Tolerância ao glyphosate e sua absorção e translocação por biótipos de Ipomoea spp

Abstract

The Ipomoea species are among the most tolerant to glyphosate. The strong selection pressure exerted by the intensive use of this herbicide in cultivated areas favors the emergence of species with high tolerance. Knowing the most common species in cultivated areas, appropriate methods of dormancy overcoming for each species and their mechanisms of tolerance to glyphosate is crucial for the establishment of strategies for prevention and management. The second chapter of the dissertation dealt with the selection of effective methods of overcoming dormancy in Ipomoea species I. indivisa, I. grandifolia and I. purpurea and determining how they affect the germination kinetics of these species. Treatments were hot water, chiseling, chiseling + cooling, chemical scarification and a check. We evaluated germinability, mean time, speed index and relative frequency of germination. In the third chapter we identified the most common species of Ipomoea in soybean crop from southwestern Paraná and west of Santa Catarina, through two experiments of response to rates of glyphosate. In preliminary experiments were defined glyphosate rates to be used in a subsequent assay, using one biotype of the species I. grandifolia, I. indivisa and I. purpurea. In the subsequent experiments, in 31 biotypes (20 I. grandifolia, 7 I. indivisa and 4 I. purpurea) were sprayed 0, 216, 432, 864, 1,296, 1,728 and 2,160 g ha-1 of glyphosate in plants with 6-8 true leaves. The performance of the herbicide was evaluated using the control at 7, 14 21 and 28 days after application (DAA), the mass of fresh (MPAV) and dry (SDW) shoots at 28 DAA. The fourth chapter aimed to identify whether foliar absorption and translocation mechanisms are determinants to tolerance of Ipomoea species and biotypes to glyphosate. Were compared one biotype tolerant (T) and one sensitive (S) of species I. grandifolia, I. indivisa and I. purpurea. When the plants had between 3 and 4 expanded leaves was applied 360 g ha-1 of 14C-glyphosate + analytical standard. We analyzed the foliar uptake and translocation 2, 4, 8, 12, 24, 48 and 72 hours after application (HAA) of the herbicide. The most common species of Ipomoea in the survey were I. indivisa, I. purpurea and I. grandifolia. Scarification with sulfuric acid was the best method of overcoming dormancy for I. indivisa and I. purpurea, and the hot water treatment was most effective in I. grandifolia. There was great variability of tolerance to glyphosate between biotypes of the same species and between species. Some biotypes required much more than the recommended dose for the species to be controlled satisfactorily. The tolerance to glyphosate in I. grandifolia biotypes was associated with reduced absorption and translocation in plants, and in I. Indivisa biotypes and I. purpurea with reduced translocation of glyphosate.