Hormesis de 2,4-d sal colina em algodoeiro cultivado no cerrado

Abstract

Some toxic substances in high doses can be stimulating or beneficial in low doses. This effect of a low dose of a toxic substance is known as hormesis. The hormetics responses of synthetic auxins, such as 2,4-D, can be expected through increased production and auxin activity. Two experiments were conducted in order to study the doses effects of herbicide 2,4-D choline salt on the morphology and productivity of non-tolerant cotton cultivated in the brasilian Savanna in different phenological stages. The first one being conducted in greenhouse conditions, and the second in the field. Treatments for both experiments were arranged by nine fractions of the mean dose of the herbicide 2,4-D formulation: choline salt: 0 (control); 0.4275; 0.855; 1.71; 3.42; 8.55; 17.1; 34.2 and 68.4 g ae ha-1, which were established as a function of the dose of 1.5 L ha-1 recommended in label: 0; 0.0625%; 0.125%; 0.25%; 0.5%; 1.25%; 2.5%; 5% and 10%. The applications of the different 2,4-D choline salt herbicide doses were performed when at least 50% of the plants entered the respective studied phenological stages. The results were submitted to analysis of variance and, when significant, the hormesis model was tested in order to describe the dose-response curves with low dose stimulation. It was observed that doses lower than 0.25% recommended dose of the 2,4-D choline salt herbicide may increase the morphological and productive variables of the cotton, and that the model used was altered as a function of exposure in different phenological stages. In addition, it was possible to observe that the characteristics of the cotton fiber are not influenced by the herbicide doses, however the exposure of the herbicide doses in plants of different ages may influence the variables fiber strength, elongation and degree of yellowing.