Maternal factors have stronger effect on family sex ratio than nuclear factors in a trans-Atlantic cross of Silene vulgaris

Background: Sex determination in cyto-nuclear gynodioecious plants (those with females and hermaphrodites) is complex, with maternally inherited mitochondrial genes (CMS factors) causing male sterility and female phenotypes, and bi-parentally inherited nuclear genes (Rf) restoring male fertility, resulting in hermaphrodite phenotypes. Many gynodioecious species harbour multiple CMS and restoration factors. Aims: We tested the hypothesis that these sex determination factors were matched between geographically proximal populations and mismatched between distant populations, with the prediction that crosses from populations from the same continents would produce relatively more hermaphrodites, and crosses across continents would produce relatively more females. Methods: We measured the progeny sex ratios from reciprocal crosses among 10 families of Silene vulgaris from North America and Europe and sequenced the mitochondrial atp1 gene for each family. Results: Our results were inconsistent with the prediction of a mismatch between geographically distant populations. Progeny sex ratios suggested that frequencies of male fertility restorer alleles had low variability worldwide. Conclusions: Progeny sex ratios suggested at least four different matching CMS and restorer loci segregating within the cross and alluded to a cost of restoration. Our results support previous research indicating that both CMS and restorer types are maintained over long time periods.