Effects of soil salinity on the expression of direct and indirect defences in wild cotton Gossypium hirsutum

Abstract

Previous studies have frequently reported effects of abiotic factors on herbivore‐induced plant defences based on effects on single plant traits. However, plants commonly express multiple defences simultaneously and these traits are often correlated. Thus, a fuller understanding of abiotic‐context dependency in plant defence requires measuring multiple traits and addressing their patterns of correlated expression. We evaluated the effects of soil salinity on the expression of direct (phenolic compounds, gossypol gland density) and indirect (volatile organic compounds, extrafloral nectar) defensive traits in wild cotton Gossypium hirsutum. Specifically, we asked whether soil salinity affects the induction of these traits, and whether it shapes trait correlations potentially underlying altered patterns of trait induction. We conducted a factorial experiment with 16 cotton genotypes where we manipulated soil salinity and defence induction by applying artificial leaf damage (25% mechanical damage and caterpillar oral secretions) and measured defence levels at different time points post damage. Leaf damage induced most traits except gossypol gland density, whereas salinity did not have a mean effect (across constitutive and induced levels) on any of the measured traits. Nonetheless, salinity prevented the induction of phenolic compounds (condensed and hydrolysable tannins), and also affected trait correlations. Specifically, phenolic compounds were negatively associated with nectar production only under salinized conditions, an apparent trade‐off that could affect the induction of phenolic compounds. In addition, positive correlations between phenolic compounds and gland density and root biomass observed under control conditions were lost under salinized conditions. Synthesis. By investigating the effects of soil salinity on the expression of multiple direct and indirect defensive traits and their underlying correlations, these findings build towards a better understanding of how abiotic context dependency shapes plant allocation to and expression of multiple defensive traits.

Effect of water availability on volatile‐mediated communication between potato plants in response to insect herbivory

“…This result is in agreement with our expectations and also supports a previous study reporting that low water availability prevented the induction of VOCs by Camellia sinensis in response to exogenous application of methyl‐jasmonate (Scott et al, 2019). Relatedly, Quijano‐Medina et al (2021) found that soil salinization hampered the induction of phenolic compounds as well as a similar trend for some VOCs in wild cotton Gossypium hirsutum plants. Such effects of abiotic stress on the induction of VOCs can be explained by allocation costs associated with the synthesis and transport of plant secondary metabolites (Wilkinson et al, 2019).…”

“…For example, recent work has shown that communication is strongly contingent upon the identity of the attacking herbivore, whereby resistance in receivers is only boosted when emitters and receivers are attacked by the same insect (Moreira et al, 2018). In addition, though much less studied, plant communication is likely contingent on abiotic factors such as soil nutrients, salinity or water availability, as these often affect plant defence induction in response to herbivory, including VOCs (Gouinguené & Turlings, 2002; Moreira et al, 2015; Quijano‐Medina et al, 2021; Sampedro et al, 2011; Suárez‐Vidal et al, 2019). There are at least two non‐exclusive mechanisms by which abiotic conditions could affect plant communication.…”

Induction by caterpillars of stored and emitted volatiles in terpene chemotypes from populations of wild cotton (Gossypium hirsutum)

“…In contrast, chemotype-specific responses to caterpillar herbivory have been described in another species ( Tanacetum vulgare ) for both leaf-stored and emitted volatiles (Clancy et al, 2020). Despite being confined to coastal habitats, Yucatanese wild cotton is subjected to substantial spatial variability in herbivore pressure and abiotic conditions (Abdala-Roberts et al, 2019; Munguía-Rosas et al, 2019; Quijano-Medina et al, 2019, 2021), which could be associated with the origin of the observed variation in HIPVs. Further work is required to understand the drivers of these differences.…”

“…Given the depletion of genetic diversity observed in modern cultivars of G. hirsutum (Yuan et al, 2021), exploring useful defensive traits in wild cotton should be considered. While volatile production in cultivated cotton has been well characterized, less is known about the volatiles produced by wild cotton (but see Loughrin et al, 1995; Hagenbucher et al, 2016; Quijano-Medina et al, 2021; Briones-May et al, 2023). G. hirsutum was domesticated at least 4,000 years ago in the Yucatán Peninsula (southeast Mexico) (Yuan et al, 2021), where wild populations still grow naturally along its northern coastline (Wegier et al, 2011; Coppens d’Eeckenbrugge and Lacape, 2014).…”

Effects of soil abiotic factors and plant chemical defences on seed predation on sea fennel (Crithmum maritimum)

“…In turn, studies have also shown that quantitative and qualitative variation in plant physical and chemical defences play an important role in determining the risk and intensity of herbivory (Feeny 1976;Marquis 1992), as well as in shaping insect herbivore communities (Richards et al 2015;Salazar et al 2016). Understanding these bottom-up effects of plant defences on phytophagous insects thus represents a fundamental challenge for explaining intra-and inter-specific variability in herbivory, one that also requires embracing the complex nature of plant defensive phenotypes by simultaneously studying multiple, often correlated, traits (Moreira et al 2020a;Quijano-Medina et al 2021).…”