CIRAD (Centre de Coopération Internationale en Recherche Agronomique pour le Développement), Station de Roujol, 97170 Petit Bourg, Guadeloupe, France.
Ann Bot. 2013 Sep;112(5):811-9. doi: 10.1093/aob/mct145. Epub 2013 Aug 1.
Dioscorea alata is 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.
Different 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.
This 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.
The 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.
盾叶薯蓣是一种多倍体物种，其倍性水平从二倍体（2n = 2x = 40）到四倍体（2n = 4x = 80）不等。倍性增加与更好的农艺性能相关。由于缺乏对盾叶薯蓣自发多倍体（三倍体和四倍体）起源的了解，限制了多倍体的繁殖效率。本研究的目的是利用流式细胞术和微卫星标记来了解盾叶薯蓣多倍体的起源。
分析了通过同型内杂交（2x × 2x）和异型间杂交（2x × 4x 和 3x × 2x）产生的不同后代，以了解通过传递给后代的杂合率来理解胚乳不亲和现象和配子起源。
本研究表明，在 2x × 2x 杂交中，只有通过二倍体雌性非配子减数的现象才能获得具有活力种子的三倍体。杂合性传递的研究排除了多精入卵和多胚的可能性，从而确定了三倍体的起源机制。3x × 2x 杂交未获得幼苗，从而证实了三倍体雌性的不育性。对 2x × 4x 杂交种子的胚乳进行的流式细胞术分析显示了胚乳不亲和现象。
主要结论是，盾叶薯蓣的多倍体是通过形成未减数配子而出现的。三倍体群体是通过二倍体雌性中 2n 配子的形成而建立和多样化的，这是由于 2n 精子形成的种子和异型间杂交的不育性导致的。四倍体是通过两个未减数配子的双侧有性多倍化形成的，这是由于三倍体的不育性导致的。
