Screening Various Bacterial-Produced Double-Stranded RNAs for Managing Asian Soybean Rust Disease Caused by Phakopsora pachyrhizi

Asian soybean rust (ASR), caused by <i>Phakopsora pachyrhizi</i> (Syd.), poses a serious threat to global soybean production. The main approach to managing this disease has been through repeated fungicide applications which have reduced efficacy due to fungicide resistance. Recently, spray-induced gene silencing (SIGS) through exogenous application of double-stranded RNA (dsRNA) has emerged as a promising approach for plant disease management. In the present study, twelve different dsRNAs targeting genes important for <i>P. pachyrhizi</i> urediniospore germination, infection of the host plant or resistant to commonly used fungicides were produced in <i>Escherichia coli</i> on a large scale. Nine of these dsRNAs significantly reduced ASR severity (by 24.0% to 81.1%) and fungal biomass (50.5% to 83.1%) compared to the control when applied as a foliar spray in our growth chamber studies. Three of the most effective dsRNAs targeting an acyltransferase (ACE), cytochrome B (CYTB1) and a reductase (S12) also significantly reduced disease severity (78.2 to 82.3%) and fungal growth (79.8 to 85.4%) compared to the control in the greenhouse studies. Further investigation of the <i>P. pachryrhizi</i> urediniospore germination and hyphal growth in the presence of these dsRNAs in vitro revealed these dsRNAs reduced the spore germination rate from 72.1% to 0.0-26.6% at 4.5 h and hyphal growth from 254.0 µm to 2.7-40.5 µm at 9 h, with dsRNA targeting the <i>S12</i> gene being the most effective. These results highlight the potential of SIGS using selected dsRNAs as a sustainable strategy for managing ASR through suppressing urediniospore germination and hyphal growth.