Author: Pravin L. Deshmukh
Till recently, enhanced crop yields were achieved through the use of fertilizers, pesticides, better crop management and exploitation of genetic resources to develop highly yielding varieties. Plant growth regulators are one of the emerging biotechnologies that could possibly boost crop productivity. Plant growth regulators are chemicals, which are naturally occurring endogenous plant hormones or are synthetic plant growth regulators, which have potential for improving the productivity of different crop species. These chemicals are applied directly to the target plant to change its life process leading to improve the quality of its produce. It is generally suggested that synthetic plant growth regulators cause their effects through changing the endogenous levels of naturally occurring hormones and hence modify growth and development of the plant in a desired director and to a desired extent.
The crop productivity under field condition is dependent upon many factors like prolonging photo synthesis, delaying senescence, reducing photorespiration bringing about better partitioning of photo assimilates, stimulating mineral uptake and invigorating nitrogen metabolism. These factors could improve the physiological efficiency of a plant resulting in higher yields and quality produce. Just like with animal hormones, plant growth regulators come in a wide variety, producing different and often antagonistic effects. In short, the combination of hormones is vital to achieve the desired behavioural characteristics of cells and the productive development of plants as a whole.
Plant Growth Regulators
They are produced in plants in very small quantities. In addition to light, carbon dioxide, water and minerals, plants need certain chemicals in order to grow. These substances are called growth regulators or hormones.
A plant growth regulator is an organic compound, either natural or synthetic, that modifies or controls one or more specific physiological process within a plant. If the compound is produced within the plant it is called a plant hormone. Although photosynthesis supplies the carbon and respiration supplies the energy for plant growth, a group of chemicals produced by plants known as plant growth regulators control the growth and development of vegetables. These chemicals act on plant processes at very low concentrations. Often these are produced at one location and translocated to another where they exact their influence; however, they may also act on the same tissue in which they are produced.
Classification for plant growth regulators
The different categories of substances affecting plant growth are known which can be broadly classified into growth promoting and growth retarding substances or into naturally occurring growth substances and synthetic growth substances. Growth regulating substances may be classified into following categories:
- Auxins, e.g. Indole acetic acid (IAA)
- Gibberellins, e.g. Gibberellic acid (GA)
- Cytokinins, e.g. Kinetin, Zeatin etc.
- Ethylene, e.g. Ethylene
- Dormin, e.g. Abscisic acid (ABA), Xanthoxin, Phaseic acid etc.
- Flowering hormones, e.g. Florigen, Anthesin, Vernalin.
- Miscellaneous natural substances. e.g. Cyclitols, Vitamins, Phytochromes etc.
- Phenolic substances, e.g. Coumarin
- Synthetic growth retardants, e.g. CCC, AMO 1618, Phosphone D, Morphactins, Malformins, Maleic hydrazide (MH) etc.
- Miscellaneous synthetic substances, e.g. Synthetic auxins, synthetic cytokinins etc.
Table: Plant growth regulators used in vegetable production;
|Crop||PGR's||Dosage||Time of spray||Remarks|
|Tomato||Triacontanol||1.25 ml/L of water||30,60 DAT||Antitranspirant|
|NAA||0.25 ml/L of water||70,90 DAT||Reduce flower and fruit drop|
|Brinjal||Triacontanol||1.25 ml/L of water||20,40 DAT||Antitranspirant|
|NAA||0.25 ml/L of water||60,90 120 DAT||Reduce flower and fruit drop|
|Chilli||Triacontanol||1.25 ml/L of water||20,40,60,80 DAT||Antitranspirant|
|NAA||0.25 ml/L of water||60,90 DAT||Reduce flower and fruit drop|
|Capsicum & Paprika||Triacontanol Planofix||1.25 ml/L of water 0.25 ml/L of water||30,60,90 DAT 70,85 DAT||Antitranspirant Reduce flower and fruit drop|
|Watermelon||Ethrel||2.5 ml/10 L of Water||2 true leaf stage (15 days) 3 times @ 1 week interval||Modification of sex expression|
|Cucumber||Ethrel||2.5 ml/10 L of Water||2 true leaf stage (15 days) 3 times @ 1 week interval||Modification of sex expression|
|Bitter Gourd||Ethrel||2.5 ml/ 10L of water||2 true leaf stage (15 days) 3 times @ 1 week interval||Modification of sex expression|
|Ridge gourd||Ethrel||2.5 ml/ 10L of water||2 true leaf stage (15 days) 3 times @ 1 week interval||Modification of sex expression|
|Snake gourd||Ethrel||1 ml/ 10L of water||2 true leaf stage (15 days) 3 times @ 1 week interval||Modification of sex expression|
|Pumpkin & Ash gourd||Ethrel||1 ml/ 10L of water||2 true leaf stage (15 days) 3 times||Modification of sex expression|
About Author / Additional Info:
Ph.D. Scholar, Department of Horticulture, Dr. Panjabrao Deshmukh Krishi Vidyapeeth, Akola, Maharashtra-444104.