Differences in ploidy levels of interploidal crosses progenies between diploids and tetraploid somatic hybrids in citrus : S02P19

One of the main objectives of citrus breeders is to obtain sterile mandarins that produce seedless fruits. Triploids are 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. Citrus somatic hybridisation via protoplast fusion allowed the creation of allotetraploid somatic hybrids that can be used as parents to generate triploid cultivars. Several crosses using diploids (female) and allotetraploid somatic 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 tetraploid somatic hybrid); and c) 'Eureka' lemon x ('Mexican lime' 'Shamouti' orange tetraploid somatic hybrid). The majority of progenies were triploid from the 3 crosses (61-76%). However diploid and tetraploid progenies were also obtained in all of them. Molecular analysis of progenies with SSR markers revealed that tetraploids were issued from a diploid male gamete and an unreduced female gamete, while diploids could be issued from a haploid ovule and a haploid male gamete. This study reveals that ploidy variations were owed to meiotic dysfunction of either the tetraploid somatic hybrids or the diploid female parent. (Texte integral)