Interação do glyphosate com ceras epicuticulares de Digitaria insularis ((L.) Fedde) em biótipo suscetível e resistente

Abstract

The resistance of weeds to herbicides is characterized as a major limitation for the cultivation of agricultural species on a large scale, so the present study aimed to evaluate the morphological and physiological factors of Digitaria insularis that cause tolerance to the herbicide glyphosate. The experiment was carried out in a randomized block design with three replications and three treatments, with doses of 1,080 (dose), 2,160 (2X dose), 4,320 (4X dose) g. a.e. ha-1] of glyphosate and a control without application of the herbicide. Weed plants were collected 72 hours after application, and were evaluated from the 1st to the 4th tiller. Specific mass was evaluated; thickness and chemical composition of epicuticular wax; intracellular concentrations of glyphosate and aminomethylphosphonic acid (AMPA). Cuticle thickness measurements for the resistant biotype were 10.05 µm for the first tiller and 26.53 µm for the fourth tiller. For the susceptible biotype, the measurements were 9.95 µm for the first tiller and 20.08 µm for the fourth tiller, showing that tolerance mechanisms increase with the perennialization of the plant. The higher concentration of tetracosane in resistant biotypes and the higher hexadecanoic concentration in susceptible biotypes result in an epicuticular wax layer with greater characteristics in resistant biotypes and lower lipophilicity in susceptible biotypes. The higher concentration of carboxylic and phenolic groups in the epicuticular waxes of resistant biotypes of D. insularis results in greater chemical reactivity of this layer. Ghyphosate concentrations were higher in the 01 tiller with a dose of 4,320 g ae ha -1 for both biotypes and decreased according to the growth of the weed, as in the 04 tiller the concentration was not sufficient to cause toxicity. The presence of AMPA was minimal in the first two tillers and very low in 03 and 04, due to little absorption of glyphosate. The results of the study indicate that the difficulty in controlling Digitaria insularis plants in advanced stages of development, with the need for carry out control at the young stage, as the epicuticular wax layer and composition change with the development of the plants.