Internode water-soluble carbohydrate dynamics as a driver of yield stability in Mediterranean wheat

Context: Stem morpho-physiological traits play a key role in carbohydrate translocation to the developing wheat grains under Mediterranean conditions. Objectives: This study aimed to evaluate the contribution of water-soluble carbohydrate (WSC) accumulation and remobilization in stem internodes during the bread wheat grain filling stage to improve grain yield and associated components in the Mediterranean Basin. Methods: A panel of ten semi-dwarf spring bread wheat genotypes, varying in phenology and stem traits, was evaluated for WSC dynamics in different stem segments (lower internodes and upper internode) throughout the grain-filling process under two contrasting environments (Gilat, semi-arid, and Zafaria, Mediterranean). The trade-offs between stem traits (solidness, diameter, peduncle length), grain size, and yield were evaluated. Results: Phenology and environmental conditions significantly affected water-soluble carbohydrate dynamics. Early-flowering genotypes (∼80 days to heading) exhibited a peak in water-soluble carbohydrate 25 days after heading. In contrast, later-flowering genotypes (∼120 days to heading) peaked at 7 or 15 days after heading in semi-arid or Mediterranean environments, respectively. Peduncle length was reduced by 27% and was associated with 55% decrease in grain yield under semi-arid environments. Despite increased water-soluble carbohydrate accumulation, remobilization efficiency dropped in upper (21%) and lower (10%) internodes under a semi-arid environment. In the same conditions, peduncle length exhibited a strong correlation with water-soluble carbohydrate remobilization (r = 0.84) and grain yield (r = 0.92). The contribution of water-soluble carbohydrate to grain weight was 54% in Zafaria (184 mm during the grain filling) and increased to 75% in Gilat (48 mm), emphasizing the reliance on water-soluble carbohydrate for grain filling under severe stress. This was evident primarily in later-flowering genotypes, which were exposed to severe terminal drought stress and relied heavily on water-soluble carbohydrate reserves. Early-flowering genotypes escaped severe terminal drought stress, while delayed-flowering genotypes endured a higher increase in heat and water deficit stresses during their grain filling. Conclusion: Our findings challenge traditional breeding strategies that minimize stem growth. We demonstrate that investment in stem internode traits enhances water-soluble carbohydrate storage and remobilization and increases grain size without a consequent trade-off in grain yield. Implications: Integrating selection for optimal phenology with enhanced stem structural investments and water-soluble carbohydrate-associated traits in semi-dwarf spring wheat offers a potential strategy to improve productivity in Mediterranean and semi-arid environments.