Elucidação de mecanismos de resistência de Cyperus iria e Echinochloa colona a herbicidas

Abstract

Weed resistance to herbicides occurs through a wide range of mechanisms, which are grouped into two: the target-site resistance mechanisms (TSR) and non-targetsite resistance mechanisms (NTSR). The most cases, related to ALS-inhibiting herbicides, occur due to specific alterations in the enzyme, causing high levels of resistance. However, herbicide metabolism may occur concomitantly. Glyphosate resistance involves both mechanisms (TSR and NTSR) and, in specific cases, is conditioned by temperature. Soil moisture conditions and plant growth stage can affect the efficiency of this herbicide. The Chapter I aimed at sequencing the ALS enzyme in C. iria resistant (CYPIR-R) and susceptible (CYPIR-S) biotypes as well as evaluate evidence of herbicide metabolism through dose-response curve using malathion (1000 g a.i. ha-1 ). In chapter II, the aims were: to assess whether different temperatures condition resistance in E. colona supposed resistant (ECHCO-SR) and susceptible (ECHCO-S) biotypes; to evaluate differential absortion/ translocation among biotypes (by HPLC and ABC transporter inhibitors - sodium ortho-vanadate and verapamil). In Chapter III, the aim was to evaluate the efficacy of glyphosate in ECHCO-SR and ECHCO-S biotypes under different soil moisture conditions and plant growth stages. In study I, the DNA chromatogram showed the presence of double peaks in the third nucleotide base at the Asp376 position, indicating aspartate mutation (GAC) to glutamine (GAG), caused by the level of ploidy, presence of alleles or gene duplication. Malathion synergized the control of bispyribac-sodium on the resistant biotype. Thus, there is evidence of related mutation and metabolism in C.iria cross-resistance. In study II, it was found that the temperature of 36-32 ° C increases the control rate with glyphosate by 2-5x for both ECHCO biotypes, compared to the temperature of 28-25 °C. However, ECHCO-SR is capable to survive the glyphosate rate above the recommended maximum, leading to practical problems, such as plant survival and, consequently, reduction in crop productivity. HPLC studies indicate differential absorption/ translocation among biotypes. In addition, pretreatment with ABC carrier inhibitors reduces the control dose of ECHCO-SR. Thus, temperature-conditioned resistance is suggested. In Chapter III, it was found that saturated soil conditions and advanced growth stage reduce the efficacy of glyphosate in E. colona.