Molecular insights and integrated management of Glomerella leaf spot in apple

Apple (Malus × domestica) is one of the world's premier fruit crops. Apple Glomerella leaf spot (GLS) is caused by Colletotrichum spp., jeopardizing global apple supply and incurring millions of dollars in annual losses. The development of resistant apple varieties has evolved from conventional selection breeding to deliberate breeding strategies that incorporate statistical analysis and experimental design, and now increasingly integrate genetic and genomic data. Innovative methods like marker-assisted selection and genetic editing have facilitated the development of cultivars resistant to GLS. Novel breeding techniques (NBTs), particularly genome editing, are increasingly vital for the precise and rapid development of disease-resistant crops. The CRISPR/Cas9 system is a powerful tool for targeted mutagenesis, enabling the development of genetically edited crops that are not classified as transgenic. Consequently, researchers are working to identify genes associated with susceptibility and resistance. The article explores the established mechanisms of interaction between the GLS pathogen and its host, as well as the innate immune responses elicited in the apple plant, to expedite the development of resistant apple varieties. Recent advances in effector biology and host gene targeting offer new avenues to enhance immunity and engineer durable resistance traits against GLS.