Evolutionary insights and cytogenetic solutions for apple orchard sustainability

Apple (Malus domestica) is a widely cultivated fruit crop of significant commercial importance. Its domestication has primarily involved hybridization and clonal propagation, enabling the selection of desirable traits. However, the genetic diversity of domesticated apple varieties remains limited, presenting challenges for breeding efforts. Wild relatives of apples serve as a valuable genetic resource for enhancing traits such as stress tolerance, disease resistance, and fruit quality. Advances in cytogenetic techniques, including fluorescence in situ hybridization (FISH), genomic in situ hybridization (GISH), and flow cytometry, have contributed to a deeper understanding of genome structure and chromosomal modifications in apples. Additionally, polyploidization plays a crucial role in stress adaptation, with triploid and tetraploid cultivars showing enhanced resistance to both abiotic and biotic stress factors. This review explores the genetic and cytogenetic mechanisms that influence stress responses in apples while highlighting the role of genomic tools and breeding strategies in developing climate-resilient cultivars. Furthermore, the application of genome-editing technologies such as CRISPR-Cas9 in apple improvement is discussed.