A Simple In-Season Bioassay for Detecting Glyphosate Resistance in Grass and Broadleaf Weeds Prior to Herbicide Application in the Field

Abstract

The implementation of a successful glyphosate resistance management strategy requires a simple and cost-effective method for detecting resistance in key weeds. To date, however, glyphosate resistance is still routinely confirmed via laborious and time consuming whole-plant pot assays using seeds collected at the end of the growing season. Here, we describe a simple, early-season bioassay for detecting evolved glyphosate resistance in grass and broadleaf weeds. It involves transplanting suspected glyphosate resistant seedlings alongside known sensitive and resistant standards into agar containing informative rates of herbicide and recording percentage survival 14 d after plating. The method was validated using sensitive and resistant populations of Lolium, Eleusine, Conyza, and Amaranthus species encompassing the main glyphosate resistance mechanisms, namely, impaired translocation, EPSPS gene duplication, and mutations. The whole plant pot and agar-based seedling tests generated comparable resistance indices in dose-response assays and percentage survival at discriminating glyphosate rates. The method was applied successfully to detect resistance in a rigid ryegrass population collected from a French vineyard well before glyphosate was applied in the field for the current season. Additionally, the test was shown to be highly transferable to several other grass and broadleaf weeds that have evolved resistance to glyphosate. One major attribute of the method is that it is capable of detecting resistance regardless of the mechanism involved. In addition to being very simple, quick and, cost-effective, it allows determination of glyphosate resistance in weeds prior to field application. It thus offers the opportunity for an informed choice of herbicides for effective weed control.

A Diagnostic Assay to Detect Herbicide Resistance in Annual Bluegrass (Poa annua)

“…], hood canarygrass ( Phalaris paradoxa L.), and green foxtail [ Setaria viridis (L.) Beauv]. Since initial development, this agar-based test has been found to be effective for detecting both target and non–target site resistance in an array of broadleaf and grass weeds of cropping systems (Jackson et al 2015; Kaundun et al 2014).…”

Diagnosing ACCase Inhibitor– Cyhalofop-butyl Resistance in <i>Echinochloa crus-galli </i>at Various Growth Stages

“…Based on the plant growth response (root or shoot) in herbicide media, the diagnostic process could be done within 1 wk. Tal et al (2000) reported a seed-bioassay to detect grass weeds resistant to ACCase inhibitor herbicides within 7 d. An agar-based Syngenta quick test has also been developed to detect glyphosate resistance in grass and broadleaf weeds species within 2 wk (Kaundun et al 2014). Although the seed-bioassay provided an effective and early-season resistant diagnosis in a short period of time, it has been difficult to exclude ungerminated seeds because of dormancy, resulting in an underestimation of the germination rate.…”

“…In similar studies of seedlings tests conducted for other species and herbicides, the successful discrimination between resistant and susceptible biotypes was also reported. In studies with Lolium species, the resistance to glyphosate evaluated with seedlings grown in agar containing herbicide could be identified within 2 wk (Kaundun et al 2014). An assay for discrimination of glyphosate resistance in Lolium multiflorum was developed using tillers with roots (Ghanizadeh et al 2015).…”

Detection of Acetyl-CoA Carboxylase (ACCase) Inhibitor Herbicides Resistance in Sterile Wild Oat (Avena sterilis L.) Using Agar Quick Test

“…Similar research was done by Brosnan et al [34], he found that the quick test using agar medium can be used to determine the resistance of 5-enolpyruvylshikimate-3-phosphate (EPSP) and ALS inhibitor herbicides in Poa annua in less than two weeks. Kaundun et al [35] described a simple, early-season experiment for detecting glyphosate resistance in monocots and dicots weed, he transplanted suspected seedlings alongside known sensitive and resistant standards into agar containing a range rate of herbicide and estimated the percentage survival species after 14 d of plating. Overall, the results of current experiment showed that resistance to ACCase herbicides (post and pre-emergence) can be detected using seed of grass weeds in agar medium.…”