Infection of rootstock mother-vines by Phaeomoniella chlamydospora results in infected young grapevines

The use of cutting material infected with Phaeomoniella chlamydospora is believed to contribute to Petri disease. Infection levels of own-rooted scion, own-rooted rootstock and grafted vines were compared in a 20-month field trial. In own-rooted rootstock and grafted vines, infection increased over time (53% and 20%, respectively, at the 20-month assessment). Infection was not observed in own-rooted scion until the 20-month assessment (22%). It was concluded that rootstock mother-vines are a primary source of the pathogen. The ability of the pathogen to move from the retained rootstock mother-vine trunk or head, into current season's growthwas investigated by determining disease levels in own-rooted rootstock vines propagated from cuttings collected at different distances from the head. Vines from dormant cuttings collected nearest the head had a higher level of infection at the 8-month assessment (42%) than those collected from further away (6-8%). At the 20-month assessment, infection in vines from close to the head and vines from actively growing cuttings collected furthest from the head were similar (53 and 55%, respectively). Black streaking, a commonly used disease assessment criterion, was found to overestimate disease. Possible sources of inoculum and disease management options for nurseries are discussed.