Development and application of a dCAPS marker for the white immature fruit rind colour gene w in cucumber (Cucumis sativus L.)

Immature fruit rind colour, a key factor influencing consumer choice, is an important external quality trait in cucumbers. The application of molecular marker‐assisted selection (MAS) can significantly improve the efficiency of the cucumber breeding process that focuses on fruit rind colours. In this study, we developed a dCAPS marker Csw_dCAPS co‐segregated with cucumber white immature fruit rind regulating gene w (Csaprr2) based on its 1‐bp ‘G/‐’ sequence insertion. Both validations of marker Csw_dCAPS among 59 cucumber commercial cultivars and 41 inbred lines showed that the Csw_dCAPS marker has 100% accuracy rates in identifying the green and white coloured immature fruit rinds controlling by alleles W and w. Application of Csw_dCAPS marker in cucumber lines XNS023‐1 and XNS023‐2 revealed that the white immature fruit rind in XNS023‐1 is also caused by the 1‐bp ‘G/‐’ insertion of gene w. We discussed the derivation of gene w in cucumber XNS023‐1 according to the genetic background differences between XNS023‐1 and XNS023‐2. Besides, this newly developed marker was also compared with the previously reported linkage marker SSR06791 to underscore the precision and reliability of Csw_dCAPS. Herein, we first reported and verified a dCAPS marker Csw_dCAPS that completely co‐segregated with the white immature fruit rind regulating gene w. We concluded that this high‐accuracy dCAPS marker can effectively facilitate the MAS breeding process of new cucumber cultivars characterized by white‐coloured immature fruits.