Abstract: [Objective] A orthogonal experiment on softwood propagation of Thuja sutchuenensis. was carried out to study the effects of different mother tree age, growth regulator, containers and substrates on the rooting rate and the root development indicators such as the number of adventitious roots, length of longest primary adventitious root, root dry mass. The internal and external environmental factors affecting softwood cutting propagation were investigated to provide theoretical and practical basis for the softwood propagation, introduction and domestication of T. sutchuenensis.[Method] An orthogonal experiment design of four factors and three levels(L9(3⁴)) was applied to study the softwood cutting propagation of T. sutchuenensis in the greenhouse of Chinese Academy of Forestry, Beijing. The rooting rate of cuttings with different treatments was investigated in 70 and 260 days after cutting. The number of adventitious roots, length of longest primary adventitious root and root dry mass per cutting were measured in 260 days after cutting. The statistical analyses of these indicators were conducted.[Result] Results indicated that:the age of mother tree had a great impact on the rooting rate and the root development of cuttings. The younger the mother tree, the higher the rooting rate of cuttings. Also, the younger the mother tree, the better the root development. The growth regulator(IBA) had a great impact on the rooting rate and the root development of cuttings. The rooting rate after cutting 70 days and the number of adventitious roots, length of longest primary adventitious root and root dry mass in 260 days after cutting were optimized by IBA(2 000 mg·L^-1) dipping in 2 minutes. The containers had little influence on the rooting rate, but it had a significant effect on the length of the longest adventitious root. The order of the merits of various containers was:black soft plastic nutrient cup > non-woven fabric nursery bag > white hard plastic nutrition cup. The effect of substrates on rooting rate varied with cultural time. The substrates had no significant influence on the rooting rate of cuttings after 70 days, but had a significant influence on the rooting rate of cuttings after 260 days. The mixed substrate with peat, perlite and vermiculite was better than that of the pure peat soil. The substrates had significant effect on the length of the longest primary adventitious root and root dry weight.[Conclusion] The rooting rate and the root development of T. sutchuenensis were not only influenced by individual factors, such as age, growth regulator, cutting container, cutting matrix, but also affected by but also affected by a comprehensive effect of those factors. With the change of root developmental stage, the dominant factors that affect the rooting rate and the root development indicators changed constantly. The best treatment for rooting rate of T. sutchuenensis softwood cutting propagation was:the cuttings from 3-year-old mother tree, the cutting by fast dipping treatment with GGR₆, and the containers of non-woven fabric and the mixed substrate with peat, perlite and vermiculite(V:V:V=1:2:1). The best treatment conditions for the root development were:the cuttings from 3-year-old mother tree, the cutting by fast dipping treatment with IBA, and containers of Black soft plastic and the mixed substrate with peat, perlite and vermiculite(V:V:V=1:1:1), with which the rooting rate was as high as 95%. Therefore, considering the two aspects of rooting rate and root development, this combination would have great application value in softwood propagation of T. sutchuenensis.

Key words: Thuja sutchuenensis, softwood cutting propagation, the age of mother tree, the growth regulator, containers, substrate, the rooting rate, the root development