Mycosystema. 2010, 29(5): 636-643.
The pathogen causing hull-less pumpkin (Cucurbita moschata) powdery mildew in Wuwei District of Gansu Province was identified as Podosphaera xanthii based on the morphology of cleistothecia and conidia, conidial germination and host range, etc. The results show that the optimum temperature, relative humidity and illumination for formation of cleistothecia on hull-less pumpkin were 20℃, 70% and 4,400lx, respectively. The host range test shows that the pathogen could infect many species of Cucurbitaceae except Luffa cylindrical. Triticum aestivum, Capsicum annuum, Lycopersicon esculentum, Trifolium repens, Medicago sativa, Phaseolus vulgaris (‘Jiadouwang’) and Phaseolus vulgaris couldn’t be infected. The pathogen could also attack Phaseolus radiatus, Vigna angularis and Helianthus annuus. The most susceptible plants were Cucurbita moschata, Phaseolus radiaus, Cucurbita pepo, Vigna angularis, Helianthus annuus, Cucumis melo and Cucumis sativus, their disease incidence rates reached 100%, and the disease index were 15.56, 14.51, 13.33, 13.33, 13.07, 12.22 and 12.22 respectively in 15 days after inoculation. The infection process was observed. The results indicate that the conidia germinate from the lateral sides in 12 hours after inoculation, and then form hyphae in 24 hours. The hypha extended and formed net-like mycelia in 36 hours and 72 hours, and finally produced conidiophores and chains of conidia in 96 hours.
