Investigate the Use of Nucleic Acids as Pesticides to Manage Major Pests and Pathogens of Crops in South Carolina

The sugarcane aphid (SCA, Melanaphis sorghi), first discovered on grain sorghum in late 2013, has gradually become a major insect pest of sorghum. It inflicts significant damage to the crop year after year, causing millions of dollars in losses throughout the sorghum-producing regions of the United States. Similarly, Armillaria root rot—also referred to as oak root rot—is a major cause of decline in peach (Prunus persica) production in the southeastern United States. This disease is caused by Armillaria mellea and Armillaria tabescens. Current management practices for controlling M. sorghi include the use of synthetic pesticides, resistant varieties, and regular scouting. In contrast, management options for Armillaria species are limited, as no specific fungicides are available apart from systemic treatments like propiconazole. Integrated pest management approaches, such as tree removal, above-ground root collar excavation, and the use of resistant germplasm, are commonly employed. The primary insecticides used to manage M. sorghi are Sivanto Prime and Transform. However, their continued application is expected to result in the development of resistant M. sorghi strains. Additionally, these insecticides can negatively impact pollinators. Therefore, to meet the growing demand for greener (environmentally benign), target-specific, and safer alternatives for managing M. sorghi in sorghum and Armillaria species in peach, this project evaluates the potential of small nucleic acid molecules complementary to essential pest and pathogen gene transcripts in preventing their growth in laboratory, greenhouse, and field settings. To address these challenges, we assessed the potential of dsRNA-induced gene silencing targeting the acetylcholinesterase gene (AChE) in M. sorghi and the fungal cytochrome P450 lanosterol C-14α-demethylase (CYP51) gene in Armillaria mellea and A. tabescens. We compared various dsRNA delivery methods for M. sorghi and found that dsRNA is absorbed through the body surface, with mortality increasing significantly when combined with leaf painting and excess diet. To enhance dsRNA stability, it was conjugated with chitosan and liposomes or replaced with 2′-deoxy-2′-fluoro-d-arabinonucleic acid antisense oligonucleotides (FANA-ASO). Our studies suggest that chitosan conjugation notably improves dsRNA stability and enhances gene silencing efficiency in aphids. In contrast, in fungi, conjugation iii with chitosan or liposomes had little effect on gene silencing efficiency compared to unconjugated dsRNA. Overall, our results indicate that dsRNA-induced gene silencing targeting the AChE gene in M. sorghi and the CYP51 genes in Armillaria mellea and A. tabescens offers a potential option to chemical treatments in control of these pests and pathogens.