Ginseng is a medicinal plant that is an important economic crop in the agricultural industry, and its continuous cropping has a particularly prominent impact.
The reasons for continuous cropping obstacles are complex, and the factors that cause them are also interrelated. It is the result of the comprehensive action of multiple factors in the plant and soil system.
Ginseng is a perennial plant with obvious obstacles to continuous cropping. The soil after planting a stubble of ginseng cannot be replanted within a few years. Ginseng planted continuously in old ginseng fields is prone to soil-borne diseases, which can lead to no harvest in severe cases.
Continuous cropping of ginseng soil microbial balance is disrupted, beneficial bacteria decrease, and pathogenic bacteria increase, resulting in a decline in the ability of ginseng to resist diseases and insect pests, and pathogenic bacteria are more likely to infect. Soil-borne diseases are very serious, and the continuous cropping obstacles of ginseng had become the bottleneck of global agricultural intensive production.
This article has done an in-depth study on the antagonistic bacteria in the soil of ginseng with different cultivation years and provided references for solving the obstacles of continuous cropping of ginseng.
Farmers often use crop rotation, fertilization, and other methods to alleviate the invasion of pathogenic bacteria. For soil-borne diseases, people generally adopt biological control methods for remediation. The use of microbial fertilizer can make benign changes to soil microorganisms, and it doesn’t change the ecological balance of the soil environment, and can effectively control the harm of pesticide residues.
Causes of Ginseng Continuous Cropping Obstacles
1. Autotoxicity
The root exudates of ginseng are organic acids, phenolic acids, and cell sloughs, but most of the substances separated from root exudates are phenolic acid compounds. Continuous cropping of crops will accumulate phenolic acids and cause self-toxicity. Through our research, it is found that the saponins secreted from the roots of ginseng remain in the soil, which can cause continuous cropping obstacles.
2. Imbalance of Rhizosphere Microecosystem
The output of ginseng has a lot to do with the physical and chemical properties of the soil.
The deterioration of the physical and chemical properties of the soil, the imbalance of nutrient element ratio, the increase of soil specific gravity and bulk density, the decrease of porosity, the increase of physical clay particles, the decrease of soil absorption performance, and the accumulation of large amounts of phosphorus will cause continuous cropping obstacles.
3. Effects of Pests and Diseases
Plant conditions and soil conditions are the prerequisites for causing pests and diseases of ginseng.
Our research found that the longer the ginseng planting period, the more serious the soil salinization and acidification. The accumulation of soil salt causes the solution concentration in the soil to be too high and the root vitality decreases. The pathogenic fungi tend to multiply under acidic conditions, and the pathogenic fungi invade as the root vitality declines. Pathogenic fungi infect the xylem of the roots of American ginseng and consume saponins to cause disease.
In addition to fungal infections, insect pests are also an important factor in the continuous cropping of American ginseng. Nematodes and mites play an important role in the root diseases of American ginseng. They can bite the roots to promote the spread of pathogens.
Biological Control Mechanism
In biological control, adding antagonistic bacteria and beneficial bacteria to the soil will form a microbial barrier in the rhizosphere, reduce plant autotoxicity, change the aeration and moisture retention of the soil, reduce the density of pathogenic bacteria in the soil, and adjust the rhizosphere micro-ecological environment to control continuous cropping obstacles.
Mechanisms of Biological Control Include:
- Inducing the expression of plant resistance mechanisms,
- Through competition with plant pathogens for nutrition and locus,
- Produce resistant metabolites to inhibit the propagation of pathogens and promote plant growth.
Trichoderma is the most widely used in biological control. At present, the action mechanism of Trichoderma harzianum in preventing and controlling soil-borne diseases of American ginseng is generally considered to have the following two types:
Competitive effect: As the growth rate of Trichoderma is faster than that of pathogenic fungi of soil-borne diseases, it takes priority to occupy the invading position of pathogens and block the source of nutrition of pathogens to prevent American ginseng from being infected by pathogens.
Antibiotic effect: Trichoderma produces a variety of antibiotics and enzymes during its life activities, and a series of cell wall degrading enzymes secreted by the antibiotics produced by Trichoderma is beneficial for them to invade various pathogens.
The use of bacteria (Bacillus subtilis) to prevent and control the infection of American ginseng by pathogens is mainly achieved through competition, parasitism, and induction of systemic resistance. Various secondary metabolites produced by antagonistic bacteria can generally inhibit the growth and metabolism of pathogenic bacteria at low concentrations, causing intracellular lysis.
Some active substances produced by actinomycetes can destroy the cell walls, cell membranes, protein synthesis systems, and energy metabolism pathways of pathogenic bacteria, thereby inhibiting or killing plant disease microorganisms and improving plant disease resistance.
The cause and mechanism of the continuous cropping obstacles of ginseng are key issues that need to be studied and understood in the development of the ginseng industry. It is not caused by a single factor such as soil microorganisms or soil environmental factors but may be a comprehensive effect produced by the interaction and mutual influence of these factors.