QTL screens for the traits reported (Table 3) were conducted using an inclusive composite interval mapping (ICIM) approach implemented in QTL IciMapping v4.0 (Wang et al., 2014). Missing phenotypes were deleted using the ‘Deletion’ command in the software. The walking speed was set at 1 cm. A suitable probability for entering marker variables in stepwise regression was chosen so that the variation explained by the model approximated the trait heritability. The regression model was then used for background genetic variation control in the ICIM QTL mapping. The LOD was calculated using 1000 permutations, with a Type 1 error being 0.05, and significant QTLs were defined accordingly.