Effects of excess root applied silicon on Triticum aestivum and Zea mays under Aphis gossypii and Schistocerca gregaria herbivory and water-stressed conditions

Triticum aestivum (wheat) and Zea mays (maize) are two of the most important staple food and industrial crops used by developed and developing countries. Drought and pest attack often reduces wheat and maize production, causing huge economic losses. Silicon has been proposed to protect plants from several biotic and abiotic environmental stresses such as pest attack and drought. Silicon accumulation in plants can increase the abrasiveness of their leaves, potentially deterring herbivory by several important pest species, such as Aphis gossypii (aphids) and Schistocerca gregaria (locusts). Silicon accumulation in plants may also reduce transpiration rates and thus increase their drought tolerance. Here, the potentially protective effects of root silicon application to Triticum aestivum and Zea mays, against both water stress and herbivory by Aphis gossypii and Schistocerca gregaria, were investigated in a series of greenhouse experiments. Na2SiO3.9H2O (Sodium Meta Silicate) was used as a source of silicon. Experiments manipulated the impact of silicon on drought and controlled plants with and without pest species present; the influence of silicon application on herbivore performance and its potential interaction with water stress was also investigated. Aphid performance was evaluated by determining the change in the population growth rate over two weeks. The influence of silicon application on locust herbivory was determined by calculating the total damage to the plants over two weeks. Silicon application increased the abrasiveness of the leaves of both Triticum aestivum and Zea mays, and enhanced their resistance to Schistocerca gregaria herbivory; however the increased abrasiveness did not have an effect on Aphis gossypii performance. Additionally silicon accumulation enhanced drought tolerance when the temperature was kept between 20-25 °C, but it had no effect on plant biomass and plant photosynthetic rate when the green-house temperature was maintained between 40-45 °C. Silicon application to crop species provides a potentially cost-effective alternative to pesticides, and may increase drought tolerance in both C3 and C4 crop species.