Efeito de doses de zinco via solo e foliar em mudas de eucalipto e na preferência de corte da formiga-cortadeira Atta Sexdens

Abstract

With the increase in cultivation in areas of the Cerrado, there is a concern about problems related to symptoms of micronutrient deficiency, such as zinc (Zn) and boron (B), and the attack of pests during the development of the culture, with emphasis on leaf-cutting ants. This work aimed to evaluate different doses of Zn in the development of eucalyptus seedlings and different modes of application, via soil and foliar, and the influence of Zn on the cutting preference of leaf-cutting ants Atta sexdens. Two experiments were set up in a completely randomized design, with five treatments and seven replications. The first experiment consisted of five doses of Zn, in the form of zinc sulfate for both experiments, 0; 2.5; 5; 10 and 20 mg/dm³ applied via soil and the second experiment consisted of five doses of Zn, 0; 2.5; 5; 10 and 20 mg/L) applied via leaves plus an extra dose of 20 mg/dm³ of Zn applied via soil. The experiments were carried out in a greenhouse and after 80 days of planting, the following were evaluated: stem diameter, height, root length, number of leaves, shoot and root dry matter, total dry matter, macro and micronutrients in leaves and gas exchange: internal carbon concentration, stomatal conductance, transpiration and net photosynthesis rate. Even though Eucalyptus urophylla seedlings did not show statistically significant differences, part of the evaluated variables showed a positive response to the application of Zn, analyzing the linear and quadratic regression graphs, mainly at doses of 10 and 20 mg/L and 10 and 20 g/dm³. To evaluate the cutting preference of leaf-cutting ants Atta sexdens for Eucalyptus urophylla seedlings, the seedlings were submitted to zinc doses of 0 (control) and 20 mg/dm³ via soil plus 20 mg/L via foliar, in the form of Zn sulfate. The seedlings used were kept in a greenhouse for up to 80 days and then submitted to laboratory evaluation. The leaves of seedlings treated with different doses of Zn were offered in Petri dishes to three colonies of ants from artificial nests of A. sexdens in the laboratory with free choice between treatments. The percentage of leaf tissue cut and transported to the nests was evaluated for 20 minutes between different doses and colonies, and four sequential offers of leaves were made. Through the data obtained, it was observed that there was no preference for cutting the leaves of eucalyptus seedlings treated with different doses of Zn by the colonies of leaf-cutting ants Atta sexdens