An Overview on the Potential of Silicon in Promoting Defence Against Biotic and Abiotic Stresses in Sugarcane

Although silicon (Si) is ubiquitous in the earth's crust, its essentiality for growth of higher plants is still under discussion. By recognising the overwhelming potential of Si in alleviating a wide range of biotic and abiotic stresses, the Association of American Plant Food Control Officials and the International Plant Nutrition Institute, Georgia, USA, have designated Si as a plant 'beneficial substance' in 2014 and 2015, respectively. Sugarcane is a Si-accumulating crop which strongly responds to Si fertilisation especially in Si-deficient soil. Due to intensive weathering prevailing in humid and sub-humid regions, most of the soil-available Si, taken up by plants in the form of monosilicic acid (H4SiO4), is lost through leaching. If the concentration of monosilicic acid is being maintained at a fixed level by soil reserves, the highly weathered soils of humid and sub-humid regions tend to become depleted in Si if continuously cultivated with sugarcane. Hence, leaching of Si from the soil coupled with plant uptake is an important factor in determining Si concentrations in soil. Consequently, it can be said that the intensive cultivation of sugarcane depletes the existing low available Si content in soil, resulting in necessity for Si fertilisation. Moreover, the uptake of Si by sugarcane (500-700 kg Si ha(-1)) sometimes surpasses those of the macronutrients (especially N, P and K). At the same time, due to change in global climate and monoculture system followed in sugarcane, it is affected by a wide range of biotic and abiotic stresses in field condition which calls for external Si supplementation to achieve sustainable growth and yield of sugarcane. The beneficial effects of Si in sugarcane include improvement of photosynthesis and lodging, enhancement of growth and development, regulation of reactive oxygen species, protection from soil salinity, reduction in metal toxicity, alleviation of freeze damage, mitigation of water stress and suppression of diseases and pests. In this review, we made an effort to compile the existing literature describing the potential of Si in promoting defence against various biotic and abiotic stresses in sugarcane and suggested possible future research perspectives.