Silicon Amendment Activates Defence Reaction, Reduces the Incidence and Damage of Phloem Feeders and Enhances Yield in Green Gram (Vigna radiata L.)

Abstract

Silicon is a beneficial element; however, its effects on phloem feeders in dicot crops, such as green gram, are not well understood. An experiment was designed to investigate the impact of silicon, in the form of orthosilicic acid amendment, on phloem feeders, defence induction, and yield in green gram over two different growing seasons. The SML 668 cultivar responded more favourably to silicon supplementation than the PDM 139 cultivar for all parameters tested during both seasons. Among the application methods, soil drenching with orthosilicic acid at a rate of 2 mL L⁻¹ significantly reduced the incidence of phloem feeders, increased the plant-available silicon content in the soil solution, and enhanced silicon deposition (1.01%) in the leaves of green gram compared to foliar application, insecticidal checks and untreated controls. The increased silicon content significantly improved total soluble sugars, total phenol content and enhanced the activity of various antioxidants and defence enzymes, including polyphenol oxidase, phenylalanine ammonia lyase, catalase, peroxidase and superoxide dismutase, thereby reducing the incidences of Aphis craccivora, Megalurothrips usitatus, Empoasca kerri and Bemisia tabaci. The soil drenching method also significantly enhanced the activity of natural enemies and increased grain yield. The benefit-to-cost ratio was highest for soil drenching with orthosilicic acid (2 mL L⁻¹), yielding ratios of 2.94 and 2.55, compared to the recommended insecticidal check, which yielded ratios of 2.51 and 2.17 during the summer and winter seasons, respectively. Both silicon supplementation methods outperformed insecticidal control in increasing seed yield, coccinellid activity, and induced biochemical defences, while also resulting in lower cultivation costs. Additionally, this method is straightforward to combine with other strategies for sustainable, environmentally friendly control of phloem feeders in green gram.