We examined the genetic relatedness of isolates of Phaeomoniella chlamydospora, which is one of the most aggressive and common causal fungi of the trunk disease Esca (aka Measles). This same pathogen causes Petri disease (aka Young Vine Decline), which affects young vines, whereas Esca affects mature vines. It is important to know if isolates of the pathogen from different vineyards in different states represent one or a few clones, or if each isolate is a different genotype. Such patterns reflect the type of spore, asexual (conidia) or sexual (ascospores), respectively, by which the pathogen spreads. Different spore types have different capacities for dispersal, different consequences for fungicide resistance, and so knowing the spore type can inform disease management guidelines. The pathogen is presumably asexual. This is in part because no one has found the fruiting bodies that produce ascospores (perithecia); the fungus produces only conidia in culture. As such, Esca is thought to be spread by conidia. We used a population genetics approach to evaluate genetic relatedness of populations from California (58 isolates), British Columbia (12 isolates), and the northeastern US (26 isolates). Isolates were genotyped with 18 microsatellite markers. We performed a genetic clustering analysis based on their genetic similarity. Genetic diversity indices were computed for each cluster of isolates. Genetic differentiation among clusters was also estimated. Three genetic clusters were identified, with two clusters consisting of isolates from British Columbia and California, and the 3rd cluster of isolates from the northeastern US. All isolates had a different genotype, suggesting that the pathogen spreads by sexual spores. High genetic subdivision (Fst = 0.28; P < 0.001) suggests that genetic and/or ecological factors may maintain genetic differentiation among these three groups. Our findings indicate a ‘hotspot’ of genetic diversity in the northeastern US, which could correspond to a center of origin of the pathogen. Genetic diversity indices were also higher than in a previous study using the same set of microsatellite markers to compare European and Australian isolates. If the northeastern US is a center of origin of the pathogen, sources of disease resistance may be present in native Vitis species. Sexual reproduction may occur on hosts other than grapevine; this could explain the absence of perithecia from vineyards.
/wp-content/uploads/2017/09/AFV-Header-Logo.png 0 0 AVF /wp-content/uploads/2017/09/AFV-Header-Logo.png AVF2012-10-15 13:05:122017-10-15 13:06:37Esca and Petri Disease: Identifying Sources of Vineyard Infections