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Induction of Silverleaf of Squash by Bemisia Whitefly from California Desert Whitefly Populations. S. Cohen, Visiting Scientist, Volcani Institute of Agricultural Research, Bet Dagan, Israel. J. E. Duffus, H. Y. Liu, and R. Perry. USDA-ARS, U.S. Agricultural Research Station, Salinas, CA 93905. Plant Dis. 75:862. Accepted for publication 18 March 1991. Copyright 1991 The American Phytopathological Society. DOI: 10.1094/PD-75-0862B.

The silverleaf syndrome in squash, induced by the feeding of the sweetpotato whitefly (Bemisia tabaci (Gennadius)), is widespread in Florida (2). Populations of B. tabaci from the desert southwest have previously not been capable of inducing typical silverleaf (1). Recent isolations of B. tabaci from California desert regions have shown these populations to be a mixture of biotypes that differ in a number of ways, including ability to induce silverleaf of squash. The physiological differences of the newly introduced whitefly biotype, including host preference, larval development, and induction of silverleaf symptoms, clearly distinguish it from the common biotype. Double-stranded RNA bands were not detected from nymph-infested leaves or from symptomatic tissue, suggesting that whitefly-induced silverleaf in California is similar to a systemic phytotoxemia. The occurrence of the silverleaf-inducing whitefly biotype on nursery stock, including poinsettia and hibiscus, in various parts of the state and the movement of such nursery stock from Florida to California are the probable vehicles for introduction of this new disease problem in California.

References: (1) N. Bharathan et al. Plant Pathol. 39:530, 1990. (2) R. K. Yokomi et al. Phytopathology 80:895, 1990.