Beet soil-borne virus (BSBV) is widely distributed in German sugar beet growing areas. Frequently it is associated with beet necrotic yellow vein virus (BNYVV), the causal agent of rhizomania disease of sugar beet. Both viruses, BNYVV and BSBV, are transmitted by the same vector, the soil-borne fungus Polymyxa betae. Similarity in particle morphology and the observation of rhizomania-like symptoms on sugar beet in fields where BNYVV is absent have led to speculation over the contribution of BSBV to rhizomania disease. Due to the high economic importance of rhizomania for the sugar beet crop and possible consequences in breeding for rhizomania resistance a research project was carried out at IfZ to examine the economic importance of BSBV. This project was funded by the association of the German sugar beet breeders („Gemeinschaft zur Förderung der privaten deutschen Pflanzenzüchtung e.V. (GFP)“). The project consisted of epidemiological studies focused on the distribution of BSBV and BNYVV in German sugar beet growing areas and of variety trials at several locations with a set of susceptible and rhizomania resistant sugar beet varieties. The project was completed by greenhouse experiments in which physiological reactions of susceptible and resistant varieties to BSBV and BNYVV – individually or in combination – were examined. The results obtained in this study allow us to answer clearly the question regarding the possible contribution of beet soil-borne virus to rhizomania disease. No evidence was found that sugar beet is damaged by BSBV nor that BSBV plays a role in rhizomania. Symptoms on beet as well as changes in metabolic parameters and yield performance typical of rhizomania could only be found on plants infected with BNYVV, not after infection with BSBV.