolates (both mating types for each species) originally isolated from New Hampshire and two isolates from West Virginia were randomly selected for use in this study. Three levels of nitrogen, three levels of phosphorus and all possible combinations were evaluated in a full factorial design (9 treatments) under two temperatures. Each isolate was grown individually in duplicate on a minimal media across those nine treatments. Growth rate was measured as hyphal extension rate by measuring the diameter of the fungal colonies over the course of six days, and then regressing diameter over time. Treatment effects were assessed with two-way ANOVA in R (version 4.2.2). We found a significant positive effect of nitrogen over fungal growth and there seems to be an interaction between that nutrient and the species while phosphorus didn’t show a significant response over the growth rate of either fungi.

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