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International audience; Citrus reticulata is considered one of the four main ancestral taxa of cultivated citrus and is widely associated with the mandarin horticultural group. However, several studies suggest introgressions of other taxa and the precise structure of the mandarin group is not known. To analyse the structuration of mandarin germplasm and the potential interspecific introgressions, 208 accessions were genotyped by the KASPar method, with sixty-seven single nucleotide polymorphism (SNP) markers mined in 27 nuclear genes and in clementine BAC-ends. These SNP markers were employed for the study of 208 genotypes comprised of 169 ` mandarin-like' genotypes and 39 genotypes belonging to ancestral taxa. Structure software was used to identify groups within the mandarin germplasm. Six mandarin groups were identified, some of them in agreement with the species defined by Tanaka. Many mandarins were located between these mandarin groups, indicating a high level of admixture between the identified parental groups. New insights in the organization of mandarin germplasm and its structure are presented in this work, which will be useful for better management of citrus germplasm collections.

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.

International audience; Citrus is an economically important world tree fruit crop with production in more than 146 countries. The center of origin for citrus is considered to be Southeastern Asia including southern China, northeastern India, and Malaysia, with secondary centers in surrounding areas. Novel and commercially significant scion and rootstock cultivars originating by natural mutation or directed hybridization were introduced during the past century. Significant genetic resource collections exist in many countries. A global citrus germplasm network was developed in 1997. Now that the International Treaty on Plant Genetic Resources for Food and Agriculture (ITPGR) has recognized Citrus as an Annex 1 crop, a global conservation strategy needs to be established. The objective of this workshop was to plan the development of this strategy. More than 60 delegates attended with representation from Argentina, Australia, Bhutan, Brazil, China, Columbia, France, Iran, Israel, Italy, Japan, Mexico, Morocco, Portugal, Spain, Turkey, UAE, US, and Vietnam. Nine oral presentations were given describing multiple aspects of genebank operations, technologies and gaps in Brazil, China, France, Australia, Spain, and the US. A draft genebank survey questionnaire was presented to the group and comments and suggested changes for improvement were received. Citrus curators and genebank managers throughout the world will be surveyed for the status and health of their collections. The surveys will be received and compiled by collaborators at the University of California, Riverside, and at the USDA ARS Riverside. This information will be compiled and reported. The strategy will include background and history of the development of Citrus as a cultivated crop, conservation protocols, vulnerabilities, and recommendations for safeguarding Citrus germplasm. This strategy will be implemented through the Global Crop Diversity Trust with collaboration from the International Society for Horticultural Science and the international Citrus research community.

International audience; Citrus fruit development and ripening are complex processes involving physiological and biochemical changes that are under hormonal, nutritional and environmental control. One of the most evident phenomena in late maturation is shedding of ripe fruit. A study made in Spain on sweet oranges showed that fruit shedding was related to the increase of sugars content of fruit pulp juice. To investigate this potential relationship between fruit abscission and internal maturity parameters we investigated the fruit maturity process of 10 clementine x mandarin hybrids and 9 commercial sweet orange varieties with different maturity period. Morphological and biochemical analyses (acidity, total soluble solids, fruit weight thickness of the flavedo, thickness of the peduncle, external colo) were carried out on fruit sets of the different varieties during the maturation process, from December to June. The abscission initiation was evaluated by measuring the force required to detach the fruit of the peduncle. Analysis showed that under the local conditions, abscission was generally not expressed even through fruit maturation was evolving. Therefore, we suppose that even though the local conditions have an important effect, abscission of citrus fruit results also from environmental-genotype interactions. Moreover, evolution of abscission and fruit parameters are not correlated suggesting the independence in the process of maturation and abscission under the environmental conditions of Corsica.

Rootstock provides better adaptation to biotic and abiotic constraints. Poncirus and its hybrids are widely used since they are tolerant to Citrus Tristeza Virus. However, when grafted, most of them are considered to be sensitive to salinity and water deficit. Diversity does exist within the Poncirus trifoliata specie but little is known regarding the behaviour variability of genotypes to abiotic constraints. The citrus diversity of 72 P. trifoliata genotypes was investigated using SSR markers. Two mayor genetic groups were clearly identified. Five genotypes, belonging to each genetic group, were then selected to investigate their properties of tolerance to water deficit. Water deficit was applied by withdrawing irrigation for 4 weeks. Physiological parameters such leaf stomatal conductance and quantum yield of PSII electron transport, soil water potential, leaf osmotic pressure and transpiration were estimated. Among genotypes, we observed that some genotypes such as' Rubidoux' were clearly more tolerant to water deficit than others such as 'Pomeroy'. Interestingly, the genotypes that were sensitive belonged to one genetic group and the tolerant ones belonged to the other group. Therefore, it sounds that among the Poncirus genus, it is possible to select genotypes as parent in breeding programs, which are more tolerant to water deficit. (Resume d'auteur)

International audience