Date of Award

Fall 2023

Project Type

Thesis

Program or Major

Microbiology

Degree Name

Master of Science

First Advisor

Jeff Garnas

Second Advisor

Anissa Poleatewich

Third Advisor

Matt Kasson

Abstract

The co –occurring fungal species Neonectria ditissima and Neonectria faginata are major canker-forming pathogens in the beech bark disease (BBD) systems which has caused restructuring of forests throughout northeastern North America. The role of nutrients in structuring microbial community interactions has been studied in BBD forests stands but has yet to be fully understood and examined under specific in-vitro conditions. This study aimed to investigate how nitrogen, phosphorus, and temperature levels influence the growth, reproduction, and competitive hierarchies between N. ditissima and N. faginata. We performed in-vitro assays where species were first individually and then jointly grown under different concentrations of N and P. Additionally, we performed mating type crossings to evaluate perithecia production. The results revealed that nitrogen concentration had a significant negative effect on the growth rate of both species, while phosphorus concentration did not exhibit a significant effect on the individual growth. N. ditissima’s growth rate was faster than N. faginata’s across treatments in the individual assays. However, neither of the isolates tested produced perithecia in culture suggesting that the nutrient and temperature conditions tested may not be optimal for sexual reproduction and that both species prioritize growth over reproduction under these conditions. In the context of mycelial interactions, N. ditissima displayed a competitive advantage over N. faginata, occupying a larger proportion of the plate and exhibiting greater growth across all nutrient and temperature combinations. However, the absence of overgrowth (covering of the fungal colony) by either species prevented a conclusive determination of competitive advantage. Additionally, phosphorus had a significant effect on the outcome of mycelial interactions, suggesting N. faginata may become more efficient at resource utilization when in contact with its congeners. Competitive deadlock defined as mycelial intermingling at the middle of the plate but no clear evidence of inhibition or overgrowth by either species was only seen under a lower temperature, which suggests that this form of niche differentiation allows co-occurrence between these species under colder climates. Our findings suggest that both species may be ecologically equivalent according to nutrition-based in-vitro responses which hints at the fact that neutral dynamics, driven by dispersal and extinction events, may play a crucial role in the co-occurrence and eventual dominance of N. faginata over N. ditissima in the BBD system. Further research is needed to explore the ecological factors contributing to their co-existence across environmental gradients and the long-term effects of nutrient availability and climate on the dominance of N. faginata in the BBD range. Understanding these interactions will aid in the development of effective management strategies to mitigate the impacts of beech bark disease.

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