Extensive Citrus Triploid Breeding Program by 2xx4x Sexual Hybridizations
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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 and usually are seedless or produce very low numbers of seeds, and do not induce the formation of seeds in other cultivars by cross pollination. The objective of our breeding program is to produce new high quality easy peeling and seedless mandarin cultivars. Citrus triploid plants can be recovered by 2xx4x sexual hybridizations. Triploid embryos are found in normal and undeveloped seeds that do not germinate under greenhouse conditions. Extensive breeding programs based on this type of hybridization require very effective methodologies for recovery of new tetraploid parents, embryo rescue and ploidy evaluation. Different approaches have been implemented to obtain new tetraploid parents. Spontaneous autotetraploid plants of apomictic genotypes have been selected from seedbeds by flow cytometry and autotetraploid plants of non apomictic genotypes have been obtained by chromosome duplication with treatments of micrografted shoot tips with colchicine or oryzalin. Symmetric protoplast fusion is also used to produce tetraploid genotypes. So far, we have obtained more than 4,400 triploid hybrids from 77 parental combinations. Protection of Plant Breeder's Rights of a triploid hybrid named IVIA-600 obtained in a hybridization between 'Hernandina' clementine and tetraploid 'Orlando' tangelo has been requested.