Cutting Propagation And Rooting Mechanism Of Dalbergia Odorifera

Dalbergia odorifera T.Chen is an important and precious rosewood tree which is indigenous to Hainan Province,China.It is widely used in high-value furniture,sculpture,Chinese Traditional medicine and others.With the economic development and constantly improvement of people’s living standards,natural wood resource of D.odorifera is far from the growing consumer’s demand,so it is urgent to develop plantation to increase the supply of wood,and improve the wood’s quality.Application of improved varieties of D.odorifera is a basis guarantee to improve the wood output and quality in forestry practice.However,it is an important way to propagate elite trees by cutting propagation.Therefore,it is of great practical significance to study the cutting propagation technology and rooting mechanism of D.odorifera to realize the large-scale of elite tree resources.On the basis of summarizing previous studies,the physiological mechanism of cutting rooting was discussed through conducting experiments on different internal and external factors affecting the growth of roots and shoots of cuttings,studying the anatomical characteristics,the dynamic change process of nutrients,endogenous hormone content and enzyme activity in the base cortex of cuttings during the key stage of adventitious root development.The different mechanism of genetics and molecular biology was explored by clone cuttings experiment and transcriptome sequencing.Finally,it provides theoretical basis and technical support for the cutting propagation technology of D.odorifera.The main results were as follows:（1）Anatomical observations show that the root primordium belongs to the induced root primordium and mixed rooting type（roots were induced from the bark and callus tissue）.The adventitious root primordium originated from the callus,the myelin rays and phloem,belonging to multiple sites to take root.In general,formation of adventitious root of D.odorifera can be divided into three stages:callus formation stage（0～10 d）,root primordium formation stage（10～20 d）,adventitious root growth stage.（2）Cutting substrate,cutting length,age of donor plant,cutting position and clones significantly affected rooting percentage and the growth of root system.Considering the rooting percentage,root and shoot development synthetically,D.odorifera cutting propagation results showed that the optimal combination was:a mixture of peat soil and vermiculite（1:1）was the preferred medium;The base branches of 2-year-old seedlings were cut into cuttings20～26 cm long for cuttings;500 mg·L^-1 IAA+750 mg·L^-1 NAA solution was used to soak the base of the cuttings for 1 min in production practice to carry out cutting propagation of D.odorifera.The mean rooting percentage of 4-year-old clones and seed seedlings was as follows:H4（56.25%）>H9（44.23%）>H1（43.75%）>H18（41.67%）>H3（39.58%）>seedlings（9.37%）.（3）The dynamic balance of nutrients（soluble sugar,starch,total nitrogen and soluble protein）,endogenous hormones（IAA,ABA,CTK and GA₃）and enzyme activities（IAAO,SOD,PPO and POD）in cuttings commonly regulate the appearance of adventitious root.The physiological indexes showed different characteristics and changing rules in the cuttings of different ages.（4）There was no significant difference in soluble sugar and starch content between young and old cuttings at different stages of cutting,which indicated that the difference in soluble sugar and starch content was not the main reason affecting the rooting percentage.During the whole cutting process,the total nitrogen content of young cuttings was always higher than that of old cuttings,and reached a significant level at 10,20 and 30 days,indicating that the difference of total nitrogen content was probably one of the main reasons for the age effect of cutting’s rooting.During the whole cutting process,the soluble protein content of young cuttings was almost between that of 5-year-old cuttings and that of 10-year-old cuttings,which indicated that there was an optimal soluble protein content for adventitious root formation of cuttings,and either high or low soluble protein content might inhibit rooting.The higher C/N value may be beneficial to the formation of adventitious roots in the cutting process,while the lower C/N value is conducive to the growth of roots.（5）The content of endogenous hormones had a great influence on adventitious root formation.Before cutting the young branches,the contents of IAA,ABA and GA₃ in young cuttings were significantly lower than those in old cuttings,while the content of CTK was significantly higher than that in old cuttings.During the cutting process,the change trend of different endogenous hormones in young and old cuttings was obviously different,so IAA,ABA,GA₃ and CTK were the main reasons for the rooting effect of different age cuttings.During the adventitious root formation stage（10～20 days of cuttings）,the increase of IAA and ABA content and the decrease of CTK and GA₃ content were more conducive to the adventitious root formation of young cuttings.（6）In the callus induction stage of young cuttings,IAAO content gradually increased,IAAO oxidized excessive IAA in the cuttings,and lower IAA contributed to the formation of callus.Therefore,higher IAAO activity contributed to the formation of callus in young cuttings.The change trend of SOD and PPO activities in young cuttings was the same during the process of cutting and rooting.The increase of SOD and PPO activities was beneficial to the formation of callus,while the decrease was beneficial to the formation of adventitious roots.The POD activity of young cuttings increased during callus and adventitious root formation,indicating that higher POD activity was beneficial to adventitious root formation of young cuttings.（7）A transcriptome sequencing analysis was conducted on the base cortex samples of cuttings after 0 d,10 d and 20 d.The results showed that 4581,6052 and 1819 DEGs were identified in AR0/AR10,AR0/AR20 and AR10/AR20,respectively.We used the Gene Ontology（GO）classification system to determine the possible functions of tagged genes.The GO ontology analysis showed that these DEGs mainly performed functions such as cellular processes,metabolic processes,biological regulation,cell components,membrane components,organelles,catalyst activity,cofactor binding,carbohydrate metabolism,DNA-binding transcription factor activity and transcriptional regulation activity.Based on KEGG database annotation information,the significantly enriched DEGs mainly performed metabolic pathways such as plant hormone signal transduction,phenyl propyl ester biosynthesis,glycolysis/gluconeogenesis,starch and sucrose metabolism,MAPK signaling pathway,copper propionate metabolism,amino acid and nucleotide sugar metabolism,and purine metabolism.