Beta breeding and genetics at East Lansing, Michigan: molecular methods, genetic diversity, and trait elucidation.

Variety and germplasm development and release have been the main goals of the USDA-ARS sugarbeet (Beta vulgaris L.) breeding program at East Lansing, MI for over 70 years. Progress has been made in improving tolerance to Aphanomyces seedling disease, Cercospora leaf spot tolerance, Rhizoctonia crown and root rot tolerance, herbicide resistance, and low-tare (smooth root) root morphology. The genetic basis of these traits is not well understood, and the current program seeks to identify genes that influence the expression of disease, quality, and morphological traits, and locate them on beet chromosomes. The out-crossing nature of sugarbeet is not well suited for large-scale genetic analyses. A strategy has been adopted that should allow genetic dissection of a variety of traits through standard genetic analyses. Briefly, a genetic male sterile seed parent that also carries a dominant self-fertility gene is paired with germplasm of interest. The resulting self-fertile hybrid is self-pollinated to produce a segregating F 2 population, which is simultaneously observed for segregation of targeted traits and tested for linkage of these traits using molecular markers. Segregation of male-sterility and self-fertility genes in the F 2 gives a range of options for further characterization. In addition, this strategy allows relatively rapid introduction of traits from wild and unadapted germplasm while simultaneously determining the genetic basis for novel traits introduced through such crosses. Using this system will allow systematic exploration of linkage relation-ships between agronomic genes from diverse germplasm sources and molecular markers.