Population-Specific Plant-To-Plant Signaling in Wild Lima Bean

Abstract

The exposure to volatiles from damaged plants can increase the resistance of the neighboring plants to herbivores. Studies have demonstrated that the strength of this response depends on the level of relatedness between the interacting plants. Indeed, a field study with Phaseolus lunatus found that the responses to induced volatiles were population-specific; individuals exposed to damaged conspecifics from the 'local' population exhibited greater resistance to herbivores than those exposed to damaged conspecifics from 'foreign' populations. Here, we repeated this study in the laboratory by placing undamaged plants near damaged plants from either their local or a foreign population. The former plants experienced less herbivory than the latter after a subsequent challenge by a generalist herbivore. To understand the role of the volatiles underlying this observed specificity, we explored the variability in the constitutively released volatiles and volatiles released after mechanical or herbivore damage among the three tested populations of P. lunatus. The total volatile emissions were 5× and 10× higher from the mechanically and herbivore-damaged plants, respectively, compared to the undamaged plants. The populations differed in their relative ratios of dominant constitutive compounds, but no pattern was observed that could explain the differential responses to induced volatiles among the populations. Overall, this study confirms the population-specific volatile-mediated interactions in P. lunatus.

Keywords: Phaseolus lunatus; herbivore-induced plant volatiles; induced resistance; volatile organic compounds; volatile-mediated interactions.

Figure 1

Means ± SEs from volatile exposure and herbivory experiment. F, I, and Y represent the Flores, Inka, and Yel populations, respectively. Dotted lines represent mean damage across all receiver populations for the damaged and undamaged emitter treatments. Asterisks represent significant differences (p < 0.05).

Figure 2

Relative proportions of VOC emissions of P. lunatus plants subjected to mechanical damage and herbivore damage by D. baleata, as well as undamaged controls. Only compounds with significant differences are depicted. Circle sizes are proportional to the average total volatile emissions of plants in each treatment.

Figure 3

Significant variation in the relative proportions of constitutively expressed VOCs from undamaged P. lunatus plants. Based on these proportional differences, Flores and Yel were putatively grouped into one chemotype, with Inka representing a second chemotype.

Figure 4

Design of the choice test feeding assay. For each treatment (damaged, n = 15; undamaged, n = 15), three receiver plants from the same population were put in a cage alone with 10 D. balteata adults for 24 h. Five replicate cages for each combination were used.