Multiple herbicide–resistant Lolium spp. is prevalent in wheat production in Texas Blacklands

Abstract

Field surveys were conducted across the Blacklands region of Texas during 2016 and 2017 to document the distribution of herbicide-resistant Lolium spp. infesting winter wheat production fields in the region. A total of 68 populations (64 Italian ryegrass, four perennial ryegrass) were evaluated in a greenhouse for sensitivity to herbicides of three different modes of action: an acetolactate synthase (ALS) inhibitor (mesosulfuron-methyl), two acetyl-coenzyme-A carboxylase (ACCase) inhibitors (diclofop-methyl and pinoxaden), and a 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) inhibitor (glyphosate). Herbicides were applied at twice the label-recommended rates for mesosulfuron-methyl (29 g ai ha−1), diclofop-methyl (750 g ai ha−1), and pinoxaden (118 g ai ha−1); and at the recommended rate for glyphosate (868 g ae ha−1). The herbicide screenings were followed by dose-response assays of the most-resistant ryegrass population for each herbicide at eight rates (0.5, 1, 2, 4, 8, 16, 32, and 64×), compared with a susceptible population at six rates (0.0625, 0.125, 0.25, 0.5, 1, and 2×). The initial screening and dose-response experiments were conducted in a completely randomized design with three replications and two experimental runs. Survivors (<80% injury) were characterized as highly resistant (0% to 20% injury) or moderately resistant (21% to 79%). Results showed that 97%, 92%, 39%, and 3% of the Italian ryegrass populations had survivors to diclofop-methyl, mesosulfuron-methyl, pinoxaden, and glyphosate treatments, respectively. Of the four perennial ryegrass populations, three were resistant to diclofop-methyl and mesosulfuron-methyl, and one was resistant to pinoxaden as well. Perennial ryegrass populations did not exhibit any resistance to glyphosate. Dose-response assays revealed 37-, 196-, and 23-fold resistance in Italian ryegrass to mesosulfuron-methyl, diclofop-methyl, and pinoxaden, respectively, compared with a susceptible standard. One Italian ryegrass population exhibited three-way multiple resistance to ACCase-, ALS-, and EPSPS-inhibitors. The proliferation of multiple herbicide–resistant ryegrass is a challenge to sustainable wheat production in Texas Blacklands and warrants diversified management strategies.

Seed traits correlate with herbicide resistance in Italian ryegrass (Lolium perenne ssp. multiflorum)

“…The resistance profile of all the test populations was determined for two ACCase-inhibitor herbicides (diclofop-methyl, Hoelon ® and pinoxaden, Axial XL ® ), one ALS-inhibitor herbicide (mesosulfuron-methyl, Osprey ® ), and the EPSPS-inhibitor glyphosate (Roundup ® Power Max). The methodology followed and detailed results of the herbicide screening are available in Singh et al 7 Double the label recommended rates were used for mesosulfuron-methyl (1X = 14.5 g a.i. ha −1 ), diclofop-methyl (1X = 375 g a.i.…”

“…Italian ryegrass is a major weed of wheat production in the Texas Blacklands prairie. Widespread herbicide resistance has been confirmed recently in Italian ryegrass populations collected in the region 7 . However, diversity for key seed traits in these populations and their association with herbicide resistance are unknown.…”

“…4,5 In Italian ryegrass, high inter-and intra-population diversity for various morphological and reproductive traits were reported by Maity et al 6 and Rosell. 2 Italian ryegrass is highly prone to herbicide resistance evolution, 7,8 and has so far evolved resistance to eight different herbicide modes of action (MOA) worldwide. 9 Italian ryegrass biotypes resistant to acetyl coenzyme-A carboxylase (ACCase)inhibitors, acetolactate synthase (ALS)-inhibitors, and the 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS)-inhibitor have been reported across at least 15 US states.…”

“…Widespread herbicide resistance has been confirmed recently in Italian ryegrass populations collected in the region. 7 However, diversity for key seed traits in these populations and their association with herbicide resistance are unknown. The objective of this study was to investigate diversity for different seed morpho-physiological traits present among the Italian ryegrass populations collected from the Texas Blacklands region and examine potential association between seed characteristics and herbicide resistance.…”

Transfer of resistance alleles from herbicide-resistant to susceptible grass weeds via pollen-mediated gene flow

“…Multiple resistance to two, three, four, and five herbicide SOAs is becoming increasingly common in Italian ryegrass populations. Instances of multiple resistance to two SOAs include resistance to ACCase and ALS inhibitors (Bobadilla et al 2021;Chandi et al 2011;Kuk et al 2000Kuk et al , 2008Rauch et al 2010;Singh et al 2020), ACCase and EPSPS inhibitors (Bobadilla et al 2021;Dickson et al 2011), ALS and EPSPS inhibitors (Bobadilla et al 2021;Henckes et al 2019), and EPSPS and glutamine synthetase inhibitors (Avila-Garcia and Mallory-Smith 2011; Fernández et al 2017;Karn et al 2018;Kurata et al 2017). Italian ryegrass populations with resistance to three herbicide SOAs have been confirmed (Bobadilla et al 2021;Brunharo and Hanson 2018;Ghanizadeh et al 2015;Liu et al 2014Liu et al , 2016Rauch et al 2010;Singh et al 2020;Vázquez-García et al 2020a;Tehranchian et al 2018).…”