Abstract:

Kushen （Sophora flavescens） is an important traditional Chinese medicinal herb and a source of botanical pesticides in China. Due to the increasing depletion of wild kushen caused by human harvesting， cultivation of this plant has become imperative. However， powdery mildew， the most severe disease affecting cultivated kushen in Lanzhou， causes leaf fall and has become a major limiting factor in its cultivation. The origin of the powdery mildew pathogen affecting kushen-whether it originates from surrounding plants or has been introduced from outside the region-remains unclear， hindering the development of effective control strategies. To address this issue， this study investigated the occurrence of powdery mildew on all cultivated plants in the kushen growing environment. The symptoms， pathogens， and mycoparasites of the various powdery mildews were compared. The results revealed that the pathogen causing powdery mildew on kushen differs from those affecting eight other surrounding plants， confirming that the source of the kushen powdery mildew is not local but introduced from outside the region. Although the anamorphic stage of the kushen powdery mildew pathogen， like those of white clover （Trifolium repens）， standing milk-vetch （Astragalus adsurgens）， cowpea （Vigna unguiculata）， and dandelion （Taraxacum mongolicum）， belongs to the genus Oidium， differences were observed in the size and shape of the conidia. The kushen powdery mildew pathogen did not produce a teleomorph， whereas the pathogens of the other four plants did. The teleomorph of the white clover andstanding milk-vetch powdery mildew pathogens was identified as Erysiphe pisi， that of cowpea as Erysiphe polygoni， and that of dandelion as Sphaerotheca fusca. In contrast， the anamorphic stage of the kushen powdery mildew pathogen was distinctly different from those of pepper， tomato， tree-of-heaven （Ailanthus altissima）， and field bindweed （Convolvulus arvensis）. The anamorph of the pepper （Capsicum annuum） and tomato （Lycopersicon esculentum） powdery mildew pathogens was Oidiopsis taurica， with Leveillula taurica as the teleomorph. The anamorph of the tree-of-heaven powdery mildew pathogen was an Ovulariopsis sp.， with Phyllactinia corylea as the teleomorph. The anamorph of the field bindweed powdery mildew pathogen produced a teleomorph identified as Erysiphe convolvuli var. dichotoma. All nine powdery mildews were found to be parasitized by mycoparasites， with no differences in the species identified-all were Ampelomyces quisqualis. This study is the first to report kushen powdery mildew as a new host for A. quisqualis.

Key words: Sophora flavescens, radix sophora alkaloids, botanical insecticide, powdery mildew, hyperparasite fungus