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

A full understanding of the pathology of esca, a chronic disease of grapevi nes, has been problematic, in part because the identity of the pathogen (or pathogens) has been difficult to determine. The wood decay symptoms of esc a have been most often associated with Phellinus igniarius or Fomitiporia p unctata. However, Koch's postulates have not been completely fulfilled beca use symptoms take many years to develop. The goal of this study was to dete rmine the identity and mode of spread of basidiomycetes associated with woo d decay in vines showing esca symptoms in Italian vineyards. Vineyards were intensively studied for the presence of basidiocarps, and mycelium was iso lated from symptomatic vines. Fruiting bodies were identified by morphology , while mycelial isolates were identified by restriction fragment length po lymorphism analysis of the internal transcribed spacer region of the nuclea r ribosomal RNA gene cluster. Fomitiporia punctata fruiting bodies and myce lium were associated with approximately 50% of the vines showing esca sympt oms in two vineyards; P. igniarius was not found in any samples. Fruiting b odies of F. punctata were found in five of six vineyards examined, but at l ow frequencies except in one vineyard. The diversity of somatic incompatibi lity types was very high; isolates from almost every vine had different som atic incompatibility types. With few exceptions, symptomatic and dead vines were not spatially aggregated within 12 vineyards. The combination of dive rse 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 associate d with wood decay of vines with esca symptoms is important for understandin g the epidemiology of this disease because F. punctata is found commonly on many woody hosts in Europe, which may represent a potential inoculum sourc e for this disease.