Activity of electrolyzed acid water for the control of trunk disease pathogens of grapevine in the nursery.

Phaeomoniella chlamydospora (Pch) and Phaeoacremonium minimum (Pmi) are among the main grapevine trunk disease pathogens in the nursery. These pathogens can cause latent 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 additional absorption was observed after 7 hours 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 had been hydrated for 7 hr in EAW no significant effect on vegetating growth performance and percentage of No. 1 quality plants was ever observed for SO4 or 1103P, whereas a reduction in both vegetative growth and No. 1 quality plants was observed in K5BB rehydrated 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 Pch and Pmi. The three-year experiments carried out in the nursery on cuttings inoculated with Pch and re-hydrated in EAW showed a remarkable reduction of the infection level in the treated plants.