POWDERY MILDEW OF VICIA FABA IN MANITOBA

Powdery mildew occurred widely on faba beans (Vicia faba L.) in Manitoba in 1974. Mycelia, and conidia were abundant on both leaf surfaces. The fungus later developed numerous cleistothecia 99–143 μm in diam, with rigid appendages, 128–286 μm in length, dichotomously branched at their apices and ending in recurved tips. Frequently, appendages were contorted and irregularly branched. Cleistothecia contained 5–8 asci. The fungus produced mildew symptoms on Lathyrus ochroleucus Hook., L. odoratus L., L. latifolius L., and Vicia americana Muhl., but failed to infect Lonicera tatarica L., Pisum sativum L., and Syringa vulgaris L. The fungus was identified as Microsphaera penicillata (Wall. ex Fr.) Lév. var. ludens (Salmon) Cooke on the basis of morphological characters and pathogenicity. Lathyrus spp. are new hosts of the fungus. L. ochroleucus and V. americana may be sources of primary inoculum of the fungus in Manitoba. Erysiphe pisi DC. reported to occur on V. faba was not found on any of the specimens.