We have used this technique to greatly expand the tetraploid germplasm available for interploid crosses ( Grosser et al., 2010a, 2010b). sinensis)-like hybrid from a cross of ‘LB8-9’ SugarBelle ® with autotetraploid ‘Hamlin’ sweet orange.īy using somatic hybridization, it is possible to produce novel germplasm at the tetraploid level that combines many good qualities of fused diploid selections. paradisi) and RBB 7-34 (Plant Patent pending), which is a very high-quality ‘Navel’ sweet orange ( C. grandis) with autotetraploid ‘Ruby Red’ grapefruit ( C. They are UF-914 (PP 26177), which is a very high-quality red grapefruit-like hybrid from a cross of ‘Siamese Sweet’ pummelo ( C. In our program, two seedless triploid hybrids produced by this method are currently being commercialized. clementina) with autotetraploid ‘Tarocco’ blood orange. These include grapefruit-like pummelo hybrids ‘Oroblanco’ and ‘Melogold’ and seedless mandarin hybrid ‘Tacle’ from a cross of ‘Monreal’ clementine ( C. Interploid hybridization of diploids with autotetraploids created by various methods has resulted in a few commercial seedless triploid hybrids in citrus. As an alternative, the combination of two unconventional methods, somatic hybridization via protoplast fusion and interploid sexual hybridization, has become an integral part of mandarin cultivar improvement programs targeting seedlessness worldwide, because they can easily overcome some mentioned biological or reproductive limitations ( Aleza et al., 2016 Grosser and Gmitter, 2011 Grosser et al., 2010a, 2010b Guo et al., 2018 Ollitrault et al., 2007). This type of cross has been successfully used to develop the commercially released seedless triploid mandarin cultivars Garbi and Safor. Specific conventional diploid crosses can generate a low percentage of triploid progeny, if the female parent can reliably produce unreduced gametes. Thus, triploid cultivars can be safely planted adjacent to other diploid cultivars like clementine that produce seedless fruit when not cross-pollinated. Triploid hybrids are generally sterile and usually produce seedless or low-seeded fruit, which has been a primary objective of mandarin breeding programs ( Frost and Soost, 1968). Moreover, most conventional diploid hybrids produce seedy fruit, which is not well accepted in the fresh citrus ( Citrus sp. Keywords: breeding citrus interploid cross tissue cultureĭevelopment of improved cultivars through conventional hybridization in mandarins has been hampered by several characteristics of their reproductive biology, mainly apomixis (nucellar polyembryony), sexual incompatibility, and long juvenility. These mandarin-derived tetraploids are valuable as potential breeding parents for interploid crosses with an aim at seedlessness and easy-peeling traits. Murcott’ embryogenic callus lines that were presumed to be of nucellar origin were actually derived unexpectedly from individual ovules of zygotic origin. The EST-SSR markers also revealed that some ‘W. Of the 65 somatic regenerants, 46 were identified as autotetraploids, 18 allotetraploids, and one undefined. Flow cytometry was used to determine the ploidy level of somatic regenerants, and nuclear expressed sequence tag–simple sequence repeat (EST-SSR) markers to determine their parental source. Sixty-five somatic regenerants were obtained using optimized formulation of enzymes and molecular weight of polyethylene glycol for improved protoplast yield and heterokaryon fusion rate, respectively. reticulata hybrid), were used in protoplast fusion with different parental combinations to generate somatic hybrids. Six mandarin cultivars, Ponkan ( Citrus reticulata), Willowleaf ( Citrus deliciosa), Kinnow ( Citrus nobilis × C.
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