Sensitivity of Petri disease pathogens to hot-water treatments in vitro.

Petri disease pathogens ( Phaeoacremonium spp. and Phaeomoniella chlamydospora) are able to colonize the vessels in the xylem of grapevine propagating material. Hot-water treatment (HWT) protocols at 50°C for 30 min have been applied in grapevine nurseries to control these pathogens with variable results. The effect of HWT in vitro at higher temperatures on Pa. chlamydospora, Phaeoacremonium aleophilum and Phaeoacremonium parasiticum isolates was determined by placing conidial suspensions and plugs of agar with mycelia in Eppendorf vials and incubated in hot water at 49, 50, 51, 52, 53 or 54°C for 30, 45 or 60 min. Conidial germination and the colony growth rate decreased with increased temperature and time combinations. Pa. chlamydospora was more sensitive than Phaeoacremonium spp. to the experimental temperatures for all periods of time. Pa. chlamydospora tolerated temperatures of 53°C, while Pm. aleophilum and Pm. parasiticum tolerated temperatures of 54°C, although the treatments above 51–52°C drastically reduced conidial germination and mycelial growth. These results highlight the need to develop HWT using temperatures above 51°C to reduce the incidence of fungal infections and ensure high-quality propagating material for grapevine growers. [ABSTRACT FROM AUTHOR]