Broadening the genetic base of sugar beet: introgression from wild relatives

The development of sugar beet as an economically important field crop coincided with our increased understanding of modern genetic principles. It was developed in the late 1700s from white fodder beet; therefore, the genetic base of sugar beet is thought to be narrower than many open-pollinated crops. The wild sea beet is the progenitor of all domesticated beet and cross compatible with cultivated beet (domestic and cultivated are given subspecies level in the same species). The breeding system of sugar beet is complex and the crop is biennial, which lengthens the generation time to almost 1 year. A genetic-cytoplasmic male sterility (CMS) system is utilized for commercial hybrid production. Early breeding objectives were to improve the concentration and extractability of sucrose and little emphasis was placed on host-plant resistance to insect, nematode, and disease pests. As production areas expanded, these pests limited production, sometimes severely. The first systematic attempts to screen exotic and wild beet germplasm for disease resistance were initiated early in the 20th century. Many undesirable traits from wild beet were reportedly introgressed with the selected disease resistance and it was only in the late 1900s that the use of wild beet genetic resources became common place in public breeding programs. In North America, a pivotal development in utilizing the genetic resources available for sugar beet breeding was the formation in 1983 of the Sugarbeet Crop Germplasm Committee (CGC). Since the Sugarbeet CGC identified enhancing the commercial sugar beet germplasm pool as a high priority, there has been an aggressive evaluation of the National Plant Germplasm System (NPGS) Beta collection. This collection now has more than 2500 accessions from within the genus Beta. In 2002, it was estimated that close to 25,000 evaluation data points (descriptors x accessions evaluated) describing the collection were available in the Genetic Resources Information Network (GRIN) database. Over 3000 evaluations described levels of resistance of sugar beet and wild beet accessions to 10 major disease and insect pests of sugar beet. As soon as the evaluation data are collected, they are used to select the sources for the pre-breeding programs. There is a lag time in sugar beet of 8-15 years between starting a germplasm development program and releasing the first germplasm, but successes of this program are available in the germplasm released to the commercial breeders. Resistance genes from wild beet for rhizomania and beet cyst nematode resistance have been commercialized.