Studies on susceptibility of pruning wounds to infection by fungi involved in grapevine wood diseases in Italy

The susceptibility of grapevine annual pruning wounds to Phaeomoniella chlamydospora, Phaeoacremonium aleophilum and Diplodia seriata was investigated over three years (2005–2007) in a 15 year-old vineyard, cv. Sauvignon blanc. Vines were pruned each year in January, February and March and the wounds were inoculated weekly with conidial suspensions, and with sterile water as a control. Penetration of the fungi into the wood was assessed after 4 weeks by plating pieces of host tissue on agar medium. The susceptibility of annual pruning wounds, expressed as the infection percentages of inoculated spurs, varied with both the trial year and the fungus inoculated. Average infection percentages of inoculated spurs in the three years were respectively 14.7, 38.5 and 50.9% for Pa. chlamydospora, 31.7, 32.2 and 49.4% for Pm. aleophilum and 84.2, 43.8 and 40.9% for D. seriata. The period of pruning was significant for the infection percentages of all fungi in 2005, and for D. seriata in 2006. Natural infection of control spurs by Pa. chlamydospora (2, 4.4, and 11.7% of spurs in the three years respectively) and by Pm. Aleophilum (0.3, 1.8, and 6.4%) began when average weekly temperatures stabilized around 10°C, while infection by D. seriata (12.2, 12 and 18.3% in the same period) occurred even below that threshold. Higher infection percentages of both artificially and naturally infected spurs in 2007 were probably due to the higher temperatures recorded in February and March (besides the use of a more efficient selective medium for the isolation of Pa. chlamydospora and Pm. aleophilum). Only artificial infections with D. seriata showed an opposite trend that cannot be explained by the weather data. Infection of one-year-old wood appeared to be an important factor in disease spread. Spurs remained liable to infections with any of the fungi for up to 4 months after pruning, and isolation percentages could be fairly high also in late spring. As a consequence, the planning of pruning does not seem to be an effective means to counteract the wood diseases caused by these fungi.