Plants; Induced disease resistance; research progress
In agricultural production, chemical pesticides are usually sprayed to control the occurrence and harm of plant diseases. However, long-term and frequent use of chemical pesticides will lead to a series of problems such as drug resistance of bacteria, increased pesticide residues in plant products, environmental pollution, and destruction of biodiversity and balance in ecosystems. With the improvement of life quality, the demand for green food is increasing day by day, and it is urgent to find new pollution-free and pollution-free prevention methods.
Plant induced disease resistance refers to the resistance of plants to harmful pathogens induced by external factors. There are two kinds of induced disease resistance: one is rapid local reaction, that is, local host cells die quickly after induced treatment, and pathogens are confined to necrotic cells and cannot be further expanded; The other is to increase or enhance the physiological metabolism of plant disease resistance and inhibit the growth and expansion of pathogenic bacteria. Induced resistance, as a new means of plant disease control in the future, has attracted wide attention.
1. Plant resistance
Plant resistance generally refers to the ability of plants to resist adverse living conditions, including resistance to pests and diseases, adverse water conditions, temperature conditions, soil conditions and mechanical damage. Among them, the mechanism of disease resistance has been fully studied. Modern research has confirmed that protein related to diseases is induced by allergic reaction and systemic acquired resistance after plants are infected by pathogens, which is the inherent biological defense function of many plants. Recent studies have also found that plants have similar reaction mechanisms to cold injury, heat injury and root stress factors (drought, waterlogging, salinity, hypoxia, etc.). ), and they all convey the feelings and cognition of stress factors through specific substances, and mobilize the defense system to resist them.
2. Factors inducing resistance
2. 1 biological factors
Biological inducers can be living bacteria, bacterial culture filtrate, bacteria and slurry or bacterial cell extracts, and saprophytic microorganisms can also induce plants to produce disease resistance. Saprophytic fungi induced cucumber resistance to anthracnose. Trichoderma harzianum T39 can not only resist botrytis cinerea, but also induce plant resistance and promote the growth of rhizosphere bacteria and rhizosphere fungi. The reported rhizosphere biocontrol bacteria with growth-promoting effect mainly come from the study of Pseudomonas. And Bacillus. Weng Qiyong and others found that the dominant bacteria JIB07 and B09 isolated from the rhizosphere of healthy crops not only improved the peroxidase activity of the treated crops, but also had resistance to pathogenic bacteria. In the field experiment, their control effects on downy mildew of Chinese cabbage reached 38.5% and 16.5% respectively. The induced resistance of growth-promoting bacteria isolated from cucumber rhizosphere to cucumber Fusarium wilt and bacterial angular leaf spot is to delay the appearance of disease symptoms and reduce plant mortality.
2.2 Physical factors
Physical factors, including dry ice injury, electromagnetic treatment, electric shock, high temperature or ultraviolet radiation, will cause the production and accumulation of phytochemicals, thus inducing plants to produce disease resistance. Ultraviolet irradiation on hypocotyl of kidney bean for 24-48h can make kidney bean resistant to anthracnose. The freezing treatment of soybean stems will lead to the accumulation of phytochemicals. X-ray and local heat treatment can also induce plant disease resistance.
2.3 chemical factors
Chemical inducers should conform to the following principles: the substance and its metabolites have no direct antibacterial activity in plants and in vitro; This substance can change the interaction between plants and pathogenic bacteria, so that plants have incompatible interaction phenotype; The substance can induce plants to develop resistance to at least one or part of pathogenic bacteria. Compared with biological factors, chemical factors have the advantages of easy production, easy transportation, easy storage, low cost, stable control effect, simple use method, little influence by field environmental factors, no direct activity on pathogenic bacteria, wide plant-induced disease resistance, no influence on non-pathogenic seedlings, and beneficial to protecting beneficial microbial populations of crops. At present, chemical factors have become an important means of plant disease control and have been widely used. At present, the main chemical inducers used are salicylic acid, Junggar acid, oxalic acid, arachidonic acid, linolenic acid, linoleic acid, oleic acid, dichloroisonicotinic acid, benzoxazole, chitosan, amino ester and so on.
