Hormesis of 2,4-D Choline Salt in Biometric Aspects of Cotton

Plant hormesis is a phenomenon that involves the presence of toxic compounds at high doses but can be beneficial at low doses. Thus, the aim of this study was to use dose-response curves to assess the effect of hormesis caused by sub-toxic of 2,4-D choline herbicide on biometric variables of cotton plants. The study adopted a completely randomized experimental design with seven replications, and the treatments consisted of nine fractions of the average rate indicated on the 2,4-D choline salt herbicide label: 0 (control); 0.4275; 0.855; 1.71; 3.42; 8.55; 17.1; 34.2 and 68.4 g ae ha-1 applied at phenological stages V4 or B4 of cotton plants. The plants were assessed for the main morphological parameters. The results were subjected to analysis of variance and, when significant, the hormesis model was tested aiming to describe the dose-response curves with low rates stimulation. The maximum hormesis effect for the variables plant height and number of leaves in cotton plants at stage V4 was estimated, in due order, for sub-doses between 1.14 and 3.02 and 1.37 and 5.54 g ae ha-1 of 2,4-D choline. The hormesis effect was not significant for total dry matter production when 2,4-D choline was applied at stage V4, irrespective of the year of study. Sub-doses between 0.855 and 1.71 g ae ha-1 of 2,4-D choline salt applied at stage B4 caused hormesis in the height, number of leaves, shoots dry matter and total dry matter of cotton plants.