• In-depth knowledge of reproductive biology and sexual recombination is key to Citrus breeding

Last update: 16 March 2018

Complex genomic structures arising from the evolution of cultivated citrus fruits greatly affect meiotic functioning and trait heredity. Although the germplasm is primarily diploid, triploidy is sought for seedless criteria and tetraploidy seems go give greater plasticity to rootstocks. Citrus varietal improvement thus raises some specific questions related to reproductive biology, sexual recombination and the creation of neo-diversity based on different ploidy compartments.

Work conducted in partnership with IVIA revealed that, in mandarins (C. reticulata), restitution of the second division of meiosis (SDR) is the source of unreduced ovules producing triploid hybrids from diploid parents (Cuenca et al., 2011, 2015; Aleza et al., 2015, 2016). SDR is also the main mechanism of 2n ovule formation in the lemon tree, associated with some other mechanisms, such as first division restitution (FDR) and post-meiotic doubling (Rouiss et al., 2017a). However, FDR appeared predominant for unreduced pollen (Rouiss et al., 2017b). This work enabled the effective analysis of genetic determinism for target traits on polyploid recombinant populations derived from 2n gametes (Cuenca et al., 2013). It also showed that tetraploidization events through doubling of the chromosome stock of nucellar cells were frequent in apomictic Citrus genotypes (Aleza et al., 2011). The team has also examined the segregation modes of tetraploid parents and the genetic structure of the resulting diploid gametes (Kamiri et al., 2011; Aleza et al., 2016; Rouiss et al., 2018).  Segregations appear complex, ranging from disomic to tetrasomic depending on phylogenomic heterozygosity. It has also been shown in partnership with IVIA that the 2n gametes of clementine arising from SDR explored multi-locus variability that is complementary to that of diploid gametes produced by doubled diploid clementine trees (Aleza et al., 2016). These results mean that consideration can be given to fine modelling of trait heredity, along with the application of more effective strategies to create neo-diversity guided by breeding objectives.

References cited

  • Aleza, P., Froelicher, Y., Schwarz, S., Agustí, M., Hernández, M., Juárez, J., Luro, F., Morillon, R., Navarro, L., Ollitrault, P. (2011). Tetraploidization events by chromosome doubling of nucellar cells are frequent in apomictic citrus and are dependent on genotype and environment. Annals of Botany, 108 (1): 37-50.
  • Aleza P, Cuenca J, Hernández M, Juárez J, Navarro L and Ollitrault P. (2015b) Genetic mapping of centromeres in the nine Citrus clementina chromosomes using half-tetrad analysis and recombination patterns in unreduced and haploid gametes. BMC Plant Biology, 15-80.
  • Aleza P. Cuenca · J., Juárez ·J., Navarro L., Ollitrault P. (2016) Inheritance in doubled-diploid clementine and comparative study with SDR unreduced gametes of diploid clementine. Plant Cell Reports. Online first. DOI: 10.1007/s00299-016-1972-4.
  • Cuenca, J., Froelicher, Y., Aleza, P., Juarez, J., Navarro, L., Ollitrault, P. (2011) Multilocus half-tetrad analysis and centromere mapping in citrus: evidence of SDR mechanism for 2#n# megagametophyte production and partial chiasma interference in mandarin cv `Fortune'. Heredity, 107 (5): 462-470.
  • Cuenca J, Aleza P, Navarro L and Ollitrault P. (2013). Assignment of SNP allelic configuration in polyploids using competitive allele-specific PCR: application to citrus triploid progeny. Ann Bot (2013) 111(4): 731-742. doi: 10.1093/aob/mct032.
  • Cuenca J, P Aleza, J Juárez, A García-Lor, Y Froelicher, L Navarro and P Ollitrault.  (2015) Maximum-likelihood method identifies polyploidisation meiotic restitution mechanism from heterozygosity transmission of centromeric loci: application in citrus. Scientific Reports. 5, 9897.
  • Kamiri, M., Stift, M., Srairi, I., Costantino, G., El Moussadik, A., Hmyene, A., Bakry, F., Ollitrault, P., Froelicher, Y. (2011) Evidence for non-disomic inheritance in a Citrus interspecific tetraploid somatic hybrid between #C. reticulata# and #C. limon# using SSR markers and cytogenetic analysis. Plant Cell Reports, 30 (8): 1415-1425.
  • Rouiss H., Cuenca J., Navarro L., Ollitrault P., Aleza P. (2017a) Unreduced megagametophyte production in lemon occurs via three meiotic mechanisms, predominantly second-division restitution. Frontiers in Plant Science, 8 (1211) : 16 p.
  • Rouiss H., Cuenca J., Navarro L., Ollitrault P., Aleza P. (2017b) Tetraploid citrus progenies arising from FDR and SDR unreduced pollen in 4x X 2x hybridizations. Tree Genetics and Genomes, 13 (1) : e10 (14 p.).
  • Rouiss H., Bakry F., Froelicher Y., Navarro L., Aleza P., Ollitrault P.. 2018. Origin of C. latifolia and C. aurantiifolia triploid limes: The preferential disomic inheritance of doubled-diploid 'Mexican' lime is consistent with an interploid hybridization hypothesis. Annals of Botany, 121 (3) : p. 571-585.

Last update: 16 March 2018