Correlations among wood colonizing microorganisms, wood discoloration, decay, foliar symptoms and rainfall in vineyards affected by esca proper

Esca has been recently considered as a complex of different diseases, involving several different fungal agents with different types of wood deterioration. This study was carried out on mature esca infected vines, in order to investigate on the microorganisms associated, the relationships between the various types of wood deterioration, the correlation of these types of deterioration, rainfall and temperatures with external symptom expression. Trials were carried out in two vineyards cv. "Sangiovese" and "Trebbiano d'Abruzzo" located in north and central Italian wine-growing areas respectively. The vineyard "Sangiovese" was surveyed for 4 years, all vines for external symptoms; rainfall and temperature data were also recorded. The trunk of about 200 vines with esca foliar symptoms collected from both vineyards was cut longitudinally. The extension and types of wood deterioration, as well as fungi involved, were determined. According to previous studies on pathogen associated to esca, fungi isolated from deteriorated wood generally confirmed the associations decay-Fomitiporia mediterranea and discoloration-Phaeomoniella chlamydospora and/or Phaeoacremonium spp. The trunk of "Sangiovese" vines proved to be very damaged showing wide areas of discoloured and decayed wood, but no correlation could be found between decay and discolouration. The wood of "Trebbiano d'Abruzzo" was affected by the same types of deterioration, but the trunk showed larger portions of healthy wood compared with what occurred in "Sangiovese". In this case a correlation between the extension of decay and discolouration could be hypothesized. Conversely a correlation between types and development of wood deterioration and foliar symptoms appearance was never observed. However, the high incidence of esca detected in 1994 in "Sangiovese" vineyard might be influenced by the amount of rainfall in June-July, compared with what have been recorded in the same period of the previous years. In this study, quali-quantitative deterioration of wood was confirmed not affecting esca external symptom, but an additional indication about the possible role of rainfall in esca symptom expression could be given.