Delivery of dsRNAs in woody plant tissues for single tree protection

Increasingly variable environmental extremes and anthropogenic disturbances are contributing to widespread, eruptive insect outbreaks and catastrophic losses in our forests. Conventional management techniques are failing to keep pace, therefore new approaches to forest pest suppression are essential. RNA interference (RNAi) is a biological pathway that when manipulated can induce host-specific gene silencing via double-stranded RNAs (dsRNAs), causing rapid insect mortality. Efficacy of the RNAi pathway has been demonstrated in several forest pests, however effective mechanisms for delivery are needed before deployment.

To evaluate in-planta delivery of exogenously applied dsRNAs, seedlings of the coniferous loblolly pine (Pinus taeda) and deciduous white oak (Quercus alba) were exposed to dsRNAs as a root soak, destructively sampled, sectioned, and tissues were evaluated for dsRNAs. Gel visualization and Sanger sequencing confirmed the presence of exogenous dsRNAs within tissues after 1, 3, 5, and 7 days of exposure. Recovery varied across dsRNA treatment, tissue type, and exposure time. In loblolly pine, recovery was most dependent on exposure time, whereas seedling height was most significant in white oak. These results shed light on the behavior and retention of exogenously applied dsRNAs within woody plant tissue and demonstrate the potential of this approach for tree protection against forests pests such as southern pine beetle (Coleoptera: Curculionidae, Dendroctonus frontalis) and white oak borer (Coleoptera: Cerambycidae, Goes tigrinus). My findings provide insight into the potential for deploying dsRNAs for single tree protection against forest pests, collectively contributing to the production of more resilient forests.