Ethyl-trinexapac as a chemical stress attenuator in coffee crops

Abstract

Glyphosate is a broad-spectrum systemic herbicide and crop desiccant, commonly used to control weeds, applied via spraying. The spraying of this herbicide often ends up reaching non-target crops, resulting in drift. In coffee cultivation, the herbicide is sprayed between planting rows with the aim of controlling weeds. However, in the event of drift, the coffee plantation may suffer from the effect of glyphosate, resulting in chemical stress. Recent studies by our research group have shown that the use of the plant growth regulator ethyl-trinexapac can stimulate the growth of dicotyledonous crops, such as eucalyptus and coffee. This physiological process is due to a change in the hormonal balance of plants, since this chemical acts in the final stages of gibberellin biosynthesis. Furthermore, work with grasses indicated that ethyl-trinexapac acts as a water stress attenuator due to an increase in the activity of antioxidant metabolism enzymes. Therefore, the objective of this work will be to evaluate the effect of subdoses of ethyl-trinexapac to attenuate the effect caused by glyphosate drift in coffee seedlings (Coffea arabica), cv. Catuaí 2 SL. Two experiments will be carried out under semi-controlled conditions for 120 days after planting (DAP) of coffee in 5 liter pots. In the first experiment, the application of ethyl-trinexapac followed by glyphosate drift will be evaluated. A randomized block experimental design will be used, with five replications, with treatments arranged in a 3x7 factorial scheme, totaling 105 experimental plots, in which the factors will be the three doses of ethyl-trinexapac (0, 90 and 150 g a.i. ha-1) and seven doses of glyphosate: 0.0; 3.6; 7.2; 18; 36; 72 and 180 g a.e. ha-1, equivalent to 0; 0.5; 1; 2.5; 5; 10 and 25% of the recommended commercial dose for weed control (720 g a.e. ha-1). In addition, a second experiment will be carried out, in which ethyl-trinexapac will be applied after exposing the seedlings to glyphosate, in order to verify the effect of this plant growth regulator to mitigate chemical stress caused by herbicide drift. The experiment will be conducted with the seedlings still in pots and the treatments will consist of three doses of ethyl-trinexapac [the same as previously described, which will be applied at 31 DAP (1 day after application of glyphosate)] and the same seven doses of glyphosate. At 30 DAP, doses of glyphosate will be applied, simulating drift caused by the application of this herbicide to control weeds between the coffee plantation rows. The experiment will be conducted in a randomized block design, with five replications. For both experiments, the relative content of total chlorophyll, photosystem II quantum efficiency and gas exchange will be evaluated, 2 and 5 days after glyphosate application, always at ten o'clock in the morning. Every 15 days the height of the plants and the diameter of the stem will be determined. At the end of the experimental period (90 DAP), leaf area and dry matter mass will also be evaluated on a precision electronic scale. The data will be subjected to regression analysis to create dose-response curves for the three conditions of ethyl-trinexapac application. With the curves obtained, the doses at which there is a loss of 50% of the photosynthetic capacity and total dry mass of eucalyptus plants (LD50) will be determined. If necessary, the data may also be subjected to analysis of variance using the F test, and the means compared using the Tukey test at a 5% probability level.