Sdudies On The Cutting Propagation Technique And Rooting Mechanism Of Thuja Occidentalis

Thuja occidentalis,also called Northern white-cedar,mainly produced in eastern United States as an evergreen tree.It is used as an environmentally friendly landscaping tree because of the beautiful canopy,strongly green leaves and the function of resisting smoke,sulfur dioxide.The foliage is rich in flavonoids,tannins and other ingredients,it has a good medical effect.Based on two-year-old cuttings,the cutting propagation system of Thuja occidentalis is optimized from the aspects of cultivars,substrates,cutting time and hormone treatment.Besides,the rooting mechanism was studied by analyzing the dynamic changes of endogenous hormones,oxidase activity and nutrient content,it aims to provide a theoretical reference for cutting propagation of Thuja occidentalis.The results are as follows:(1)The effects of different cultivars,substrates,cutting time,hormone type,hormone concentration and dippingtime on the rooting were significant.The optimal cutting propagation system of Thuja occidentalis was as follows:based on two-year-old cuttings of 'Green Giant',cutting in the substrate of V(perlite):V(peat soil)= 3:1,cutting on autumn,treating with K-IBA for 10s,the rooting rate was 92.22%.(2)Morphological observation showed cuttings rooted both from the callus at base and primary phloem,wherein rooting from basal callus was the main type.The formation of adventitious roots was divided into three stages:0-24days for callus formation,24-48d for adventitious root formation,48-60d for adventitious root elongation.(3)Endogenous hormones(IAA,ABA,ZT,GA)have an important regulatory role in rooting The contents of IAA,ZT,GA decreased in the callus formation period,and increased in adventitious root formation and elongation period.The content of ABA decreased in the whole rooting process.K-IBA promoted the synthesis of IAA,inhibited the synthesis of ABA,ZT,GA,and formed high ratio of IAA/ZT,IAA/ABA,which promoted rooting.(4)The activity changes of POD,PPO and IAAO are closely related to the formation of adventitious roots.In callus formation period,the activity of POD and PPO increased,IAAO activity decreased;in adventitious root formation period,POD and PPO activity decreased,IAAO activity increased;in adventitious root elongation period,POD activity increased slightly,PPO activity stabilized,IAAO activity decreased.K-IBA promotes the rooting by raising the activity of POD,PPO and reducing the activity of IAAO.(5)The metabolism of nutrients has an important effect on rooting.In callus formation period,the content of soluble protein,soluble sugar,total nitrogen increased,starch content decreased;in adventitious root formation period,the content of soluble sugar,soluble protein decreased,starch content increased,total nitrogen content remained stable,in adventitious root elongation period,the content of nutrients increased.K-IBA is beneficial to the accumulation of soluble protein and soluble sugar,improving the utilization efficiency of starch and formed high C/N ratio resulting in a better rooting.