Differences in ploidy levels of interploidal crosses progenies between diploids and tetraploid somat

One of the main objectives of citrus breeders is to obtain sterile mandarins that produce seedless fruits. Triploidsare a response to these criteria. A way for triploid creation is sexual crosses between diploids and tetraploids. However, the scarcity of the natural tetraploid gene pool has been a restriction for using this method. Citrussomatic hybridisation via protoplast fusion allowed the creation of allotetraploid somatic hybrids that canbe used as parents to generate triploid cultivars. Several crosses using diploids (female) and allotetraploidsomatic hybrids (male) were conducted by CIRAD: a) ‘Fortune’ mandarin x (‘Willow leaf’ mandarin ‘Star Ruby’ grapefruit tetraploid somatic hybrid); b) ‘Eureka’ lemon x (‘Star Ruby’ grapefruit ‘Corsican’ citron tetraploidsomatic hybrid); and c) ‘Eureka’ lemon x (‘Mexican lime’ ‘Shamouti’ orange tetraploid somatic hybrid). Themajority of progenies were triploid from the 3 crosses (61-76%). However diploid and tetraploid progenieswere also obtained in all of them. Molecular analysis of progenies with SSR markers revealed that tetraploidswere issued from a diploid male gamete and an unreduced female gamete, while diploids could be issuedfrom a haploid ovule and a haploid male gamete. This study reveals that ploidy variations were owed tomeiotic dysfunction of either the tetraploid somatic hybrids or the diploid female parent.