Genetic Dissection of Drought Tolerance in Tomato Using Simple Sequence Repeat Markers: A Comprehensive Review

Tomato (Solanum lycopersicum) is an economically important crop whose productivity is increasingly constrained by drought stress under changing climatic conditions. Conventional breeding for drought tolerance is often slow because this trait is quantitatively inherited and strongly influenced by environmental factors. Molecular markers, particularly Simple Sequence Repeats (SSRs), have become valuable tools for improving selection efficiency and accelerating breeding progress. This review examines the role of SSR markers in the development of drought-tolerant tomato cultivars. The physiological, biochemical, and molecular responses of tomato to drought stress, including growth reduction, photosynthetic impairment, osmotic adjustment, hormonal regulation, and oxidative stress responses, are briefly discussed. The genetic characteristics of SSR markers, including their high polymorphism, co-dominant inheritance, and multi-allelic nature, are highlighted as key advantages for genetic analysis and breeding applications. Furthermore, the review synthesizes recent findings on the use of SSR markers for genetic diversity assessment, Quantitative Trait Loci (QTL) mapping, and identification of genomic regions associated with drought-related traits such as relative water content, chlorophyll stability, root architecture, and proline accumulation. The application of SSRs in Marker-Assisted Selection (MAS), including marker-assisted backcrossing and QTL pyramiding, is also discussed. Finally, the review evaluates the continuing relevance of SSR markers in the genomic era, emphasizing their complementary role alongside Single Nucleotide Polymorphism (SNP) markers, Genome-Wide Association Studies (GWAS), and Genomic Selection (GS). Integrating SSR-based approaches with modern genomic tools offers a promising strategy for developing climate-resilient tomato cultivars and enhancing future food security.