PLANT GROWTH REGULATORS IN VEGETABLE PRODUCTION : AN OVERVIEW

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 trees. These chemicals act on plant processes at very low concentrations. Often they are produced at one location and transported to another, where they exert their influence; however, they may also act on the same tissue in which they are produced. Plant growth regulators are organic chemical substance, other than nutrients and vitamins which regulate the growth of plant when applied in small quantities. PGR are used in different forms like liquid, powder, paste etc. “Hormone” is Greek word derived from “hormao”,which means to stimulate. Thimone (1948) suggested the use of term phytohormones as the organic substance, which are produced naturally in plants, synthesised in one part and usually translocated to other part where in every small quantity affect the growth and other physiological function of the plants. To distinguish them from the animal hormones they are termed as phytohormones. Auxin was the first hormone

to be discovered in plants and at one time considered to be only naturally occurring plant growth hormone.

Growth, development and yield analysis in crop plants helps in understanding the contribution of various growth and yield components. Plant growth regulators considered as a new generation of agrichemicals when added in small amounts, modify the growth of plants usually by stimulating or modifying one part of the natural growth regulatory system, thereby the yield is enhanced. Higher production through breeding is a continuous endeavour of mankind. But, these methods are however, not only time consuming but also costly. The growth regulators have therefore, been known to be one of the quick means of increasing production. Similarly, nutrients are inorganic substances necessary for the normal growth and development of plants and have important role in various enzymatic processes, assimilation, oxidation and reduction reactions and help in increasing the biomass and pod yield. Hence, the present investigation was carried out to find out the suitable growth regulators and micronutrients to increase the yield and yield components in okra.

2.Commercial Utility of PGRs in vegetable crops Stimulation of fruit set

Poor fruit set is a major problem in solanum crops. In tomato apply 4-CPA, or 2,4-D@2-5ppm or PCPA 50-100ppm enhance the fruit set, and earliness.

Inhibition of sprouting : Application of MH @ 2500 ppm 15 days before harvesting prevents sprouting of onion in storage. Soaking potato tuber in IAA @ 250 to 1000 ppm solution or prolongs dormancy and thiourea @ 1% breaking the tuber dormancy.

Flowering : Application of GA at 50 mg/l to young leaves of non- flowering varieties of potato, when floral buds had just formed, resulted in flower induction in all varieties. MH delayed flowering in okra. GA has been reported to induce early flowering in lettuce.

Seed Germination : Pre-showing treatment of seed with growth regulators has been reported to enhance seed emergence. Okra IAA, NAA @ 20ppm enhances seed germination,In tomato, higher germination with GA3 at 0.5 mg/l, and 2,4-D at 0.5 mg/l is reported. Soaking of seeds in ethephon at 480 mg/l for 24 h improved germination in muskmelon, bottle gourd, squash melon and watermelon at low temperature.

Seed Dormancy : Potato tubers fail to sprout before the termination of rest period; chemicals reported to break the rest period are GA, ethylene chlorhydrin and thiourea. For breaking of dormancy in potato comprise the vapour treatment with ethylene chlorhydrin (1 liter per 20 q) followed by dipping in thiourea (1%) for 1hr. finally in GA (1 mg/l) for 2 seconds. Lettuce is another vegetable in which treatment with GA has been reported to break seed dormancy induced by high temperatures.

Sex expression : Sex expression the treatment with growth regulators has been found to change sex expression in cucurbits, okra and pepper. GA 3 (10-25 ppm), IAA (100 ppm) and NAA (100 ppm) when sprayed at 2-4 leaf stage in cucurbits, then they have been found to increase the number of female flowers. Whereas, GA 3 (1500-2000 ppm), silver nitrate (300-400 ppm) and Silver thiosulphate (300-400 ppm) sprayed at 2-4 leaf stage induces male flower production in cucurbits

Parthenocarpy : Auxin produced seedless fruits in cucumbers and watermelon, PCPA 50-100 ppm induced parthenocarpy in tomato and brinjal, application of 2,4-D at 0.25% in lanolin paste to cut end of styles or foliar sprays to freshly opened flower cluster has been reported to induced parthenocarpy.

Gametocides : Plants growth regulators possess gametocidal actions to produce male sterility this can be used for F1 hybrid seed production. MH at 100 to 500 mg/l in okra, okra, peppers and tomato, GA3 in onion, 2,3- dichloro-isobutyrate (0.2 to 0.8%) in okra, muskmelon, okra, onion, root crops, spinach and tomato and TIBA in cucumber, okras, onion, and tomato. GA at 100 mg/l can also be used for inducing male sterility in pepper.

Hybrid seed production : Ethephon has been used for producing female lines in some cucurbits. Successful F1 hybrid in butter-nut squash has been made by using female line produced with ten weekly sprays of ethephon. Plant growth regulators have also been used for maintenance of gynoecious lines. In cucumber, GA3 sprays have been made to induce staminate flowers in gynoecious lines. Silver nitrate at 500 mg/l has been reported to be as effective as GA3 in inducing male flowers on gynoecious lines of cucumber. However, in muskmelon foliar sprays of Silver thiosulphate at 400 mg/ l was found best for induction of male flower on gynoecious lines.

Fruit ripening : Ethephon, an ethylene releasing compound, has been reported to induce ripening in tomato and pepper. Application of ethephon at 1000 mg/l at turning stage of earliest fruits induced early ripening of fruits thus increasing the early fruit yield by 30-35%. Postharvest dip treatment with ethephon at 500-2000 mg/l has also been reported to induce ripening in mature green tomatoes.

Fruit yield enhancer : Soaking of seed in NOA at 25-50 mg/l, GA at 5-20 mg/l and CIPA at 10-20 mg/l, 2,4-D, 0.5 mg/l or thiourea at 10-1 M have been reported to improve fruit yield in tomato. In brinjal soaking of seedlings roots in NAA at 0.2 mg/l and ascorbic acid at

250 mg/l has been reported to produce higher fruit yield.

3. PGRs effect onseed germination

Asparagus seeds were soaked in different growth regulators like IAA, IBA, naphthalene acetic acid and various concentrations of GA3 to evaluate their effect on germination. It was found that GA3 had a significant effect on germination rate as compared to control, IAA, IBA and NAA during light and dark period.

4. PGRs effect ongrowth and development

Plant growth regulator affects the physiology of plant growth and influence the natural rhythm of a plant. (IAA) and (GA) can manipulate avariety of growth and developmental phenomena in various crops. IAA has been found to increase the plant height; number of leaves per plant, GA stimulated stem elongation increase dry matter accumulation. The application of ethrel in Watermelon (Citrullus janatus) at 500ppm concentration brought significant improvement in vegetative characters of plants i.e.main vine length and number of secondary branches.

The effects of growth regulators and grafting were additive for flower numbers, percentage capsule set,and number of seeds. Chemical names used: (BA), (2, 4-D), (ethephon), (GA3).

5. PGRs effect onyield attributed traits IAA and GA3 can increase fruit size withconsequent enhancement in seed yield. It also increases the flowering, fruit set . GA stimulated stem elongation increase dry matter accumulation and enhance vegetable seed yield. It was noticed both the fruit number and fruit yield significantly affected hormones. . #AgriSpaceBlog