Citropsis gilletiana for Citrus Germplasm Enhancement and Cultivar Development

African cherry-oranges (Citropsis species) are near Citrus relatives that are a source of novel traits that could be used for improvement of Citrus, but until recently conventional breeding methods have failed. Citropsis sp. are graft compatible with Citrus, but are only marginally sexually compatible (resulting hybrids have been sterile). Somatic hybridization has been useful for making hybrids between Citropsis and Citrus. All Citropsis species are from tropical Africa, and recent publications suggest Africa as the source of the Liberobacter family responsible for Huanglongbing (HLB) disease. Genes for resistance to this disease and possibly other tropical diseases and afflictions may be present in this gene pool, among which C. gilletiana has been documented as exhibiting outstanding resistance to the burrowing nematode Radopholus similis and to Phytophthora. Using biotechnology methods and traditional breeding, hybrids were created between Citrus and Citropsis gilletiana Swingle & M. Kellerm, in an attempt to exploit traits for improving Citrus germplasm. The first sexual hybrid using an intergeneric tetraploid somatic hybrid (Nova mandarin hybrid + C. gilletiana) was made when it flowered for the first time in December 2014, over 20 years since this hybrid was created. This is the first and only documented flowering of an intergeneric Citrus somatic wide hybrid. A single seedling was obtained using ovule rescue techniques, as fruit failed to develop naturally past 30 days. Somatic hybrids were also obtained using W. Murcott mandarin callus and Red Cooper grapefruit callus respectively combined with C. gilletiana leaves. Hybrids have been identified phenotypically and confirmed using flow cytometry and molecular markers.