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Role of silicon in rice blast resistance

Rice is the second most important food crop after wheat in Pakistan. In last few years rice yield has been found diminishing and nutritional imbalance has been reported as one of major reasons. In a more specific study of nutrients; the micronutrients have now have been found equally important as macronutrients although they are required in a minute quantity. Balancing the micronutrients for rice cultivation enhances the quality and yield. Micronutrients such as silicon are the most important for sustainable production of Basmati rice. Among all the micronutrients assimilated by plants, silicon alone is consistently present at concentrations similar to those of the macronutrients. Its concentration in different plants ranges from 0.1 per cent (similar to phosphorus and Sulfur) to more than 10 per cent of whole plant dry matter.
Silicon is an important micronutrient for healthy and competitive growth of all cereals including rice. Role of silicon in plant health and growth has been investigated in silicon accumulating crops and it seemed significantly affecting. Research evidences proved that adequate uptake of silicon can increase the tolerance of agronomic crops especially rice to both abiotic and biotic stress, which ultimately improves crop yield and quality. Low silicon uptake has been proved to increase the susceptibility of rice to diseases such as rice blast, leaf blight of rice, brown spot, stem rot and grain discoloration.
Among all rice diseases, the rice blast is most devastating. It is found in 85 rice growing countries of World and may cause up to 75 per cent yield reduction. An integrated control strategy for implementation in environments with high epidemic potential to blast includes the use of partially resistant cultivars, early sowing or seedlings transplanting, water and nitrogen management, seed treatment with fungicides as well as foliar and soil application of silicon. Applying fungicide to control the disease is neither economical nor environment friendly.
Furthermore, rice blast spreads very fast and the use of resistant varieties is considered as a short term remedy. Silicon can decrease the intensity of blast as effectively as some fungicides, mainly because it has the potential to increase the partial resistance of cultivars to the same level observed in cultivars with complete resistance. It has also been reported that rice blast severity is directly related with silicon deficiency in soils. In this context, soil amendment with Si can be considered an effective strategy to decrease blast intensity, especially when rice is cultivated in Si-deficient soils. There are different hypotheses on how silicon confers and induces resistance to some plants specially rice against diseases such as blast.
Effects of silicon on yield are related to the deposition of the element under the leaf epidermis which results a physical mechanism of defense, reduces lodging, increases photosynthesis capacity and decreases transpiration losses. Silicon can be deposited by the plants at the infection site thus inhibiting the penetration of cell walls by the attacking fungus. The ability of silicon solution to reduce the impact of plant diseases has been clearly described in the case of rice blast.
Many scientists working on role of silicon in plant growth have concluded that reduced amount of silicon in plant develops necrosis, disturbance in leaf photosynthetic efficiency, growth retardation which aggravates attack of rice blast. Although silicon has not been considered important for vegetative growth but it aids the plant in healthy development under stresses in different grasses especially in rice. Plant tissue analysis has revealed the optimum amount of silicon is necessary for cell development and differentiation. So following the recent research it is needed to enter micronutrients like silicon in rice nutrient management for efficient control of rice blast.
The writer is a Ph.D. Scholar in the University of Agriculture Faisalabad, Pakistan.


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