A rootstock-centered perspective on the regulation of alternate bearing in fruit trees

Alternate bearing in most perennial fruit tree species refers to the phenomenon whereby high-yielding on-years are followed by low or nearly no fruiting off-years. This variability complicates orchard management, especially under unpredictable weather patterns. Alternate bearing is regulated by both endogenous and environmental signals, and recent studies suggest that rootstocks could play a role in its modulation. Beyond affecting scion growth and nutrient status, rootstocks influence developmental behavior through long-distance signaling. They participate in hormonal metabolism, nutrient uptake, water transport, and chromatin conformation in scion tissues. Epigenetic changes, including DNA methylation and histone marks, have been implicated in regulating flowering-related genes in response to environmental and developmental cues. This review explores possible contributions of the rootstock to alternate bearing through physiological, molecular, and epigenetic signals-such as signaling molecules and chromatin states associated with flowering-as working hypotheses. The role of rootstocks in shaping source-sink dynamics, interpreted throughout the resource budget model, and their potential influence on stress responses are also discussed in relation to alternate bearing rhythmicity. Finally, emerging strategies aimed at mitigating alternate bearing intensity, including genome editing, marker-assisted selection, and microbiome-based strategies, are highlighted as promising for stabilizing productivity under changing climate conditions.