Effect of temperature on the development of fruiting bodies of Phaeoacremonium minimum and Phaeomoniella chlamydospora on grapevine cuttings in vitro, and survival of both pathogens in vineyards.

In this study, isolates of Phaeoacremonium minimum and Phaeomoniella chlamydospora, fungal pathogens associated with Petri and esca diseases of grapevine, were used to determine the effect of temperature on the development of their fruiting bodies in vitro. Perithecia of Pm. minimum and pycnidia of Pa. chlamydospora were induced at 5, 10, 15, 20, 25 and 30ºC on pieces of 1-year-old grapevine cuttings of 110 Richter rootstock, which were incubated for 45 days under continuous white light. Both species were able to produce abundant fruiting bodies at temperatures ranging from 15 to 25ºC, but Pm. minimum produced more perithecia at 25ºC and Pm. chlamydospora produced more pycnidia at 20ºC. At 30ºC, only very few reproductive structures were observed. Calculated optimal temperatures ranged from 23.3ºC to 25.6ºC, and equations providing a proper description of temperature effect on Pm. minimum and Pa. chlamydospora fruiting bodies development were obtained. Moreover, the development of fruiting bodies and the survival of both pathogens on artificially inoculated grapevine cuttings was investigated in two vineyards. No fruiting bodies were observed during the vineyard experiments, but both fungal species were systematically recovered by fungal isolation from the cuttings. Differences in pathogen survival based on incidence data were observed relative to the species, location and time of exposure, and generalized linear-mixed models analysis showed a progressive reduction of inoculum viability with time. The present research increases our knowledge about the biology and epidemiology of Pm. minimum and Pa. chlamydospora, being particularly useful to improve epidemiological models that could be developed for Petri and esca diseases prediction.