Abstract

Background and aimsRootstocks are widely used in walnut to modulate vigor and stress tolerance, yet the extent to which rootstock traits translate into scion-level drought performance remains uncertain. We evaluated whether contrasting clonal rootstocks ('RX1', 'VX211') and a Juglans regia seedling rootstock modify root hydraulic capacity and, in turn, the water status and gas exchange of potted 'Chandler' under progressive water deficit.MethodsChandler' was grafted onto J. regia seedlings (CH/JU) or onto clonal 'RX1' and 'VX211' (CH/RX1, CH/VX211). Ungrafted 'RX1' and 'VX211' were included to characterize genotype-dependent traits in the absence of a graft union. Plants were maintained under well-watered (WW) or progressive water deficit (WD) conditions. We measured trunk diameter, root dry mass, root hydraulic conductance and conductivity (Kr25, Lr25; HPFM), leaf water potentials, gas exchange, turgor loss point (TLP) and hydroscape area (HA), and whole-plant transpiration in WD (gravimetric).ResultsWD reduced gas exchange, whereas root dry mass and trunk diameter did not differ between water treatments. Root biomass and hydraulic traits differed among scion-rootstock combinations, with CH/JU and 'VX211' generally exhibiting higher Kr25 and/or Lr25 than 'RX1'. Across grafted combinations, TLP was similar and HA values were low, while CH/JU showed a comparatively smaller HA.ConclusionsUnder the conditions and drought trajectory tested, rootstock-related differences in root traits were not consistently mirrored by large differences in scion water status or gas exchange. These results suggest that rootstock effects on drought performance may be context dependent and warrant further evaluation across scion genotypes and under field conditions.