Abstract
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.
Highlights
Auxin herbicides were the first class of selective products used to control eudicots in cereal crops. 2,4-D was the first herbicide commercially available having this mechanism of action, being introduced to the market nearly 70 years ago
The results found in this study corroborate those by Byrd et al (2016), who reported that injury percentages higher than 29 and 49% were observed 14 days of application (DAA) for rates of 2.0 and 40 g ae ha-1 of 2,4-D choline salt applied at the growth stage V4 of cotton
Based on the results found in two years of conduction of this study, it can be seen that sub-doses of 2,4-D choline salt applied at stage V4 of cotton plants may increase the plant height and be conducive to greater leaves production, since the hormesis model was significant for these variables, exhibiting coefficients of determination higher than 0.90 (Table 1; Figure 3)
Summary
Auxin herbicides were the first class of selective products used to control eudicots in cereal crops. 2,4-D was the first herbicide commercially available having this mechanism of action, being introduced to the market nearly 70 years ago. Herbicides of this class have been discovered and marketed, and, along with this diversification, a broad range of weed control has arisen, increasing the usefulness and importance of this group of herbicides, especially in areas with plants that have been proven to be resistant to other mechanisms of action (Cobb & Reade, 2010). The amine formulations are more water soluble and require hours to traverse the cuticle. Due to this fact, the possible washes after application are less resistant, and they are susceptible to precipitate formation, if applied with water with high cation contents (Foloni, 2016). Despite the improvements with regard to volatilization, there is still uncertainty about the environmental risk of this formulation, due to the extensive and often inadequate use of the active principle (Marcinkowska et al, 2017). 2,4-D choline salt, in turn, provides a reduced potential for off-target movement of physical particles, significantly decreasing the percentage of spray volume with fine jas.ccsenet.org
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