Gibberellin applications have been shown to increase fruit size, reduce cluster compactness, and improve fruit quality in grapes. (congerdesign/Pixabay)

Plant growth hormones, also known as plant growth regulators, play an important role in the growth and development of plants. These hormones are naturally occurring compounds that regulate various physiological processes in plants, such as cell division, elongation, differentiation, and flowering. In agriculture, plant growth regulators are used to enhance crop yield, improve plant quality, and reduce the impact of environmental stress.

There are five major types of plant hormones: auxins, gibberellins, cytokinins, abscisic acid, and ethylene. These plant growth regulators have revolutionized modern agriculture by allowing farmers to produce crops more efficiently and sustainably.

Auxin

Auxin is a plant hormone that regulates various aspects of plant growth and development. It promotes cell elongation in the stem and other tissues, regulates root development, and enables the plant to respond to light. Auxin also plays a role in fruit development and ripening, and inhibits leaf and fruit dropping. Additionally, auxin is involved in wound healing by promoting cell division and growth.

Auxin is widely used in agriculture and farming for its various functions. One of its applications is as a rooting hormone to promote root growth in cuttings, seedlings, and transplants. Auxins , in its synthetic form of  indole-3-butyric acid (IBA) and naphthaleneacetic acid (NAA) stimulate the development of new roots, thereby increasing the chances of successful propagation.

Auxins can also be used to promote seed germination and seedling growth. In some plants, seeds may have dormant seeds that need to be activated by the presence of auxin. Treatment with synthetic auxins such as indole-3-acetic acid (IAA) or NAA can break seed dormancy and stimulate germination. Additionally, auxins are used to enhance seedling establishment in crops by stimulating the growth of lateral roots and improving nutrient uptake.

Auxin is used in parthenocarpy to induce the development of seedless fruits. Parthenocarpy is the process of fruit development without fertilization, which leads to the formation of fruits that do not contain seeds. Auxins such as 2,4-D and NAA are applied to flowers or young fruits to promote the development of seedless fruits in cucumber, tomato, and watermelon. The use of auxins in parthenocarpy has several advantages, including the production of uniform, high-quality fruits without the need for pollination or seed formation. This technique is particularly useful for crops that produce small or poorly developed seeds, as well as those that are difficult to pollinate, such as tomatoes and cucumbers.

Auxin-like herbicides, such as  2,4-D, is also used to control broadleaf weeds in crops like corn, soybeans, and wheat.

Gibberellins

Gibberellins naturally promote stem elongation, seed germination, flowering, fruit development, and leaf expansion, and also help in responding to environmental stressors such as drought and cold.

In agriculture and farming, gibberellins have several practical uses that can improve crop yield and quality. One important use of gibberellins is to promote stem elongation and height in crops. By making plants taller, light penetration and increase photosynthesis. This is particularly useful for crops like rice, which benefit from increased height and improved lodging resistance.

Gibberellins can also be used to induce flowering and fruit development in crops, which can improve yields and quality. For example, in grapes, gibberellin applications have been shown to increase fruit size, reduce cluster compactness, and improve fruit quality. In addition to promoting flowering and fruit development, gibberellins can also be used to break seed dormancy and promote seed germination.

The application of gibberellins can also lead to the production of seedless grapes. Gibberellins stimulate the growth of the plant’s ovary and the production of the hormone auxin, which can trigger fruit development even in the absence of fertilization.

Abscisic acid

Abscisic acid (ABA) is a plant hormone that plays a role in regulating various aspects of plant growth and development. In farming, ABA has several practical applications that help crops cope with stress, promote optimal growth and development, and enhance the quality and yield of crops.

One of the primary uses of ABA is to improve drought tolerance in crops. It can help crops survive in water-stressed environments

Another practical use of ABA in farming is to promote seed dormancy. By promoting seed dormancy, ABA can help ensure that seeds remain viable for longer periods of time, and can also prevent premature germination under unfavorable conditions. This is particularly useful for farmers who need to store seeds for extended periods before planting.

Cytokinins

One of the main practical uses of cytokinins in farming is their ability to promote lateral bud growth, resulting in more branching and more productive plants. This is especially useful in crops such as grapes, apples, and olives, where more branching can increase yield and improve fruit quality. Additionally, cytokinins can promote uniform fruit development and ripening, which can be beneficial for harvesting and storage.  Spraying cytokinins on citrus fruits can improve their color and size, making them more marketable.

Another application of cytokinins in agriculture is in tissue culture, where they are used in plant propagation. By adding cytokinins to plant tissue culture media, they can promote the growth of new shoots and roots from explants. This is an important technique for mass-producing plants with desirable traits, such as disease resistance or high yield.

Cytokinins are also used to delay senescence in cut flowers, fruits, and vegetables. By applying cytokinins to harvested plants, their lifespan can be extended, allowing for longer storage and transportation times. This can be especially useful for crops such as lettuce, broccoli, and flowers, which are highly perishable.

Ethylene

Ethylene is a gaseous plant hormone responsible  for the growth, development, and stress responses of plants. It has many practical uses in farming making it a valuable tool for farmers and plant growers.

One of the most significant practical uses of ethylene in farming is to promote the ripening in fruits. It is commonly used to ripen fruits such as bananas, tomatoes, and mangoes,  allowing farmers to harvest fruits when they are still firm and transport them to markets where they can be sold at the right stage of ripeness.

Another important practical use of ethylene in farming is to regulate plant growth. Ethylene can promote or inhibit plant growth depending on the concentration of the hormone present. High concentrations of ethylene can inhibit stem elongation, making it useful for controlling plant height and preventing lodging. On the other hand, low concentrations of ethylene can promote stem elongation, making it useful for promoting the growth of certain plants.

Ethylene is also used in farming to induce flowering and fruiting in some plants. In pineapple cultivation, for example, ethylene is used to promote flowering and fruiting, allowing for the production of uniform and high-quality fruit. Ethylene can also be used to induce flowering in ornamental plants, such as orchids, and to promote fruit set in certain fruit trees, such as mango.

In addition to its uses in ripening, growth regulation, and fruiting, ethylene is also used in farming to stimulate the senescence of leaves and to induce the shedding of fruits and leaves. In some crops, such as cotton and tobacco, ethylene is used to promote the shedding of mature leaves, allowing farmers to harvest the plants more efficiently.

Plant growth regulators are important in agriculture because they help farmers maximize crop yield and quality. By promoting optimal growth and development processes, plant growth regulators can help farmers produce more food with less land and fewer resources. Because of this, the use of plant growth regulators is becoming increasingly important for ensuring food security and sustainability.

By understanding how these hormones function and how they can be manipulated, farmers can utilize their potential to improve the quality of crops. As research continues to advance, it is likely that there will be more ways to optimize plant growth and development using these natural compounds.