Genetic diversity in selected, historical US sugarbeet germplasm and Beta vulgaris ssp maritima

Diversity among sugar beet accessions released over the first 50 years of p ublic breeding in the United States was examined to ascertain a baseline of genetic diversity and to gauge the effect of breeding on the loss or gain of diversity over this time period. Accessions were chosen as released germ plasm from the major breeding stations contributing to the US germplasm poo l and their presumed ancestors from Europe, including representatives for t he wild forms Beta vulgaris ssp. maritima. Sixty nine polymorphic RAPD frag ments were used for gene frequency analysis, and heterozygosity was determi ned within and among groups of accessions related either by breeding statio n or simply inherited agronomic characters for monogerm seed and restoratio n of fertility in a cytoplasmic male-sterile background. In general, hetero zygosity within releases declined with time, but total genetic diversity in the US germplasm pool remained constant. Breeding for the agronomic charac ters had a marked influence in reducing diversity.