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

Previous studies have 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 induction of direct (phenolic compounds, gossypol gland density) and indirect (volatile organic compounds, extrafloral nectar) defensive traits in wild cotton (Gossypium hirsutum). We asked whether soil salinity affects the induction of these traits, and whether it shapes trait correlations potentially underlying salinity effects on 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 caterpilla...