Population Genetics of Fungi Associated with Esca Disease in French Vineyards

Abstract

Among the fungi isolated from vines showing symptoms of esca disease, the ascomycetes Eutypa lata (Ela), and the hyphomycetes Phaeoacremonium chlamydosporum (Pch) and P. aleophilum (Pal) appear to precede the activity of the decay fungus, Fomitiporia punctata (Fop) which seems to come at the end of the wood degradation process. We carried out studies on the population genetics of these fungi in order to gain more insight into their mode of propagation and life history as well as on their ability to evolve in response to control practices. Random Amplification Polymorphic DNA (RAPD) markers were used to study the genetic relationships among isolates at different geographic levels. Particular attention was given to the diversity existing at vineyard level. Diversity was also studied at regional level and supraregionally among populations from different regions. Ela isolates from single vineyards were all of different haplotypes and there was no gametic disequilibrium between RAPD markers. These findings strongly suggested that the population structure of the heterothallic Ela is shaped by random mating, being spread only by its ascospores. This population structure was also found at the regional scale with no genetic differentiation among Ela populations from different French regions. In Fop populations, an exclusive spread by basidiospores seemed to occur and genetic differentiation was very weak. RAPD markers were more difficult to detect for Phaeoacremonium species, indicating they had less polymorphism than Ela and Fop. Several different haplotypes of Pch and Pal were found at vineyard level, suggesting several outside sources for the primary inoculum. Populations of Pch and Pal from different regions appeared weakly differentiated. These results indicate that French viticultural regions have to be considered as unique epidemiological unit when considering control measures.