Five 5.5-year-old hybrid families seedling ortets in larch nursery of Maojingba forest farm,Hebei Province,were used as regenerating materials in this experiment,the effect of IBA concentration and soaking time on rooting of semi-hardwood cuttings of hybrid larch and the response of different hybrid families to auxin treatment were systematically studied,and the genetic parameters of rooting under different auxin treatments were estimated. The results showed that suitable IBA treatment had an obvious effect on accelerating rooting and root development of hybrid larch cuttings. Rooting percentage increased with enhancing IBA concentration or extending soaking time,but decreased when reaching a certain concentration and soaking time. The root number increased with enhancing IBA concentration or extending soaking time,however,one-sided rooting percentage had reverse trend. Rooting percentage and root development of Larix kaempferi 73-2×Hybrid 93-16 were better than other hybrid families,the percentage of rooted cutting was up to 94% and mean root number per cutting was 5.3 by 200 mg·L-1 IBA soaked with 20 min. The following hybrid family was L. kaempferi 12 ×L.gmelinii 9,whose percentage of rooted cutting was up to 87% and mean root number per cutting was 4.8 by 400 mg·L-1 IBA soaked with 30 min. Genetic parameters of rooting traits changed greatly under the different auxin treatments,the trend of changes in the heritability of root number and rooting percentage with the IBA concentration and soaking time was similar to the root number and rooting percentage by the different auxin treatments.
