Integrated physiological and biochemical screening of commercial and novel grapevine rootstocks under drought stress

Climate change is increasing drought frequency and severity in Mediterranean viticulture, making drought-resilient rootstocks essential for future vineyard sustainability. This study used the Microcosmo controlled field simulator to compare six grapevine rootstock genotypes (161.49-C, Dog Ridge, cc114, cc125, cc136 and cc177) under progressive water deficit monitored by soil-moisture sensors. Drought reduced gas exchange rates in all genotypes, albeit with distinct patterns. Dog Ridge exhibited an initial sharp decline, while cc125, cc136 and 161.49-C displayed basal gas exchange maintenance. cc114 and cc177, on the other hand, exhibited linear decreases. Maximum PSII efficiency remained largely unaffected, whereas effective PSII efficiency and electron transport rate decreased mainly under severe drought. Biochemical profiling revealed contrasting adaptive strategies. Most genotypes increased superoxide dismutase, sucrose synthase and HSP70. cc125 showed the strongest coordinated activation of antioxidant, metabolic and protein-protection responses. Aquaporin accumulation was high in cc114 and cc136, but low in cc177, suggesting different hydraulic regulation strategies. Glucose and fructose accumulation supported osmotic adjustment in cc125 and cc114. In contrast, Dog Ridge exhibited sugar depletion, and cc136 failed to increase hexoses despite strong sucrose synthase induction. Markers of oxidative status, including antioxidant power, phenolic compounds, flavonoids and malondialdehyde, revealed that antioxidant activation does not necessarily prevent membrane lipid peroxidation. Overall, cc125 was the most promising non-commercial genotype, demonstrating high water-use efficiency, sustained photosynthetic performance, osmotic adjustment and strong stress-protein induction. cc114 exhibited a balanced response involving hydraulic regulation, flavonoid accumulation and moderate oxidative damage. In contrast, cc136 exhibited early photosynthetic activity but was susceptible to oxidative damage. These findings demonstrate that combining physiological, metabolic, protein and oxidative markers is an effective way of identifying novel grapevine rootstocks that are suited to Mediterranean viticulture in areas with limited water.