Stomatal Morphology, Leaf Nutrients and Molecular Adaptations Are Associated With Scald Resistance in Barley

Scald, caused by Rhynchosporium secalis, can reduce grain yield by up to 40% in susceptible cultivars. To investigate physiological and molecular responses associated with scald resistance in barley, we compared a susceptible cultivar, Atlantis, with a resistant cultivar, Yangsimai 3, under uninoculated control and R. secalis-inoculated conditions. Relative to the uninoculated control, Atlantis showed significant reductions in shoot and root length (20.6% and 22.9%), shoot and root dry weight (27.7% and 28.3%), SPAD value (30.9%) and chlorophyll fluorescence (10.8%), whereas Yangsimai 3 showed smaller changes. Under R. secalis inoculation, Yangsimai 3 showed lower stomatal conductance and smaller stomatal pore size, more stable K⁺ and Ca²⁺ contents, lower malondialdehyde (MDA) and hydrogen peroxide (H₂O₂) levels and higher superoxide dismutase (SOD, ~32%), peroxidase (POD, ~41%) and catalase (CAT, ~31%) activities, indicating stronger antioxidant capacity. qRT-PCR analysis further showed generally enhanced gene expression in inoculated Yangsimai 3 involving Ca²⁺ signalling (HvCAM1, HvCAM24 and HvCDPK3), K⁺ transport (HvHAK1 and HvGORK), antioxidant defence (HvCDS1, HvSOD2 and HvCAT1), phytohormone signalling (HvAOC, HvLOX2 and HvJIP60), stomatal regulation (HvOST1 and HvSLAC1) and MAPK-mediated immune signalling (HvMPK3 and HvMPK14), whereas reactive oxygen species (ROS) production was more strongly induced in Atlantis. These results suggest that scald resistance in Yangsimai 3 is associated with stomatal regulation, ion homeostasis, antioxidant defence and defence-related gene expression.