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Occurrence of Glyphosate-Resistant Junglerice in Louisiana

Applied Research

Matthew Foster
Assistant Professor
LSU AgCenter
St. Gabriel

Abstract

Herbicide-resistant weeds pose a serious threat to agricultural production worldwide. Junglerice [Echinochloa colona (L.) Link] is a troublesome weed that is among the top 15 weed species resistant to the greatest number of herbicide sites of action. In 2023, junglerice plants that survived two applications of glyphosate were collected from a fallow sugarcane field in Napoleonville, LA. Plants were grown to maturity and seeds were collected for greenhouse experiments. In 2024, dose-response assays were conducted in the greenhouse to compare the putative glyphosate-resistant (GR) junglerice population (LA-2) to a known susceptible population (GS). Glyphosate doses included 0, 0.125, 0.25, 0.5, 1, 2, 4, 6, 8, 10, and 12 times the field-use rate (840 g ae ha-1). Plants were treated at the 2-tiller growth stage in a spray chamber. Percent visual control (0-100%) ratings were conducted at 7, 14, and 21 days after treatment (DAT). Dry weights were recorded 21 DAT. To identify alternative control options, dose-response assays were also conducted with quizalofop-P-ethyl, clethodim, glufosinate, and paraquat. Data were subjected to ANOVA in SAS and log-logistic regression in R. Experiments to determine the potential mechanism of resistance in the LA-2 population were also conducted. RNA was extracted from the progeny of a junglerice plant that survived glyphosate treatment. A section of the 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) containing the Pro-106 site was cloned sixteen times and sequenced. Since no junglerice EPSPS sequences were present in GenBank, the sequences were aligned with glyphosate-susceptible Italian ryegrass [Lolium perenne L. ssp. multiflorum (Lam.) Husnot] EPSPS. Dose-response data showed the GR50 of the LA-2 population was 4.6 times greater than the GS population. The LA-2 population survived up to 6 times the field-use rate of glyphosate (840 g ae ha-1). Quizalofop-P-ethyl, clethodim, glufosinate, and paraquat at field-use rates were effective in controlling the LA-2 population (96 to 99% control). Sequence data showed a Pro-106-Thr EPSPS target-site mutation in the LA-2 population, which has been documented in GR junglerice. Results from this research provide insight into how junglerice evolved resistance to glyphosate in Louisiana and which herbicides still provide acceptable control.

Poster has NOT been presented at any previous NACAA AM/PIC

This poster is being submitted for judging. It will be displayed at the AM/PIC if not selected as a State winner. The abstract will be published in the proceedings.

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Authors: Matthew Foster, Prashant Jha, Alice Wright, Renee Naquin
  1. Foster, M. Assistant Professor , LSU AgCenter , Louisiana, 70776
  2. Jha, P. Professor , LSU AgCenter, Louisiana, 70803
  3. Wright, A. Research Agronomist , USDA-ARS, Louisiana, 70360
  4. Naquin, R. Extension Agronomy Agent , LSU AgCenter, Louisiana, 70071