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Role of Wild Grasses in Epidemics of Powdery Mildew n Small Grains in Israel. Nava Eshed, Faculty of Agriculture, the Hebrew University of Jerusalem, Rehovot, Israel; I. Wahl, Faculty of Agriculture, the Hebrew University of Jerusalem, Rehovot, Israel, Junior author’s present address: Division of Mycology and Plant Pathology, Tel-Aviv University, Tel-Aviv, Israel. Phytopathology 65:57-63. Accepted for publication 25 July 1974. DOI: 10.1094/Phyto-65-57.

Three hundred and twenty-three conidial isolates of Erysiphe graminis from about 40 species of 16 genera of native wild Gramineae collected throughout Israel were used to inoculate seedlings of cultivated barley, wheat, and oats, grown in the greenhouse. Similar tests were made with 152 collections of fertile cleistothecia of E. graminis obtained from 26 species of 12 genera of grasses. Fungal isolates infectious on the small grains originated almost exclusively from intrageneric grasses, mainly from allied species. One exception was that conidia and ascospores from Triticum dicoccoides were compatible with cultivated wheat and barley. This specialization of E. graminis on grasses contrasts sharply with the broad host ranges of isolates from cereals. Despite the limited number of species which harbor pathogens infectious on small grains, they are important in the epidemics of powdery mildew because of their wide distribution and the seasonal coordination of their life cycles with that of the pathogen. Those grasses are infected in the fall by primary ascosporic inoculum liberated from cleistothecia which oversummer on their stubble. After infection, the conidia multiply and disseminate to cultivated small grain crops throughout the growing season. Cleistothecia preserved on the grass refuse enable oversummering of the fungus in the absence of live hosts.