Growth regulators

• Plant growth regulators

Plant growth regulators are divided into plant hormones produced inside plants and artificially synthesized chemicals with hormone-like activity. As long as there is a trace amount of this substance, it can promote or inhibit the growth and development of plants, but excessive use can also cause damage. The discovery of this substance provides horticultural workers with a new method to control plant growth and development.

Plant growth regulators can be roughly divided into six categories, namely: auxin, gibberellin, cytokinin, abscisic acid, ethylene and growth retardants.

(1) Auxin

Auxin is the earliest discovered plant hormone. It is widely distributed in higher plants and is concentrated in tissues with vigorous growth. Compounds similar to auxin are commonly used in flowers, including acetic acid, acetic acid, acetic acid, 2,4-D2, 4,5-T, etc. It has a significant effect on promoting growth, stimulating cambium activity, the formation of new roots, inducing parthenocarpy and fruit development, etc.

(2) Gibberellic acid

Gibberellic acid exists in young plant tissues such as young shoots, young roots, immature seeds, and embryos. There are many types of gibberellic acid, and now it can be artificially produced through fermentation. The most commonly used is gibberellic acid GA3. The function of gibberellic acid is to promote the elongation of plant internodes and break the dormancy of seeds, tubers, and buds. It can partially replace the effects of low temperature and long daylight, promote flowering of long-day plants and biennial plants, induce parthenocarpy and inhibit aging. It has a great impact on the growth of new shoots and a slow effect on roots.

(3) Cytokinin

Cytokinin includes natural kinetin and a variety of synthetic similar substances. Natural kinetin exists in taro tips, root tips, immature seeds, germinating seeds, and growing fruits. Commonly used cytokinins in flowers include 6-benzylaminopurine, zeatin, kinetin, etc. Its function is to promote cell division, cell body expansion, bud differentiation, break apical dominance, promote lateral bud growth, inhibit aging, etc. It has the effect of breaking dormancy and promoting germination of seeds and buds.

(4) Abscisic acid

Abscisic acid is widely present in higher plants. It is found in various young and old organs and tissues, but the content varies in different organs and at different developmental stages. It is higher in organs or tissues that are about to fall off or enter dormancy. The effect of abscisic acid is similar to that of short-day. It can stimulate flowering of some short-day plants, inhibit or stop flowering of some long-day plants, affect tuber formation, and promote leaf aging and dormancy.

(5) Ethylene

Ethylene is found in many plant tissues, with the highest content in ripening fruits. Other organs such as flowers, leaves, stems, roots, and seeds produce ethylene. Combustion also produces ethylene. Ethylene can promote fruit color change and ripening, promote leaf fall and aging, inhibit organ elongation, promote flowering of some plants, promote sex transformation of some plants, differentiate into more female flowers, and inhibit the undifferentiation of some flowers. Ethylene is a gas at room temperature and its application is limited. Ethephon was developed in the 1960s. It is an acidic liquid that releases ethylene gas when the acidity decreases after spraying. Its production promotes the application of ethylene in plant growth and development. It can be used to irrigate the center of the plant, irrigate the soil, and spray on the leaves.

(6) Growth retardants

Growth retardants have the effect of limiting the extension of the stem, inhibiting the growth advantage of the plant's apex, and promoting the growth of lateral branches. The types used in flowers include quaternary ammonium (AmO-1618), chlormequat (CCCC), succinylamine (B9), maleate (MH), etc.

2. Application of growth regulators

The application of plant growth regulators in flowers has been developing rapidly, but it has two sides. If used properly, it can improve the quality of flowers, save costs, quickly play the role of general maintenance measures, and promote the development of flower production. However, if used improperly, it can have the opposite effect. Therefore, when using it, you should pay close attention to the type, degree, plant variety, application site on the plant, usage amount, and environmental conditions (such as temperature, light, etc.). It is mostly used as a powder or solution. The powder can be sprayed, sprinkled, dipped, or applied. The liquid can be used for root irrigation, local immersion, spot application, and stem and leaf spraying.

Application of plant growth regulators in flowers:

(1) Promote rooting of cuttings

Indolebutyric acid has a significant effect, and low concentrations of 2,4-D also have an effect. After use, it can promote the rooting of azalea, camellia, camellia sasanqua, osmanthus, Michelia, Milan, magnolia, bougainvillea, purple shrub and carnation, and has the same effect on layering. There are three ways to use the agent: ① Dipping method: Use a lower concentration for species that are easy to root, and a slightly higher concentration for species that are difficult to root. Generally, 50-100PPm is used to dip the base of the cuttings for about 12-24 hours. ② Quick dipping method: Indolebutyric acid is 500-1000ppm, and the base of the cuttings is dipped for 5-7 seconds. ③ Use of powder: Add the compound to talcum powder, the dosage is 0.1-0.3%. When using, first wet the base of the cuttings, then dip in powder or spray.

(2) Promote seed germination

The seeds of Pseudo-Areca catechu can be soaked in 100ppm gibberellin for 24 hours to make them germinate earlier. Cyclamen (rabbit flower), yellow orchid, petunia, and primrose can also germinate earlier by being treated in the above solution. Iris can be soaked in ethephon before dry storage to make the germination uniform.

(3) Promote main growth, enhance air growth, and prevent aging

After the rubber tree is treated with 100ppm naphthaleneacetic acid to promote rooting, 500ppm naphthaleneacetic acid is mixed into mud, applied to the roots, and then potted. The growth will be significantly accelerated. After the cuttings of fuchsia take root, spraying with gibberellin will also accelerate its growth.

