Preparation of Plant Growth Regulators and their Uses
Growth regulator is a broad term and all growth-regulating compounds either endogenously or exogenously produced come under this category. In relation to plants, terms like hormones or phytohormones are synonymous to each other. Plant hormones or Plant Growth Regulators are organic compounds, other than nutrients, produced endogenously by plants, which in low concentrations regulate plant physiological processes.
The horticulture industry is indirectly dependent on plant growth regulators as these are exclusively used for different purposes in all stages of the plant growth for desired manipulations viz., treatment of seeds for enhancing their germination, rooting of cuttings, induce flowering, deblossming, fruiting, yield, ripening, improving fruit quality and as postharvest treatments for better shelf-life. For the propagation of cuttings and layers, treatments of IBA growth regulators are used for inducing roots early rooting.
These Growth Regulators are applied as powder form, solutions form, and paste form. Most of the
hormones are not easily dissolved in water. Thus, it is necessary to dissolve
them first in a suitable solvent viz., acetone or ethanol or alcohol. The growth regulators are required in a very
minute quantity; therefore, precise weighing is of utmost importance and any
mistake can be harmful to the plant. The different heopreparations of growth
regulators are as follows;
Peparation of Growth Regulators
1. Powder Form:
The required quantity of the hormone is weighed precisely with the help of sensitive balance for the preparation of hormonal powders. It is dissolved in ½ litre ethanol, methanol or acetone in a beaker. This material is poured into one kilogram of talc taken in mortar and mixed thoroughly with a glass rod. After mixing, the mixture is kept open in air for few hours. The alcohol will evaporate soon, after which, the dried talc is ground to a fine powder. This fine powder should be kept in air tight containers to avoid moistening and can be used as and when required.
2. Solution Form:
For the preparation of hormonal solutions, the required quantity
of hormone is weighed accurately in a physical or electronic
balance. It is then dissolved in few drops of acetone or alcohol or ethanol. The final volume is made with distilled water
after the complete dilution of contents. The pH of the solution should be neutral. In case, the pH of the
solution would be high or less, it may not serve the purpose, rather it would affect the process
adversely. The pH of the solution can be adjusted with the help of 0.1 N HCl or 0.1 N KOH. All the hormonal
solutions should preferably be prepared fresh and can be stored at low temperatures in a refrigerator for some
time but stored preparations may loose their properties and become
inactive.
3. Paste Form:
The required quantity of
the hormone is weighed and dissolved completely in a few drops of alcohol/ethanol/acetone. The required quantity of the
lanolin (a product similar to grease and greenish-yellow in colour) is also weighed and heated
slightly in a beaker under a gentle flame. When the lanolin is slightly liquidified, the dissolved hormone is
poured into it. The contents are dissolved thoroughly with constant stirring
with a glass rod. The
contents are then allowed
to cool down. The paste is thus ready for use.
Methods of Application:
1. Lanolin paste
This technique is most common for laboratory experiments. As this paste is prepared from fat the growth regulator doesn't dry out, thereby maintaining a constant concentration of the compund in contact with the treated organ.
2. Immersion into dilute or concentrated solutions
The cuttings or the seeds can be soaked in the dilute solution of the growth regulator for 10-24 hrs. Dipping in a concentrated solution is recommended for rapid action. The proximal end of the cutting should be dipped in the solution.
3. Spraying method
This method of growth regulator application is comparatively easy and quick. The dilute solutions are sprayed on the crop foliage with several types of sprayers. The effectiveness of the application depends on the ability of the growth regulator to penetrate through leaf cuticles into the mesophyll cells.
4. Dust method
The growth regulator is dusted over the surface of the plant in the form of powder. This method is commonly used in rooting of cuttings. The cuttings may first be moistened with water at the basal end and then dipped in powder and planted on the lower end in the soil.
5. Aerosol and vapour method
These methods are widely adopted in green house plants for promoting fruitsetting, inducing parthenocarpy and controlling the fruit drop. The aerosol method is based on preparing a growthregulater solution of low boiling point.For vapour form the active compound must be volatile.
Calculation for Plant Growth Regulators:
Q1. 1pppm of Growth Regulator preparation
Answer:
1ppm = 1mg of growth regulator in 1 lit of water
Q2. Prepare a GA3 growth regulator at the concentration of 10ppm and the final volume of solution should be 5 lit. (Try to solve it)
Answer: ?
Precautions to be taken
Ø A proper solvent like acetone or ethanol etc should be used so as to dissolve
the growth regulators.
Ø At once, a minute
quantity of hormone
is used. So, don't buy more than what is required.
Ø Check the date
of expiry of the hormone.
Ø The weighing
of growth regulators should be done precisely and accurately on an electronic balance.
Ø These hormones are photo-sensitive and photo-degradation occurs if exposed to light. Thus, these should be stored in dark or amber-coloured bottles. The solutions should always be made fresh.
