Situation and evolution of sanitary status in chestnut stands

Hypovirulence is currently present and stable in most of the monitored Italian chestnut woods and vegetative recovery of trees is evident everywhere. The effectiveness of hypovirulence is due to the natural spread of normal, intermediate and white strains of Cryphonectria parasitica which may or may not contain dsRNA, but have different levels of virulence. This mixture of isolates enables synergies to exalt host resistance and to improve the spread of dsRNA among pathogen populations, thus overcoming any problems of vegetative incompatibility. The dynamic of ink disease, which has re-appeared in recent years and is very worrying due the severity of the damages, now seems to be more under control. Some foci appear to be exhausted and almost partially recovered, while others are still in slow expansion. For this disease micro site condition and weather behaviour appears to be determining factors even if the spread of more pathogenic lines of the parasite cannot be excluded. Other constraining factors could influence this situation as: years with arid periods in both winter and summer, new virulent lines of the parasite and the effect of massive and persistent attacks of Chinese wasp, Dryochosmus kuryphilus