QTL mapping for petiole shape in non-heading Chinese cabbage

Non-heading Chinese cabbage (NHCC) is an important leafy vegetable in China. Petiole shape is crucial for NHCC, and cultivating diverse and abundant petiole shapes is essential to meet consumer demand. Understanding the genetic mechanism for petiole shape is significant for variety innovation. Petiole length (PL), petiole width (PW), and petiole thickness (PT) emerge as cardinal phenotypic proxies for shape characterization. In this study, 127 RILs from Wutacai and Erqing were used for QTL mapping. Genetic analysis revealed that PL, PW, and PT are dominant traits controlled by multiple genes. To obtain comprehensive and accurate QTL, phenotypic data collected from three locations and BLUP values were used for QTL mapping. 19 stable QTLs were detected and distributed as four for PL, seven for PW, and eight for PT. The QTL on chromosomes A03 and A04 were detected in all three traits and shared similar physical positions. The QTL <italic>qPL.A03.1</italic>, <italic>qPW.A03.1</italic>, and <italic>qPT.A03.1</italic> showed negative additive effects, signifying the contributions for slender, wider, and thicker petiole from the Erqing allele. The QTL <italic>qPL.A04.1</italic> and <italic>qPT.A04.1</italic> exhibited positive additive effects, whereas <italic>qPW.A04.1</italic>showed negative additive effect, which suggested that the Wutacai allele contributed to slender and thicker petiole and contributions from Erqing allele led to wider petiole. Candidate genes analysis in parental lines revealed that <italic>BcIAA31</italic> and <italic>BcBOP2</italic> were the promise candidate genes in QTL on chromosomes A03 and A04. These findings advance mechanistic understanding of petiole morphogenesis and establish a molecular toolkit for marker-assisted pyramiding of optimal petiole traits in NHCC breeding programs.