Novel evidence for systemic induction of silicon defences in cucumber following attack by a global insect herbivore

Abstract

1. Silicon (Si) is a beneficial nutrient that has been reported to ameliorate many abiotic and biotic stresses in plants, including insect herbivory. Insect herbivory has been shown to induce Si defences in plants, although the magnitude and nature of induction remain largely ambiguous. In particular, it is unclear whether herbivore induction of Si defences is confined to attacked tissues (local) or occurs elsewhere in the plant (systemic). 2. We grew cucumber, Cucumis sativus L. plants (var. Burpless F1 and Beit Alpha), an intermediate Si accumulator, hydroponically under Si-supplemented or Si-free conditions and measured the level of Si induction caused by a polyphagous chewing insect, the cotton bollworm, Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae). We also examined the impacts of Si on insect performance by conducting in vitro feeding assays on excised leaves (ex situ) and intact leaves on plants (in situ). 3. Herbivory significantly increased Si accumulation both locally in attacked leaves (21% increase in Beit Alpha and 17% in Burpless F1) and systemically in non-attacked leaves (19% increase in Beit Alpha and 10% in Burpless F1). Si supplementation significantly increased % foliar Si and C:N ratio, while significantly decreasing larval relative consumption (RC) and relative growth rate (RGR) in the in situ assays. In ex situ assays, however, Si only reduced larval RGR when fed on Beit Alpha plants. 4. Our results confirm that Si-based defences can also operate in moderate Si-accumulating plants and, for the first time, that insect herbivory induces systemic Si accumulation equivalently between plant varieties.

Assessment of Silicon- and Mycorrhizae- Mediated Constitutive and Induced Systemic Resistance in Rice, Oryza sativa L., against the Fall Armyworm, Spodoptera frugiperda Smith

“…Larvae fed on plants supplied with silicon gained 20% less weight compared to larvae fed on control plants (Figure 1). This result is consistent with numerous other studies showing that the application of silicon, either through foliar spray or soil amendment, reduces the growth, development, and reproduction of insects [14,41]. In rice, silicon supplementation increases silicon content [17].…”

Silicon Fertilisation Affects Morphological and Immune Defences of an Insect Pest and Enhances Plant Compensatory Growth

“…Larvae fed less on + Si plants (i.e., as evident from the lower levels of frass production) and displayed retarded growth rates which are in line with the existing literature on the effects of Si against chewing herbivores, including folivores (Biru et al 2021;Islam et al 2020;Johnson et al 2020), borers (Kvedaras et al 2009;Nikpay et al 2015) and root feeders (Frew et al 2017). The three-fold decrease in larval growth rates observed here due to malnutrition could potentially impact biocontrol by natural enemies.…”

“…Research on Si-based plant defence against herbivores has mostly focused on plant resistance, with the role of Si in tolerance relatively neglected. Furthermore, herbivory often induces increased Si accumulation in plants (Islam et al 2020;Massey et al 2007), however, how Si induction impacts the production of other inducible defence structures such as trichomes remain understudied, though there are reports that Si can enhance constitutive trichome density (Biru et al 2021;Johnson et al 2021).…”

Silicon in the Soil–Plant Continuum: Intricate Feedback Mechanisms within Ecosystems

“…Among the biotic stressors known to affect plant Si content, herbivory is the one that was studied the most [ 143 ]. Exposure to invertebrate [ 144 , 145 , 146 , 147 ] and vertebrate [ 144 , 148 ] herbivores induces Si uptake and accumulation in grasses. Comparable induction by artificial clipping [ 149 , 150 , 151 ] further supports that this induction is directly associated with biomass removal or damage.…”

“…Qualitatively, cell wall ASi hinders cell wall breakdown in animal intestines, reducing the released amount of chlorophyll and other nutritious compounds that can be digested by herbivores [ 290 ]. These two mechanisms, with the addition of low preference to Si-rich plant foods, often results in reduced herbivore growth [ 140 , 146 , 267 , 272 , 280 , 282 , 288 ] and even cause a herbivore population decline [ 157 , 159 , 161 ]. There is even some evidence that plant Si can cause urolithiasis [ 58 , 291 , 292 , 293 ] and be carcinogenic [ 294 ].…”