Low level resistance of goosegrass (Eleusine indica) to glyphosate in Rio Grande do Sul-Brazil

Abstract

In the last growing seasons, goosegrass (Eleusine spp.) control failures have been observed following application of glyphosate on Roundup Ready® soybean in Rio Grande do Sul (RS) - Brazil, suggesting this species' resistance to the herbicide. Thus, the objectives of this study were to identify the occurrence of goosegrass resistance to the herbicide glyphosate in RS; and to determine the predominant species of the genus Eleusine, as well as the LD50 and GR50 of the suspected resistant biotypes. Two experiments were conducted under greenhouse conditions: one to identify the biotypes resistant to glyphosate, and the other, a dose-response curve experiment, as well as a study of the botanical characteristics of the species. In the first experiment, 39 biotypes were tested, mainly Eleusine indica, collected with suspected resistance to glyphosate. The glyphosate dose was 2,160 g e.a. ha-1, and the control was evaluated at 28 days after treatment. All biotypes were effectively controlled,with the biotypes from the municipality of Boa Vista do Incra showing greater tolerance. Two biotypes suspected of resistance (12.1 and 12.3) and a susceptible biotype in a dose-response experiment were tested at the following doses: 0, 135, 270, 540, 1,080, 1,620, and 2,160 g e.a. ha-1. The results of this experiment showed that biotype 12.1 does not present resistance to glyphosate and biotype 12.3 has a low level resistance since it is effectively controlled by the herbicide at the maximum dose.

Goosegrass Resistant to Glyphosate in Brazil

“…Although there are no goosegrass population resistant to glyphosate in Brazil, populations with low levels of resistance have been detected in Rio Grande do Sul (Vargas et al, 2013). Even though it is important for the scientific community, this kind of resistance has low practical impact on the field, since the recommendation dose is normally lethal to these populations.…”

“…The population of goosegrass in Rio Grande do Sul characterized as low-level resistant to glyphosate showed a resistance factor of 1.52 (Vargas et al, 2013). As for the resistance factors 6 obtained for the populations 19 and 25 in this study (RF = 3.99 to 6.81) are more similar to reports of goosegrass resistant to glyphosate in Tennessee, USA (RF = 3,1 to 7,4) (Mueller et al, 2011) and in Malaysia (RF = 8 to 12) (Lee and Ngim, 2000).…”

Evaluation of the Mechanism Responsible for the Low-Level Resistance to Glyphosate in Goosegrass

“…And the third one to the shikimate accumulation of these biotypes. Two biotypes were used, considered as having LLR (Boa Vista do Incra, RS, -28.940277 S and -53.411684 W) and another one, susceptible (Camaquã, RS, -30.839221 S and -51.862697 W), determined in previous studies (Vargas et al, 2013).…”

“…The treatments were arranged in a factorial design, whose factor A tested the goosegrass LLR biotype and another biotype notoriously susceptible (Vargas et al, 2013). And factor B consisted in the application or not of malathion insecticide, an inhibitor of cyt-P450 monooxygenase.…”

“…LLR was observed in a biotype of goosegrass originating from Brazilian city Boa Vista do Incra, RS, when using up to 1,080 g of acid equivalent (a.e.) ha -1 of glyphosate, showing a resistance factor of 1.17 (Vargas et al, 2013).…”