Fusarium head blight (FHB) caused by Fusarium species is a major threat to food safety and security by reducing crop yields and contaminating grains. RNA interference (RNAi) technology has been widely applied in plant protection. Host-induced gene silencing (HIGS) and spray-induced gene silencing (SIGS) have been shown to be effective at controlling plant diseases and pests. However, HIGS application has been limited by availability of efficient plant transformation systems and public acceptance of genetically modified organisms. SIGS is limited by the cost of dsRNA synthesis and its short life span. Therefore, it is critical to develop alternative RNAi production and delivery systems. Endophytes form intrinsic relationships with their hosts and inhabit the hosts without causing damage. Delivery of RNAi using endophytes is cost-effective and sustainable. Sarocladium zeae is an ideal candidate since it has been demonstrated to provide biocontrol function towards Fusarium in corn and wheat. To reduce FHB and mycotoxin contamination, our goal was to produce and deliver RNAi using an endophytic fungal strain S. zeae 34560 (Sz34560). First, we generated a Sz34560 RNAi strain expressing a GFP hpRNA construct and examined the GFP-dsRNA and -siRNA production. We confirmed GFP-dsRNA production in the Sz34560 GFP-RNAi strain. Second, we generated a F. graminearum strain expressing an RNAi construct targeting the trichothecene biosynthesis gene TRI5, which is essential for trichothecene production. We showed that F. graminearum TRI5-RNAi strain significantly reduced TRI5 expression and trichothecene production in liquid agmatine media. Then we introduced the TRI5-RNAi construct to Sz34560 and generated multiple Sz34560 TRI5-RNAi strains. We demonstrated that the Sz34560 TRI5-RNAi strain produced TRI5-dsRNA and reduced trichothecene produced by F. graminearum when co-cultured in vitro. Preliminary results showed FHB and mycotoxin reduction in wheat heads treated with Sz34560 TRI5-RNAi strains followed by F. graminearum inoculations. Further investigations are underway to determine the effectiveness of reducing FHB and toxin contamination using different treatment methods using Sz34560 RNAi strains.

This material is based upon work supported by the U.S. Department of Agriculture. This is a cooperative project with the U.S. Wheat & Barley Scab Initiative. Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture.