AN EXTENDED LINKAGE MAP OF SUGAR-BEET (BETA-VULGARIS L) INCLUDING 9 PUTATIVE LETHAL GENES AND THE RESTORER GENE-X

An extended genetic map of sugar beet (Beta vulgaris L.) is presented encompassing 177 segregating markers (2 morphological traits, 7 isozymes, and 168 RFLP markers) on 9 linkage groups. The linkage map comprises 1057.3 cM equivalent to an average generic spacing of 6.0 cM/marker. The length of individual linkage groups varies between 80.7 (group VIII) and 167.4 cM (group VII). The number of markers per linkage group ranges between 13 and 24. No indication of duplicate regions was found, con firming the true diploid nature of B. vulgaris. Twenty-six markers (15%) deviated significantly (alpha = 0.01) from the expected segregation ratio. This distorted segregation was probably caused by linkage with lethal genes. Four such genes (designated Let 1b, Let 5b, Let 6b, Let 8) could be located at discrete positions due to their absolute linkage to skewed RFLP markers. The restorer gene X has been located terminally on linkage group III, 9.6 cM distant from RFLP marker pKP1238.