THE GENETIC-STRUCTURE OF BETA-VULGARIS SSP MARITIMA (SEA BEET) POPULATIONS - RFLPS AND ISOZYMES SHOW DIFFERENT PATTERNS OF GENE FLOW

Genetic variation in 12 populations of sea beet was assessed at nine i sozyme and seven RFLP loci. Mean observed heterozygosity, diversity in dex and number of alleles per locus were not significantly different b etween the two classes of marker. The genetic structure of 10 of the p opulations was analysed using seven of the isozymes and six of the RFL Ps. F-ST values between all pairs of populations were calculated separ ately for the isozymes and RFLPs. F-ST values were converted to amount s of gene flow (Nm) between populations under the assumptions of an is land model. A regression of log Nm against log distance was used to te st for isolation by distance. Mantel tests showed a highly significant decrease in Nm with distance for RFLPs but not for isozymes. It is su ggested that uniform balancing selection may operate to maintain appro ximately equal allele frequencies among populations at the isozyme loc i. If this is true then isozymes may be unsuitable for modelling the s pread of neutral transgenes.