Biostimulants are neither pesticides nor fertilizers, but a substance containing certain ingredients and microorganisms. When applied to plants or rhizosphere, their effect is to stimulate the natural processes of plants, regardless of nutritional ingredients. The international market generally divides biostimulants into eight categories, including humic acid, beneficial chemical elements of complex organic materials, inorganic salts (including phosphites), seaweed extracts, chitin and chitosan derivatives, anti-transpiration agents, free amino acids and other nitrogen-containing substances.
Seaweed extracts can affect plant disease resistance from both abiotic and biotic stresses. In the process of abiotic stress, most of the time, after applying seaweed extracts, the plant itself absorbs effective substances, produces corresponding gene transformation, or synthesizes new enzymes to cope with changes in the external environment, thereby producing disease resistance. Biological stress is mostly the effective substances in seaweed extracts, which directly interfere with the growth of pathogenic organisms, thereby maintaining good growth of plants.
Plant growth-promoting rhizobacteria (PGPR) can improve plant growth, control plant pathogens, improve plant absorption of nutrients and minerals, and enhance plant resistance to various biotic stresses and tolerance to abiotic stresses. Common plant growth-promoting rhizobacteria include Trichoderma harzianum, Trichoderma viride, Beauveria bassiana, etc.
Microbial secondary metabolites are applied through seed germination, soil infiltration, and foliar spraying. They regulate phenolic compounds, hormones, siderophores, lipopeptides, terpenoids, pyrones, etc. in plants, thereby increasing antioxidant enzyme expression/activity, photosynthesis/photosynthetic pigments, inducing systemic resistance, the production of osmolytes, and glutathione levels, thereby alleviating biotic stresses such as insects and plant pathogens faced by plants, as well as abiotic stress processes such as drought salinization and heavy metal pollution, and ultimately improving plant resistance under stress and crop yield and quality.
Chitin and its derivatives have many beneficial effects, such as promoting plant growth, improving plant nutrition, and regulating and improving plant resistance to abiotic and biotic stresses. The beneficial activities of chitosan are mainly related to increased photosynthetic activity, tolerance to abiotic stresses such as drought, salinity and extreme temperature, and increased antioxidant enzyme activity and expression of defense genes. The main activity of oligochitosan is related to the induction of secondary metabolite biosynthesis and the activation of plant natural immunity through signal perception and transduction, expression of defense genes and the accumulation of protective secondary metabolites.
Chitosan oligosaccharide are a class of oligomers generated by hydrolysis of chitosan. Because of their high solubility, they are easily absorbed and utilized, especially Chitosan oligosaccharide with a molecular weight of less than 10,000 show unique physiological activity and functional properties. As a new class of physiologically active substances, oligosaccharides have the effect of inhibiting viruses, bacteria and fungi, so they have great potential for application in plant growth regulation and disease resistance. As a new generation of biological pesticides, chitosan oligosaccharides have incomparable advantages over traditional chemical fertilizers and pesticides in terms of increasing production, improving agricultural product quality, resisting stress, resisting pests and diseases, being natural and non-toxic. Studies have shown that chitosan oligosaccharides can increase the production of fruits, vegetables and grain crops by 10% to 50%, and have good disease resistance. They are safe, trace, efficient and low-cost, and can be used in biological pesticide products, which is of great significance to the sustainable development of agriculture.
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