Abstract
Background and Aims Dioscorea alatais a polyploid species with a ploidy level ranging from diploid (2n = 2x = 40) to tetraploid (2n = 4x = 80). Ploidy increase is correlated with better agronomic performance. The lack of knowledge about the origin of D. alata spontaneous polyploids (triploids and tetraploids) limits the efficiency of polyploid breeding. The objective of the present study was to use flow cytometry and microsatellite markers to understand the origin of D. alata polyploids.MethodsDifferent progeny generated by intracytotype crosses (2x × 2x) and intercytotype crosses (2x × 4x and 3x × 2x) were analysed in order to understand endosperm incompatibility phenomena and gamete origins via the heterozygosity rate transmitted to progeny.ResultsThis work shows that in a 2x × 2x cross, triploids with viable seeds are obtained only via a phenomenon of diploid female non-gametic reduction. The study of the transmission of heterozygosity made it possible to exclude polyspermy and polyembryony as the mechanisms at the origin of triploids. The fact that no seedlings were obtained by a 3x × 2x cross made it possible to confirm the sterility of triploid females. Flow cytometry analyses carried out on the endosperm of seeds resulting from 2x × 4x crosses revealed endosperm incompatibility phenomena.ConclusionsThe major conclusion is that the polyploids of D. alata would have appeared through the formation of unreduced gametes. The triploid pool would have been built and diversified through the formation of 2n gametes in diploid females as the result of the non-viability of seeds resulting from the formation of 2n sperm and of the non-viability of intercytotype crosses. The tetraploids would have appeared through bilateral sexual polyploidization via the union of two unreduced gametes due to the sterility of triploids.
Highlights
Dioscorea alata is a monocot that belongs to the family Dioscoreaceae
The diploid internal reference 639a was used for flow cytometry
The major conclusion of this study is that polyploids in D. alata might have appeared as a result of 2n gamete formation
Summary
Dioscorea alata is a monocot that belongs to the family Dioscoreaceae. This gender includes .600 species (Ayensu and Coursey, 1972) of which the three main cultivated species are D. rotundata, D. alata and D. trifida. Yams are an important food crop in tropical and sub-tropical regions They are dioecious herbaceous vines cultivated for their starchy tubers. Dioscorea alata is a polyploid species with a ploidy level ranging from diploid (2n 1⁄4 2x 1⁄4 40) to tetraploid (2n 1⁄4 4x 1⁄4 80). The triploid pool would have been built and diversified through the formation of 2n gametes in diploid females as the result of the non-viability of seeds resulting from the formation of 2n sperm and of the nonviability of intercytotype crosses. The tetraploids would have appeared through bilateral sexual polyploidization via the union of two unreduced gametes due to the sterility of triploids
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