Beyond physical resistance : novel aspects of plant silicon defences against arthropod herbivores

Abstract

Silicon (Si) fertilisation has received increasing recognition in recent years for ameliorating biotic stresses in plants, including damage by pest herbivores. Si defences are effective against chewing herbivores as silicification makes plants abrasive and tougher, whereas sap-feeding insects are thought to be less affected. There are still substantial knowledge gaps regarding the effects of Si on direct and indirect (i.e. whereby plants benefit from natural enemies of herbivores) plant defences against herbivorous arthropods. Moreover, it is unknown how anti-predator defences (e.g. morphological, behavioural, and immune defences) of herbivorous insects are affected when feeding on Si-rich diets nor whether Si mediates interactions (e.g. competition, facilitation) between herbivores of different feeding guilds. Using plants with contrasting capacity for Si accumulation (i.e. low, moderate, and high Si-accumulators) and pest herbivores from different feeding guilds (i.e. chewing, sap-feeding, and cell-content feeding), this work explores some novel facets of plant Si defences against herbivorous pests. Overall, this work examined some novel aspects of plant Si defences across different Si-accumulating plants against herbivorous pests belonging to different feeding guilds. Specifically, this work investigated (i) the magnitude and locality of Si induction in plants following insect herbivory (chapter 2); (ii) how Si impacts induced direct (chapters 2, 4, 5, and 6) and indirect (chapter 3) plant defences against herbivorous pests; (iii) the plant-mediated effects of Si on the anti-predator defences of insect herbivores (chapters 4 and 6); and (iv) the impacts of Si on plant-mediated interspecific interactions between chewing and sap-feeding insect herbivores (chapter 5). Taken together, this work underpins that Si fertilisation can augment direct and indirect plant defences against pest herbivores and could be a sustainable management strategy for chewing and cell-feeding herbivores. Si could also play a part in pest biocontrol by promoting natural enemy attraction and undermining the anti-predator defences of insect herbivores. In contrast, Si fertilisation could provide a competitive advantage to sap-feeding insects by diminishing the performance of co-occurring chewing insects. Potential areas of future research and the limitations of the current work are discussed.

Date of Award	2022
Original language	English