Genetic diversity is enhanced in wild x cultivated hybrids of sugarbeet despite multiple selection cycles for cultivated traits

Authors: Fugate, Karen; CAMPBELL, LARRY - Former ARS Employee; COVARRUBIAS-PAZARAN, GIOVANNY - University Of Wisconsin; Rodriguez Bonilla, Lorraine; Zalapa, Juan

Submitted to: Genetic Resources and Crop Evolution
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/21/2021
Publication Date: 3/4/2021
Citation: Fugate, K.K., Campbell, L.G., Covarrubias-Pazaran, G., Rodriguez-Bonilla, L., Zalapa, J.E. 2021. Genetic diversity is enhanced in wild x cultivated hybrids of sugarbeet despite multiple selection cycles for cultivated traits. Genetic Resources and Crop Evolution. 68:2549-2563. https://doi.org/10.1007/s10722-021-01149-w.
DOI: https://doi.org/10.1007/s10722-021-01149-w

Interpretive Summary: Breeding crop plants with related wild plant species is a method commonly used to introduce new characteristics into crop plants to improve crop yield, crop quality, or resistance to unfavorable production conditions or disease. The breeding of cultivated crop plants with their wild relatives, however, also introduces undesirable traits from the wild parent and these are removed by breeders by choosing among the progeny of these breeding efforts for plants that do not exhibit these undesirable traits or exhibit them to a lesser extent. The question arises, however, whether selection to remove undesirable traits inherited from wild plant parents also removes the desirable traits of the wild parent which can be used to improve the cultivated crop. Research, therefore, was conducted to determine the extent that selection of progeny from sugarbeet lines obtained by crossing cultivated sugarbeets with wild sugarbeet relatives for typical sugarbeet root shape, high sucrose content and a resistance to flowering during the production season, reduced the ability of these lines to contribute new and potentially useful traits from the wild parent. Although choosing progeny for typical cultivated sugarbeet traits reduced the contribution of the wild parent in the resulting sugarbeet lines, these lines retained many of the genetic traits and characteristics of their wild parents. These lines, therefore, are useful resources that can be used in sugarbeet breeding programs to introduce new traits into the sugarbeet crop to improve productivity and tolerance to unfavorable environmental conditions or disease.

Technical Abstract: Genetic diversity is enhanced by introgressing wild germplasm into breeding lines and populations. Such introgression, however, commonly introduces wild traits that must be removed by backcrossing and selection before lines are useful for elite breeding programs. Selection against wild characteristics is expected to reduce genetic diversity in introgressed lines. However, the effect of such selection on genetic diversity has not been evaluated for sugarbeet (Beta vulgaris L.). Therefore, genetic diversity was determined for 24 germplasm releases derived from cultivated sugarbeet by wild sea beet (B. v. subsp. maritima) crosses after undergoing multiple selection cycles for cultivated traits and compared to the diversity of their wild parents and cultivated sugarbeet lines using simple sequence repeat (SSR) analysis. Diversity in germplasm derived from wild x cultivated crosses was intermediate of wild and cultivated lines in observed heterozygosity, inbreeding coefficient, and the number of alleles, private alleles, and low frequency alleles. Principal component and neighbor joining analyses demonstrated that wild x cultivated-derived germplasm shared greater similarity with cultivated germplasm than to their wild parents, while STRUCTURE analysis indicated that wild x cultivated-derived germplasm was an admixture of wild and cultivated-derived germplasm. Diversity, therefore, was enhanced in germplasm derived from wild x cultivated crosses, although selection for cultivated traits reduced the diversity added by introgression with wild accessions. Nevertheless, the enhanced genetic diversity in germplasm releases derived from wild x cultivated crosses identify these lines as a resource for unique genes and alleles to improve crop productivity, adaptation, and disease tolerance in sugarbeet.