Abstract
BACKGROUND: Lettuce is one of the most important and widely cultivated leafy vegetables globally. The morphophysiological mechanisms involved in the stresses caused by high temperatures and water scarcity in different lettuce genotypes remain unknown. Additionally, the presence of bioactive compounds in the leaves must also be monitored as they can prevent serious health conditions. Despite the importance, there are no studies integrating adaptation to tropical conditions with nutritional biofortification. Therefore, our objective was to characterize the photosynthetic and water use efficiency, and agronomic-nutritional potential of lettuce strains to select tropicalized and biofortified genotypes. Eighteen lettuce strains and two commercial cultivars were evaluated. The means were compared using the univariate and multivariate analysis. A Kohonen Self-Organizing map (SOM) was generated to compare the genotypes according to the variables analyzed. RESULTS: Some strains exhibited high chlorophyll and carotenoid contents, delayed bolting, agronomic potential, reduced transpiration rate, better stomatal control, intrinsic water use, photosynthetic apparatus efficiency, and reduced oxidative stress. The strains UFU-189#3#2#1 and UFU-199#2#1#1 showed the highest levels of chlorophyll and carotenoids (2.53 mg 100 g⁻¹ and 0.412 mg 100 g⁻¹, respectively). Evaluating the structural performance of photosystem II (PSII), the strains UFU-199#1#1, UFU-215#1#2, and UFU MiniBioFort-2015#1 showed the lowest values for minimum fluorescence (FO) (6685.17, 7000.33, and 8984.83, respectively) and the highest potential quantum yield of PSII (Fv/Fm) (0.81, 0.83, and 0.79, respectively). CONCLUSION: This study provides compelling evidence that biofortified lettuce strains developed under the UFU breeding program combine agronomic vigor, physiological efficiency, and biofortification.