Polyphasic Approaches in Apple Rootstock Propagation: Integrating Conventional and Advanced Strategies for Climate-Resilient Horticulture

Abstract

Apple (Malus domestica) cultivation depends almost entirely on clonally propagated rootstocks to confer uniformity, size control, precocity and resistance to biotic and abiotic stresses. As climatic variability intensifies, the nursery and breeding sectors face mounting pressure to reconcile time-honoured propagation methods, such as mound layering, hardwood cuttings and field grafting, with rapidly evolving biotechnological tools, including micropropagation, genomic selection and genome editing. This review adopts a polyphasic perspective, examining how conventional vegetative propagation techniques and advanced molecular and tissue-culture-based strategies can be combined within a single, coherent production pipeline to deliver climate-resilient apple rootstocks at commercial scale. The physiological and anatomical basis of adventitious root formation is synthesised alongside the hormonal, transcriptional and epigenetic networks that govern rooting competence in difficult-to-root dwarfing genotypes. Genomic advances, including the identification of dwarfing loci and haplotype-resolved rootstock genomes, are considered together with marker-assisted and genome-editing approaches that promise to accelerate the breeding of rootstocks combining ease of propagation with stress tolerance. Particular attention is given to drought, waterlogging, heat, cold and salinity tolerance, as well as to apple replant disease and rhizosphere microbiome interactions, which collectively determine orchard establishment success under changing climatic conditions. The review further explores how virus elimination, mycorrhizal inoculation, biostimulant application and bioreactor-based micropropagation can be integrated with conventional nursery operations to improve propagation efficiency without compromising genetic fidelity. By drawing together physiological, molecular and applied horticultural evidence, this synthesis aims to inform researchers, breeders and nursery practitioners seeking to design propagation systems capable of sustaining global apple production under future climatic scenarios.