Electrolyzed acid water: A clean technology active on fungal vascular pathogens in grapevine nurseries

Phaeomoniella chlamydospora (Pc) and Phaeoacremonium minimum (Pm) are among the main grapevine trunk disease pathogens affecting vines in the nursery. These pathogens can cause infections of the propagation material often appearing as dark wood streaking, and are associated with decline occurrence in young vineyards. The infection may occur during the grafting process, particularly during hydration. Promising preliminary results were obtained in the nursery using electrolyzed acid water (EAW) for the hydration of cuttings; EAW is characterized by low values of pH (2.5), high oxidation reduction potential (ORP>1000) and a certain amount of free chlorine. No differences in absorption kinetics were recorded between EAW and tap water, nor among 1103P, K5BB and SO4 rootstocks. In all combinations no significant additional absorption was observed after 7 h of immersion. In order to assess the characteristics of EAW after the contact with the inner plant tissues ORP and pH were measured from the liquid extracted from rootstocks after immersion in EAW. The values of the liquid, named "weakened" EAW (wEAW) (625-650 mV ORP and 3.1-3.3 pH), were significantly different from the values of both EAW and the liquid extracted after immersion in tap water. When the propagation material was hydrated for 7 h in EAW no significant effect on vegetating growth performance and percentage of certifiable plants was observed for SO4 or 1103P, whereas a reduction in plant vegetative growth was observed in K5BB hydrated vines at 12hr hydration. EAW and wEAW gave no significant reduction of in vitro mycelial growth, whereas a consistent decrease in conidial germination was observed in Pc and Pm. The three-year experiments carried out in the nursery on cuttings inoculated with Pc and hydrated in EAW showed a remarkable reduction of the infection level in the treated plants.