Cutting Propagation Techniques For Three Acacia Species And Their Rooting Mechanism

Acacia trees belong to the genus Acacia of family Mimosaceae. They are characterized by fast growing, tolerance to poor soils, improvement of soil fertility by nitrogen fixation, and have become an important group of tree species widely planted for timber plantation development for industrial purposes in Southern China. However, due to constraints of shortage of seed sources, techniques for layering and grafting and other propogation methods, the plantation development of acacias has not met the current market demand. In order to promote the use of fine Acacia clones in silvicultural practices and enhance the production values of acacia plantations, there exists immediate significance in the establishment of appropriate propagation technology systems.Using cuttings of Acacia mangium, A.auriculiformis and a hybrid of A. mangium and A. auriculiformis (hereafter referrs to as"the hybrid") as test materials, a series of studies were conducted on the effects of rooting substrates, type and concentration of auxins, time of auxin treatments, and length and parts of cuttings on the cuttings'rooting characters. Also, the dynamic changes in nutrient contents, levels endogenous hormone and oxidase activities in cuttings were analyzed and the mechanism of cutting propagation was further studied. The main results are as follows:1) The highest rooting percentage was obtained from cuttings of the hybrid and A. mangium treated with IBA 400 mg.L^-1 for 2 hours and cuttings of A. auriculiformis treated with IBA 200 mg.L^-1 for 2 hours. The use of yellow subsoil as substrates led to the best rooting effectveness of cuttings; rooting rates of the hybrid, A.mangium and A.auriculiformis were 86.67%, 93.33% and 90%, respectively. The highest subordinate function value (1.46) for the hybrid was recorded in cuttings of 10-15 cm long, while A.mangium and A.auriculiformis produced the highest subordinate function values of 1.37 and 1.07, respectively by cuttings of 15-20 cm long. The rooting effectiveness of cuttings was different among the different cutting parts, the lignified top part of cuttings had the best rooting effectiveness. According to the observation of rooting process of the three species, rooting started on the 10th day after cutting for the hybrid and A.auriculiformis and reached the peak in 15-20 days after cutting. Cuttings of A.mangium began rooting in 10-15 days and reached the peak in 25-30 days after cutting . Based on the location of emergence of adventitious roots of the three species, the adventitious roots of the hybrid and A.auriculiformis originated preliminarily from the cortex of cutting's bottom section, and those of A.mangium mostly originated from the cortex, and also the callus of cuttings'bottom section.2) Higher levels of IAA, ABA, GA and ZR were demanded by cuttings of A.mangium and A.auriculiformis for the emergence of adventitious roots. For the hybrid, IBA treatment increased the content of IAA and decreased the content of ABA of the cuttings. Changes in IAA content were contrary to ABA, thus benefited the formation of adventitious roots. Changes in contents of nutrients such as starch, soluble sugar and soluble protein exhibited a certain regularity with the development of rootings. The content of mutrients in the base of cuttings decreased markedly during the period of induction of primordial rooting and the formation of adventitious roots, owing to the requirement of energy and substance for the rooting process. In the later period of rooting, the content of nutrients showed an uptrend, this might be due to the reduction of nutrient requirement after rooting. Tests of activities of POD and PPO in cuttings indicated that POD and PPO activities correlated significantly with rooting. The exogenous IBA could increase the cuttings'POD and PPO activities. The activity of POD had two peaks during rooting process, while PPO promoted rooting through producing"IAA- Hydroxybenzene-Acid".