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Aphid-Transmissibility Variants of Citrus Tristeza Virus in Infected Citrus Trees. B. Raccah, Virus Laboratory, Agricultural Research Organization, The Volcani Center, Bet Dagan, Israel; G. Loebenstein(2), and Sima Singer(3). (2)(3)Virus Laboratory, Agricultural Research Organization, The Volcani Center, Bet Dagan, Israel. Phytopathology 70:89-93. Accepted for publication 27 July 1979. Copyright 1980 The American Phytopathological Society. DOI: 10.1094/Phyto-70-89.

Each of four orange trees infected with citrus tristeza virus (CTV), contained several variants of the virus that differed in aphid transmissibility. In order to ascertain the presence of these variants, small pieces of budwood of two trees, from which an overall low rate of transmission (7.5%) had been obtained, were grafted on 2-yr-old orange plants. When those plants were used in aphid-transmission experiments, highly (above 30%), intermediate (520%), and poorly (less than 5%) aphid-transmissibility variants were obtained. One of these trees came from an orchard in which no natural spread had been observed for two decades, although recently natural spreading had become apparent, and the second tree was grafted with budwood originating from this orchard. Using the same procedure with two trees from a region where natural transmission was evident during the last decade and overall transmission rates reached 25%, poorly transmissible variants also were obtained. Aphids apparently transmit simultaneously more than one isolate, as a spectrum of variants was observed from aphid-inoculated seedlings. It is suggested that tristeza-infected trees may harbor more than one variant; and that trees from a location where only limited natural spread is observed could contain CTV variants that are highly transmissible, but which are quantitatively suppressed by a dominating poorly transmissible variant.