Plant growth regulators are organic compounds with growth and development regulating effects similar to natural plant hormones. They play a vital role in agricultural production. They can effectively regulate the growth process of crops to achieve stable and increased yields, improve quality, and enhance crop resistance.
I. Common types and effects
(I) Auxins
Auxins mainly include indoleacetic acid and its homologues, naphthaleneacetic acid and its homologues, and phenol compounds. Among them, indolebutyric acid has strong activity, stable properties, and is not easy to degrade. It is widely used in fruit trees, mainly for promoting rooting, inducing female flowers and parthenocarpy, elongating the ovary wall, stimulating seed differentiation and formation, accelerating fruit growth, and increasing fruit setting rate. Naphthaleneacetic acid and its homologues have strong biological activity and are widely used. For example, NAA can be used for rooting of cuttings, promoting flower bud formation, and preventing fruit drop before harvest. Commonly used phenol compounds include 2,4-D, anti-drop agent, sodium nitrophenolate, etc., which can promote rooting, increase fruit setting, and prevent fruit drop before harvest.
(II) Gibberellic acid
Commonly used gibberellins are GA3 (920) and GA4+7. They are mostly made by fermentation of Gibberellic acid fungi and are biological PGRs. Gibberellic acid can quickly break the dormancy of organs such as seeds, tubers and bulbs, promote germination, and is widely used in potatoes. It is suitable for a variety of crops, such as cotton, tomatoes, potatoes, fruit trees, rice, wheat, soybeans, tobacco, etc., and can promote their growth, germination, flowering and fruiting, stimulate fruit growth, increase fruit setting rate, and have a significant yield-increasing effect on crops. For example, when rice, wheat, and sorghum begin to fill grains at the end of flowering, spraying the ear and flag leaf with 20-25 mg/kg gibberellin solution can increase grain weight and grain number; after corn blooms and fertilizes, gibberellin treatment can promote filling, reduce barren grains, and increase corn cob rate.
(III) Cytokinins
Commonly used cytokinins are ZT, BA, CPPU, TDZ, etc. There are two most obvious physiological effects of cytokinins: one is to promote cell division and regulate its differentiation. In tissue culture, the ratio of cytokinins to auxins affects the differentiation of plant organs; the other is to delay the degradation of protein and chlorophyll and delay aging. For example, cytokinins are broad-spectrum plant growth regulators that have the effects of promoting growth, resisting diseases, resisting stress, and increasing yields. They can accelerate cell mitosis, promote cell enlargement and differentiation, promote organ formation, activate cell vitality, effectively regulate growth, delay aging, resist drought and cold, and increase color, thereby achieving the effect of bright, enlarged, and beautiful and balanced fruits.
(IV) Ethylene
Ethylene includes ethylene generators and ethylene inhibitors. Ethylene generators mainly include ethephon, ethylene silicon, etc. Their main effects include inhibiting vegetative growth, promoting lateral bud germination; promoting flower bud formation; assisting mechanical harvesting; promoting maturity and coloring; thinning flowers and fruits; delaying flowering period, improving cold resistance; and promoting dormancy. Ethylene inhibitors inhibit the synthesis of ACC, a precursor of ethylene synthesis, by inhibiting the activity of aminocyclopropanecarboxylic acid synthase, thereby inhibiting the generation of ethylene.
(V) Abscisic acid
Abscisic acid has an antagonistic effect on GA. Natural abscisic acid is listed as one of the five major plant hormones, along with auxin, ethylene, gibberellin, and cytokinin. It can improve the drought and salt tolerance of plants, and is of great value in the development and utilization of medium and low-yield fields, as well as afforestation and greening of deserts. ABA is also an effective inhibitor of seed germination, so it can be used in seed storage to ensure the storage quality of seeds and fruits. In addition, ABA can also cause the rapid closure of leaf stomata, which can be used to preserve flowers, regulate flowering period, promote rooting, etc., and has great application value in flower gardening.
(VI) Growth retardants and growth inhibitors
After being absorbed by plants, growth retardants can reduce the division and elongation of apical meristem cells, reduce the rate of new shoot extension growth, and have a temporary inhibitory effect on growth, which can be reversed by GA. Such as PIX, CCC, PP333, etc. The main effects of paclobutrazol are to reduce the extension growth of branches and promote the formation of short branches; promote flower bud formation; increase fruit setting; mature early; bloom in time and bear fruit in the opposite season; reduce pruning and improve labor efficiency; improve drought resistance and cold resistance. Growth inhibitors are of two types: natural extraction and artificial synthesis. They completely inhibit the growth of new shoot apex, have a permanent inhibitory effect, and cannot be reversed by GA. Natural inhibitors include ABA, salicylic acid, jasmonic acid, etc. Artificial synthesis includes triiodobenzoic acid, holistic element, and green fresh element, etc. Triiodobenzoic acid TIBA is an anti-auxin regulator that can hinder the transport of auxin and GA in the phloem, inhibit branch growth, open angle, and promote flower bud formation.
- Precautions for use
There are many things to pay attention to when using plant growth regulators. Only correct use can ensure the healthy growth of plants and achieve the desired effect.
First of all, it is crucial to choose the right plant growth regulator. Different plant growth regulators have different effects and should be selected according to actual needs. For example, if you want to promote early maturity of seeds or fruits, you can use ripening regulators such as ethephon; if you want to promote rooting of cuttings, you can choose auxin regulators such as indolebutyric acid. At the same time, different crops have different sensitivities to growth regulators, such as cotton is sensitive to dwarfing, fruit trees are sensitive to “920”, etc. In production, the correct choice should be made according to the sensitivity of crops to growth regulators.
Secondly, use strictly according to the instructions. Different plant growth regulators have different usage methods and concentration requirements. Generally speaking, the dosage of plant growth regulators per mu is only a few grams or milliliters. Using too high a concentration will disrupt the normal physiological activities of plants and even harm them. For example, auxin promotes root growth at low concentrations, but inhibits growth at higher concentrations. At the same time, some regulators, such as a certain gibberellin that is used more in production, must be dissolved in alcohol or warm high-proof liquor before they can be used on water; and some regulators need to be prepared into a “mother liquor” before use and then prepared into the required concentration to ensure uniformity of the agent.
In addition, pollution should be prevented. If the plant growth regulator used is toxic or inedible, ensure that enough time has passed before the vegetables are harvested so that the chemicals can be degraded or diluted. Avoid direct contact with the edible part of the vegetables to avoid potential harm to human health. When using pheromone regulators, it is necessary to prevent harm to beneficial insects. For example, the sex attractant core of the golden moth has a strong trapping effect on wall bees, so it is not suitable to use it during the flowering period of fruit trees.
In addition, attention should be paid to the timing of use. Plant growth regulators must be used at the critical time of plant growth to achieve maximum effectiveness. For example, chlorfenapyr should be used on cucumbers on the day when the cucumbers bloom. If it is used when the cucumbers have reached about 10 cm in length or later, the taste will be poor and the quality will decline.
In short, the correct use of plant growth regulators requires comprehensive consideration of multiple factors, selection of suitable regulators, strict use in accordance with the instructions, prevention of contamination, and grasping the timing of use, so that plant growth regulators can play the greatest role in agricultural production and horticultural cultivation.
