NURSERY PRACTICES INFLUENCE PHAEOMONIELLA CHLAMYDOSPORA INFECTIONS IN GRAPEVINE GRAFTED ROOTSTOCKS

Phaeomoniella chlamydospora (W. Gams, Crous, M.J. Wingf. et L. Mugnai) Crous et Gams, involved in brown streaking of rootstocks, Petri and esca disease of grapevine, is frequently detected in one-year-old vines. The presence of the fungus as environmental contaminant in nurseries was ascertained with several investigations, while it remains unclear in which way the fungus infects rootstocks. This study was aimed at evaluating the influence of several steps of the routine process for producing grafted rootstocks on P. chlamydospora infection. Specific actions were taken singularly or in combination, i.e. sterile water was used in pre-grafting or pre-callusing hydration, blades of grafting machines were cleaned with 4% sodium hypochlorite solution, and decontaminated soil was used to plant grafted-cuttings. At root-stock uprooting, nucleic acids were extracted from wood fragments from the crown and graft union of at least 150 rootstocks per treatment, and nested-PCR was used for P. chlamydospora detection. In combination, the above-cited actions lead to a significant (P = 0.05) reduction (57%) of infection frequency as compared with the normal nursery practice. The decrease of infection frequency due to single actions ranged from 8% (decontamination of grafting machines) to 62% (hydration of grafts and cuttings in sterile water). Such findings suggest that each investigated step can contribute significantly to P. chlamydospora infection of grafted rootstocks. Further studies are in progress for establishing the weight of each step on rootstock infection by P. chlamydospora to prevent spreading of the pathogen to new vineyards.