Geminiviruses infecting tomato: genetic diversity, distribution, natural and genetically engineered resistance

Tomato (Solanum lycopersicum) is a popular and widely cultivated vegetable crop across the world. The tomato yield is affected by various diseases, and geminiviruses infestation is most damaging. The geminiviruses infecting the tomato are highly diverse, and a large number of species (107) are reported from 39 different countries. India and Brazil are the diversity hotspots for the geminiviruses infecting tomato. The resistance development in tomato against geminiviruses is reported via breeding and biotechnological approaches. To date, six different resistance genes (Ty-1, Ty-2, Ty-3, Ty-4, ty-5, and Ty-6) have been identified from the wild-type tomato and transferred into the cultivated tomato lines by breeding for resistance development. Gene pyramiding through breeding has also been practiced, and gene combinations like Ty-1 + Ty-2, Ty-1 + Ty-2, Ty2 + Ty3, Ty2 + ty5, and ty5 + Ty6 were transferred to tomato cultivar for broader resistance development. The promising and durable resistance has also been developed through various biotechnological strategies like pathogen-derived resistance, peptide aptamers, RNA silencing (antisense RNA, artificial miRNA, RNA interference, or small interfering RNA), resistant gene transfer, clustered regularly interspaced short palindromic repeats (CRISPR), and CRISPR-associated protein 9. The biotechnological strategies mainly deal with targeting geminiviral genes or early stages of geminivirus infection to prevent symptom development and virus accumulation. All these different approaches are beneficial for developing resistance and getting better yield and productivity in tomato.