The influence of temperature and vapour pressure deficit on conidia germination and germ tube production in an Australian Podosphaera xanthii isolate

Abstract Powdery mildew of cucurbits, caused by Podosphaera xanthii , is an economic constraint in cucurbit production worldwide. This study examined the influence temperature and vapour pressure deficit (VPD) on rate conidial germination formation germ tubes Australian P. isolate 12 – 48 h after inoculation. Two experiments were prepared inoculating cucumber, cv. crystal salad, leaf-discs using a spore settling tower. The first experiment incubated inoculated cucumber at eight temperatures between 8 35 °C under saturated (SVP), second compared 18 VPD conditions 0.038 1.797 kPa, six humidity chambers (33% 99% relative humidity) three (22 °C, 25 28 °C). Leaf-discs cleared, stained microscopically inspected for number tubes. optimal was 28ºC SVP, where more than 50% conidia had germinated h, 85% h. Fewer recorded other treatments 17 31 °C. percentage significantly lower when 0.13 2.5 with response to varying approximately 10%, indicating difficulty associating above kPa. Germ tube highest ºC lowest treatment near producing least Germination reduced increased. able produce primary relatively dry conditions, such as 2.53 but these results show infection would be less likely require longer incubation. provides crucial step simulating powdery infections plants may lead model capable providing risk forecasts or fungicide management decision support tools.