Insights into the Genetic Improvement of Tomato

Tomato (Solanum lycopersicum L.) is considered one of the most significant vegetable crops globally. The worldwide production of tomato is reported to be 186.82 million tonnes from an area of 5 million hectares, with a productivity of 36.97 tonnes/hectare. China leads in tomato production by contributing 64.86 million tonnes which is approximately 34.72% of the total global production, followed by India (11.01%, 20.57 million tonnes), Turkey (7.06%, 13.20 million tonnes) and the USA (6.54%, 12.22 million tonnes). Tomato is considered as a protective food due to essential poly-nutrients and anti-oxidants, particularly lycopene and β-carotene. Despite its high nutritional value, tomato crop is highly susceptible to various bacterial, fungal and viral diseases such as the Tomato leaf curl virus (ToLCV), which causes a significant yield loss reaching up to 100%. The recent developments in functional genomics approaches, particularly whole-genome sequencing of tomato, have propelled research and enabled the application of genome editing techniques such as zinc finger nucleases (ZFN), transcription activator-like effector nucleases (TALENs) as well as clustered regularly interspaced short palindromic repeats/CRISPR-associated proteins (CRISPR/Cas). These techniques offer precision and efficiency in targeting gene sequences. Useful genes like extended shelf life (e.g., RIN—Ripening Inhibitor), carotenoid synthesis pathways (e.g., LCY-E—Lycopene ε-cyclase, SGR1—Stay Green 1, Blc—Beta-lycopene cyclase, LCY-B11—Lycopene β-cyclase 1 and LCY-B21—Lycopene β-cyclase 2) as well as genes conferring biotic and abiotic stress tolerance (e.g., DMR6–1—Downy Mildew Resistance 6–1 and GRX—CGFS-type glutaredoxin) have been targeted using genome editing techniques like CRISPR/Cas9 in tomato.