New Promising Citrus Triploid Hybrids Selected from Crosses between Monoembryonic Diploid Female and Tetraploid Male Parents

Abstract

The breeding of citrus triploid hybrids started at Istituto Sperimentale per l'Agrumicoltura spell out in Acireale, Italy, in 1978 (Starrantino and Reforgiato, 1981). The strategy used has been to cross a monoembryonic 2x female parent with a 4x male parent. The imbalance between the embryo and endosperm ploidy (3:4) makes seeds from such crossings incapable of germinating in vivo. However, in vitro cultivation has been used to rescue the embryos. In this paper we report the main characteristics of triploid hybrids from 22 different parents, including sweet orange [ Citrus sinensis (L.) Osbeck], mandarin ( C. reticulata Blanco), clementine ( C. reticulata Blanco), grapefruit ( C. paradisi Macf.), pummelo [ C.maxima ], tangor ( C. reticulata × C. sinensis ), lemon [ C. limon (L.) Burm. f.], citron ( C. medica L.), and Fortunella hindsii (Champ.) Swing. Tetraploid parents are duplex because they originate from the doubling of chromosome number of the nucella or of other somatic tissues. The segregation and recombination process results in triploid hybrids with characteristics that are nearer to the 4x parent than the 2x one. This strategy is important in obtaining seedless hybrids similar to a parent after generations of backcrossing.