Efeito de substratos e da biofortificação com zinco sobre aspectos agronômicos e conteúdo de fitoquímicos de microverdes

Abstract

Microgreens are plants harvested prematurely, usually up to three weeks after germination, when the cotyledonary leaves are fully expanded and turgid and the first true leaf is at an early stage of development. Research about microgreens is a promising branch of science, and there are few studies aimed at evaluating different aspects in this area of crop production. Given this context, this research work had two fronts: the study of substrates and agronomic biofortification with zinc and its effects on aspects related to plant growth, production and content of phytochemical compounds in microgreens. Two experiments were conducted in a very simple soilless cultivation system, using plastic trays filled with a 1 cm height substrate layer and automatic supply of nutrient solution by sub-irrigation, installed in a plastic greenhouse. The first aimed to evaluate the cultivation of lettuce, beet, red cabbage and basil microgreens in conventional substrates, commonly used for raise vegetable seedlings (Carolina Soil®-seedlings, carbonized rice husk and a mixture of both) and alternative substrates (textile fiber and jute). The results obtained from the experiment 1 indicated that the substrate Carolina Soil®- seedlings is the most suitable medium regarding the conciliation of growth, yield and content of L-ascorbic acid and carotenoids. Textile fiber, for red cabbage and basil, as well as carbonized rice husk and the mixture Carolina Soil®-seedlings + carbonized rice husk, for the four species, are promising alternatives. In general, the cultivation in jute causes damage to plant growth, yield and content of Lascorbic acid and carotenoids. However, it provides a higher content of total phenolic compounds in beet and red cabbage tissues. The second experiment refers to the evaluation of the increase in zinc concentration (0, 5, 10, 20, and 30 mg L-1) of Hoagland's nutrient solution at 50% concentration and its effects on the biofortification of beet, basil and red cabbage microgreens. The obtained results in experiment 2 allow us to conclude that the supplementation of the nutrient solution with 5 or 10 mg L-1 of zinc allows an increase in the zinc content in the tissues of the microgreens evaluated from a minimum of 115% to a maximum of 586%, in relation to the content present in microgreens produced with the same standard solution with zero dose of Zn, without any reduction in plant growth, fresh yield and content of phytochemical compounds. Supplementation with doses of 20 and 30 mg L-1 should be disregarded, because, even with no damage to the parameters evaluated, Zn levels in plant tissue can reach potentially toxic values for humans.