The Citrus Variety Improvement Program in Turkey

Abstract

Almost all of the citrus trees in Turkey are infected with one or more virus and virus-like diseases which induce large economic losses. The establisment of a Citrus Variety Improvement Program for Turkey (CVIPT) was needed to solve this problem. To accomplish this, computer controlled greenhouse facilities covering 7,000 mZ plus 1,800 mZ of screenhouses were established to conduct biological indexing and to maintain virus-tested, foundation plants, and also to propagate budwood increase plants. These facilities are located at the Antalya Citrus Research Institute in Serik. The program began with36 candidate trees often cultivars which were selected from the best commercial groves in Turkey. A laboratory facility was constructed at Serik and equipped to do shoot tip grafting (STG), thermotherapy, ELISA and polyacrylamide gel electrophoresis (PAGE). At present, 382 STG plants have been obtained. Of these, 79 have been indexed to a variety of indicator plants and 69 were found free of the major virus and virus-like diseases of citrus. As of October, 1992,5,000 healthy citrus plants were being grown under screen, and 25,000 sour orange seedlings were budded with virus-tested buds. A long term budwood release program is being planned with the establisbment of a foundation block of trees. These trees will be derived from both STG and heat treated sources, and will be extensively indexed for a broad range of citrus pathogens. Index words. Shoot-tip grafting in vitro, virus indexing, certification, clean budwood. Virus and virus-like diseases are one of the main factors causing low citrus fruit production in Turkey (3,7,8). The use of budwood from infected trees for nursery propagation is primarily responsible for distributing diseases (12). The diseases of tristeza exocortis, cachexia, concave gum, psorosis, psorosislike pathogens, gummy bark, gummy pitting, vein enation and satsuma dwarf are known to be present in Turkey (1,2,3,4,5,7,8). Our objective is the freeing of citrus pathogens and the propagation of "virus-tested" citrus budwood for establishing new orchards of clean trees. We were supported in our efforts by a Technical Cooperation Program with the Food and Agricultural Organization of the United Nations (FAO) (10,ll). This program began in February 1988 and consisted of the following steps: 1) selection of trees; 2) indexing; 3) elimination of pathogens by shoot tip grafting (STG); 4) reindexing of the STG plants; 5) establishing foundation and budwood increase plants; 6) propagation and increase of healthy nursery stock. Selection of trees. A ten-year selection program was carried out in the Mediterranean and Aegean Regions of Turkey, and 36 candidate trees were established at the Antalya Citrus Research Institute. These consisted of ten sweet oranges, nine mandarins, and 17 lemons. Later varietal selections of three grapefruits, one lemon, three sweet oranges, and seven mandarins were added to the program. These candidate trees were carefully chosen for fruit bearing qualities and trueness to type. Indexing. These 36 selected candidate trees were indexed for citrus tristeza virus (CTV), stem pitting tristeza (CTV-SP), seedling yellows tristeza (CTV-SY), citrus tatterleaf virus (CTLV), citrus exocortis viroid (CEVd), various citrus viroids (CVd), citrus cachexia viroid (CCaVd), stubborn disease, psorosis and psorosislike pathogens (PLP), satsuma dwarf virus (SDV) and vein enation (VE). The candidate trees were biologically indexed to indicator plants by the methods described by Roistacher (12). Table 1 lists the indicator plants used, the pathogens indexed and indexing conditions. Serological indexing using ELISA was later included for detection of stubborn, CTV and SDV. 402 Twelfth IOCV Conference TABLE 1 INDICATOR PLANTS, PATHOGENS INDEXED, AND INDEXING CONDITIONS Temperature (C) Indicator Pathogens Plants/ plants indexed Replicates container Night Day Mexicanlime Sour orange Duncangrapefruit Sweet orange (Pineapple) Mandarin (King, Kara, Dweet) Lemon (Kara) Citrange (Rusk, Troyer) 861-S-1 Citron/roughlemon Parson's Specialmandarinl rough lemon Madamvinous sweet orange White sesame CTV, VE CTV,SP CTV-SY PLP