Submitted to: Journal of Theoretical and Applied Genetics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 30, 1998
Publication Date: N/A
Interpretive Summary: The genetic base in sugar beet is thought to be narrow since it is a relatively recently introduced crop and few plants may have been involved in its origin. If true, the lack of genetic variation in sugar beet would hinder sugar beet improvement in the future. An analysis of sugar beet germplasm which has been released in the United States during the period between 1920 and 1970 was performed to see if genetic variation had decreased over this time, and if so what were the major reasons for this decline. It was concluded that diversity had not declined overall, but breeding had reorganized the distribution of genetic variation such that early varieties showed little differences between themselves but later releases were often different from one another. The most severe loss of genetic diversity was seen in sugar beets that had been specifically inbred as the result of breeding for a few essential agronomic traits. These results are important because they establish a baseline of genetic diversity with which to examine future genetic erosion in sugar beet. They also indicate that diminishing returns may be expected in efforts to further select improved types within some existing materials. Broadening the genetic base of sugar beet would seem to be prudent.
Technical Abstract: Diversity among sugar beet accessions released over the first 50 years of public breeding in the United States was examined to ascertain a baseline of genetic diversity and gauge the effect of breeding on the loss or gain of diversity over this time period. Accessions were chosen as released germplasm from the major breeding stations contributing to the U.S. germplasm pool and their presumed ancestors from Europe, including representatives for the wild forms Beta vulgaris ssp. maritima. Using 69 polymorphic RAPD fragments for gene frequency analysis, heterozygosity was determined within and among groups of accessions related either by breeding station or simply-inherited agronomic characters for monogerm seed and restoration of fertility in a cytoplasmic male sterile background. In general, heterozygosity within releases declined with time but total genetic diversity in the U.S. germplasm pool remained constant. Breeding for the agronomic characters had a marked influence in reducing diversity.