3) Mr. Kidanemaryam Reta

Climate change exposes grapevines to combined salinity and water-deficit stress in arid regions. While grafting enhances tolerance in single-stress studies, how rootstocks mediate scion responses to combined stresses remains unclear. This three-year study examined how two commercial rootstocks (1103 Paulsen “PL1103” and Sélection Oppenheim 4 “SO4”) grafted with cv.Syrah respond to combined stresses through integrated metabolomic, physiological, and agronomical analyses under three irrigation levels (66%, 100%, 133% of control water) and two salinity treatments (control and 2.5 dS m-1). Soil electrical conductivity increased from 2.09 to 8 dS m⁻¹ under combined stress, causing yield reductions and phenological shifts above rootstock-specific thresholds. Water-level dominated responses with fundamental rootstock-specific differences: SO4 grafts lessened combined stress effects while PL1103 showed additive trends. Both experienced substantial physiological stress (stem water potential below -2.0 MPa, reduced stomatal conductance), but SO4 maintained superior chloride exclusion and a 28% yield advantage with higher stability index (1.8 vs 1.2) and lower yield reduction (-16.5% vs 28.7%). GC-MS-based central metabolite profiling revealed both grafts accumulated protective compounds including, amino acids and sugars under combined stress, with ~10-fold higher levels in PL1103 grafts. However, the metabolic responses were dominated by the phenological stages over environmental stress, preserving trajectories despite changes during berry ripening. Network analysis emphasized the greater tolerance of SO4 grafts to stress, exemplified by relatively stable network connectivity compared to a significant increase of metabolic network connectivity in PL1103 grafts. This multi-level study demonstrates that rootstock selection bring systemic plant changes and is crucial for developing climate-resilient viticulture.