Effect of hot-water treatments above 50 °C on grapevine viability and survival of Petri disease pathogens

Rootstocks (41 B Mgt., 140 Ruggeri, 161-49 Couderc, 1103 Paulsen and 110 Richter) and scion/rootstock combinations (Bobal/1103 P, Merlot/110 R, Tempranillo/110 R and Tempranillo/161-49 C) were hot-water treated (HWTed) at 50, 51, 52, 53, or 54 °C for three periods: 30, 45 or 60 min. Four groups of 10 cuttings were treated for each temperature and time, and four additional groups of 10 untreated cuttings were prepared as controls. At the end of the growing season, cutting sprouting and shoot weight were evaluated. In a second experiment, healthy cuttings of ‘110 R’ rootstock were vacuum-inoculated with conidial suspensions (106 conidia mL−1) of one isolate of either Phaeomoniella chlamydospora or Phaeoacremonium aleophilum. These cuttings were subjected to the treatments indicated above. Four groups of 10 cuttings were treated for each temperature, time and isolate, with their respective controls. Isolations were made immediately after the treatments and at the end of the growing season, when cutting sprouting and shoot weight were evaluated. Results demonstrated that it is possible to hot-water treat grapevine planting material in Spanish nurseries using protocols with temperatures of up to 50 °C. HWTs at 53 °C are able to eliminate Pa. chlamydospora completely and strongly reduce the re-isolation of Pm. aleophilum from grapevine wood. These findings will contribute to the development of an effective control for Petri disease in grapevine propagating material in Spanish grapevine nurseries.