| Panax ginseng（Panax ginseng C.A.Mey.）as a good product for both medicine and food,the market demand for ginseng production and quality is increasing,ginseng seedlings is the key to the quality of production,ginseng soilless seedling substrate is mostly based on grass charcoal,but grass charcoal resources are not renewable,ginseng soilless seedling compound substrate based on coconut bran is rarely reported,in addition,ginseng seedlings in the process of seedling is very easy to grow,and then collapse,chemical control technology can effectively control crop growth,but need to strictly control the concentration of application.However,the application concentration should be strictly controlled.Therefore,we investigated soilless ginseng seedlings with different proportions of coconut bran-based substrates to observe the physical and chemical properties of the substrates and the morphological and physiological indicators of ginseng seedlings.In addition,three plant growth retardants（paclobutrazol,chlormequat chloride,and allylconazole）at three concentrations each were designed for foliar spraying to control ginseng growth and to observe the agronomic traits,physiological indicators,and metabolites of ginseng seedlings in ginseng cavity tray seedlings.The objective was to investigate the effects of different coconut bran ratios and plant growth retardants on the growth and development of ginseng seedlings,with a view to establishing the optimal ratio of coconut bran as the main compound substrate and screening the most suitable types and concentrations of agents to inhibit the growth of ginseng seedlings.The main results of the study are as follows:（1）As the proportion of coconut bran in the seedling substrate decreased,the substrate air-water ratio increased and the aeration porosity increased,from 14.13%to 22.03%.The alkaline nitrogen content became lower in each treatment group after the addition of coconut bran,but the fast-acting phosphorus and fast-acting potassium contents were significantly higher than the control group of grass charcoal:vermiculite=5:3（V）,where the coconut bran:vermiculite=2:1（V）treatment group had no significant differences in stem thickness,root length,fresh weight,dry weight,root to crown ratio,strong seedling index,chlorophyll a/b content,POD activity,CAT activity and MDA content compared with the control group CK,especially The best result was obtained in the coconut husk:vermiculite=1:1（V）treatment group,and the leaf area,underground dry and fresh weight,root to crown ratio,strong seedling index,soluble protein,SOD activity,POD activity,and MDA content were significantly higher than those in CK（P<0.05）,and the score of 0.936 in the comprehensive analysis of affiliation function was higher than that of 0.775 in the control group.（2）The height of ginseng seedlings decreased with increasing concentrations of paclobutrazol(100mg·L-1-300mg·L-1),chlormequat chloride(100mg·L-1-300mg·L-1)and uniconazole(25mg·L-1-75mg·L-1)in the application range,and stem thickness increased and then decreased with increasing concentrations.Both applications inhibited the leaf area growth of ginseng seedlings,and the leaf area decreased with increasing concentration（mainly for inhibiting leaf length）,and significantly promoted the root growth,and the root to crown ratio increased with increasing application concentration.plant height,while the effects on the increase of stem thickness,root length and root weight all reached significant differences（P<0.05）,and the least inhibitory effect on the growth of ginseng leaf area.（3）Among the three plant growth retardants,uniconazole was the most effective in increasing chlorophyll content of ginseng seedlings,with the highest in the C2 treatment group.Y（II）and ETR values increased with increasing concentrations of plant growth retardant application in a certain concentration range,and Y（II）values of the PSII system,with decreasing NPQ and increasing q P.Foliar application of uniconazole at 75mg·L-1was most favorable for chlorophyll fluorescence parameters Fv/Fm,Y（II）,ETR,NPQ and q P in ginseng seedlings,and the leaf PSII reaction center had the greatest capacity for light energy capture,transfer and conversion as well as photosynthetic efficiency.The application of plant growth retardants significantly enhanced the antioxidant enzyme activities,especially POD activity,and reduced the leaf MDA content of ginseng seedlings.Collectively,the foliar spray of uniconazole50mg·L-1was most beneficial in enhancing the antioxidant enzyme activities of ginseng seedlings,reducing the degree of cell membrane lipid peroxidation,and improving plant stress resistance.（4）The spraying of plant growth retardants increased the root saponin content of ginseng seedlings by regulating the distribution of substances and accumulating more primary metabolites for the synthesis of secondary metabolites.In particular,it significantly increased the accumulation of soluble sugars and soluble proteins,with little effect on polysaccharide content.All treatment groups significantly increased the total amount of eight saponins in ginseng seedlings,except for the treatment groups of paclobutrazol 300mg·L-1and uniconazole25mg·L-1,and the foliar spray of chlormequat chloride 300mg·L-1and uniconazole 75mg·L-1treatment groups reached the maximum saponin content,which was significantly higher than the control group.significantly increased（P<0.05）... |
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