Herbivore specificity and the chemical basis of plant–plant communication in Baccharis salicifolia (Asteraceae)

Abstract

It is well known that plant damage by leaf-chewing herbivores can induce resistance in neighbouring plants. It is unknown whether such communication occurs in response to sap-feeding herbivores, whether communication is specific to herbivore identity, and the chemical basis of communication, including specificity. We carried out glasshouse experiments using the California-native shrub Baccharis salicifolia and two ecologically distinct aphid species (one a dietary generalist and the other a specialist) to test for specificity of plant-plant communication and to document the underlying volatile organic compounds (VOCs). We show specificity of plant-plant communication to herbivore identity, as each aphid-damaged plant only induced resistance in neighbours against the same aphid species. The amount and composition of induced VOCs were markedly different between plants attacked by the two aphid species, providing a putative chemical mechanism for this specificity. Furthermore, a synthetic blend of the five major aphid-induced VOCs (ethanone, limonene, methyl salicylate, myrcene, ocimene) triggered resistance in receiving plants of comparable magnitude to aphid damage of neighbours, and the effects of the blend exceeded those of individual compounds. This study significantly advances our understanding of plant-plant communication by demonstrating the importance of sap-feeding herbivores and herbivore identity, as well as the chemical basis for such effects.

Relative effects of genetic variation sensu lato and sexual dimorphism on plant traits and associated arthropod communities

“…35 ha in the University of California San Joaquin Marsh Reserve (33°39′47″N, 117°51′7″W; CA, USA), the same field site where our past studies of this plant have been conducted (Mooney et al 2012b;Moreira and Mooney 2013;Abdala-Roberts et al 2016;Moreira et al 2016;Abdala-Roberts et al 2017). To get distinct genotypes, we collected cuttings from wildgrown plants that were separated by approximately 900 m. Cuttings were dipped in a 20% solution of Dip 'N Grow Root Inducing Concentrate (Dip 'N Grow Inc., Clackamas, OR) and planted in perlite for 6 weeks in a greenhouse.…”

Specificity of plant–plant communication for Baccharis salicifolia sexes but not genotypes

“…We measured total emission of individual VOCs as a proportion to the internal standard (Moreira et al. ).…”

“…We chose pinocarvone because its emission significantly increased after U. macolai feeding (control, 8625.20 ± 4629.06 ng/h; U. macolai feeding, 24444.00 ± 3498.25 ng/h; Moreira et al. ) and significantly varied between plant sexes (see Results ). We also chose the treatment containing a blend of six VOCs because all these compounds were highly inducible after U. macolai feeding (Moreira et al.…”

“…, Moreira et al. ). The composition of herbivore‐induced VOC blends is known to be highly specific to plant genotype (e.g., Degen et al.…”

Herbivore‐specific plant volatiles prime neighboring plants for nonspecific defense responses

“…As for phloem‐feeding herbivores, specialist and generalist aphids differentially induce direct defenses in Arabidopsis (Mewis et al, ). Whether primed plants also differentially regulate defenses against generalist and specialist herbivores after perceiving herbivore‐specific HIPVs from damaged conspecific neighbors has not received much attention (Moreira et al, ).…”