Mapping of QTLs detected in a broccoli double diploid population for planting density traits

The planting density of broccoli can directly affect the yield and overall health of plants. Nonetheless, studies on the genetic base of planting density in broccoli are rather limited. In this study, the important planting density-dependent factors of broccoli, plant height (PH), maximum outer petiole length (PL) and leaf width (LW), were investigated during 2017 and 2018. In this study, mapping of QTL for PH, PL and LW based on a DH population in broccoli, and as well as the interaction between QTLs and the environment. The DH population was constructed with 176 genotypes obtained from F1 hybrid produced by crossing two different inbred lines 86101 (P1) and 90196 (P2). In our study, a linkage group including a total of 438 SSR markers were constructed covering a length of 1168.26 cM using QTL IciMapping 4.0 software. Finally, there were mainly four QTLs (phc1, phc2, phc4−2, phc4−3), one QTL (plc6−2), and two QTLs (lwc1, lwc3−1) corresponding for PH, PL and LW recurred during the two years. In three environments, inclusive composite interval mapping (ICIM) analysis showed that there was a major QTL for PH at 7.20 cM on chromosome 1 with a high explanatory contribution rate of 20.05 %. The QTL at the 11.10 cM position of chromosome 6 was located for the PL with a high explanatory contribution rate of 20.02 %. The QTL at the 147.00 cM position of chromosome 3 was located on LW with a high explanatory contribution rate of 19.97 %. Interestingly, we found an overlap region (pplc4) in the chromosome 4 containing three QLTs for traits PH, PL, and LW (phc4−2, plc4−3, and lwc4−2). According to this study, the possible positions of candidate genes were screened to provide a basis for further locating and cloning genes for plant height, maximum outer petiole and leaf width, which would be beneficial to breeding of broccoli and the Brassica crops, especially in high planting density.