Efeito da aplicação de estresse hídrico sob a qualidade de alface (Lactuca sativa L.)

Abstract

Lettuce (Lactuca sativa L.) is the most widespread leafy vegetable in the world, grown in several countries. However, commercially available cultivars have a low content of functional compounds, compared to several other vegetables. In addition, the postharvest period is characterized as a stressful stage, affecting the quality of this vegetable. One strategy that has been shown to be effective in increasing the content of functional compounds in plants is the application of abiotic elicitors, such as drought stress at moderate levels. This is because when perceiving this stress, plants induce the production of compounds related to defense metabolism, which include compounds from their secondary metabolism, which have a functional effect when ingested in the diet. In addition, there is evidence that plants submitted to these elicitors have greater tolerance to subsequent stresses, such as those arising from the postharvest storage. This work aims to evaluate the effect of the pre-harvest application of moderate levels of water stress on the pre and postharvest quality of lettuce. For this, lettuce plants were grown with the volume of water needed to saturate 100% of the soil (C, control), 90% of the soil (EH 90%), 80% of the soil (EH 80%), or they were subjected to short-term acute stress (EH), where the plants were grown in the same condition as the control, but did not receive water for 4 days before harvest. After harvesting, a portion of plants was stored at 6-8 °C and 80% humidity for postharvest analysis. The application of moderate drought stress resulted in plants with higher biomass in treatments EH 90% and EH and did not affect the color or firmness of the plants. The EH 80% treatment stood out in terms of quality parameters, as it resulted in plants with a higher content of carotenoids, chlorophylls, caffeic acid, mono-caffeic-tartaric acid, Malercyl glucoside of quercitin, quercitin-3-O-glucuronide, and greater total antioxidant activity at harvest. Plants submitted to moderate water stress did not show changes in firmness during storage, but showed an increase in the content of flavonoids, in EH, and a smaller number of phenolic compounds that have been negatively affected by storage. The results indicate that the application of moderate water stress, especially at the 80% level, on lettuce represents an interesting strategy to improve the quality of this vegetable at harvest and after storage.