The Spatial Structure of Sexual and Cytonuclear Polymorphism in the Gynodioecious Beta vulgaris ssp. maritima: I/ at a Local Scale

Corresponding author: Joël Cuguen, Laboratoire de Génétique et Evolution des Populations Végétales, UPRESA CNRS 8016, FR CNRS 1818, Bâtiment SN2, Université de Lille I, 59655 Villeneuve d'Ascq Cedex, France., joel.cuguen{at}univ-lille1.fr (E-mail)

Communicating editor: O. SAVOLAINEN

We have analyzed the spatial distribution of the sex phenotypes and of mitochondrial, chloroplast, and nuclear markers within two gynodioecious populations of Beta vulgaris ssp. maritima. Within both populations, sexual phenotype variation is controlled mainly by the cytoplasmic genotype, although in one study population a joint polymorphism of cytonuclear factors is clearly involved. In spite of contrasts in the ecology (mainly due to different habitats), a clear common feature in both populations is the highly patchy distribution of cytoplasmic haplotypes, contrasting with the wide distribution of nuclear diversity. This high contrast between cytoplasmic vs. nuclear spatial structure may have important consequences for the maintenance of gynodioecy. It provides opportunities for differential selection since nuclear restorer alleles are expected to be selected for in the presence of their specific cytoplasmic male sterile (CMS) type, but to be neutral (or selected against if there is a cost of restoration) in the absence of their CMS type. Selective processes in such a cytonuclear landscape may explain the polymorphism we observed at restorer loci for two CMS types.

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