Antitranspirants are the materials or chemicals which decrease the water loss from plant leaves by reducing the size and number of stomata. Nearly 99 per cent of the water absorbed by the plant is lost in transpiration. Antiranspirants and is any natural applied to transpiring plant surfaces for reducing water loss from the plant. There are of four types.
1. Stomatal closing type: Most of the Tran spirants occur through the stomata on the leaf surface. Some fungicides like phenyl mercuric acetate (PMA) and herbicides like Atrazine in low concentration serve as antitranspirants by inducing stomatal closing. These might reduce the photosynthesis. PMA was found to decrease transpiration than photosynthesis.
2. Film forming type: Plastic and waxy material which form a thin film on the leaf surface and result into physical barrier. For example ethyl alcohol. It reduces photosynthesis eg. Tag 9; S – 789 foliate.
3. Reflectance type: They are white materials which form a coating on the leaves and increase the leaf reflectance (albedo). By reflecting the radiation, vapour pressure gradient and thus reduce transpiration. Application of 5 percent kaolin spray reduces transpiration losses. eg. Diatomaceous earth product (Celite), hydrated lime, calcium carbonate, magnesium carbonate, zincs sulphate etc.
4. Growth retardant: These chemicals reduce shoot growth and increase root growth and thus enable the plants to resist drought. They may also induce stomatal closure. Cycocel is useful for improving water status of the plant.
Antitranspiratnts are also useful for reducing transplantation shock of nursery plants (Horticultural plants) Examples / Different antitranspirants:
1. Metabolic inhibiter like phenyl mercuric acetate, some alkanyl succinic acids.
2. Growth retardant such as A.B.A. Cycocel.
3. Herbicides, fungicides
4. Salicylic acid.
5. Colourless plastics, silicon oil, wax or plastic.
6. White reflecting materials (e.g. Kaolin) emulsions or white wash.
Good features of contranspirant
1. Non toxicity
2. Non permanent damage to stomata mechanism.
3. Specific effects on gard cells and not to other cells.
4. Effect on stomata should persist at least for one week.
5. Chemical or material should be cheap and readily available.
Role of antitranspirants in annual field crops:
In general field crops are highly dependent or current photosynthesis for growth and final yield. Therefore it is unlikely that currently available antitranspirant would increase yield of an annual crop unless crop suffers stressed from inadequate water and or a very high evaporative demand, particularly during a moisture sensitive stage of development.
Fuahring (1973) sprayed stomata inhibiting or film forming anti – Tran spirants on field grown sorghum under limited irrigation conditions, he found that grain yield increases 5 to 17% and application of antitranspirant just before the boot stage was more effective than later sprays.