Below we provide a list the work performed over the two-year reporting period and the main findings of each. As noted, two publications have resulted from this work with more being prepared to submit for peer review. This work has been discussed at several seminars and one congress in 2018 Due to covid-19, planned congresses in the summer of 2020 were canceled.
• A two-season field experiment to study intraspecific communication. The design consisted of incubating branches of a sagebrush plant of a predetermined chemotype with damage-induced plant volatiles (DIPVs) from sagebrush with the same or different chemotypes. Leaves from experimental branches were used for 1 of 4 assays: 1) enzyme activity, 2) gene expression 3) a bioassay with a sagebrush specialist beetle and 4) a total herbivore damage assay at the end of the growing season.
o We observed a 25% and 40% decrease in herbivory when exposed to DIPVs from different or the same chemotype, respectively, when compared to an ambient air control.
o The total herbivory assay agreed with gene expression levels and enzymatic activity.
o We found interactive effects between emitting and receiving chemotypes, indicating the complexity of plant-to-plant communication. For example, we observed non-reciprocal chemotypic perception. This non-reciprocity occurs in interspecies communication, but this is the first documentation of this phenomenon occurring between individuals of the same species.
• A single season field experiment studying interspecific communication between sagebrush and tobacco.
o We did not detect an effect of sagebrush DIPVs on glandular exudate production in receiver tobacco plants, nor decreased leaf damage by herbivores. Sagebrush is known to induce resistance in tobacco plants. Our inability to detect an effect of DIPVs regardless of chemotype likely stems from the low abundance of the primary tobacco herbivore, Manduca quinquemaculata. Because this work was done in collaboration within a larger study, the results were still published.
• A major objective of CVVOC was to develop relatively fast and reliable indicators of volatile-mediated communication and induced resistance. To this end, we developed 3 different assays: 1) bioassay with herbivores, 2) enzymatic assays and 3) gene expression assays using RT-PCR.
o All assays were able to distinguish between leaves exposed to DIPVs and control leaves. To date, only the bioassay has been published.
• We conducted a laboratory experiment in growth chambers using sagebrush grown in a glasshouse from seeds collected at our field sites in California, USA. Here we utilized air pumps to deliver DIPVs from emitter branches to receiver plants of known chemotypes under controlled conditions.
o The results largely reflected those seen in the field experiment with one major exception: we were able to detect a weak effect of DIPVs on VOC emissions of undamaged plants. Though attempted, we were unable to detect this in the field, likely due to the weak nature of the effect.
