Management of pest insects and plant diseases by non-transformative RNAi

Since the discovery of RNA interference (RNAi), scientists have made significant progress towards the development of this unique technology for crop protection. The RNAi mechanism works at the mRNA level by exploiting a sequence-dependent mode of action with high target specificity due to the design of complementary dsRNA molecules, allowing growers to target pests more precisely compared to conventional agrochemicals. The delivery of RNAi through transgenic plants is now a reality with some products currently in the market. Conversely, it is also expected that more RNA-based products reach the market as non-transformative alternatives. For instance, topically applied dsRNA/siRNA (SIGS - Spray Induced Gene Silencing) has attracted attention due to its feasibility and low cost compared to transgenic plants. Once on the leaf surface, dsRNAs can move directly to target pest cells (e.g., insects or pathogens) or can be taken up indirectly by plant cells to then be transferred into the pest cells. Water-soluble formulations containing pesticidal dsRNA provide alternatives, especially in some cases where plant transformation is not possible or takes years and cost millions to be developed (e.g., perennial crops). The ever-growing understanding of the RNAi mechanism and its limitations has allowed scientists to develop non-transgenic approaches such as trunk injection, soaking, and irrigation. While the technology has been considered promising for pest management, some issues such as RNAi efficiency, dsRNA degradation, environmental risk assessments, and resistance evolution still need to be addressed. Here, our main goal is to review some possible strategies for non-transgenic delivery systems, addressing important issues related to the use of this technology

Nontransformative Strategies for RNAi in Crop Protection

RNAi in crop protection can be achieved not only by plant-incorporated protectants through plant transformation (transgenic) but also by nontransformative strategies such as formulations of sprayable dsRNAs used as direct control agents, resistance factor repressors, or developmental disruptors. Therefore, the RNAi-based biopesticides are expected to reach the market also in the form of nontransgenic strategies such as sprayable products, stem injection, root drenching, seed treatment, or powder/granule. While the delivery of dsRNA by transgenic expression is well established, it requires generations of crop plants and is costly, which may take years and delays for practical application, depending on the regulatory rules, plant transformability, genetic stability, and public acceptance of genetically modified crop species. DsRNA delivery as a nontransgenic approach was already published as a proof-of-concept work, so it is time to point out some directions on how the real potential for agriculture and crop protection is