Genetic diversity in populations of the fungi Phaeomoniella chlamydospora and Phaeoacremonium aleophilum on grapevine in France

Isolates of Phaeomoniella chlamydospora ( Phc ) and Phaeoacremonium aleophilum ( Pha ), two haploid, deuteromycetous fungi, were obtained from vines showing symptoms of esca disease in different localities in two French regions, and within a single vineyard in one of these regions. The population genetic structure was determined in both fungi using random amplified polymorphic DNA (RAPD) analysis. Populations of Phc showed similar levels of diversity at local and regional levels. The most frequent Phc haplotypes were found in every population, and the frequencies of positive alleles of markers were similar across populations. The hypothesis that recombination had occurred was rejected for the full set of samples, but not for the samples reduced to haplotypes, indicating that Phc may be a recombining species. Different features were identified in Pha populations. First, the southern population of Pha appeared more diverse than the south-western populations. Second, genetic differentiation was identified between Pha populations from southern and south-western regions for several RAPDs. Finally, in the southern population of Pha no evidence for recombination was obtained, even by reducing the sample to haplotypes. Within the single vineyard surveyed, several haplotypes of both fungi were recovered and randomly distributed. Thus different infection events appeared to have occurred on a low spatial scale. Data from this study showed that haplotypes of both fungi were distributed over long distances geographically, and that most of the vineyards surveyed were infested by more than one haplotype of Phc and Pha .     

Fungi associated with esca disease in grapevine

Cross sections of woody stems of 309 diseased grapevines collected in France showed two kinds of necrosis typical of esca: a) A central light-colored necrosis of soft consistency, consisting of three zones, preceded by a centrally discolored wood, and b) a sectorial light-colored necrosis composed of two zones preceded by a sectorial brown necrosis. Isolations showed that different microflora was associated with each necrosis. Phaeoacremonium aleophilum and Phaeoacremonium chlamydosporum occurred in the discolored wood and the zones bordering the central decayed wood. Eutypa lata was the main fungus isolated from sectorial brown necrosis and the zones adjoining the decay wood. Phellinus punctatus was isolated from the sectorial and central decayed wood. Stereum hirsutum was present in decayed wood of 15 grapevines with esca symptoms not inhabited by P. punctatus. Wood decay tests and pathogenicity tests showed that S. hirsutum and P. punctatus were responsible for the decayed wood. Phaeoacremonium chlamydosporum and S. hirsutum produced a centrally discolored wood similar to that found in esca-affected vines. Phaeoacremonium aleophilum caused a sectorial brown necrosis of soft texture. From these studies, it was found that esca is a complex disease involving several microorganisms whose role in the process leading to wood degradation is discussed.     

Applicability of rep-PCR genomic fingerprinting to molecular discrimination of members of the genera Phaeoacremonium and Phaeomoniella

This study examined the applicability of rep-PCR genomic fingerprinting to molecular typing of Phaeoacremonium and Phaeomoniella species found on grapevines and associated with the esca syndrome. Fingerprints obtained by rep-PCR were compared with those obtained by microsatellite-primed PCR. The rep-PCR patterns clearly separated the species, and in some cases revealed intraspecific variability. Dendrograms revealed a clear genetic distance between Phaeomoniella chlamydospora and the three Phaeoacremonium species analysed. The results demonstrate that rep-PCR can be a complementary or alternative strategy to other molecular methods as a tool for identification of species and strains of these two genera.     

Genetic structure of the grapevine fungal pathogen Phaeomoniella chlamydospora in southeastern Australia and southern France

In this study, 18 microsatellite loci were used to examine the genetic structure and mode of reproduction of Phaeomoniella chlamydospora, the fungus that causes Petri disease of grapevine and is involved in another grapevine disease, esca. A total of 60 southeastern Australian isolates were tested and compared with 64 isolates from southern France. The French population possessed relatively high genotypic diversity (G = 29·2) whilst the Australian population showed low genotypic diversity (G = 11·1), consistent with a limited founder population. Haplotypes from four different grapevine cultivars were not significantly differentiated (Φpt values effectively zero). Likewise, genetic differentiation of haplotypes from different regions within each country was not significant, although small but significant genetic differentiation (9%) was identified between Australia and France. Based on bootstrapped cluster analysis, there did not appear to be any genetic groups within the overall sample of isolates. Significant linkage disequilibrium identified in both countries, together with overrepresented, widespread identical haplotypes, indicated limited genetic recombination and a largely clonal structure consistent with the absence of an observed sexual cycle in this species.     

Grapevine trunk diseases: complex and still poorly understood

This review presents an overview of eutypa dieback, esca and botryosphaeria dieback, the predominant grapevine trunk diseases worldwide. It covers their symptomatologies in the trunk, leaves and berries; the characteristics of the different fungal species associated with them; and host–pathogen interactions. Here, the host–pathogen relationship is defined at the cytological, physiological and molecular levels. Currently available experimental tools for studying these diseases, both in vitro and in the field, are discussed. Finally, a progress report on their control, which, since the ban of sodium arsenite, comprises chemical, biological and/or sanitation methods, is presented.