Cultivo hidropônico de alface em condição de elevada temperatura: avaliação do desempenho de cultivares e suplementação com magnésio

Abstract

The lettuce (Lactuca sativa) is the most commercialized leafy vegetable in the world, having its consumption predominantly in the form "in natura", being the crisp type the most commercialized in Brazil. However, lettuce comes from temperate climates, presenting some limitations when cultivated in regions with temperatures above 28 °C, being susceptible to express early bolting, which affects the production and quality of this leafy vegetable. In this sense, this work aimed to evaluate the performance of cultivars of crisp lettuce in hydroponic system under high temperature conditions, and in different magnesium (Mg) concentrations in the nutrient solution. To this end, two trials were conducted in an entirely randomized design. The first trial evaluated the productive, physiological and postharvest quality performance of nine cultivars of crisp lettuce. The second trial evaluated the effect of concentrations of 0.01, 0.5, 1, 2 and 4 mmol L-1 on antioxidant enzyme activity, electrolyte leakage from leaves, physiological performance, growth, yield and postharvest quality of two lettuce cultivars (Olinda and Monica), one tolerant and the other sensitive to high temperature conditions. The cultivars Olinda and Cristina expressed the best productive performance, besides presenting tolerance to early bolting. We also highlight the differences between the cultivars Olinda and Cristina, which serve two distinct markets in alfaculture. The cultivar Olinda serves the functional food market demand, for presenting a high content of antioxidant compounds, while the cultivar Cristina attends the traditional Brazilian market, which consumes crisp lettuce with a light green color. We also observed that among the materials tested, the variety Mônica was the most susceptible to bolting in regions with hot climates. Regarding the effects of Mg concentrations, we observed that the optimal concentrations of Mg in the cultivar Mônica reduced the productive and postharvest losses, however, it was not enough to mitigate the expression of early bolting. Yet, Mg promoted improvements in antioxidant responsiveness, photosynthetic performance, growth and production of lettuce cultivars, with estimated critical concentrations of 2.44 mmol L-1 and 2.92 mmol L-1 , respectively for Olinda and Monica cultivars.