Reduced Virulence of an Introduced Forest Pathogen over 50 Years.

Bradshaw Bradshaw,Ormond Ormond,Bulman Bulman,Mcdougal Mcdougal,Chettri Chettri,Ozturk Ozturk,Cox Cox,Dupont Dupont

doi:10.3390/microorganisms7100420

Bradshaw Bradshaw, Ormond Ormond + Show 6 more

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https://doi.org/10.3390/microorganisms7100420

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Abstract

Pathogen incursions are a major impediment for global forest health. How pathogens and forest trees coexist over time, without pathogens simply killing their long-lived hosts, is a critical but unanswered question. The Dothistroma Needle Blight pathogen Dothistroma septosporum was introduced into New Zealand in the 1960s and remains a low-diversity, asexual population, providing a unique opportunity to analyze the evolution of a forest pathogen. Isolates of D. septosporum collected from commercial pine forests over 50 years were compared at whole-genome and phenotype levels. Limited genome diversity and increased diversification among recent isolates support the premise of a single introduction event. Isolates from the 1960s show significantly elevated virulence against Pinus radiata seedlings and produce higher levels of the virulence factor dothistromin compared to isolates collected in the 1990s and 2000s. However, later isolates have no increased tolerance to copper, used in fungicide treatments of infested forests and traditionally assumed to be a strong selection pressure. The isolated New Zealand population of this forest pathogen therefore appears to have become less virulent over time, likely in part to maintain the viability of its long-lived host. This finding has broad implications for forest health and highlights the benefits of long-term pathogen surveys.

Highlights

Healthy forests are critically important for the health of the planet
Using a retrospective approach with historical samples of D. septosporum collected from New Zealand forests over a period of nearly 50 years, we explored whether genomic data support the hypothesis that a single genotype of D. septosporum was introduced into New Zealand
Single nucleotide polymorphism (SNP) variants were determined for each of the isolate genomes compared to the D. septosporum NZE10 reference genome

Summary

Introduction

Healthy forests are critically important for the health of the planet. People depend on trees for provision of food, construction materials, and landscaping. Sequestration of carbon by forest trees is vital for mitigating climate change [1,2]. Over their long lives, forest trees have to contend with many biotic and abiotic challenges that threaten their health. In the last two decades, forest disease epidemics have become more frequent and anthropogenic impacts, including climate change, have been implicated in these outbreaks [3,4,5,6,7]. The increase in global trade has facilitated the spread of pathogens into new locations, while changing land-use practices and intensive commercial forestry regimes have impacted on the severity of diseases and even awakened latent pathogens [8,9]

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