Population-specific plant-plant signaling in wild lima beans

Authors: GROF-TISZA, PATRICK - University Of Neuchatel; MORELON, STEPHANIE - University Of Neuchatel; DESURMONT, GAYLORD - European Biological Control Laboratory (EBCL); BENREY, BETTY - University Of Neuchatel

Submitted to: Plants
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/2/2022
Publication Date: 9/6/2022
Citation: Grof-Tisza, P., Morelon, S., Desurmont, G., Benrey, B. 2022. Population-specific plant-plant signaling in wild lima beans. Plants. 11(18):2320. https://doi.org/10.3390/plants11182320.
DOI: https://doi.org/10.3390/plants11182320

Interpretive Summary: Plants damaged by herbivores produce odors. These odors can be perceived by neighboring plants as a warning signal, prompting them to increase their levels of chemical defenses before they, too, are attacked by herbivores. This phenomenon called "priming" of plant defense, has been hypothesized to be more effective if the emitter plant and the receiver plant are closely related (same species or same population). Here we tested this hypothesis with lima bean plants. We used three populations of lima beans coming from three geographical areas in Mexico and exposed plants from the three populations to odors damaged plants from their own population or from a different population. Exposed plants were then presented to herbivores in choice-tests. Interestingly, plants exposed to damaged plants from their own population were less attacked than the others in choice-tests, confirming the hypothesis. In parallel, volatile collections were made on damaged and undamaged plants from the three populations. These analyses only revealed very minor changes in odors or in ratios of odors among the three populations. In conclusion, our results show that the strength of priming indeed depends on the relatedness between the emitter and the receiver plant, but the precise volatile cues responsible for this result remain a mystery.

Technical Abstract: Exposure to volatiles from damaged plants is known to increase the resistance of nearby conspecific plants to herbivores. A few studies have demonstrated that the strength of this resistance response depends on the level of relatedness between the interacting plants. This implies that plants are more responsive to signals emitted by conspecific neighbors within the same (i.e., ‘local’) population compared to those signals emitted by individuals from ‘foreign’ populations, resulting in greater resistance. A previous field study with wild lima bean, Phaseolus lunatus, demonstrated that responses to volatiles from damaged plants are indeed population specific. Here we tested this under laboratory conditions by placing undamaged plants near mechanically damaged plants from their local population or with damaged plants from a foreign population. In most combinations, the former plants experienced less herbivory than the latter after subsequent exposure to Diabrotica balteata beetles, which are generalist chewing herbivores. To understand the role of volatiles underlying this observed specificity, we explored the variability in constitutively released volatiles and volatiles released after mechanical or herbivore damage among the three tested populations of P. lunatus. Total volatiles emissions were about 5x and 10x higher from the mechanically- and herbivore-damaged plants, respectively, compared to undamaged control plants. Populations differed in relative ratios of emissions of the dominant constitutive compounds, but no obvious pattern could be observed that could be linked to the differential responses to herbivory among populations. Overall, this study confirms stronger within- population plant-plant volatile-mediated interactions in P. lunatus. Not detecting chemical cues underlying population-specific induced resistance suggests that either these cues are comprised of minor compounds or depend oncomplex changes in the ratios of compounds, or they are emitted substantially later than that seen in other model species. KEY WORDS: herbivore-induced plant volatiles, Phaseolus lunatus, volatile organic compounds, volatile-mediated interactions, priming, induced resistance.