Abstract
To predict the response of plant pathogens to climate warming, data are needed on current thermal adaptation, the pathogen's evolutionary potential, and the link between them. We conducted a common garden experiment using isolates of the fungal pathogen Rhynchosporium commune from nine barley populations representing climatically diverse locations. Clonal replicates of 126 genetically distinct isolates were assessed for their growth rate at 12°C, 18°C, and 22°C. Populations originating from climates with higher monthly temperature variation had higher growth rate at all three temperatures compared with populations from climates with less temperature fluctuation. Population differentiation in growth rate (QST) was significantly higher at 22°C than population differentiation for neutral microsatellite loci (GST), consistent with local adaptation for growth at higher temperatures. At 18°C, we found evidence for stabilizing selection for growth rate as QST was significantly lower than GST. Heritability of growth rate under the three temperatures was substantial in all populations (0.58–0.76). Genetic variation was lower in populations with higher growth rate at the three temperatures and evolvability increased under heat stress in seven of nine populations. Our findings imply that the distribution of this pathogen is unlikely to be genetically limited under climate warming, due to its high genetic variation and plasticity for thermal tolerance.
Highlights
There is an ample evidence that climate warming affects the distribution of species (Parmesan 2006)
Hemibiotrophic fungal pathogens of annual crops such as R. commune provide excellent model systems for the study of thermal adaptation because they are found in agro-ecosystems that are globally distributed across a wide range of climates
The lower two experimental temperatures of 12°C and 18°C led to significantly higher growth rate compared with 22°C, which was considered stressful for the pathogen
Summary
There is an ample evidence that climate warming affects the distribution of species (Parmesan 2006). The likely reason is that distributions are often strongly affected by the breadth of tolerance for temperature (e.g., for animals: Andrewartha and Birch 1954; for plants: Woodward and Williams 1987). Thermal performance may not be fixed within species but may vary among populations due to adaptation to prevailing local conditions (Huey and Kingsolver 1989; Angilletta et al 2002). Divergent thermal performance in relation to climate heterogeneity within current species distributions may provide insight into past temperature adaptation. Assessing genetic diversity parameters can reveal whether local populations will be able to track future changes in temperature, even in the absence of gene flow. The parallel study of both local adaptation and genetic variation within populations should reveal the potential of populations to adapt to changing temperatures
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