Temporal changes in pathogen diversity in a perennial plant-pathogen-hyperparasite system.

Area of Science:

• Population genetics
• Mycology
• Plant pathology
• Evolutionary biology

Background:

• Hyperparasites influence pathogen and host population dynamics, impacting pathosystem evolution.
• The evolution of perennial host pathogens under hyperparasite pressure is understudied.
• Cryphonectria hypovirus 1 (CHV1) is a mycovirus that reduces the virulence of the chestnut blight pathogen, Cryphonectria parasitica, acting as a biocontrol agent in Europe.

Purpose of the Study:

• To investigate temporal changes in the genetic diversity of Cryphonectria parasitica.
• To assess the prevalence of Cryphonectria hypovirus 1 (CHV1) in C. parasitica populations over time.
• To understand the long-term impact of CHV1 on the pathogen's genetic structure and diversity.

Main Methods:

• Analysis of genome-wide diversity in C. parasitica populations sampled approximately 30 years apart in southern Switzerland.
• Assessment of CHV1 prevalence in the sampled pathogen populations.
• Identification of selection signals at vegetative incompatibility (vic) loci.

Main Results:

• Pathogen population structure and CHV1 prevalence remained stable over the 30-year study period.
• Evidence of recent population bottlenecks influencing C. parasitica structure was observed.
• Strong balancing selection signals at a vic locus, indicative of negative frequency-dependent selection, were detected.

Conclusions:

• CHV1 prevalence and C. parasitica population structure are stable over decadal timescales.
• Inbreeding and genetic drift likely contribute to low vic type diversity.
• The efficacy of CHV1-mediated biocontrol against chestnut blight is likely maintained due to stable virus infection rates and pathogen diversity.