Crop-wild interaction within the Beta vulgaris complex: a comparative analysis of genetic diversity between seabeet and weed beet populations within the French sugarbeet production area.

Abstract

AbstractAmong the commonly listed risks associated with environmental release of genetically engineered cultivars is the hybridization of transgenic plants with wild relatives. The beet complex is of particular interest, as crop (Beta vulgaris ssp. vulgaris), wild (B. vulgaris ssp. maritima) and weedy forms are all interfertile and can be found in sympatry in various places in Europe, hence heightening the likelihood of accidental hybridization events. In northern France, sugarbeet fields can be found close to the coastline, together with the common wild seabeet populations. Nine wild populations and 12 weedy populations were sampled and examined for diversity of chloroplastic and nuclear DNA using polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) and microsatellite length variation. Most of the weed populations were characterized by a unique haplotype, named Owen CMS and characteristic of cultivated lineages. Although no diagnostic allele was depicted using microsatellite markers, a highly significant genetic differentiation was found between weed and wild forms. Furthermore, weed populations displayed a significantly lower allelic diversity in addition to a systematic heterozygote deficit compared with Hardy-Weinberg expectations. This suggests either an introgression between genetically differentiated gene pools within the region of seed production (i.e. a spatial Wahlund effect, as well as a temporal one), or the presence of self-compatibility alleles commonly used in breeding programmes. Taken together, our results seem to indicate a low overall level of gene flow from weed to seabeet populations in the French sugarbeet production area. Nevertheless, gene exchanges from crop to wild relatives were depicted for some seabeet populations, indicating the possibility of local introgression and highlighting the importance of case-by-case and long-term monitoring surveys.