Genetic structure of Italian population of the grapevine downy mildew agent, Plasmopara viticola

Abstract

Downy mildew, caused by the Oomycete Plasmopara viticola, is one of the most important diseases affecting the Eurasian grapevine, Vitis vinifera. The pathogen originated in Northern America and its presence was signalled for the first time into Europe in 1878. In this study, the genetic variability and structure of Italian P. viticola population was investigated by genotyping 106 P. viticola strains belonging to 12 different regions, at 31 microsatellite markers. As a result of the high percentage of missing data, 96 strains and 19 loci were retained for the data analysis. The overall Italian population presents absence of clones, evidence of sexual and asexual reproduction and a low genetic diversity, as expected for an introduced pathogen, but a slightly higher genetic diversity than that found in other European populations, based on allelic diversity at the investigated microsatellite loci. Out of 19 loci, half shows deviation from Hardy-Weinberg equilibrium and, indeed, structure analysis indicates the presence of two separate genetic clusters, with little but significantly different distribution according to geography (west-east gradient) and climatic conditions.

The Climate-Driven Genetic Diversity Has a Higher Impact on the Population Structure of Plasmopara viticola Than the Production System or QoI Fungicide Sensitivity in Subtropical Brazil

“…The recombination through sexual reproduction, as suggested by our results, may allow P. viticola to adapt quickly to environmental changes and management practices including fungicides and resistant cultivars (McDonald and Linde, 2002;Milgroom, 2015). In Europe, P. viticola populations are also panmictic and admixed from two genetically distinct clusters (Fontaine et al, 2013;Maddalena et al, 2020) and a rapid adaptation to different fungicide groups (Blum et al, 2010;Delmas et al, 2017;Fontaine et al, 2019) and to resistant cultivars (Peressotti et al, 2010) has been reported. Although other two different genetic pools were observed in the São Paulo populations, no admixed genotype was detected, which is consistent with lack of recombination inferred from the reproductive mode analysis.…”

Europe as a bridgehead in the worldwide invasion history of grapevine downy mildew, Plasmopara viticola

“…are found on wild Vitis species across North America (33,34), and it remains unknown which lineages were responsible for grapevine downy mildew invasions in vineyards across the world. In most temperate regions, P. viticola populations present widespread footprints of recombination, indicating the occurrence of frequent sexual reproduction (21,24,26,27,29,31,36). European invasive populations display little genetic diversity and have a weak but significant population structure at the continental scale (22,25).…”

Rpv29, Rpv30 and Rpv31: Three Novel Genomic Loci Associated With Resistance to Plasmopara viticola in Vitis vinifera

“…To maximize the genetic variability of the pathogen and allow the detection of accessions that were resistant to a wide range of pathogen strains, field populations of P. viticola were used for the experimental inoculations ( Toffolatti et al, 2016 ). Recent studies demonstrated that the European and Italian P. viticola population is divided in two genetic clusters, separated over an east-west gradient ( Fontaine et al, 2013 ; Maddalena et al, 2020 ). In this study, east and west populations of P. viticola coming from Italy, at S. Maria della Versa (Pavia; East population) and Casarsa della Delizia (Pordenone; West population), and Georgia (West), were mixed to perform experimental inoculations.…”

“…P. viticola was introduced into France from North America during the XIX century together with American wild Vitis species and rapidly spread across Europe dividing into two genetically distinct groups ( Fontaine et al, 2013 ; Maddalena et al, 2020 ). Structure analysis indicated that the European and Italian P. viticola populations is formed by two separate genetic clusters, distributed according to a geographical gradient (East-West) and climatic conditions ( Fontaine et al, 2013 ; Maddalena et al, 2020 ). P. viticola is a polycyclic pathogen able to biotrophically grow on tissues (leaves, shoots, and clusters) of susceptible Vitis species and, particularly, V. vinifera .…”