Inheritance patterns and heterosis of key floral traits in interspecific hybrids of Clematis tientaiensis × C. lanuginosa: implications for breeding compact cultivars

Clematis cultivars are predominantly developed through hybridization, yet the genetic architecture of key ornamental traits remains poorly understood. In this study, C. lanuginosa and C. tientaiensis , along with their F 1 progeny, were utilized to investigate the inheritance patterns of ten floral and vegetative traits. Specifically, we analyzed flower stalk length (FS), flower diameter (FD), sepal length (CL), sepal width (CW), stamen length (SL), pistil length (PL), Leaf blade length (BL), Leaf blade width (BW), blooming period (BBP), and flower color value (CCV) using heterosis analysis and a major gene plus polygene mixed genetic model. Ten phenotypic traits exhibited continuous, unimodal, and skewed distributions, with eight traits showing leptokurtic patterns (kurtosis > 0) and two traits showing platykurtic patterns (kurtosis < 0) across both populations, indicative of quantitative traits controlled by multiple genes. In Cross I, BL (-2.41) and BW (-2.04) displayed significant negative mid-parent heterosis, whereas BBP (7.99) and CCV (1.08) exhibited positive mid-parent heterosis. In Cross II, BL (-3.47) and BW (-1.61) showed significant hybrid depression, while BBP (6.54) and CCV (0.36) demonstrated significant mid-parent heterosis. Genetic analysis identified the optimal inheritance models as follows: Model 2MG-AD (two major genes with additive-dominance effects) for FS, FD, CL, and CW, with the first gene pair showing predominant additive effects (d a = 1.81, 2.76, 1.31, and 0.70, respectively); Model 2MG-A (two major genes with additive effects) for SL, with the second gene pair contributing larger additive effects (d b = 0.39); Model 2MG-ADI (two major genes with additive-dominance-epistatic effects) for PL and BL, with negative dominance effects (h a = -0.55 and -1.15, respectively); Model 2MG-EA (two major genes with additive-equal effects) for BW and BBP, with additive effects of 0.65 and 10.86, respectively; and Model 1MG-A (one major gene with additive effects) for CCV, with an additive effect of 1.62. Except for BW, the major gene heritability for the remaining nine traits exceeded 88%, suggesting that these traits are under strong genetic control under the specific environmental conditions of this study. These findings provide valuable genetic information to support future breeding efforts in Clematis .