फलों की फसल के सुधार में पादप विकास नियामकों की भूमिका

Plant growth regulators refer to an organic compound other than nutrients and vitamins which are active at low concentrations in promoting, inhibiting or modifying growth and development. The naturally occurring (endogenous) growth substances are commonly known as plant hormones, while the synthetic ones are called growth regulator.

Plant hormone is synthesised in one part of the plant and translocated to another part, where in very low concentrations it causes a physiological response. The plant hormones are identified as promoters (auxins, gibberellin and cytokinin), inhibitors (abscissic acid and ethylene) and other hypothetical growth substance (florigen, flowering hormone, etc).

Application of plant growth regulators results in better output as it improves the internal physiology of developing fruits to improve fruit set, reduce fruit drop and to amend various physiological disorders in order to improve quality and yield.

Ethylene is known as the ‘ripening’ hormone. Manipulations of fruits and vegetables are done by either exogenous ethylene or inhibitors of ethylene production. However, other plant growth regulators are also used in horticultural production and have ramifications for postharvest quality.

Many of the commercially available plant growth regulators are used in stone fruit production. Auxins are used to enhance the size of stone fruits. Gibberellins are used for increasing fruit size and firmness of cherries and peaches. In addition, when peaches are treated at the end of pit hardening, gibberellin can delay storage disorders such as internal browning and woolliness development.

Inhibitors of gibberellin synthesis which inhibit shoot elongation have also been used to increase fruit size by decreasing the competition between fruit and vegetative growth. These plant growth regulators have also been found to decrease fungal infections, either by delaying ripening or senescence, or by altering the structure of the fruit.

Other well-known plant growth regulators have been used to affect biotic and abiotic stresses of harvested fruits and vegetables. Salicylic acid and jasmonic acid induce defense reactions in fruits and vegetables that help prevent fungal infection and induce resistance to low temperature injury.

Growers and researchers should be aware that plant growth regulators applied in the field may have beneficial carry-over effects on postharvest quality.

Classification of Plant Growth Regulators:

1. Auxins {IAA, IBA, NAA, 2, 4-D etc}
2. Gibberellins {GA_1, GA_2, GA₃ etc}
3. Cytokinenins {Kinetin, Zeatin}
4. Etylene {Ethrel}
5. Dormins {Abscissic Acid (ABA), Phaseic Acid}
6. Flowering Hormones {Florigin, Anthesin, Vernalin}
7. Phenolic Substances {Coumarin}
8. Miscellaneous Natural Substances {Vitamins, Phytochrome Tranmatic Substances}
9. Synthetic Growth Retardants {CCC, AMO-1618, Phosphin - D, Morphacting, Malformis}
10.  Miscellaneous Synthetic Substances {Synthetic Auxins, Synthetic Cytokinins}

Uses of Plant Growth Regulators in Fruit crops:

1. Flowering:

• Ethylene responsible for flowering in pineapple
• Acetylene, calcium carbide, ethephon and NAA(10-15 ppm) used to induce flowering in pineapple
• In litchi, NAA replaces girdling for improved flowering
• SADH promots flowering in apple, pear, peach and blueberry
• Grapes and lemon respond to CCC with increased flowering

2. Fruiting:

• In fruits like apple, pear, fig, grapes etc. GA₃ application produce parthenocarpic fruits
• Soil application of paclobutrzol (cultar) @ 5g per tree is effective in regulating fruiting in mango
• Cytokinin in grapes is used for parthenocarpic fruit set
• Application of GA₃ has increases fruit set in strawberry, peach, plum and cherry
• Application of GA₃ @25 ppm increase fruit set in Thompson seedless variety of grape

3. Fruit Thinning:

• NAA application at post bloom for thinning in apple
• DNOC (sodium 4,6-dinitro-o-cresol) in stone fruits
• Pre-bloom application of GA₃ for optimum fruit set and loose and attractive clusters in grapes

