Identification and spread of Fomitiporia punctata associated with wood decay of grapevine showing symptoms of Esca disease

ABSTRACT A full understanding of the pathology of esca, a chronic disease of grapevines, has been problematic, in part because the identity of the pathogen (or pathogens) has been difficult to determine. The wood decay symptoms of esca have been most often associated with Phellinus igniarius or Fomitiporia punctata. However, Koch's postulates have not been completely fulfilled because symptoms take many years to develop. The goal of this study was to determine the identity and mode of spread of basidiomycetes associated with wood decay in vines showing esca symptoms in Italian vineyards. Vineyards were intensively studied for the presence of basidiocarps, and mycelium was isolated from symptomatic vines. Fruiting bodies were identified by morphology, while mycelial isolates were identified by restriction fragment length polymorphism analysis of the internal transcribed spacer region of the nuclear ribosomal RNA gene cluster. Fomitiporia punctata fruiting bodies and mycelium were associated with approximately 50% of the vines showing esca symptoms in two vineyards; P. igniarius was not found in any samples. Fruiting bodies of F. punctata were found in five of six vineyards examined, but at low frequencies except in one vineyard. The diversity of somatic incompatibility types was very high; isolates from almost every vine had different somatic incompatibility types. With few exceptions, symptomatic and dead vines were not spatially aggregated within 12 vineyards. The combination of diverse somatic incompatibility types and lack of spatial aggregations are not consistent with the hypothesis that the disease is spread clonally through roots or by pruning tools. The correct identity of basidiomycetes associated with wood decay of vines with esca symptoms is important for understanding the epidemiology of this disease because F. punctata is found commonly on many woody hosts in Europe, which may represent a potential inoculum source for this disease.