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Achene Blemish Syndrome: A New Disease of Sunflower in Israel. D. SHTIENBERG, Department of Plant Pathology, Agricultural Research Organization, The Volcani Center, P.O. Box 6, Bet-Dagan 50250, Israel. Plant Dis. 78:1112-1116. Accepted for publication 9 May 1994. Copyright 1994 The American Phytopathological Society. DOI: 10.1094/PD-78-1112.

A new disease has affected sunflower (Helianthus annuus) achenes in Israel. Infection produces small, scattered lesions on the surface of the shell. Lesions are brown, black, or gray and some are surrounded by dark halos; they range in size from 0.5 to 2 mm and may be round, oval, elongate, or irregular. Infected crops are viewed by the industry as being of lower quality and therefore fetch a lower market price. Several fungi were isolated from infected achenes. The four steps of Koch's postulates were completed for Alternaria alternata, Cladosporium sp., and Ulocladium atrum. Artificial inoculation trials revealed that A. alternata induced a significantly higher disease incidence than the other two fungi and that inoculation with a mixture containing spores of all three fungi resulted in a higher disease incidence than that obtained by inoculation with each pathogen alone. Achenes were susceptible to infection only at the time of their development, but symptoms were only visible just before physiological maturity. A field trial demonstrated that western flower thrips (Frankliniella occidentalis) are associated with infection of the achenes. The effects of nine fungicides on disease severity were examined in two field trials in 1992. Although some fungicides significantly reduced disease severity, their effect was relatively minor and in general they were not highly effective.