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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.

In sugar beet breeding, sugar yield is mainly influenced by root yield and sugar content. In this short communication several indices to select for both traits simultaneously are compared in order to find the best one. The indices are correlated with the base index of Williams (1962) from independent experiments. The indices differ in the amount of information necessary for the calculation of their weights. Three different series of each eight sites gave similar results. The optimum index, using all information from phenotypic and genotypic variances and covariances, did not perform best. Sugar content with its higher heritability must have a larger weight than root yield. Heritabilities as index weights performed best, but two other indices using heritabilities and phenotypic but no genetic covariances also performed well. [ABSTRACT FROM AUTHOR]