Vivekanand Tiwari
Dana Charuvi

Horticultural crops, including vegetables, fruits, and ornamental plants, are of high value to human health and culture. The changing climatic conditions, which bring on more frequent and unexpected stress events such as drought, heat waves, chilling or frost, excess radiation, floods, and salinity, are the major devastating abiotic stresses, compromising the productivity and quality of horticultural crops. Improving these crops for better yield and quality, as well as for tolerance to both biotic and abiotic stresses, is an ongoing effort, mostly achieved by conventional breeding approaches. Transgenic means, by which specific genes can be overexpressed, silenced, mutated, or edited, allow overcoming some of the bottlenecks of conventional breeding, for example, the lengthy duration, sexual incompatibility, and limited genetic variability. Furthermore, transgenic approaches serve as a valuable tool for functional characterization of genes, assisting in marker selection for breeding programs. Although transgenic crops have still not been fully accepted by society across the globe, the evolution and advancement in genome-editing tools, such as the clustered regularly interspaced short palindromic repeats (CRISPR)-associated (Cas)–based systems, may bring on a change to this trend. In this chapter, we outline the various transgenic methodologies and genetic manipulation approaches utilized and highlight the recent technological advancements in this field. Taking tomato (Solanum lycopersicum) as the most studied horticultural crop via transgenic means, we summarize studies employing such means to improve abiotic-stress tolerance, discussing osmotic, drought, ionic, temperature, light, and heavy-metal stress.