Biofortification of Baby Leaf Lettuce with Iron and Zinc: Agronomic and Nutritional Impacts

Inadequate intake of Fe and Zn is prevalent in a large part of the world’s population, and agronomic biofortification has been a strategy to improve the nutritional quality of food and, consequently, the nutrient intake by people. The objective of this study was to evaluate the effects of Fe and Zn concentrations in the nutrient solution on the morphophysiological traits, nutritional quality, and biofortification of two cultivars of baby leaf lettuce in a deep water technique hydroponic system. Two experiments were conducted, one with ‘Vanda’ lettuce (green) and the other with ‘Luminosa’ lettuce (reddish). Six treatments were evaluated, in a 3 × 2 factorial scheme, corresponding to the concentrations of Fe (2.0, 4.0, and 8.0 mg L−1) and Zn (0.06 and 0.24 mg L−1), with four replicates. ‘Vanda’ proved to be more productive, while ‘Luminosa’ has a higher nutraceutical value. The growth traits, yield, and leaf contents of carotenoids and anthocyanins of both cultivars were not influenced by the increase in Fe and Zn concentrations in the nutrient solution. There was a 25% and a 33% increase in the content of phenolic compounds in ‘Vanda’ and ‘Luminosa’, respectively, when the Fe concentration increased from 2 to 8 mg L−1. The Fe content in ‘Vanda’ was influenced only by the Fe concentration in the nutrient solution and increased by 13% between 2 and 8 mg L−1 of Fe. For ‘Luminosa’, there was an interaction, but the highest Fe contents in the shoot were observed with 8 mg L−1 of Fe, which were 24 and 38% higher than those obtained with 2 mg L−1 of Fe at Zn concentrations of 0.06 and 0.24 mg L−1, respectively. The study showed the importance of evaluating the biofortification for cultivars. While ‘Vanda’ baby leaf was biofortified only with Fe, ‘Luminosa’ was biofortified with both micronutrients.