Abstract

Background  Barnyardgrass (Echinochloa crus-galli (L.) P. Beauv.) is an annual weed affecting many field crops. A glyphosate-putative-resistant barnyardgrass population was found from a soybean field in southern Brazil.

Objective  This study aimed to confirm this resistance in Rio Grande do Sul (RS) and identify its mechanism.

Methods  Dose-response curves were generated using a three-parameter nonlinear regression model to assess control efficacy and shoot dry weight reduction. Resistance factors (RF) were calculated across two generations from the resistant (BR20Esp016) and susceptible (BR19Esp001) populations. cDNA was synthesized from total RNA extracted from the plants, and the EPSPS gene was sequenced from both populations.

Results  Based on the glyphosate required to reduce dry weight by 50% (GR₅₀), the resistance biotype had RFs of 2.4 and 2.6 and values of 2.4 and 13.9 for the same variable for the self-fertilization generation (F2). A mutation was detected in the EPSPS gene, where proline (CCA) is replaced by alanine (GCA) at position 106, conferring resistance to EPSPS-inhibiting herbicides in barnyardgrass.

Conclusion  Glyphosate resistance in the barnyardgrass biotype BR20Esp016 is due to target-site resistance associated with a mutation in the EPSPS gene.

Echinochloa Crus-galli; EPSPs-Inhibiting Resistance; Mutation