Soil calcium deficiency in Sorana bean (Phaseolus vulgaris L.) ecotype reveals adaptive strategies through differential physiological and yield responses

The common bean (Phaseolus vulgaris L.), a key crop within the Fabaceae family, is one of the most widely grown and consumed legumes in the world. However, many genotypes and landraces remain understudied, including the Sorana ecotype, traditionally cultivated in Italy along the Pescia river. It is well-adapted to alluvial, sandy soils with low calcium content. To investigate its adaptive mechanisms to calcium deficiency, we grew Sorana bean plants under control (2 mM Ca²+), moderate (0.4 mM), and severe (0.2 mM) calcium deficiency conditions, from sowing to pod harvest. Both calcium-deficient conditions negatively affected plant biomass, photosynthetic pigment levels, polyphenol content, and stomatal conductance. Interestingly, moderate calcium deficiency enhanced yield, harvest index, and pod harvest index, indicating great sink strength and a shift in resource allocation. Bean skin thickness, a defining trait of this ecotype, was also influenced by calcium availability. At the molecular level, abscisic acid-related genes showed differential expression depending on calcium concentration, suggesting a threshold-dependent activation of stress-response pathways. Our results indicate that Sorana adapts to calcium-poor environments by prioritizing seed production over vegetative growth. This strategy, along with its distinctive agronomic traits, positions Sorana as a valuable genetic resource for breeding programs aimed at improving crop resilience and yield under suboptimal soil conditions.