GENETIC VARIATION IN A FUNGAL PATHOGEN: RESPONSE TO HOST DEFENSIVE CHEMICALS

Area of Science:

• Plant pathology
• Chemical ecology
• Evolutionary biology

Background:

• Scots pine (Pinus sylvestris) defends against pathogens by releasing cortical resin.
• This resin contains a variable mixture of monoterpenes, creating a chemically diverse environment for pathogens.
• Pathogen populations may evolve in response to this chemical heterogeneity.

Purpose of the Study:

• To investigate the evolutionary response of the canker pathogen Crumenulopsis sororia to the chemically diverse monoterpene environment of Scots pine.
• To determine if monoterpene variability in Scots pine leads to disruptive selection on pathogen populations.

Main Methods:

• Collected isolates of Crumenulopsis sororia from natural Scots pine populations.
• Measured isolate growth rates with and without five host monoterpenes.
• Assessed heritable variation in growth rate and monoterpene tolerance.

Main Results:

• Substantial heritable variation in growth rate and monoterpene tolerance was observed in Crumenulopsis sororia isolates.
• No significant genetic trade-offs were found between growth rates in different monoterpene environments or tolerance levels.
• Positive or non-significant genetic correlations suggest limited potential for disruptive selection driven solely by monoterpene variability.

Conclusions:

• While Scots pine exhibits chemical diversity, this variability alone may not drive the evolution of specialized pathogen subpopulations.
• The absence of trade-offs suggests that pathogens can adapt to multiple monoterpene profiles without significant fitness costs.
• Understanding the interplay between plant chemical defenses and pathogen evolution is crucial for predicting forest pest resistance.