Exogenous Application of dsRNA for Protection against Tomato Leaf Curl New Delhi Virus

Tomato leaf curl New Delhi virus (ToLCNDV) is an emerging plant pathogen, fast spreading in several Asian and Mediterranean regions, considered the most harmful geminivirus infecting cucurbits in the Mediterranean. ToLCNDV infects plant and crop species belonging to several families, including Solanaceae, Cucurbitaceae, Fabaceae, Malvaceae and Euphorbiaceae. Up to now, the introgression of ToLCNDV resistant traits in crops is still challenging. Plant protection by the delivery of dsRNA molecules homologous to a target pathogen is a cutting-edge biotechnological approach based on the natural phenomenon of RNA interference (RNAi), already shown to be effective against different RNA viruses and viroids. On the contrary, the efficacy of this approach against DNA viruses is still controversial. In the present study we focus on Cucurbita pepo (zucchini), among the most affected crops by ToLCNDV infection; the protection induced by exogenous application of a chimeric dsRNA targeting all the coding regions of the DNA-A of the ssDNA virus ToLCNDV was evaluated, in terms of percentage of infected plants, symptoms appearance and viral titer. Our results indicate that the treatment with exogenous dsRNAs has limited efficacy against ToCVNDV. Limitations and possible optimizations for the use of RNAi-based approaches against DNA viruses are discussed.