# Investigating the impact of temperature on growth rate of the root rot fungus, Gymnopus fusipes

## TL;DR

This study determines the optimal temperature for the growth of the root rot fungus Gymnopus fusipes, finding that 25°C is best, and shows no local adaptation among isolates from different regions.

## Contribution

The study provides the first data on G. fusipes growth rates across ecologically relevant temperatures and identifies 25°C as the optimal growth temperature.

## Key findings

- Gymnopus fusipes grows optimally at 25°C, with a UK isolate showing the highest growth rate.
- No local adaptation to temperature tolerance was observed among geographically diverse isolates.
- Growth rates varied significantly across the tested temperature range (4–37°C).

## Abstract

Gymnopus fusipes is an understudied root rot pathogen associated with multiple tree species and is linked to episodes of oak decline across the United Kingdom and Europe. Although the reported distribution of G. fusipes is broad, many observations rely solely on visual identification of fruiting bodies, which can be unreliable, and lack confirmation by molecular and/or isolation data to verify this broad ecological range. Given the paucity of information regarding the true ecological distribution of G. fusipes, it is difficult to predict and model the potential distribution of the species under both current and future climate scenarios. In this study, to determine the growth capabilities of G. fusipes across a range of ecologically relevant temperatures, five geographically diverse isolates of G. fusipes were grown at five different temperatures ranging from 4–37°C, to determine the optimal temperature for G. fusipes growth, and to establish whether geographically diverse isolates exhibit local adaptation to temperature tolerance. Incubation temperature had a significant effect on G. fusipes growth rate, with 25°C representing the optimum (P<0.001). Isolates had differing growth rates at each of the temperatures, with an isolate from the UK having the highest overall growth rate across all five temperatures tested (P<0.001), and at the optimum, increased by a mean value of over 4915 mm2. Local adaptation to temperature tolerance was not found in the isolates tested. These data demonstrate the optimal incubation temperature for future laboratory studies on G. fusipes and provide the first data on the growth rate of this pathogen across ecologically relevant climate ranges that may inform land managers, modellers, and policy makers in predicting the current and potentially future geographical limits of this widespread root rot pathogen.