4. Propagation:

• Gibberellins are used for seed germination and substitution of chilling requirement
• Rooting of cuttings
• 100-500 ppm IBA for soft wood
• 500-1500 ppm IBA for semi hard wood
• 2000-5000 ppm IBA for hard wood
• GA₃ has antagonistic effect on rooting of cuttings & root initiation in layered plants

5. Use in Tissue culture:

• In banana, low concentration of IAA and high level of BA essential for rapid growth of explants
• In grapes, BA and NAA for establishment of explants
• IBA helps in rapid multiplication

6. Breaking of seed and bud dormancy:

• GA₃ used for accelerated seed germination in citrus, aonla, grapes, ber, annona, apple, peach etc.
• ABA is involved in regulating abscission and dormancy
• In pecan, GA₃ has significantly reduced/substituted the period of seed stratification.
• GA₃ sprays for termination of rest period of buds in peach and apple
• Use of dormax for substitution of chilling in Kiwi and pecan
• Cytokinins break bud and seed dormancy

7. Control of Vigour:

• SADH/ paclobutrazol effective in reducing the growth of pear, peach, lemon, apple, litchi, apricot, plum and mango
• Ethrel treatment beneficial in mango, grapes and avocado.

8. Fruit growth and maturity:

• Post bloom application of CPPU, a derivative of cytokinins to increase the berry size in kiwi

9. Prevention of Fruit drop:

• Fruit drop, an abscission phenomenon, often occurs due to auxin deficiency in growing fruits and could be prevented by the exogenous application of synthetic auxins such as NAA and 2,4-D and 2.4.5-T in mango and citrus
• Application of 2,4-D @ 10 ppm has given the best pre-harvest fruit drop control in 'Hamlin' orange

10. Harvesting:

• Ethrel sprays for induced harvesting in walnut, pecan, olive, cherry and grapes

11. Improvement of fruit quality:

• GA₃ for loose clusters, decrease fruit set, reduce number of berries per cluster increase size of remaining berries and improvement of berry size in grapes. GA₃ (50-100 ppm), NAA (25-50 ppm)
• Dipping bunches in GA₃ (75 ppm) for 10 seconds for size improvement in grapes
• Foliar application of NAA @ 30 ppm increased the fruit weight, acidity, juice per cent peel and yield over control in Nagpur mandarin
• Application of NAA @ 40 ppm in pear cv. ‘Conference’ and ‘Blanquilla’ and improved fruit retention per cent and fruit yield
• Application of GA₃ @ 25 ppm increased the fruit weight, volume, TSS, ascorbic acid, peel and yield in ‘Nagpur’ mandarin

12. Fruit Ripening:

• Ethrel application in apple for uniform ripening and early fruit maturity
• Ethylene used to stimulate the ripening of fruits. For example, tomatoes and citrus fruits
• Ethephon in citrus prior to storing ensures post harvets degreening
• In lemons, dipping in 1000 ppm ethephon for attaining marketable yellow colour
• Ethrel are used in ripening of banana, mango etc
• Ethylene Promotes abscission and senescence of both leaves and flowers

References:

Kumari, S., Bakshi, P., Sharma, A., Wali, V., Jasrotia, A. & Kour, S. (2018). Use of Plant Growth Regulators for Improving Fruit Production in Sub Tropical Crops. International Journal of Current Microbiology and Applied Sciences.7.659-668. 10.20546/ijcmas.2018.703.077.

Suman, M., Sangma, P. D., Meghawal, D. R. & Sahu, O. P. (2017). Effect of plant growth regulators on fruit crop. Journal of Pharmacognosy and Phytochemistry.6(2): 331-337.

TNAU Agritech Portal, Agriculture, Plant Nutrition: Plant Gowth Regulators.

Author

Archit Singh

Research Scholar, Department of Horticulture,

Institute of Agricultural Sciences, Banaras Hindu University,

Varanasi-221005 (U.P.) India

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