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Germplasm characterization is now possible and more reliable using improved molecular markers and genomic tools. Previously citrus cultivars were primarily described according to their morphological or horticultural traits, but trueness-to-type can now be confirmed using molecular markers, thereby limiting inadvertent cultivar misidentification. Following routine testing the reported parentage of two mandarin hybrids is now questioned. ‘Orri’ mandarin is derived from ‘Orah’ mandarin by induced mutation, and was reportedly bred by crossing ‘Temple’ tangor and ‘Dancy’ mandarin. ‘Orri’ has excellent organoleptic qualities, and other favorable traits. With ‘Dancy’ as the pollen parent, at least some degree of susceptibility of ‘Orri’ to Alternaria brown spot (ABS) might be expected, but it is more likely to have inherited a high degree of susceptibility; yet ‘Orri’ appears to be immune to ABS. SSR analysis provided evidence that excludes ‘Dancy’ as the pollen parent of ‘Orah’. Further testing revealed the likely pollen parent candidate as ‘Kinnow’ mandarin. ‘Fortune’ mandarin was a popular late-maturing mandarin cultivar until the high incidence of ABS rendered the cultivar uneconomical to produce in certain citrus production regions. This exceptionally late, high quality, attractive cultivar is reported to have originated from a ‘Clementine’ mandarin A— ‘Dancy’ cross. However, two independent molecular marker studies revealed that the pollen parent of ‘Fortune’ is possibly ‘Orlando’ tangelo and not ‘Dancy’. In both cases, the pollen parent of ‘Orri’ and ‘Fortune’ mandarin hybrids appears not to be ‘Dancy’ as published. This information will assist geneticists and breeders to re-interpret heritability studies on ABS susceptibility of mandarins and their hybrids.

A comprehensive citrus breeding and genetics program was established at the UF/CREC during the mid-1980s combining conventional breeding with tools provided by tissue culture, emerging biotechnologies, molecular genetics and genomics. Scion Improvement: The Florida citrus industry is 90% processing sweet oranges. A major goal has been to develop new cultivars for Not From Concentrate (NFC) juice production with emphasis on increasing juice quality and expanding seasonal availability. Improved clones from seedling introductions, budwood irradiation and somaclonal variation will be discussed. The fresh fruit industry in Florida is dominated by grapefruit and seedy mandarins. Primary objectives for fresh fruit improvement include expanding seasonal availability, development of canker tolerant and low furanocoumarin grapefruit, and development of seedless, easy-peel mandarins. The focus of our program has been on parent development, and seedless triploid production via interploid crosses; strategies and successes will be discussed. Rootstock Improvement: Initial focus was on improving soil adaptation, tree-size control to facilitate harvesting and cold-protection, and disease resistance, especially to blight, CTV-induced quick decline and Phytophthora. Breeding objectives have since been expanded to include tolerance of the Diaprepes/Phytophthora complex and Huanglongbing HLB, and development of rootstocks that facilitate advanced citrus production systems (ACPS). Progress from conventional breeding (both 2x and 4x) and somatic hybridization will be discussed. Genetic Engineering: Due to the HLB and canker epidemics, focus has been on disease resistance gene discovery, transformation, and evaluation of transgenic plants; progress will be discussed.

The availability of a saturated genetic map of Clementine was identified by the International Citrus Genome Consortium as an essential prerequisite to assist the assembly of the reference whole genome sequence based on a Clementine derived haploid. The primary goals of the present study were to establish a Clementine reference map, and to perform comparative mapping with pummelo and sweet orange. Five parental genetic maps were established with SNPs, SSRs and InDels. A medium density reference map (961 markers for 1084.1 cM) of Clementine was established and used by the ICGC to facilitate the chromosome assembly of the haploid genome sequence. Comparative mapping with pummelo and sweet orange revealed that the linear order of markers was highly conserved. Reasonable inferences of most citrus genomes should be obtained by mapping next-generation sequencing data against the haploid reference genome sequence. Skewed segregations were frequent and higher in the male than female Clementine potentially leading to false interpretation of the genetic determinism of phenotypic traits. The mapping data confirmed that Clementine arose from hybridization between 'Mediterranean' mandarin and sweet orange and identified nine recombination break points for the sweet orange gamete that contributed to the Clementine genome. Introgression of pummelo genome fragments were identified in heterozygosity in each chromosome. Moreover, it appeared that the genome of the haploid Clementine used to establish the citrus reference genome sequence was inherited primarily from the 'Mediterranean' mandarin. The usefulness of this genetic map, anchored in the reference whole genome sequence, is discussed. Citrus Research and Development Foundation 108O568 Ministerio de Ciencia e Innovación: AGL2008-00596-MCI, 2008/121, IPT-010000-2010-43, PSE-060000-2009-8, AGL2007-65437-C04-01/AGR European Commission Citrus Research and Development Foundation itl-bio-03-10122 015453 This work was principally funded by the French ANR CITRUSSEQ project. The European Commission, under the FP6-2003-INCO-DEV-2 project CIBEWU (n°015453), the Spanish Ministerio de Ciencia e Innovación grants, AGL2007-65437-C04-01/AGR and AGL2008-00596-MCI, the Spanish PSE-060000-2009-8 and IPT-010000-2010-43 projects, the Prometeo project 2008/121 Generalidad Valenciana, the Turkish TUBITAK Project No: 108O568; the California Citrus Research Board and UC Discovery grant itl-bio-03-10122 and the Florida Citrus Research and Development Foundation (CRDF), grants #67 and 71 also contributed to the work.

Highly efficient plant regeneration from protoplasts via somatic embryogenesis in citrus has allowed for expanding applications of somatic hybridization and cybridization to citrus variety improvement with increasing complexity. Citrus somatic hybrids are now possible from most desirable parental combinations, and hybrid plants have been produced from approximately 300 combinations to date, including more than 150 at the CREC. Applications for citrus scion improvement target the development of improved seedless fresh fruit varieties, and include symmetric somatic hybridization to produce superior alloteteraploid breeding parents (for use in interploid crosses to generate seedless triploids), haploid + diploid fusion for direct triploid production, and targeted cybridization to transfer mtCMS (cytoplasmic male sterility) from Satsuma mandarin to seedy but otherwise desirable diploid cultivars. The primary application for rootstock improvement is the production of symmetric somatic hybrids to combine complementary rootstocks without breaking up successful gene combinations. Rootstock somatic hybridization is providing opportunities for improving disease and insect resistance, soil adaptation, and tree size control. Wide somatic hybridization provides an opportunity for gene transfer from related species, including some that are sexually incompatible. Extensive field research on citrus somatic hybrid rootstocks combined with emerging molecular analyses of citrus has allowed for the development of additional strategies for rootstock improvement. These include rootstock breeding and selection at the tetraploid level using somatic hybrid parents, and the resynthesis of important rootstocks such as sour orange at the tetraploid level, via fusion of parents selected specifically to overcome the deficiencies of the original rootstock. Ongoing examples of each strategy will be provided, along with suggestions for extending the technology to other commodities.