No evidence of modulation of indirect plant resistance of Brassica rapa plants by volatiles from soil‐borne fungi

Abstract

Upon herbivory, plants emit specific herbivore‐induced plant volatiles (HIPVs) that can attract natural enemies of the herbivore thus serving as indirect plant resistance. Not only insect herbivores, but microorganisms may also affect HIPV emission before or after plant colonisation, which in turn can affect behaviour of natural enemies of the herbivore. Yet, it remains elusive whether volatiles from microorganisms influence HIPV emission and indirect plant resistance. In this study, we investigated whether exposure of Brassica rapa roots to volatiles from soil‐borne fungi influence HIPV emission and the recruitment of natural enemies of Pieris brassicae larvae. Using a two‐compartment pot system, we performed greenhouse and common‐garden experiments, and we profiled plant HIPV emission. We found that exposure of plant roots to fungal volatiles did not affect the number of P. brassicae larvae recollected from the plants, suggesting a neutral effect of the fungal volatiles on natural predation. Likewise, in a greenhouse, similar numbers of larvae were parasitised by Cotesia glomerata wasps on control plants as on fungal volatile‐exposed plants. Additionally, chemical analysis of HIPV profiles revealed no qualitative and quantitative differences between control plants and fungal volatile‐exposed plants that were both infested with P. brassicae larvae. Together, our data indicate that root exposure to fungal volatiles did not affect indirect plant resistance to an insect herbivore. These findings provide new insight into the influence of indirect plant resistance by fungal volatiles that are discussed together with the effects of fungal volatiles on direct plant resistance.

Enhanced parasitisation of caterpillars and aphids on field‐grown Brassica oleracea plants upon soil amendment with insect exuviae

“…VOC were provisionally annotated by comparing their mass spectra and their AI values, as they were experimentally determined by Moisan et al. (2020), with those of the reference Wageningen Mass Spectral Database of Natural Products and NIST library (National Institute of Standards and Technology). For each putatively identified VOC, an individual aligned mass peak with a minimum peak height of 9.95 × 10 7 counts across all samples was selected.…”

“…Peak intensity of the VOCs was not correlated with fresh shoot biomass, or with caterpillar damage on the P. xylostella infested plants (Pearsons product moment correlation, r 2 < 0.02) and was thus not normalised for fresh shoot biomass, or herbivore damage. VOC were provisionally annotated by comparing their mass spectra and their AI values, as they were experimentally determined byMoisan et al (2020), with those of the reference Wageningen Mass Spectral Database of Natural Products and NIST library (National Institute of Standards and Technology). For each putatively identified VOC, an individual aligned mass peak with a minimum peak height of 9.95 × 10 7 counts across all samples was selected.…”

Social networking in crop plants: Wired and wireless cross‐plant communications

“…Plant growth–promoting and endophytic bacteria can induce plant volatile synthesis to attract parasitoids and entomopathogens (Bell, Naranjo‐Guevara, Santos, Meadow, & Bento, 2020; Disi, Mohammad, Lawrence, Kloepper, & Fadamiro, 2019; Maggini et al, 2020). By contrast, there has been one report showing that endophytic microbes do not have a significant effect on plant VOC profiles and the behaviour of herbivores and their parasitoids (Moisan et al, 2020).…”