Occurrence of grapevine trunk disease pathogens in rootstock mother plants in South Africa
The incidence of grapevine trunk disease pathogens in grapevine rootstock mother plants from different cultivars, ages and growing areas in South Africa was determined by means of isolations from the basal and pruning wound ends of 2-year-old stubs. Phaeoacremonium spp. and Cylindrocarpon spp. occurred at very low incidences (average 0.12% and 0.17%, respectively). Phaeomoniella chlamydospora was most frequently isolated and significantly more from cvv. 101-14 Mgt and Ramsey than cvv. 99 Richter and 110 Richter mother plants. It was not evident whether Pa. chlamydospora invaded the mother plants via pruning wounds. However, it appeared as if Botryosphaeria and Phomopsis species invaded rootstock mother plants through unprotected pruning wounds. Results from this survey suggest the presence of latent infections of trunk disease pathogens in rootstock mother plants and highlight the need for pruning wound protection to prevent these infections.