Prolonged exposure is required for communication in sagebrush

Volatile communication allows plants to coordinate systemic induced resistance against herbivores. The mechanisms responsible and nature of the cues remain poorly understood. It is unknown how plants distinguish between reliable cues and misinformation. Previous experiments in which clipped sagebrush branches were bagged suggested that cues are emitted or remain active for up to 3 days. We conducted experiments using plastic bags to block emission of cues at various times following experimental clipping. We also collected headspace volatiles from clipped and unclipped branches for 1 h, transferred those volatiles to assay branches, and incubated the assays for either 1 or 6 h. We found that assay branches that received volatile cues for less than 1 h following clipping of neighbors failed to induce resistance. Assay branches that received volatile cues for more than 1 h experienced reduced herbivory throughout the season. Branches incubated for 6 h with volatiles that had been collected during the first hour following clipping showed induced resistance. These results indicate that sagebrush must receive cues for an extended time (> 1 h) before responding; they suggest that the duration of cue reception is an important and overlooked process in communication allowing plants to avoid unreliable, ephemeral cues.