Abstract: To screen molecular markers linked to genes tightly controlling flesh root diameter of turnip（Brassica campestris L. ssp. rapifera Matzg）and to identify the QTL number，effect and location in the map，two F₂ populations from the cross between Chinese cabbageBre-1-1-1-1and turnip W-2-1-8-1 were studied in spring and autumn. The flesh root diameters of F₂ populations were changed continuously and marked bias towards the parent turnip，suggesting that it was quantitative trait，controlled by multiple genes. Four QTLs for controlling flesh root diameter were screened in spring F₂ population，mapped on A09，A07，A02 and A03，respectively. A QTL locus frs-1 was detected on partial linkage group A09，which was constructed with 23 markers screened by bulked segregation analysis（BSA）in autumn F₂ population，the contribution of frs-1 to the total variation was 36.07% with LOD score of 8.19. This locus was a novel and major QTL，stable detection across the two seasons and useful for marker-assisted selection and for gene cloning of flesh root diameter.

Key words: turnip, flesh root, diameter, QTL