Detailed Explanation of the Correct Techniques for Using Plant Growth Hormones
There are many application methods for plant growth hormones, varying with the type of hormone and the purpose of use. Different methods of use produce different effects; improper methods can even be harmful. Therefore, careful selection must be made before experimentation. For example, treating (smearing) the lower stem nodes of corn with gibberellin results in earlier and more numerous aerial roots than spraying with solution. When corn is perfused with gibberellin solution, the plants become shorter and can produce more ears; spraying or smearing with solution often inhibits tillering, while seed soaking instead promotes tillering. At the same time, some methods are convenient to use, while others are more troublesome; some methods are suitable for field use, while others are suitable for pot experiments. In short, flexible selection should be made according to actual needs.
1. Solution spraying: Solution spraying is a commonly used method in the application of plant hormones. According to the purpose of application, leaves, fruits, or whole plants can be sprayed. Spraying should be uniform, and the amount of solution used should be sufficient to moisten the sprayed parts. It is generally best done in the evening or when the morning dew has dried; spraying is not suitable before rain or under scorching sun. Depending on the duration of efficacy and the need, one or multiple sprayings can be carried out.
2. Solution dripping: This method is mostly used for treating plant stem apical growing points, flowers, or dormant buds. Dripping auxin or gibberellin solution onto stem growing points promotes elongation of apical tissues more noticeably than the spraying method. This method allows quantitative application of the agent, with relatively precise dosage, and is suitable for scientific research; it is also used in production for the propagation and cultivation of some valuable trees and ornamental plants.
3. Solution soaking: This is one of the earliest methods applied to the cutting propagation of woody plants. Indoleacetic acid and naphthaleneacetic acid are used to soak cuttings to promote rooting. During treatment, a certain concentration of the above hormone solution is first poured into a container to a depth of about 1.6 cm, then the morphological lower end of the cutting is soaked in the solution, taken out after a certain period, and inserted into a sand tray to promote rooting. Solution soaking is divided into slow soaking and quick soaking. The slow soaking method uses a low-concentration aqueous solution (10-100 ppm) for 12-24 hours, then the cuttings are removed. The quick soaking method uses a high-concentration 50% alcohol solution (above 1000 ppm); cuttings are treated for 5 minutes and then removed, and after the alcohol evaporates, they are inserted. The quick soaking method is more convenient than the slow soaking method, and the absorbed dosage is also more uniform. At the same time, it can avoid the disadvantage of the slow soaking method, in which leaf water evaporation and changes in temperature, humidity, and other conditions affect the absorption of the agent by cuttings. In addition, the soaking method is also commonly used for soaking fruits and seeds, including seeds and seed tubers. For example, soaking fruits in ethephon aqueous solution to ripen tomatoes and other fruits. Soaking soybeans and mung beans in gibberellin solution to promote bean sprout growth. Soaking seeds with chlormequat to increase wheat tillering. Soaking potato tubers in gibberellin to break the dormancy of summer-harvested potatoes, etc.
4. Solution smearing: This method is used on a certain organ of the plant, such as leaves, buds, stems, and cut surfaces of branches, to observe certain physiological effects produced by a certain hormone on the plant. For example, smearing cytokinin solution on one side of a leaf allows observation of its effect on delaying leaf senescence. The duration of efficacy of solution smearing is relatively short, so it is not suitable for application in fields.
5. Solution soil drenching: This method involves applying the solution into the soil or mixing it with fertilizer and soil before application. Soil treatment with hormones was first applied to vegetable crops and later extended to cereal crops. Some growth inhibitors, such as chlormequat, phosfon-D, and AMO-1618, are very effective when applied by solution soil drenching or mixed with soil. However, the growth inhibitor B9 produces toxicity when applied by solution soil drenching. Therefore, B9 is not suitable for this method. The effect of solution soil drenching is greatly related to soil texture. For example, chlormequat generally works best when applied in loam; for clay or sandy soil, solution spraying is best.
6. Solution culture: A certain concentration of plant hormone is added to the plant culture solution, and germinated seeds or seedlings are transferred into the culture solution so that the roots absorb both nutrients and hormones. This method can be used to study the physiological effects of plant hormones on roots and aboveground parts. Its effects are similar to those produced by the solution soil drenching method, but with the solution culture method, the amount of hormone used can be controlled very precisely, and observation is also more convenient, making it a research tool for the physiological effects of plant hormones.
7. Solution injection: This is mostly used for woody plants. The procedure is to first drill a small hole in the trunk of a fruit tree, with a depth of 1/3-1/2 of the trunk diameter. Then the prepared hormone aqueous agent is placed in a container, one end of which is connected to a thin rubber tube, with a short piece of thin glass tube inserted at the tube opening. A small piece of foam plastic is stuffed into the tube opening to regulate the dripping speed so that water drips out slowly in drops, and then the glass tube is inserted into the drilled hole, where it is absorbed by the fruit tree trunk. For root injection of fruit trees, select a root close in thickness to the rubber tube, cut it off, peel off a section of cortex, and insert the xylem of the cut root into the rubber tube connected to the container holding the plant hormone aqueous agent, so that it is absorbed through the cross-section of the root xylem.
8. Oil-based smearing: This method is similar to solution smearing, but has more advantages. The stems, stalks, and leaf surfaces of some plants have much wax or fuzz, and fruits are round and smooth; if treated with solution, the liquid is easily lost. With oil-based smearing, it adheres easily, is convenient for absorption, and the liquid lasts longer, generally requiring only one treatment. Whenever a plant part is treated locally, the effect on that part is obvious, but after the smeared agent is absorbed locally, it can also be transported to other parts of the plant, producing an overall effect on the plant.
9. Powder dipping, drenching, and spraying
① Powder dipping is a method used in large-scale cutting propagation of woody plants. Compared with the solution soaking method, it has the advantages of shorter treatment time and longer retention of the agent. The powder concentration varies with different types of cuttings; generally, the concentration of naphthaleneacetic acid powder used for woody plants is 500-2000 ppm. For some woody plants that are difficult to root, a higher concentration (5000-12000 ppm) must be prepared to promote rooting of cuttings. For cuttings of herbaceous plants, the concentration of naphthaleneacetic acid powder can be appropriately reduced. During treatment, the morphological lower end of the cutting is moistened with water and then dipped in the powder, and it is sufficient to coat the cut surface fully with powder. To prevent the powder adhering to the lower end of the cutting from falling off when inserted into the seedbed, a small furrow can first be opened in the seedbed, the powder-treated cuttings placed obliquely in each furrow, and then soil added and compacted in the furrow.
② Powder spraying can be carried out with a sprayer, and in large-scale applications, aircraft spraying is also used. Powder spraying treatment requires a large amount of powder, and solution spraying can also achieve the same purpose as powder spraying. Therefore, it is used relatively little in production.
In addition, attention must also be paid to the shelf life of the agents. Some regulators are relatively stable in nature, which is favorable for transportation and long-term storage, such as zengchanling. However, some regulators have a certain shelf life at room temperature. For example, gibberellin generally has a shelf life of two years and should not be stored too long. The original powder of some regulators can be preserved for a long time, but once prepared into an aqueous solution, it easily deteriorates. For example, after ethephon is prepared into an aqueous solution, it should be used promptly; the lower the concentration, the faster it loses efficacy. After gibberellin is prepared into a dilute solution, even if stored in a refrigerator, it can only be preserved for a short time (shelf life of only about one week).