Study On The Role Of Some Factors Affecting The Epidemics Of Wheat Powdery Mildew In Mazandaran Province

Powdery mildew caused by Blumeria gamines f. sp. tritici (Erysiphe gamines f. sp. trifici) has become one of the most widespread and important diseases of wheat in several provinces of Iran including Mazandaran. The impact of environmental (temperature, relative humidity, rainfall and number of sunny days) on the incidence and severity of the disease and the alternative hosts of the causal agent were studied during 1996-1999 in Mazandaran province. Wheat cultivars Atrak, Milan, Tajan, Falat, Hirmand and Rasoul were grown in six locations in central Mazandaran. Stepwise regression analysis with cultivars as treatments and locations as replications was employed. The results revealed existence of a linear correlation between disease severity and mean air temperature in all cultivars. There was a linear increase in disease severity with rise in temperature until mid-May, when powdery mildew reached its peak in severity. The fungus appeared to oversummer and overwinter as cleistothecium. The cleistothecia were fully matured, with fully developed asci and ascospores in July- August and emptied in late September. Cleistothecia appear to play a role, in addition to conidia and hyphae, in persistence and dispersal of the fungus. Powdery mildew infection of Aegilops triuncialis, Phalaris minor and Lolium temolentum were observed and pathogenicity of B. graminis f. sp. trifici on these weed species was confirmed by artificial inoculation. This is the first report on infection of Aegilops triuncialis and Lolium temolentum by the wheat powdery mildew in Mazandaran.