Host plants of the powdery mildew fungus Podosphaera xanthii in Taiwan

Abstract

Podosphaera xanthii is presently considered as one of the powdery mildew fungi with the broadest host range. Confusion is caused by taxonomical and nomenclatural changes of the host plants and the fungal parasite. Based on the list of powdery mildews from Taiwan from 1998, an updated list of host plants of P. xanthii in this country is presented. New hosts from Taiwan are wild and horticultural herbs and woody plants collected between 2011 and 2020. Fifteen plant species were found to be the host of P. xanthii based on new collections of the anamorph and internal transcribed spacer (ITS) sequences. Among them, Cuphea carthagenensis, Cuphea hyssopifolia, Erigeron bellioides, Mazus pumilus, Phyllanthus tenellus, Salvia farinacea, and Sphagneticola trilobata were new hosts worldwide, whereas Bidens pilosa, Eclipta prostrata, Pouzolzia zeylanica, and Torenia fournieri were new hosts in Taiwan. Four further plant species were confirmed as known hosts (Emilia sonchifolia, Sesamum indicum, Trema orientalis, Zinnia elegans). Asteraceae contained most host species in Taiwan, which appeared proportional to the high species diversity in this plant family. The second highest host diversity in the Cucurbitaceae, however, was not proportional to plant diversity. Although the fungus is able to cause similar symptoms on a broad range of hosts, certain host species showed specific responses to infection. In some species, infection remains limited to old leaves, whereas in other species, only young leaves or mainly stems are infected.