Plant-mediated effects on an insect–pathogen interaction vary with intraspecific genetic variation in plant defences

Abstract

Baculoviruses are food-borne microbial pathogens that are ingested by insects on contaminated foliage. Oxidation of plant-derived phenolics, activated by insect feeding, can directly interfere with infections in the gut. Since phenolic oxidation is an important component of plant resistance against insects, baculoviruses are suggested to be incompatible with plant defences. However, plants among and within species invest differently in a myriad of chemical and physical defences. Therefore, we hypothesized that among eight soybean genotypes, some genotypes would be able to maintain both high resistance against an insect pest and high efficacy of a baculovirus. Soybean constitutive (non-induced) and jasmonic acid (JA)-induced (anti-herbivore response) resistance was measured against the fall armyworm Spodoptera frugiperda (weight gain, leaf consumption and utilization). Indicators of phenolic oxidation were measured as foliar phenolic content and peroxidase activity. Levels of armyworm mortality inflicted by baculovirus (SfMNPV) did not vary among soybean genotypes when the virus was ingested with non-induced foliage. Ingestion of the virus on JA-induced foliage reduced armyworm mortality, relative to non-induced foliage, on some soybean genotypes. Baculovirus efficacy was lower when ingested with foliage that contained higher phenolic content and defensive properties that reduced armyworm weight gain and leaf utilization. However, soybean genotypes that defended the plant by reducing consumption rate and strongly deterred feeding upon JA-induction did not reduce baculovirus efficacy, indicating that these defences may be more compatible with baculoviruses to maximize plant protection. Differential compatibility of defence traits with the third trophic level highlights an important cost/trade-off associated with plant defence strategies.

Variation in Methyl Jasmonate-Induced Defense Among Norway Spruce Clones and Trade-Offs in Resistance Against a Fungal and an Insect Pest

“…The presence or absence of trade-offs among defense components against specific pests, and the consequences for effective resistance, can vary depending on plant genotype or species in question (e.g., Koricheva et al, 2004 ; Erb et al, 2011 ; Moreira et al, 2014 ; Hahn and Maron, 2016 ; Shikano et al, 2017 ). For instance, not all genotypes respond equally to attack by the same pest in conifers, as they can vary, e.g., in their allocation to constitutive and induced defense (e.g., Ott et al, 2011 ; Sampedro et al, 2011 ; Villari et al, 2014 ; Moreira et al, 2016 ; Pimentel et al, 2017 ; Reglinski et al, 2019 ).…”

Can Herbivore-Induced Volatiles Protect Plants by Increasing the Herbivores’ Susceptibility to Natural Pathogens?

“…In a multitrophic context, the eventual outcome of the interaction between plant and herbivore is also modulated by pathogenic microbes, which is assumed to be due to direct as well as indirect effects of toxic phytochemicals on entomopathogen persistence and infectivity (19)(20)(21). Although some authors have speculated about the possibility of plants promoting the action or abundance of microbial entomopathogens (22), not much information is available about the impact of HIPVs on the pathogenicity of entomopathogens.…”

Bottom‐up trait‐mediated indirect effects decrease pathogen transmission in a tritrophic system

“…, Shikano et al. ). For the gypsy moth, increases in tannins increased leaf consumption (Elderd et al.…”

“…However, it is well known that induction of secondary metabolites in soybeans affects the production of foliar phenolics and their composition within the leaf tissue (Shikano et al. ). Induction of these defenses can be costly for the plant as it reduces biomass, seed set, and germination (Accamando and Cronin ).…”