Water deficit or drought is one of the most severe factors limiting plant yield or fruit quality. Thus, water availability for irrigation is decisive for crop success, such as the case of highbush blueberry (Vaccinium corymbosum L.). Therefore, drought stress may compromise blueberry production due to lower fruit weight or fruit yield. Despite this, it is unclear if there is any difference in the response of blueberry cultivars to water deficit, either in terms of physiological and molecular parameters, or in terms of their sensitivity or resistance to drought. In this study, we determined the effect of drought on different physiological parameters in blueberry plants (relative water content (RWC), photochemical efficiency of photosystem II (Fv/Fm), Carbon Isotopic Discrimination, and proline content) in six V. corymbosum cultivars. We also explored molecular responses in terms of gene expression coding for late embryogenesis abundant proteins. Finally, we estimated cultivar water deficit resistance using an integrative model based on physiological results. Upon water deficit conditions, we found reductions in Fv/Fm, RWC, and isotopic discrimination of ¹³C (Δ¹³C), while proline content increased significantly for all cultivars. Additionally, we also found differences in the estimated water deficit resistance index. These results indicate differences in water deficit resistance, possibly due to variations in cultivars’ genetic composition.

Soil salinity is a major constraint on global crop productivity, highlighting the importance of strategies to enhance plant stress tolerance. This study investigated whether root-associated fungal endophytes derived from a salt-tolerant quinoa ecotype could establish associations with a salt-sensitive ecotype and confer systemic physiological and molecular stress-mitigation responses. Fungal endophytes—two Alternaria spp. and one Setophoma sp.—were isolated from roots of Pandela (salt-tolerant genotype) and inoculated BO75 (salt-sensitive ecotype) under severe salt stress (400 mM NaCl). Physiological (potential photochemical efficiency, survival), biochemical (malondialdehyde, proline), molecular (expression of ion transporter genes CqSOS1 and CqNHX1), and elemental (Na⁺, K⁺, Cl⁻ distribution by μ-XRF) responses were evaluated. In the salt-sensitive BO75 genotype, endophyte inoculation was associated with improved stress performance, evidenced by reduced oxidative damage (lower MDA), higher proline accumulation, and enhanced photochemical efficiency. Furthermore, the reduced expression of CqSOS1 and CqNHX1 suggests an improved ionic balance in inoculated plants. Conversely, re-inoculating Pandela yielded negligible effects, suggesting that these endophytes primarily benefit genotypes lacking inherent salt tolerance. These findings indicate that transferring fungal endophytes from halophytic ecotypes can significantly mitigate stress in sensitive genotypes, highlighting their potential for enhancing crop resilience in saline environments.