Rapid identification of agronomically important genes is of pivotal interest for crop breeding. One source of such genes are crop wild relative (CWR) populations. Here we used a CWR population of <200 wild beets (B. vulgaris ssp. maritima), sampled in their natural habitat, to identify the sugar beet (Beta vulgaris ssp. vulgaris) resistance gene Rz2 with a modified version of mapping-by-sequencing (MBS). For that, we generated a draft genome sequence of the wild beet. Our results show the importance of preserving CWR in situ and demonstrate the great potential of CWR for rapid discovery of causal genes relevant for crop improvement. The candidate gene for Rz2 was identified by MBS and subsequently corroborated via RNA interference (RNAi). Rz2 encodes a CC-NB-LRR protein. Access to the DNA sequence of Rz2 opens the path to improvement of resistance towards rhizomania not only by marker-assisted breeding but also by genome editing.

Forty-one accessions of the genusBeta representing wild and cultivated species of all sections were analyzed by DNA "fingerprinting". Four sugar beet minisatellite DNA probes revealed characteristic banding patterns with Southern-hybridizedBeta DNA restricted withHindIII. A total of 111 polymorphic RFLP bands were scored across all accessions. Cluster analysis based on genetic similarity estimates for all 820 combinations of accessions revealed the following results. (1) All accessions could unambiguously be identified by a characteristic RFLP banding pattern. (2) The sugar beet cultivars examined displayed a low level of genetic diversity; they showed high similarity toB. Vulgaris ssp.maritima but low genetic similarity to the other wild species of section I. (3) In most cases, the present taxonomic classification of the genusBeta was confirmed. Species of sections II, III, and IV were clearly distinguishable from those of section I except forB. Macrocarpa, which showed high similarity to wild species of section II. In a second experiment, 108 single-copy RFLP probes from sugar beet were Southern hybridized withB. procumbens DNA. A surprisingly low degree of homology (34%) was found. The results are discussed with regard to the taxonomic classification of the genusBeta.

This chapter reviews topics on: the sugarbeet breeding research community; the genus Beta and its useful characters; bottlenecks to the utilization of Beta genetic resources; breeding approaches to broaden the genetic base of Beta (introgression from the primary gene pool; introgression from the tertiary gene pool; incorporation from the primary gene pool; incorporation from the secondary gene pool). The future role of gene banks in germplasm enhancement programme is also discussed.

Resistance to four foliar diseases of sugar beet (Beta vulgaris ssp. vulgaris), virus yellows caused by Beet mild yellowing virus (BMYV) and Beet yellows virus (BYV), powdery mildew (Erysiphe betae) and Cercospora leaf spot (Cercospora beticola), was assessed in up to 600 accessions of closely related wild and cultivated Beta species. Most accessions were from the Section Beta, a taxon containing types most closely related to, and sexually compatible with, sugar beet and therefore most valuable for use in crop improvement. Between 1–12% of accessions were highly resistant (resistance scores of ≤2 on an international standardised resistance scale of 1–9) to these diseases. These levels, however, underestimate the potential number of resistant sources available from this section as some accessions with intermediate mean resistance scores contained a significant proportion of highly resistant plants within segregating populations. Variation in resistance to all diseases except BYV was observed within the Section Beta. Much higher levels of resistance were observed, and more frequently, in more distantly related sections of the genus Beta. Accessions of the Section Corollinae were highly resistant to both viruses (>62% of accessions tested), but less so to Cercospora (15%) and they were very susceptible to powdery mildew. Section Procumbentes accessions were highly resistant to BMYV and Cercospora (100%) but less so to powdery mildew (50%) and BYV (20%). However, sexual incompatibility between these sections and sugar beet make utilisation of these sources impractical using conventional breeding methods

This chapter summarizes the procedure used to select the crop wild relative (CWR) species for inclusion in the European Red List and the process and results of undertaking the regional assessments using the IUCN Red List Categories and Criteria (IUCN, 2001). The results of this initiative show that a significant proportion of the species assessed are threatened or are likely to become threatened in the near future and that some crop gene pools or crop groups, such as the cultivated beets, are particularly at risk. These species should be subject to immediate conservation gap analysis and concerted actions.