Study On The Good Variety Of Guangxi Dendrobium Candidum In Tissue Culture

Dendrobium candidum is a precious traditional Chinese herbal medicine which belongs to Dendrobium species, Orchidaceae. It tops the list of Nine Medicinal Herb in China with the folk name of "Lifesaver". It is widely distributed in provinces of the southern area of Qinling Mountain. At present, the wild recourses of D. candidum have been endangered because of over-exploitation, as well as its low survival and growth rate. However, an increasing demand for D. candidum in recent years, so artificial cultivation on a large scale is the only way to solve this contradiction. This article takes the good varieties of D.candidum in Guangxi which have screened for years by Guangxi Junjie Biological Technology Co., Ltd. in tissue culture., and strives for construction the propagation system which is favorable for Guangxi D. candidum. The results of the experiments are as follow(the D. candidum in the flowing without the indicated strain names is Guilin strain):1. The seed of D. candidum plant in the medium MS+NAA0.5mg L+20% potato juice can induce high quality of PLBs, the growth of PLBs is mainly affected by the planting density. When inducing cluster buds by stem, 1/2MS+NAA0.05mg/L+6-BA0.5mg/L+KT0.1mg/L +LH1.0g/L (lactoalbumin hydrolysate) is the most favorable medium with the induction rate of 31.8%. Increasing the amount of KT and LH and adding 2,4-D, the stem shoots out buds and swells, but no PLBs is induced.2. To cultivate protocorm with different medium. PLBs has the maximum growth coefficient in MS medium, and the three strains have differentiation of varying degrees. MS+ NAA 1.0mg/L+6-BA 1.0mg/L+20% potato juice has extensive applicability to the propagation of three strains of PLBs.3. MS medium is better for differentiation of PLBs than 1/2 MS medium, without vitrification. Adding NAA alone to MS medium for inducing the differentiation of PLBs, it is of good differentiation state at a concentration of 0.2mg/L. When NAA is constant in concentration and 6-BA is changed in concentration, the concentration of 6-BA at 0.3mg/L is more favorable for the differentiation of PLBs. Adding high concentration of KT is not favorable for the differentiation of PLBs, so its concentration should be preferably below 0.1mg/L. MS+NAA 0.5mg/L+6-BA0.5mg/L+KT0.1mg/L is the most favorable medium for the differentiation of PLBs with the differentiation rate of 100%.4. The growth status of tissue culture seedling in MS medium is better than in other mediums. Adding NAA in MS medium for plantlet strengthening, then different strains have different growth situation. Guilin strain grows best in medium with 0.5mg/L NAA, with light green tissue culture seedling. Baishi Moutain strain grows well in medium with 0.3mg/L NAA. Rong County strain grows fast in medium with 1.0mg/L NAA. The results indicate that different D. candidum has different needs for auxin. In the experiment for plantlet strengthening with NAA and 6-BA used cooperatively, the medium MS+NAA0.5 mg/L+6-BA0.5mg/L+20% potato juice has extensive applicability to three strains plantlet strengthening based on the above results, which indicates that complex hormone is more favorable for plantlet strengthening of D. candidum. Tissue culture seedling becomes browning of varying degrees when plantlet strengthening with NAA and KT used cooperative. By way of comparison, the tissue culture seedling becomes stronger and grows faster in a medium of 0.2mg/L KT with NAA of different concentration. It is found that when plantlet strengthening with NAA,6-BA and KT used cooperatively, MS+NAA0.3 mg/L+6-BA0.5+KT0.2+20% potato juice has the best effect of plantlet strengthening. Adding 0.5g/L activated carbon in the medium can effectively prevent from browning, and 1.5g/L activated carbon can promote the growth of tissue culture seedling.5. When the growth coefficient for induced cluster buds by stem in minimal medium is 3/4MS, the sprouting grows faster and it is more favorable for inducing cluster buds by stem. The growth rate is low when inducing cluster buds with 1.Omg/L 6-BA and NAA of different concentration, and the growth rate is maximized when the concentration of NAA is 0.4mg/L. Inducing cluster buds with 0.1mg/L KT and 6-BA of different concentration, the growth coefficient is the highest with the concentration of 6-BA within the range of 0.3～0.4mg/L, which indicates that 6-BA within certain range is favorable for inducing cluster buds. It is found that inducing cluster buds with KT of different concentration and 0.4mg/L 6-BA, the average sprouting rate is the highest when the concentration of KT is at 0.8mg/L.From the results of this article,the most favorable medium of inducing cluster buds by stem is MS+6-BA0.3～0.4mg/L+ KT0.1mg/L+LH1.0g/L, Inducing cluster buds by stem is better than by apical bud with high survival rate. Removing leaves of sem and planting it into medium vertically is more favorable for germinating.6. NAA used alone for root induction is with poor effects, while NAA and IBA used cooperatively may develop the root. Moreover, adding 6-BA with concentration of higher than 0.1mg/L may decline the quality of root, so the medium favorable for Guangxi D. candidum is MS+NAA1.0mg/L+IBA1.0mg/L+20% potato juice or MS+NAA1.0mg/L+IBA1.0mg/L+6-BA 0.1mg/L+20% potato juice. With well-developed roots and over 3 induced roots on average, it has good rooting effects.7. Measurement on the polysaccharide content of three strains D. candidum in Guangxi and this experiment shows the following results. Guilin D. candidum is of highest content in polysaccharide with up to 32.16%, and its mannose content is highest as well with up to 25.616%. The results show that Guilin D. candidum is of high quality and better than the other two varieties, so it is worth to be popularized.