Topical Spray of dsRNA Induces Mortality and Inhibits Chilli Leaf Curl Virus Transmission by Bemisia tabaci Asia II 1

Abstract

<i>Chilli leaf curl virus</i> (ChiLCV; genus: <i>Begomovirus</i>), transmitted <i>by Bemisia tabaci</i> (Gennadius) (Hemiptera: Aleyrodidae) in a persistent-circulative manner, is a major constraint in chilli production. The present study demonstrates for the first time that a topical spray of naked double-stranded RNA (dsRNA) on chilli plants causes mortality and inability to acquire and transmit ChiLCV in <i>B. tabaci</i>. dsRNA targeting <i>heat shock protein 70</i> (<i>hsp70</i>) and <i>fasciclin 2</i> (<i>fas2</i>) of <i>B. tabaci</i> Asia II 1 was first assessed under controlled conditions through oral delivery. <i>Hsp70</i> and <i>fas2</i> dsRNA resulted in up to 82.22% and 72% mortality of <i>B. tabaci</i> and around 12.4- and 8.5-fold decreases in mRNA levels, respectively, 24 h post-ingestion. ChiLCV copies in <i>hsp70</i> dsRNA-fed <i>B. tabaci</i> steadily decreased with an increase in dsRNA concentration and were undetectable at a higher concentration of dsRNA. However, ChiLCV copies significantly increased in <i>fas2</i> dsRNA-fed <i>B. tabaci</i>. Transmission of ChiLCV by <i>B. tabaci</i> was completely inhibited post-24 h feeding on <i>hsp70</i> dsRNA at 3 μg/mL. Naked <i>hsp70</i> dsRNA was topically sprayed on ChiLCV-infected chilli plants like an insecticide. 67.77% mortality of <i>B. tabaci</i>, 4.6-fold downregulation of <i>hsp70</i> mRNA, and 1.34 × 10¹⁵-fold decreased ChiLCV copies in <i>B. tabaci</i> were recorded when adults were exposed to the dsRNA-treated plants under semi-field conditions. Foliar application of naked dsRNA reduced the ChiLCV transmission by 75% without any visible symptoms in the inoculated plants. A total of 2 consecutive sprays of dsRNA provided significant protection to <i>B. tabaci</i> for up to 20 days under semi-field conditions.