Differential Induction of Resistance Mechanisms by Methyl Jasmonate in Two Vaccinium corymbosum L. Cultivars Under Combined Water Deficit and Aluminum Toxicity

This study aimed to determine the stress mechanisms induced by foliar methyl jasmonate (MeJA) application in <i>Vaccinium corymbosum</i> cultivars subjected to water deficit (WD) and aluminum toxicity (Al). Two <i>V. corymbosum</i> cultivars, Star and Legacy, were subjected to different treatments in an Andisol: control (80% field capacity and low Al saturation), combined WD + Al (50% field capacity and 85% Al saturation), and different concentrations of foliar MeJA application (10 μM, 50 μM, and 100 μM) under WD + Al conditions. The determination of photosynthetic pigments, osmolytes, and organic acids, as well as the auxin levels and the expression of <i>Aluminium-Activated Malate Transporter</i> (<i>ALMT</i>) and <i>Multidrug and Toxic Compound Extrusion</i> (<i>MATE</i>) genes, was analyzed at 7 and 21 days. Foliar MeJA application increased chlorophyll a, b, and carotenoid levels, mainly at 50 µM, exhibiting early Star responses with up to 1.5-fold higher pigment accumulation, and a later increase in Legacy with up to 1.4-fold higher accumulation. Proline increases up to 2.2-fold in roots and sugar by 1.4-fold in leaves of both cultivars. The MeJA application increases the auxin levels by up to 2.3-fold in Star roots at 7 days and by up to 1.4-fold in Legacy leaves at 21 days. MeJA-induced upregulation of <i>ALMT</i> and <i>MATE</i> gene expression facilitated Al detoxification, with malate and citrate levels increasing up to 2-fold. Hierarchical clustering confirmed that the Star cultivar activated resistance mechanisms early, while the Legacy cultivar exhibited delayed but sustained resistance mechanisms. MeJA improves <i>V. corymbosum</i> resistance to combined WD + Al stress by modulating photosynthetic pigments, osmolytes, organic acids, and hormone regulation. This finding underscores the biotechnological potential of MeJA application to improve stress resilience and optimize crop performance under adverse environmental conditions.