The Role of Anti-Transpirant In Improving Crop Growth And Yield Potential

Transpiration is the process of water movement through a plant and its evaporation from aerial parts, such as leaves, stems, and flowers. Water is necessary for plants but only a small amount of water taken up by the roots is used for growth and metabolism, near about 99% of adsorbed water is lost by plants through the transpiration process. Transpiration occurs mainly through the stomatal apertures and can be called as necessary devils of plants. In this process, the opening of the stomata allows the movement of water from leaf to air through water potential difference between leaf and ambient air and causes liquid loss of water. Transpiration helps to keep water balance of the plants, changes osmotic pressure of cells, and enables mass flow of mineral nutrients and water from roots to shoots. Two major factors influence the rate of water flow from the soil to the roots: the hydraulic conductivity of the soil and the magnitude of the pressure gradient through the soil. Both of these factors influence the rate of bulk flow of water moving from the roots to the stomatal pores in the leaves via the xylem.  If the water potential in the ambient air is lower than the water potential in the leaf airspace of the stomatal pore, water vapor will travel down the gradient and move from the leaf airspace to the atmosphere. This movement lowers the water potential in the leaf airspace and causes evaporation of liquid water from the mesophyll cell walls. Thus the transpiration process occurs within the plant cell. This process is an unavoidable evil as stomata also allows the gaseous exchange of plants simultaneously.

Therefore the principle of regulating transpiration from the plant is nowadays the greatest concern as a means of water conservation. It can be reduced without a comparable reduction in photosynthesis because the diffusion resistance of the stomata constitutes a greater fraction of the whole diffusion pathway for water vapour than for CO₂.It indicates water can be saved without a significant reduction in crop growth. Therefore, the use of antitranspirant in a larger extent need to be followed. Some basic concepts of antitranspirant is discussed below-

Antitranspirants are substances applied to the plants for the purpose of reducing transpiration (water loss) without causing a significant effect on other plant processes, such as photosynthesis & growth. They have also been used to protect leaves from salt burn and fungal diseases. These are also called as transpirant suppressants, best transpirants can reduce transpiration loss up to 30-40%.

How they reduce Transpiration (water loss):

Antitranspirants may reduce transpiration in three different ways:

1. By reducing the absorption of solar energy and thereby reducing leaf temperatures and transpiration rates.

2.    By forming thin transparent films which hinder the escape of water vapors from the leaves.

3.  By promoting closure of stomata (by affecting the guard cells around the stomatal pore), thus decreasing the loss of water vapors from the leaf.

Types of Antitranspirants:

1.      Stomatal closing type: They induce stomatal closing or decrease size and number of stomata which subsequently reduce the photosynthesis. Example, Phenyl Mercuric Acetate(PMA), Abscisic Acid(ABA), and high Co₂ Conc. The closing of stomata affects the rate of CO₂ diffusion into leaf leading towards a low rate of photosynthesis.

 

a) PMA is a widely used chemical for the stomatal closer. When Phenyl Mercuric Acetate is sprayed at very low concentrations, results in a partial closure of stomata for 2 weeks. But it has disadvantages that it is toxic to veg and fruit crops. It inhibits the phosphorylation process and causes damage to foliage by blocking photosynthesis. Although success is reported at glasshouse studies and effectiveness is limited at field conditions.

b) CO₂ is also an effective antitranspirant. A little rise is conc. From 0.03-0.05% induces partial closure of stomata and its higher conc. can result in complete closure of stomata affecting adversely photosynthesis and respiration process.

c) ABA induces stomatal closing, thus reducing excess water loss from leaves and consequently water uptake from roots. Based on this stress alleviation function, ABA can be considered as a metabolic antitranspirant to protect plants under stress conditions (Mansfield, 1976)

d) Herbicides such as triazine, atrazine, simazine which are the inhibitors of Electron Transport Chain at QA and QB sites but at the lower concentration they can also be used as antitranspiratns.

 

2.      Film-forming type: Plastic and waxy material which form a thin colorless film over the leaf surface and result in a physical barrier. These glossy films then reduce water loss on plants while at the same time allow them to breathe normally by passing CO₂ into leaves through lower epidermis. Colorless plastics, silicone oils, low viscosity waxes are some examples of film-forming types. They can also be divided into two category-

a)      Thin-film forming type- Hexadeconol

b)     Thick film-forming type- Mobileaf, polythene S-60

c)   Other-examples are Cetyl alcohol, Methanol, Tracotanol, Paclobutrazol, Brassinollide, Resorcinol, etc.

 

Disadvantages-

o   Affects only at low temp but not at a high temp.

o   Comes in the way of gas exchange.

o   Form the mechanical barrier for stomatal movement.

 

 

3.     Reflecting type: These are most commonly clay-based and increase the reflection of light from leaf surface thus reducing leaf heating and vapor pressure gradient from leaf to atmosphere, thus water losses can be reduced. The water is loss is reduced without affecting CO₂ assimilation. Example- Kaolinite(Kaolin), Lime water( Limewash). Kaoline normally sprayed at 2-5 % and form a thin film coating on the leaf surface. Other- Celite( diatomaceous earth), hydrated lime, calcium carbonate, Mg carbonate, Zinc sulfate, 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. Example- Cycocel, Phosphon-D, Maleic Hydrazide(MH), CCC[( 2-chloroethyl) Trimethyl ammonium chloride].

Effects on Field Crops and Plants:

An increase in yield of an annual crop was observed after the application of antitranspirants. Meider(1967) found that the stimulation of opening in barley by photosynthesis, through there was also evidence of a more direct effect on stomata mechanism. According to Rao and Bhatt(1990), Kaolinite was the most effective antitranspirant at all the growth stages of onion crops. Ibrahima and Selim(2010) found that irrigation every 12 days intervals combined with spraying kaolin at 6% concentration to summer squash cv. Eskandrani might give the chance for increasing water use efficiency and produce satisfactory and good marketable fruit yield under similar conditions of this work. Peter.S.Kettlewell 2014 shows that film antitranspirants applied to wheat before the drought-sensitive stage of meiosis can increase yield, despite reducing photosynthesis, and that this increase is associated with improved pollen viability. 

 

Reference:

·   “Antitranspirants”. Agriinfo.in. N.p., 2016. Web. 5 Mar. 2016.

·   “Can Antitranspirants And Antidesiccants Improve Vegetable Transplant Survival? Weekly Crop Update”. Agdev.anr.udel.edu. N.p., 2016. Web. 5 Mar. 2016.

·   http://ecoursesonline.iasri.res.in

·   Meidner, H. (1967): The effect of kietin on stomatal opening and the rate of intake of carbon dioxide in mature primary leaves of barley.J.exp. Bot. 18, Page(s): 556-561

·   Mansfield, T . A. (1976): Delay in the response of stomata to abscisic acid in CO2-free air. Journal of Experimental Botany, Vol 11, Page: 559.

·   Rao, N.K.S, Bhatt,R.M.(1990):Responses of onion to antitranspirants-plant water balance. Plant Physiology & Biochemistry.Vol.17 No.2,page(s):69-74

·   Ibrahima and Selim(2010): Effect of irrigation intervals and antitranspirant(Kaolin) on summer squash(Cucurbita pepo L.)growth, yield, quality, and economics. Journal of Soil Sciences and Agricultural Engineering Article 8, Volume 1, Issue 8, Page(s): 883-894

·   Peter S.Kettlewell (2014 ): Waterproofing Wheat — A Re-Evaluation of Film Antitranspirants in the Context of Reproductive Drought Physiology. Outlook on Agriculture,Volume: 43 issue: 1, page(s): 25-29