3. Induced disease resistance mechanism
Since people discovered the phenomenon of plant disease resistance, they have conducted in-depth research on it. Although the mechanism of inducing disease resistance has been preliminarily understood, many aspects need to be further explored. The mechanism of plant induced disease resistance is complex, involving a series of structural and functional changes such as tissue, cell and analysis. Generally speaking, there are four factors that induce plant disease resistance.
3. 1 When pathogenic bacteria infect plants, they often lignify the impregnation site quickly, leading to lignin deposition. The technical synthesis of lignin precursors-phenols can also reduce the biological activities of pathogenic membranes, enzymes and toxins.
3.2 After induction treatment, the activities of peroxidase, polyphenol oxidase, phenylalanine ammonia-lyase and chitinase in plants were greatly improved. The increase of POD and PO activities can increase the content of phenolic oxides in plants, thus inhibiting the action of enzymes in the cell wall of pathogenic bacteria. PAL is the key enzyme and rate-limiting enzyme in phenylpropionic acid-like metabolic pathway, which can catalyze the direct denitrification of L- phenylalanine to form trans-carnosic acid, thus promoting the synthesis of lignin.
3.3 Plants can produce plant antitoxin after induced treatment. Plant defensins are a kind of antibacterial secondary metabolites produced or accumulated by plants infected by pathogenic bacteria or induced by various biological, physical and chemical factors. Generally speaking, they have low molecular weight and lipophilicity, and are one of the important substances in plant defense reaction. They are highly toxic to pathogens, but their specificity is not obvious. PA can be formed in both disease-resistant and susceptible plants, but it forms quickly in disease-resistant plants and reaches its peak in the early stage of infection.
3.4 Plants can produce course-related proteins after induction treatment. Course-related proteins are soluble proteins with broad-spectrum resistance produced by plants stimulated and stressed by pathogens or different factors. They have the characteristics of low molecular weight and proteolysis, and some PRP proteins also have enzymatic activity. PRP was first classified from the allergic reaction site of tobacco inoculated with TMV. Later, it was found that pathogens such as fungi, bacteria and viruses can also induce PRP after infecting plants. PXP can directly kill or resist the activity of pathogens. In some plants, the induced expression of PRP protein is considered as one of the biochemical indexes of plant disease resistance.
4. Application and development of plant induced disease resistance in agriculture and forestry production
Plant diseases have always been the main bottleneck restricting the high and stable yield, high quality and safe production of crops. It is the most effective and economical measure to cultivate and popularize disease-resistant varieties by using plant disease resistance. Plant inducibility is suitable for both dicotyledonous plants and monocotyledonous plants, but generally it only has obvious effect on seedlings. Induced resistance can be effectively resisted through the induced expression of various defense genes and the synergistic effect of products. In most cases, gene expression is the result of molecular recognition and information transmission acting on the corresponding regulatory elements in gene structure after induced signal stimulation. By studying the mechanism of plant induced disease resistance, people may use recombinant DNA technology to explore the defense potential of plants, especially the regulatory elements and startup of receiving signals, which will have a far-reaching impact on disease resistance genetic engineering and gene construction strategies.
Although the research of plant disease resistance mechanism has accumulated a lot of information in histopathology, physiology and molecular biology, further research on induced resistance mechanism will eventually lay a foundation for plant disease resistance genetic engineering and the utilization of induced resistance, and will also greatly enrich the theory of comprehensive management of crops and cash crops, which is harmless to people and livestock, can minimize the use of pesticides and reduce the pollution of pesticides to the environment, and is an ideal choice for developing pollution-free cultivation of crops and cash crops and producing safe green food in the future. The development and industrialization of efficient, non-toxic and broad-spectrum inducers will have a great impact on all mankind and the whole ecosystem.
refer to
[1] Guo Zhen, Hu Xiaoping, Yang Zhiwei, Li Zhenqi; Induced resistance of virulent strain You Ⅱ to wheat stripe rust Ⅰ. Preliminary observation on induced resistance [J]. Journal of Northwest A&F University (Natural Science Edition), S 1, 2005
[2] Yi, Ye Hua. Exogenous chemicals induced maize resistance to Curvularia leaf spot [J]; Plant protection; Issue 5, 2005
Qiu, Yang Xiufen, Zeng Hongmei, Guan Chunyun. Alternaria tenuiflora protein elicitor induces cotton disease resistance and changes of related enzymes [J]. China Biological Control, 03, 2007.