Triploid seedless mandarin breeding in France

Small citrus is an increasing component of the world citrus industry. New high quality, parthenocarpic, sterilemandarin varieties will play a pivotal role for its sustainable development. To produce seedless varieties,the CIRAD breeding program is focused on triploid hybrid selection. The first method to develop triploidprogenies exploits 2n gametes that are naturally produced by diploid cultivars to obtain triploids in 2x X2x crosses. The second method is based on interploid crossings (2x X 4x and 4x X 2x). For the last strategythe parental tetraploid gene pool has been diversified by selecting spontaneous tetraploids in apomicticcultivars, generating doubled diploids by colchicine treatments and production of allotetraploids by somatichybridization. Several thousand triploid hybrids have been created by CIRAD using these strategies with thesupport of embryo rescue and ploidy evaluation by flow cytometry. This breeding program is supported bybasic and methodological research performed in collaboration with IVIA (Spain), DAK (Morocco) and INRA(France) in the following topics: (1) citrus germplasm management and characterization, (2) studies ofpolyploidization mechanisms, tetraploid meiosis and its implications on the genetic and phenotypic structureof triploid progenies, and (3) studies of the implication of polyploidy on genomic and phenotypic expression.