Resistance to viral yellow leaf curl in tomato through RNAi targeting two Begomovirus species strains

Tomato yellow leaf curl disease caused by different begomovirus species leads to substantial tomato production losses worldwide. In Taiwan, the monopartite tomato leaf curl Taiwan virus (ToLCTWV) and bi-partite tomato yellow leaf curl Thailand virus (TYLCTHV) are the predominant begomovirus species causing this disease. Resistance genes are available in wild tomato species and a continuous search for new resistance genes and alternative control methods is required to respond to the rapid evolution of virus strains. RNA interference is an efficient technology to induce resistance against viral pathogens. Six different sections of the ToLCTWV genome were tested in transformed tomato for their capacity to reduce symptoms and inhibit viral DNA accumulation. The two most effective constructs for ToLCTWV infection carried regions of the C1 and C2 genes, and portions of either the C3 or C4 gene of ToLCTWV. A RNAi construct containing fusions of C1, C2 and C3 sections of ToLCTWV and the corresponding sections of the TYLCTHV DNA-A genome were introgressed into tomato line CLN1621L. R 1 and R 2 families were challenged using viruliferous whiteflies in separate screen houses for ToLCTWV and TYLCTHV. Sixteen and 12 R 2 plants derived from one primary transformant remained symptomless until at least 3 weeks after exposure to ToLCTWV and TYLCTHV, respectively, and accumulated only very low titres of viral DNA, as shown by real-time polymerase chain reaction analysis. Our results suggest that expression of bi-viral RNAi constructs in tomato can lead to resistance against two different tomato infecting begomovirus species.