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Three different citrus-producing regions of Turkey-Edremit Gulf, Coastal Aegean, and eastern Black Sea-were surveyed in 2005 and 2006. A total of 119 samples were collected from Satsuma Owari mandarin (Citrus unshiu) trees grafted on Citrus tristeza virus (CTV)-resistant Poncirus trifoliata rootstocks in commercial groves and home gardens. All samples were tested for the presence of CTV by direct tissue blot immunoassay (DTBIA) and double antibody sandwich enzyme-linked immunosorbent assay (DAS-ELISA) using young shoots. The samples that tested positive were indexed for biological properties. The results obtained from DTBIA tests showed that 20 of 119 (16.8%) tested trees were infected with CTV and 99 trees were virus free. All samples that tested positive in DTBIA were also positive in DAS-ELISA. After biological indexing, none of these 20 isolates showed any symptoms on sour orange, grapefruit, and sweet orange plants, but all isolates induced vein-clearing symptoms on Mexican lime (Citrus aurantifoli) in 9 months. Some isolates also caused leaf-cupping and chlorosis in Mexican lime. However, 15 months after initial grafting, all isolates induced mild to moderate stem-pitting on Mexican lime. In addition, young tissues, petioles, and leaf samples were collected periodically at monthly intervals for I year (2006) from a 25-year-old Satsuma Owari mandarin grafted on P. trifoliata in the Edremit Gulf. CTV was readily detected in tissue blots of young shoots and petioles from CTV-infected plants during the autumn, winter, and spring seasons. Similarly, the highest ELISA values were obtained in April; the lowest values were noted in September. This study showed that DTBIA is a rapid, sensitive, and reliable procedure for detecting CTV under field conditions. |
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