The Mandarin Triploid Breeding Program in Spain
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AutorNavarro,Luis; Aleza,Pablo; Cuenca,Jose; Juarez,Jose; Pina,Jose A.; Ortega,Carmen; Navarro,Antonio; Ortega,Violeta
Production of seedless citrus fruits is required for the fresh market because consumers do not accept seedy fruits. Development of new seedless mandarin cultivars has a high priority for many citrus industries worldwide. The recovery of triploid hybrids is the most promising approach to achieve this goal, since triploids have a very low pollen and ovule fertility. They are seedless or produce very low numbers of seeds and do not induce the formation of seeds in other cultivars by cross pollination. In Spain we are carrying a triploid breeding program since 1996 based on 2x x 2x, 2x x 4x and 4x x 2x sexual hybridizations followed by embryo rescue and flow cytometry, together with the use of different approaches to produce new tetraploid parents. The objective is to obtain new high quality easy peeling and seedless mandarin cultivars. More than thirty spontaneous autotetraploid apomictic genotypes to be used as male parents have been selected from seedbeds by flow cytometry. Also nine autotetraploid non apomictic genotypes, mainly to be used as female parents, have been obtained by chromosome duplication with treatments of micrografted shoot tips with colchicine or oryzalin. Symmetric protoplast fusion is also being used to produce allotetraploid genotypes. So far, we have obtained more than 5,500 triploid hybrids from 130 parental combinations by 2x x 2x pollinations, more than 4,300 triploid hybrids from 100 parental combinations by 2x x 4x pollinations, and more than 5,600 triploid hybrids from 103 parental combinations by 4x x 2x pollinations. In 2008 we released the first cultivars originated in the program, the seedless late maturing mandarins 'Garbi' and 'Safor', obtained from 2x x 2x crosses. More than 400,000 trees of these cultivars have been planted by growers during the last three years.