Effects Of Defoliating Agent Spraying On The Growth And Quality Of Panax Notoginseng

Defoliation is a natural phenomenon in the process of plant senescence.In this process,plants minimize their energy consumption by means of nutrient transport and dormancy,which is an important survival strategy for plants to cope with environmental stresses such as freezing injury.In the previous study,it was found that the winter defoliation of Panax notoginseng was obvious in high latitude and high altitude areas such as Xundian,but the content of effective components in the underground part was significantly higher than that in the above areas.It is speculated that leaf senescence may promote the reflux of nutrients in the leaves of P.notoginseng,resulting in an increase in the effective components accumulated in the roots.In this study,the agents that can artificially promote defoliation were screened,and the effect of defoliant on the defoliation of P.notoginseng was clarified by exogenous spraying.The effect and mechanism of defoliant on inducing defoliation and promoting nutrient return of P.notoginseng were explored.It is proposed to explore a kind of artificial defoliation and quality improvement technology that can be popularized and applied in low latitude and low altitude,and provide key technical support for promoting high-quality production of P.notoginseng.The main results are as follows:1.Ethephon can be used as notoginseng defoliant.Two commonly used and safe defoliants（ethephon and thidiazuron）were screened and diluted 100,200,400,800 and1600 times respectively for foliar spraying.The defoliation effects of different defoliants on P.notoginseng were evaluated by comparing the defoliation rates among different treatments.The higher the concentration of ethylene treatment,the more obvious the defoliation effect.The 100-fold dilution of ethephon could completely defoliate the P.notoginseng plants,and thidiazuron had no defoliation effect on P.notoginseng.2.Exogenous spraying ethephon diluted 800 times can significantly increase the dry weight and saponin content of the main root of P.notoginseng in high latitude and high altitude cold area.The optimal induction concentration was screened by exogenous spraying of five concentrations of ethephon.The effects of different defoliants on the growth and quality of P.notoginseng were evaluated by measuring the fresh and dry weight of P.notoginseng plants,the occurrence of root rot and the content of saponins.After Xundian Yangjie Y800 treatment,the dry weight of main roots increased by24.18%,and the contents of saponins Rb₁,Rg₁,Rd,R₁and Re increased by 35.95%,23.45%,2.96%,7.36%and 33.32%,respectively.3.Exogenous spraying of ethephon can promote the transport of leaf carbon and nitrogen sources to the underground.Metabolomic analysis of the leaves treated with800-fold dilution of ethephon showed that the proportion of different substances in ethephon treatment and water control was 22.2%for organic acids,55.6%for sugars and their derivatives,3.7%for amino acids,and 18.5%for others.The main pathways were steroid biosynthesis,purine metabolism,sulfur metabolism,butyric acid metabolism,alanine,aspartic acid and glutamic acid metabolism,arginine and proline metabolism,pentose and glucuronic acid conversion,ascorbic acid and arabinose metabolism,amino sugar and nucleotide sugar metabolism,which mainly promoted the C,N and S metabolism of leaves.4.After spraying ethephon diluted 800 times,it can promote the accumulation of dry matter in the main roots of P.notoginseng in low latitude and low altitude hot and humid areas,and increase the saponin content of the main roots.Different concentrations of ethephon were sprayed exogenously in Donghui Town,Lancang County.By evaluating the fresh and dry weights of different treatments and the content of five saponins,the potential of ethephon to promote the application and promotion of defoliation technology was analyzed.After Y800 treatment,the contents of ginsenoside Rb₁,Rg₁,Rd,R₁and Re in the main roots of P.notoginseng increased by 39.99%,27.90%,14.34%,16.27%and 27.91%,respectively,and the five saponins increased by27.44 mg/plant.The dry weight of the main root increased by 0.395 g on average.According to the production of 10000-12000 plants per mu of Lancang Sanqi in 2022,the yield per mu could increase by at least 3.95 kg.In summary,exogenous spraying of ethephon can effectively induce the senescence and abscission of P.notoginseng leaves,and promote the accumulation of dry matter and saponins in the underground part of P.notoginseng.This study clarified the effect of defoliant on inducing defoliation of P.notoginseng and promoting yield and quality improvement,and provided a research basis and theoretical basis for revealing the mechanism of senescence-mediated nutrient reflux and metabolic regulation of P.notoginseng.According to the research results,it is recommended to use 800 times diluted ethephon solution for defoliation in production,which can achieve effective leaf shedding within 20 days,increase the dry weight of the main root plant by 0.395 g/plant,the saponin content by 27.44 mg/plant,and increase the yield per unit area by more than3.95 kg.It has certain popularization and application benefits.