The role of silicon in mitigating the incidence and damage of yellow stem borer in rice crops is well proven. However, the underlying mechanisms offered by silicon amendment in rice crops against yellow stem borer were not explored or poorly understood. Here, we have shown that silicon supplement to rice plants at 200 mg/kg of soil, improved silicification in stem tissues by increased length, width (18.1-32.5%), and area (6.6-14.2%) of silica cells and silicon content given over scanning electron microscopy and electron-dispersive spectrophotometric analysis. The increased activities of antioxidant and defense enzymes such as catalase (106-215%), superoxide dismutase (74.5%), peroxidase (52.1%), phenylalanine ammonia lyase (74%), and polyphenol oxidase (47.3%) in rice plants supplemented with silicon and infested with yellow stem borer at different durations were shown. The enhanced concentrations of total sugars (23.6%) and total phenols (18.4%) were also observed due to silicon supplement to rice plants. However, the defense enzyme activities were less in rice plants without silicon supplementation and yellow stem borer infestation. The outcome of the study highlighted the impact of silicon in activating the defense responses in rice plants infested with yellow stem borer. Silicon supplementation should be considered as one of the alternative and sustainable measures for integrated management of yellow stem borer in rice across ecosystems.

Yellow stem borer of rice Scirpophaga incertulas, significantly reduce rice production throughout Asia. Silicon (Si) amendment in rice for resistance against biotic stress is gaining importance to protect crops from insect herbivory. Exogenous application of silicon in form of DAE (diatomaceous earth) at 0.5 to 2.5 g kg(-1) and RHA (rice husk ash) at 5.0 to 15.0 g kg(-1) soil significantly improved silicon uptake and reduced borer damage in both susceptible (TN1) and moderately resistant (GNR3) rice cultivars exhibiting the enhanced resistance against S. incertulas with a yield benefit to the tune of 1.91- fold over control. Si addition through DAE at 2.0 g kg(-1) soil registered a maximum of 1.55 and 2.27- fold increased Si uptake by TN1 and GNR3 plants respectively as against a corresponding increase of 2.37 and 2.24-fold by 12.5 g RHA kg(-1) soil. Chlorophyll was highest in plants receiving low dose of silicon and showed a downward trend with increase in dose. Feeding stimuli from S.incertulas larvae led to intense leaf silicificationly with significant increased silica cell deposit per mm row length, increased lobe size, and minimal distance between adjacent silica cells as evidenced from scanning electron microscopic studies. Increased Si content along with biotic stress activated antioxidant enzyme (super oxide dismutase, catalase, and peroxidise) defense in rice to mitigate oxidative stress. RHA supplemented plants with YSB infestation showed increased activity of the non-oxidative enzymes like phenylalanine lyase (3.5- fold) and tyrosine ammonia lyase (13.0 -fold) over control conferring a greater defense to paddy through induction of signal transduction process. The study thus, demonstrated the benefit of soil amendment with DAE and RHA in inducing host resistance against S. incertulas, as an eco-holistic approach in pest management in rice. Further, the finding is expected to be helpful in genetic mapping of known YSB resistance gene markers of candidate genes like hexose transporter, amino acid transporter and other genes related to defense signal mechanisms via jasmonic acid pathway.