Tree Growth, Yield, and Fruit Quality of Ortanique Tangor on Eleven Rootstocks in Cyprus

Growth, yield, and fruit quality were recorded for Ortanique tangor (Citrus reticulata Blanco) on 11 rootstocks until the trees were 12 years old. Trees on Volkameriana (C. volkameriana Pasq.), rough lemon, and 'Estes rough lemon (C. jambhiri Lush.) were more productive per unit of tree size, and their cumulative yields per tree were significantly higher than those of trees on the other rootstocks. There was no significant difference between cumulative yields of Ortanique on the following rootstocks: sour orange (C. aurantium L.), 'Palestine' sweet lime (C. limettioides Tan.), 'Red' rough lemon (C. jambhiri Lush.), Rangpur (C. limonia Osbeck), and Amblycarpa (C. limonellus var. amblycarpa Hassk.). However, yield on these rootstocks was significantly higher than on Carrizo and Troyer citranges (C. sinensis (L.) Osbeck × Poncirus trifoliata (L.) Raf.) and 'Swingle' citrumelo (C. paradisi Macf. × P. trifoliata (L.) Raf.). The high productivity per unit of tree size of 'Palestine' sweet lime suggested that this rootstock could be used advantageously in closely spaced plantings. Rootstocks affected fruit size, weight, rind thickness, juice content, total soluble solids concentration (SSC), and total acids, but the differences were not large enough to be of practical importance. Citrus is one of the most important crops in Cyprus. In 1990 it occupied 7300 ha or 20% of the total irrigated land. Citrus production in 1990 reached 170,000 t of which 30% was oranges, 40% grapefruit, 22% lemons, and 5% mandarins. Ortanique is a new crop for Cyprus but has expanded rapidly during the last few years as a result of the high demand in the export market. The origin of this attractive and promising variety is unknown, but Ortanique is reported (Jamaica Citrus Growers Assn., 1963) to be an old chance seedling that came to the attention of C.P. Jackson of Chellaston, Mandeville, Jamaica, in 1920. Because of the presence of wild orange and so-called tangerine trees in the vicinity of the original tree, and the distinctive features of the fruit, it was considered to be a natural tangor and was given the name Ortanique by H.H. Cousins. The name was a synthesis coined from or(ange), tan(gerine), and (un)ique. The present clone probably represents a nucellar seedling of the parent tree (Hodgson, 1967). In Cyprus, all citrus varieties are mainly budded on sour orange, which generally is the most commonly used rootstock, particularly in the Mediterranean region. Although sour orange was considered a satisfactory rootstock in several citrus-producing areas such as South Africa, South America (Brazil, Argentina), Florida, Texas, and a part of California, it had to be replaced in some of these areas as a result of its susceptibility to citrus tristeza virus (Wallace, 1956a, 1956b; Salibe, 1973). The occurrence of tristeza in the Mediterranean area (Bitters, 1973; Mendel, 1956) and its detection in Cyprus (Kyriakou and Polykarpou, 1989; Papasolomontos and Economides, 1968) have stimulated a search for alternative rootstocks. The currently lim- ited presence of tristeza in Cyprus does not preclude the possibility that the disease will not become a problem in the future. As an assurance for future plantings, a research program was initiated in Cyprus to find a suitable rootstock to replace sour orange if tristeza becomes epidemic. We here present data on the