The use of RNA interference (RNAi) technology to control pests is explored by researchers globally. Even though RNA is a new class of pest control compound unlike conventional chemical pesticides, the evolution of pest resistance needs to be considered. Here, we first investigate RNAi-based biopesticide resistance of Fusarium asiaticum, which is responsible for devastating diseases of plants, for example, Fusarium head blight. Five resistant strains were isolated from 500 strains that treated with UV-mutagenesis. The mutation common to all of the five resistant mutants occurred in the gene encoding Dicer2 (point mutations at codon 1005 and 1007), which were under strong purifying selection pressure. To confirm whether the mutations in Dicer2 confer resistance to RNAi, we exchanged the Dicer2 locus between the sensitive strain and the resistant strain by homologous double exchange. The transformed mutants, Dicer2^R1005D and Dicer2^E1007H, exhibited resistance to dsRNA in vitro. Further study showed that mutations of R1005D and E1007H affected the intramolecular interactions of Dicer2, resulting in the dysfunction of RNase III domain of Dicer2. The amount of sRNAs produced by Dicer2^R1005D and Dicer2^E1007H was extremely reduced along with variation of sRNA length. Together, these findings revealed a new potential mechanism of RNAi resistance and provided insight into RNAi-related biopesticide deployment for fungal control.

Fusarium graminearum is a fungal plant pathogen which causes Fusarium head blight (FHB), a devastating disease on cereal crops. Here we report that FgPMA1 could be a new target to control FHB by the application of double-stranded RNA (dsRNA) of FgPMA1. FgPMA1 was divided into 6 segments to generated RNA interference (RNAi) constructs (FgPMA1RNAi-1, -2, -3, -4, -5, and -6), and these constructs were transformed in F. graminearum strain PH-1. The expression of FgPMA1 reduced by 18.48, 33.48 and 56.93% in FgPMA1RNAi-1, FgPMA1RNAi-2 and FgPMA1RNAi-5, respectively. FgPMA1RNAi-1, -2, and -5 mutants inhibited fungal development, including mycelium growth, mycelial morphology, asexual and sexual development, and toxin production. The length of lesions on wheat leaves, wheat coleoptiles and wheat ears were shorter after infection with FgPMA1RNAi-1, -2, and -5 mutants than wild type PH-1. These results showed that three segments (FgPMA1RNAi-1, -2, and -5) exhibited effective silencing effects. After treatment with 25 ng µL^–1 dsRNA of these segments in vitro, the growth rate of mycelium growth was significant decreased, mycelium became deformed with bulbous structure at the tip, and the mycelium lost the ability to produce conidia in F. graminearum strain PH-1, Fusarium asiacitum strain 2021 and phenamacril-resistant strain YP-1. After application of FgPMA1RNAi-1-dsRNA and FgPMA1RNAi-2-dsRNA to wheat ears, pathogenicity reduced 34.21–35.40%.