Role of ‘B’ Nutrition: Water, the most important component of life, is rapidly becoming a critically short commodity for humans and crop production. Limited water supply is one of the major abiotic factors that adversely affect agricultural crop production worldwide. Drought stress influences the normal physiology and growth of plants in many ways. It results in an increase of solute concentration outside the roots compared to the internal environment of the root and causes reverse osmosis. As a result, the cell membrane shrinks from the cell wall and may eventually lead to death of the cell.
Strategies for Solving the Problem of Drought
Over the past several years, however, “molecular markers” have been used for identification of tolerance carrying genes in addition to adequate selection technology. “Comparative gene mapping” has allowed simultaneous insights into corresponding genes of several crops and their incorporation into domestic selected material for the purpose of increasing their tolerance to drought. At a practical level, the former method includes recombination of genes of different parents, one of which at least is required to have mechanisms and properties of tolerance to drought. The latter method includes an identification of genes playing part in the expression of tolerance to drought, their isolation and transfer into different genotypes by genetic transformation.
Irrigation is the only method that provides a complete solution to the problem of drought. However, irrigation should not be treated as a method of combating drought as it is essentially a means of intensive and modern agricultural production. It is crucial to determine a rational regime of irrigation and plants’ water requirements.
Boron (B) has a primary function related to cell wall formation in plants. The plants suffering from drought stress may be stunted. Boron improves the drought tolerance in plants by improving sugar transport, flower retention, pollen formation and seed germination. Boron nutrition under drought condition results in reduction in stunted appearance (resetting), barren ears due to poor pollination, hollow stems and fruit (hollow heart) and brittle, discolored leaves and loss of fruiting bodies.
Boron and Drought Resistance in Wheat
Foliar application of this (B) key nutrient alleviates the deficiencies and increases drought tolerance by maintaining key physiological processes.
- Boron (0.5%) improves pollination. Boron is involved in flowering, pollen viability and its uptake from the soil is greatly reduced during drought. Deficiency can lead to decreased fruit set.
- Gluten percentage can be enhanced by spraying 1% Boron solution at flowering stage which is owing to an enhanced N & P uptake efficiency during grain and protein formation.
- Under drought stress, grain yields decreased but Boron application can compensate it by increasing the percentage of gluten.
- Studies have confirmed an increased yield of grain of wheat with Boron spraying due to fact that Boron deficiency leads to decreased transfer of food to grain during flowering.
- Proline, glycine betain, sugars and active osmotic substances tend to accumulate under drought in wheat plants and these made compatibility in plant by making more negative osmotic potential. Boron facilitates their accumulation.
- Boron and N applications in wheat can stimulate larger flag leaf area-an index of amount of grain yield per spike.
- Better use of N, synthesis of carbohydrates, water utility, protein synthesis etc. are all mediated by combination of N and Boron applications under drought and these constitute enhancements in yield both quantitatively & and qualitatively.
- Boron also has a role in cell division, forming buds, leaves and chlorophyll synthesis and N uptake, i.e. plants have more LAI with Boron nutrition and photosynthesis will be more too accordingly.
- Crop Growth Rate (CGR) tends to enhance with Boron spraying but unto a limit after which Boron cause toxicity.
- Net Absorption Rate (NAP) also fluctuates positively with Boron levels but at higher levels of Boron, the negative relationship is observed.
Boron and Drought Resistance in Rice
Boron (B) deficiency is spreading in most of rice growing soils. Although considered tolerant, rice suffers with B deficiency resulting in substantial yield loss.
Reasons of B deficiency
- Low soil pH
- Calcareous nature of soil
- B leaching and fixation
Physiologically, B deficiency may result in loss of integrity and function of membrane, and decrease in cell wall stability resulting in structural damage in plants. However, reproductive stage of plants is more sensitive to B deficiency than the vegetative stage.
- Boron application to rice fields increased rice growth and grain yields in soils low in B.
- Foliar fertilization is more effective and economical as this may instantly repair plant tissues damaged specifically from B deficiency.
- Although foliage applied B improves the grain yield of rice, understanding the physiological mechanism of yield improvement by foliar applied B and its grain bio-fortification potential is lacking.
- Foliar application of B substantially enhanced leaf elongation.
- Foliar applied B significantly affected the water relation attributes.
- Likewise B application significantly affected the chlorophyll-a (Chl-a) and total Chl contents.
- Boron application significantly improved the grain yield and yield-related parameters.
- Boron application significantly improved the B contents in leaves and kernels.
- There was strong negative correlation of panicle sterility with Fw, Fs, RWC and leaf B contents in rice cultivars. However, kernel yield and kernel B contents were positively correlated with Fw, Fs, RWC and leaf B contents in rice cultivars.
- Micronutrient malnutrition is a major human health problem in the developing world however; bio-fortification offers an attractive and economical solution of this important issue. Increase in kernel B contents by foliage application of B indicated that, other than breeding efforts, foliage application of micronutrients is also a pragmatic option.
To sum up and put an end to this discussion, Boron is an important nutritional constituent of many metabolic and physiological processes in wheat and rice plants. It can be inferred from the above that this element has direct and indirect roles in the components forming grain yields of the two crops. Current investigations have shown the grim importance of Boron nutrition in alleviation of drought so that the globally important crops viz. wheat and rice can be made resistant against drought conditions. The studies on well-founded and mass scale level are needed to provide solutions for prevailing water scarcity in countries especially Pakistan to mitigate the situation from getting worse. Food security is a key drive behind such research and, in fact, this might provide world with the enhanced yields to feed the ever growing numbers.