Physiological Response to Salinity in Novel M-Series Grapevine Rootstocks: A Comparison with Commercial Standards

Rising soil salinity poses significant challenges to Mediterranean viticulture. While some rootstocks effectively reduce salt accumulation in grafted scions, the mechanisms and performance of novel rootstocks remain largely unexplored. This study compared two novel M-series rootstocks (M2, M4) with established commercial rootstocks (1103 Paulsen, R110) to evaluate their physiological responses and salt tolerance under irrigation with varying salinity levels (0, 25, 50, and 75 mM NaCl) over 5 months. Growth parameters, photosynthetic efficiency, chlorophyll content (SPAD), ion homeostasis, and visual symptoms were monitored. Results revealed genotype-specific strategies: 1103 Paulsen exhibited robust photosynthetic efficiency and ion exclusion, maintaining growth and chlorophyll stability; M2 demonstrated superior biomass retention and moderate ion compartmentalization but showed reduced photosynthetic performance at higher salinity levels; R110 displayed effective ion management at moderate salinity but experienced significant growth reduction under severe stress; and M4 was the most sensitive, with severe reductions in growth and ion homeostasis. Organ-specific responses highlighted roots acting as primary ion reservoirs, particularly for sodium and calcium; leaves exhibited high potassium and chloride concentrations, critical for photosynthesis but prone to ionic imbalance under stress; and stems and wood played a buffering role, compartmentalizing excess sodium and minimizing damage to photosynthetic tissues. The reported findings provide valuable insights for rootstock selection and breeding programs, particularly for regions facing increasing soil and water salinization challenges.