(4) Make the plant dwarf, increase branches, dense flowers, and beautiful plant shape

　　It can dwarf the plants of chrysanthemum, poinsettia, hibiscus, cineraria, and geranium, increase side branches, and produce a dense, rounded shape. The dosage is 1000-3000ppm. If African violets are immersed in KT kinetin for 24 hours, their petioles can produce a large number of adventitious buds; if 1% BA is applied to orchid roots, it can promote the production of adventitious buds. If it is used on small pieces of begonia cuttings, it can cause many adventitious buds to grow on the edges of leaves. If poinsettia is sprayed with 500ppm, its branches will increase, and the effect is the same as pinching. In addition, after being treated with dwarfing, the stems of cockscomb, coleus, carnation, globe amaranth, hydrangea, and glass jade are significantly shortened. After using B9, the plants of cosmos, marigold, zinnia, chrysanthemum, etc. are significantly shortened.
(5) Control dormancy

20ppm of abscisic acid can make the plant fall leaves and go dormant and improve its cold resistance. Apply 500-1000ppm of gibberellin to the dormant buds of peony and herbaceous peony, and they will sprout and grow in a few days. Soak the dormant bulbs of tuberose with 100-200ppm of gibberellin to promote germination.
(6) Reduce respiration and prolong the life of flowers

　　Using 6BA to soak chrysanthemum, dianthus, and asparagus can reduce the respiration rate of plants and keep them fresh. Spraying 10ppm gibberellin on young geraniums can increase the flowering time by 2 weeks. Soaking flamingo in a solution containing cytokinins at a certain temperature can reduce damage during transportation and enhance cold resistance.

(7) The role of flower tissue in wall culture

　　These chemicals play an important role in regulating the formation of tissue culture organs. The most influential ones are auxin and cytokinin. Organ formation is controlled by the ratio of the two. When the concentration of auxin is high, it is conducive to the formation of roots; when the concentration of cytokinin is relatively low, it can promote the formation of buds.

3. When using plant growth regulators, you must pay attention to the following issues :

   1. Must work closely with cultivation technology

    Growth regulators are not nutrients, but only regulate the growth and development of plants. Therefore, they cannot replace the normal metabolism of plants, and cannot be separated from the correct cultivation technology. In order to achieve high yields, the use of growth regulators must be closely coordinated with various cultivation measures. For example, using ethephon to treat cucumbers can increase the number of female flowers. In theory, more female flowers will produce more fruits, which will inevitably increase the yield. However, in fact, if there is insufficient water and fertilizer, and improper management, even if more female flowers bloom, they will not bear fruit, or if they bear fruit, the fruit will be very small, and ultimately the goal of high yield will still not be achieved.

   2. Meet the external environmental conditions necessary for plant growth and development

Growth regulators cannot replace the light, temperature, water, air and other requirements for the normal growth and development of plants. If you only pay attention to the use of growth regulators, but do not pay attention to meeting the external conditions necessary for the growth and development of plants, you will not be able to achieve good results. For example, Guangzhou people like to plant potted daffodils every Spring Festival. In order to grow daffodils beautifully, you must first understand that daffodils are positive plants and need sufficient sunlight. On the basis of meeting this condition, you can use plant growth regulators to treat daffodils to make the plant dwarf, with thick branches, dark green leaves, many branches, and a long flowering period, which improves the ornamental value and becomes the multi-flowered dwarf daffodils that people love now.

3. Five taboos when using plant growth regulators

First, avoid using drugs instead of fertilizers. Plant growth regulators are regulating substances in organisms. The use of plant growth regulators cannot replace fertilizers, water and other agricultural measures. Even for promoting regulators, there must be sufficient fertilizer and water conditions to work.
　　 Second, avoid changing the concentration. The correct use of growth regulators includes the correct use period, the correct use concentration and the correct use method. Among these three, if any link is not mastered well or there is a problem, it will directly affect the use effect. Flowers have strict requirements on the use concentration of plant growth regulators. If the concentration is too high, the leaves of flowers will become thicker and brittle, deformed, or the leaves will dry up and fall off, or even the whole plant will die; if the concentration is too low, the desired effect will not be achieved. Therefore, do not increase or decrease the concentration at will. Different plants, or different growth and development stages of the same plant, or different application purposes require different use techniques, and must be operated correctly according to the specified technical requirements.
　　 Third, avoid not seeking timeliness. When using plant growth regulators, the appropriate use period should be determined according to its type, duration of efficacy and cultivation needs to avoid unnecessary losses.
　　 Fourth, avoid violating the natural time. In arid climate conditions, the concentration of the liquid medicine should be reduced. On the contrary, when it is used with sufficient rain, the concentration should be appropriately increased. The time of application should be after 10 am and before 4 pm. If it rains within 4 hours after application, additional application should be made.
　　 Fifth, avoid mixing them at will. Although mixing several plant growth regulators or mixing them with pesticides and fertilizers can reduce labor and bring about comprehensive benefits, it must be decided on the basis of fully understanding the enhancement or inhibition effect after mixing. For example, Ye Mian Bao and Peng Shi Bao are acidic and cannot be mixed with alkaline pesticides and fertilizers; Plant Power 2003 can only be used on various crops with clear water. If it is mixed with other pesticides and fertilizers, it will not increase production and reduce fertilizer efficiency, causing unnecessary losses.