Silicon-mediated defence response in chilli against yellow mite infestation

Chilli yellow mite is a major pest of chilli, which causes significant damage to both leaves and fruits. Synthetic acaricides, though widely used for control, pose environmental risks and often give unsatisfactory results due to pest resistance. Therefore, this study aimed to enhance the resistance of chilli plants against mite by applying silicon (Si), a natural element, in two forms- CaSiO₃ and K₂SiO₃, at concentrations of 0.1%, 0.5% and 1.0%. Results showed that Si application significantly reduced mite infestation while having no effect on their natural predator, the ladybird beetle. CaSiO₃ at 0.1% Si led to the lowest leaf infestation rates (7.6 ± 1.5%, 4.4 ± 0.4% and 2.4 ± 0.4% after the first, second and third sprays, respectively), and produced the highest number of healthy fruits at both the first and second harvests (345.8 ± 5.3 g/plant and 335.0 ± 4.2 g/plant, respectively). Si treatment increased the thickness of both the upper and lower leaf epidermis, especially with CaSiO₃ and K₂SiO₃ at 1.0% Si. It also elevated the levels of the stress-responsive hormones salicylic acid and jasmonic acid relative to the control, particularly with CaSiO₃ at 0.1% Si. Principal component analysis revealed that mite infestation was negatively correlated with both acid levels and leaf epidermis thickness. Thus, Si application presents a promising, eco-friendly strategy for managing mite infestations in chilli plants.