Multiple introductions and recombination in Cryphonectria hypovirus 1: perspective for a sustainable biological control of chestnut blight.

Nicolas Feau,Cyril Dutech,Daniel Rigling,Cécile Robin,Jérémie Brusini

doi:10.1111/eva.12157

Abstract

Cryphonectria hypovirus 1 (CHV1) is a mycovirus which decreases the virulence of its fungal host Cryphonectria parasitica, the causal agent of chestnut blight recently introduced in Europe. The understanding of the evolutionary processes which have shaped CHV1 populations in Europe is required to develop a sustainable biocontrol strategy targeting chestnut blight and effective in European chestnut forests. To retrace the evolutionary history of CHV1, we analyzed sequences from two genomic regions on a collection of 55 CHV1 strains from France and northern Spain, two countries where multiple introductions of C. parasitica occurred. Several recombination events and variable selection pressures contributed to CHV1 evolution, agreeing with a non-clock-like diversification rate. These two mechanisms may be at the origin of CHV1 population diversity observed in western Europe. Considering the actual prevalence of CHV1 and its association with host genotypes, multiple introductions of CHV1 may have occurred in Europe, some of them directly from Asia and some of them through North America. Although some viral strains remained with low frequency in their introduction area, multiple infections might have allowed homologous recombination within parental sequences. Some of these recombinant lineages are associated with the spread of CHV1 in European regions.

Highlights

There is growing evidence that global change could boost chronic impacts of plant pathogens, for example through climate warming that releases constraints on their development or through transport of exotic species (Pautasso et al 2012)
Lineages A1-B1, A2-B1 and A3-B3 correspond, respectively, to the subtypes F1, F2 and I, which were previously defined by a RFLP approach and open reading frames (ORFs) A sequencing (Alleman et al, 1999; Gobbin et al 2003)
Our finding of one fungal isolate infected by two different viral lineages provides evidence that such multiple infections in C. parasitica may occur in populations where different viral lineages coexist

Summary

Introduction

There is growing evidence that global change could boost chronic impacts of plant pathogens, for example through climate warming that releases constraints on their development or through transport of exotic species (Pautasso et al 2012). This prediction tends to be confirmed in forests where several new tree diseases emerged during the two last decades. Mycoviruses, which decrease fungal virulence, are seen as promising agents to mitigate fungal tree diseases Such viruses, infecting and replicating in pathogenic fungi, are causing a fungal debilitation which results in an overall decrease in reproduction rates and/or vegetative growth, and are, beneficial to the host plant (Pearson et al 2009). The use of mycoviruses as biological control agents requires an understanding of their ecology and evolution (Roderick et al 2012)

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