Optimization Study on Growth Regulators for Water-Cultured Cutting Propagation of Gardenia jasminoides 'Lingdi Zhenzhi’

To screen the optimal combination of plant growth regulators for hydroponic cuttings propagation of the new G.jasminoides cultivar 'Lingdi Zhenzhi’,optimizing rooting efficiency and root system development quality. Using semi-lignified branches of 'Lingdi Zhenzhi’ as material,a three-factor,three-level L₉(3³)orthogonal experiment was conducted(Factor A:IAA,IBA,NAA;Factor B:200,300,500 mg·L^-1;Factor C:soaking time 2,4,6 h). Root rate,root length,root number,and root efficiency index(REI)were measured 30 days after cutting. The optimal treatment combination was determined through range analysis and analysis of variance. Results indicated that regulator type(R_A=34.81)was the dominant factor influencing rooting rate(IBA > IBA > NAA),followed by concentration(R_B=18.89)and duration(R_C=4.07). The highest average root number was achieved with IBA 300 mg·L^-1 soaked for 6 h(1.94±0.54 roots);The longest root length was achieved with IBA 500 mg·L^-1 for 2 h immersion(2.12 ± 0.72 cm). The highest root effectiveness index(REI)of(1.85 ± 0.66)was obtained with IBA 300 mg·L^-1 for 6 h immersion,reflecting synergistic enhancement in both root quantity and quality. Based on four indicators-total rooting rate,root number,root length,and REI—membership function analysis identified the optimal treatment as IBA 200 mg·L^-1 soaked for 4 h. yielding a rooting rate of 62.22% and an REI of 1.42. This combination significantly outperformed others,establishing it as the optimal plant growth regulator regimen for promoting rooting in hydroponic cuttings of 'Lingdizhenzhi’. This formulation achieves a balanced improvement in both rooting efficiency and root system quality.