Temporal susceptibility of grapevine pruning wounds to trunk pathogen infection in South African grapevines
Eutypa lata and Phaeomoniella chlamydospora, as well as several species in Botryosphaeriaceae, Phomopsis and Phaeoacremonium are known trunk pathogens of grapevines, which use pruning wounds as infection portals. Duration of pruning wound susceptibility to some of these pathogens was largely unknown. To address this question, plants of the cv. Chenin Blanc in a vineyard in the Stellenbosch area of South Africa were pruned at two stages, and then spray-inoculated with spore suspensions of E. lata, Pa. chlamydospora, Neofusicoccum australe and Phomopsis viticola directly after pruning, and 1, 2, 3, 7, 10, 14, 17 and 21 days after pruning. Eight months after inoculation, pathogen incidence in the treated wounds was determined by means of isolation from the pith and xylem tissue of treated plants. Lesions observed in these tissues were also measured and recorded. Results indicated that, irrespective of pathogen inoculated, pathogen incidence in the inoculated pruning wounds of both mid- and late winter declined with increasing wound age. The rate of decline was much slower in 2004 compared to 2005; however, wounds remained susceptible for 3 or more weeks after pruning in both years. Late winter wounds were more susceptible to infection than wounds made earlier in the season, while xylem tissue of pruning wounds generally proved more susceptible to all pathogens compared to exposed pith tissue.