Citrus Virus and Virus-like Diseases in the Eastern Mediterranean Region of Turkey

Abstract

A survey of the virus and virus-like diseases of citrus in the Eastern Mediterranean region was done between 1985 and 1992, using indicator plants, ELISA or culturing techniques. A total number of fourteen diseases was identified. The most important were the psorosis and psorosis-like pathogens (sweet orange, grapefruit, mandarin), stubborn (navel orange, grapefruit), gummybark (sweet orange) and cachexia (mandarin). Recently, the number of crinkly leaf-type infected trees has increased dramatically. Although the number of trees infected with citrus tristeza virus was very low, it remains a threat to the Turkish citrus industry due to the use of sour orange as rootstock and the high abundance of the vector Aphis gossypii. Citrus is one the most valuable ex-port products of Turkey. This is espe-cially the case in the Eastern Mediter-ranean region, where about 70 % of the production is concentrated. Despite the suitability of the growing of citrus, the yield is about 40 % less compared to other Mediterranean countries. Most of the citrus trees are infected with at least one virus or virus-like dis-ease. Because of the heavy economic impact of citrus viral diseases a bud-wood improvement program was es-tablished at the University of Cukurova in Adana in 1986 and later a second citrus variety improvement program started its work in Antalya in 1988 (4). Very little is published about the occurrence and distribution of citrus diseases in the Eastern Mediterranean region of Turkey other than those by foreign F A 0 consultants (11). The pur-pose of this paper is to report on the occurrence of citrus virus and virus-like diseases in the Eastern Mediterra-nean Region of Turkey. MATERIAL AND METHODS Survey. Field survey and labora-tory identification of diseases on citrus was done between 1985 and 1992. Apart from the general survey onnavel oranges and Satsuma mandarins, sev-eral orchards of different grapefruit and mandarin varieties were inspected for virus diseases. To identify the virus diseases ob-served during the survey, citrus trees revealing symptoms attributable to virus or virus-like diseases were selec-ted and indexed for the main viruses in greenhouses. Inoculum sources were either buds, bark chips or side-grafts. At least four indicator plants were inoculated for each disease and source tree and one healthy control and a positive control, if available, were added. Test trees were indexed for cit-rus tristeza virus (CTV) and vein ena-tion (VE) on Mexican lime. To detect and identify psorosis A, Madame Vin-ous indicator plants were used, for con-cave gum Kara lemon and for cristacor-tis Orlando tangelo. Citrus infectious variegation (CIVV) and citrus crinkly leaf type virus (CLTV) were detected on rough lemon. After inoculation all indicator plants were grown under cool temperatures (25 C maximum day and 20 C minimum night). The citrus exocortis viroid (CEVd) was identified on Etrog citron and citrus cachexia vir-oid (CCaVd) on Parson's Special man-darin kept under warm conditions (35 C day and 27 C night). Citrus stubborn disease (CSD) was transmitted by side-grafts to Madame Vinous sweet orange seedlings grown under warm tempera-tures. For the diagnosis of satsuma dwarf virus (SDV) leaf tissue extract was mechanically inoculated to white sesame (for details on indexing methods used, see 7).