Role of plant growth regulators in some vegetables


Dr.
C.M. Ayyub, Sana Saleem, Alqa Yousuf (IHS, UAF)

Plant
hormones

Plants produce some natural substances in their tissues particularly growing points, these are called plant hormones. These are produced in minute amount in one part of the plant and then these hormones transferred to their required location to regulate the activities of plant. These are also called phyto-hormones.

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Plant
growth regulators (PGRs)

Hormones
are synthesized by plants itself but some time they need to apply exogenously. But
when we talk about PGRs, these are synthetic or artificial products, which
produce reaction almost identical to natural substances when applied to plants.
The use of PGRs is much easy to apply so this is useful for farmers. Plant
hormones and plant growth regulators are classified in to five categories i.e.
auxin, cytokinins, gibberellins, ethylenes, abscisic acids. A lot of mechanisms
have been proposed but still its actual mode of action is not yet found. A lot
of PGRs are available in the markets.

Auxin
 

The
natural form of auxin is indole-3-Acetic acid and synthetic form is IBA (indole-3-butyric
acid), 2,4-D (2,4-Dichlorophenoxyacetic acid), NAA (Naphthaleneacetic acid).
This compound gives positive effect on formation of bud, stimulating root
growth and development, induce flowering, inducing the formation of
parthenocarpic fruit and prevent from abscission and sprouting. It is also use
for eradication of weeds.

Cytokinins

The
common synthetic cytokinins are kinetin, zeatin and benzyladenine. It is also
known as anti-auxins because they help in growth of lateral buds and inhibit
apical dominance. The function of cytokinins includes cell division (pea), cell
enlargement (pumpkin) and differentiation. They help to break seed dormancy
(lettuce), induce flowering and prevent aging of plants.

Gibberellins

It
is the second growth regulator. Gibberellins or gibberellic acid help in seed
germination and seedling growth, stem elongation, flowering and sex expression
(maleness), fruit setting, promote bolting and to break seed dormancy. They
have lot of thypes.

Ethylene

It
is a colorless gaseous hormone. In cells it increases the width only not the
length. It causes inhibition of root growth and stimulate the formation of
adventitious roots. It induces ripening of fruits (tomato). It stimulates
senescence and accession of leaves and also helps in induction of femaleness
(cucumber, squash and melon). Now a day ethylene generators are available for
artificial ripening of fruits.

Abscisic
acid

This
hormone produced in response to stress. It has direct effect on seed dormancy
and also acts as inhibitory chemical compound. It is responsible for closing of
stomata and inhibits protein formation and activity of mRNA. It also promotes
abscission of leaves and fruits. It also plays vital role in triggering the
defensive mechanisms of plants as it signals the onset of stress. Its high
concentrations in the plants normally causes plants harmful effects leading to
die.

Role
in vegetables

Potato

In
potatoes 250 ppm ethrel foliar spray increase yield as well as diameter of
shoot, plant height and number of tubers per plant. Ethylene, GA3
and thiourea (1% aqueous solution for 1 hour) break dormancy in potatoes. Soaking
tubers in 10 ppm to 15ppm GA3 for 10 to 20 minutes breaks dormancy
in potato. Foliar application of 50mg/l of GA3 induce flowering in
all potato varieties when apply on young leaves. At 60 days after transplanting
application of GA3 increase height of plant while late application
induce maximum sprouted tubers and increase its physiological age.

Tomato

Plant
growth regulators increase yield of tomato plant and also effect on its growth
parameters. Pre sowing treatment with 100ppm NAA, IAA and IBA enhance seed
germination in tomato. 300 ppm GA3 sprays use for earlier flower
production and increasing number of fruits per plant. It also increases yield
in tomato. Seed treatment with 2,4-D @ 2-5 ppm induce parthenocarpy in tomato
and gives early fruit setting. In normal or even adverse condition fruit
setting can be enhanced in tomato by application of 5 ppm kinetin, 10 ppm NAA
or GA3 or 2,4-D (1-5 ppm). Post-harvest treatment with ethephon at
500-2000 mg/l induces ripening in mature green tomatoes. 10 days before
transplanting 60 ppm GA3 spray increase yield per hectare of variety
Roma.

Cucurbits

Cucurbits
are group of summer vegetables belongs to cucurbitaceae family. Growth
regulators change sex expression in cucurbits, pepper and okra. 100 ppm IAA or
NAA and 10-25 ppm GA3 when apply on 2-3 leaf stage it will increase
female flowers in cucurbits, while 1500-2000 ppm GA3 increase male
flowers production. GA3 and NAA (20 ppm+100 ppm respectively)
increase vine length and number of leaves per plant. Same application gives
maximum yield in cucumber. In bottle gourd fruit setting can be enhanced by
foliar application of 400 ppm maleic hydrazide or 50 ppm triodobenzoic acid at
2 to 4 leaf stage.

Onion

Gibberellic
acid use in high concentration (2%) acts as gametocide when it is applied at
beginning of bolting process. For reducing physiological weight loss and to
avoid spoilage dip roots in 100 ppm NAA. Ethylene and CCC (Cycocel) application
increase shelf life of onion and delay sprouting of bulbs.

Chilies

In
normal or even adverse condition fruit setting can be enhanced in chilies by
application of 5ppm kinetin, 10 ppm NAA or GA3 or 2,4-D (1-5 ppm). Ethephon
@ 150ppm increases number of fruits per plant. 4ppm concentration of 2,4-D also
increase shoot dry weight, number of seed per fruit and number of fruits per
plant. 60ppm concentration of NAA increase flower number per plant, seeds
number per fruit and fruit yield per plant in capsicum.

Okra

20
ppm IAA and NAA application increase seed germination in okra. Application of
150ppm GA3 reduced number of days for first harvesting. All yield
attribute such as number of pod per plant and pod length increases by application
of thiourea @ 500ppm. GA3 @ 50 ppm improved seed quality related
characters such as pod weight, 100 seed weight.

Cabbage

Maximum
profitable yield can be obtained by 120 ppm GA3 spray in cabbage. By
using 80 ppm concentration of NAA plant height, number of leaves per plant,
head weight and yield increases. Combine application of IAA 10 ppm and GA3
70 ppm increase plant height, crud diameter, number of leaves, leaf length and
yield per hectare. Higher concentration of NAA (140 ppm) enhances yield and
vegetative parameters in cauliflower. 

Brinjal

Application
of 2,4-D at 2-5 ppm in lanolin paste induce parthenocarpic fruits in brinjal
when apply to freshly opened flower clusters. In normal or even adverse
condition fruit setting can be enhanced in brinjal by application of 5ppm
kinetin, 10ppm NAA or GA3 or 2,4-D (1-5 ppm).  Higher yield can be obtained by 4 ppm 2,4-D
spray. Higher fruit yield and number of fruits per plants can be obtained by 40
ppm NAA application.

All
physiological process occurs in crop plants such as growth, development,
formation of roots and shoots, sprouting, flowering and ripening are regulating
by plant growth regulators. These PGRS are also useful to attain maximum yield
and to improve product quality attributes in vegetable production.

Conclusion

These
are being applied in commonly now a day, but these is need to research out
which method should be used for its application. Some PGRs are effective in
soil amendment some show best results with some foliar applications. It is also
of much important to check its combine effect. It is notable to see its weather
these are effective alone or with some other chemicals. The stage of plant at
application is also a important. The dose we apply paly vital role because they
become useless at high concentration or even toxic. Moreover, it is utmost
desire to synthesize all PGRs in Pakistan for both commercial and analytical
grades. So that it must be cost effective as some PGRs are so costly.



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