Leveraging bud sport–derived low-chill alleles to sustain Mediterranean stone fruit production under warming winters

Climate change is progressively reducing winter chill accumulation in temperate regions, posing a critical threat to the sustainability of stone fruit production systems. In Mediterranean and semi-arid areas, substantial declines in chill portions are projected in warming scenarios, particularly in traditionally productive zones, compromising the complete fulfillment of chilling requirements (CR) and thus affecting flowering phenology, fruit set, and yield stability. This challenge requires rapid adaptive strategies capable of maintaining crop productivity under increasingly mild winters. In this context, spontaneous somatic mutants (“bud sports”) may represent a valuable yet underexploited genetic resource for climate adaptation. These naturally occurring variants can exhibit altered phenological traits without the need for long-lasting breeding programs. A representative example is ‘Búlida Precoz’, an apricot mutant derived from the widely cultivated ‘Búlida’. ‘Búlida Precoz’ shows a significant reduction in chilling requirements (33.7 vs. 47.5 chill portions, a 29% reduction) and advances flowering by approximately 17 days as compared to ‘Búlida’. From an agroclimatic perspective, the incorporation of such new low-chill alleles into breeding programs has the potential to significantly expand the spatial and temporal suitability of fruit production. Climate projections for Spain indicate that areas currently marginal for high-chill cultivars may remain viable only for genotypes with reduced CR, particularly under pessimistic, high-emission, warming scenarios (RCP8.5), where chill accumulation declines sharply across Mediterranean environments. Here, we apply this agroclimatic framework to the 'Búlida' / 'Búlida Precoz' pair, mapping where the low-chill mutant would still satisfy its CR while the parental cultivar would not. Thus, the deployment of low-chill mutants could enable the maintenance, or even extension, of cultivation areas by aligning genotype requirements with future climatic conditions.

This work highlights the synergistic value of integrating genomics and agroclimatic modeling to address climate-driven constraints in temperate fruit crops. Specifically, it illustrates how the identification and utilization of novel alleles derived from bud-sport mutants can provide an efficient pathway for rapid adaptation to low-chill winters. Finally, these findings support the development of climate-resilient ideotypes and contribute to safeguarding the productivity and economic viability of fruit agroecosystems under current climate change.