Spray application of dsRNA reduces aphid transmitted ZYMV infection in Cucurbita pepo

Exogenous application of double-stranded RNA (dsRNA) for protection against plant viruses has been demonstrated in a range of pathosystems. Here, we demonstrate the protective efficacy of spray-induced gene silencing (SIGS) in zucchini plants (Cucurbita pepo) against virulent zucchini yellow mosaic virus (ZYMV) upon mechanical inoculation and importantly, aphid mediated transmission under glasshouse environs. We show treatment of plants with 300 ng μL^-1 ZYMV_CP-dsRNA (∼240 - 270 μg plant ^-1) reduced infection rates by ∼73 - 100% when all plants sprayed at day 0 were challenged by mechanical inoculation up to 15-days post-treatment, but not at 20 days post treatment. Similarly, plants treated with 600 ng μL^-1 of ZYMV_CP-dsRNA (∼480 - 540 μg plant ^-1) on day 0 and exposed to viruliferous Myzus persicae aphids at day 5 post spray showed a ∼93% reduction in infection rate, with significant protection maintained when plants were primarily challenged at day 10 post spray (∼75%), but not when challenged at day 15 post spray. Furthermore, we investigate the translocation and persistence of dsRNA molecules on plant hosts and ultimately challenged the ability of the virus to establish infection. Our results demonstrate that spray-on dsRNA application offers a significant window of protection against virulent ZYMV with one treatment. Our study further defines the potential for spray-on RNA based viricidal applications to provide a sustainable alternative to chemical-based method of targeting vectors as a means of virus control.