Point Mutations and Cytochrome P450 Can Contribute to Resistance to ACCase-Inhibiting Herbicides in Three Phalaris Species.

José G Vázquez-García,Joel Torra,Ricardo Alcántara-De La Cruz,Candelario Palma-Bautista,Rafael De Prado

doi:10.3390/plants10081703

José G Vázquez-García, Joel Torra + Show 3 more

Open Access

https://doi.org/10.3390/plants10081703

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Abstract

Species of Phalaris have historically been controlled by acetyl-coenzyme A carboxylase (ACCase)-inhibiting herbicides; however, overreliance on herbicides with this mechanism of action has resulted in the selection of resistant biotypes. The resistance to ACCase-inhibiting herbicides was characterized in Phalaris brachystachys, Phalaris minor, and Phalaris paradoxa samples collected from winter wheat fields in northern Iran. Three resistant (R) biotypes, one of each Phalaris species, presented high cross-resistance levels to diclofop-methyl, cycloxydim, and pinoxaden, which belong to the chemical families of aryloxyphenoxypropionates (FOPs), cyclohexanediones (DIMs), and phenylpyrazolines (DENs), respectively. The metabolism of 14C-diclofop-methyl contributed to the resistance of the P. brachystachys R biotype, while no evidence of herbicide metabolism was found in P. minor or P. paradoxa. ACCase in vitro assays showed that the target sites were very sensitive to FOP, DIM, and DEN herbicides in the S biotypes of the three species, while the R Phalaris spp. biotypes presented different levels of resistance to these herbicides. ACCase gene sequencing confirmed that cross-resistance in Phalaris species was conferred by specific point mutations. Resistance in the P. brachystachys R biotype was due to target site and non-target-site resistance mechanisms, while in P. minor and P. paradoxa, only an altered target site was found.

Highlights

The genus Phalaris L. has a complicated taxonomic history
Dry weight values gradually decreased in all Phalaris spp. populations as the doses of herbicides increased; the dry weight reductions differed between species depending on the herbicide
It should be noted that the metabolic resistance governed by Cyt-P450 found in P. brachystachys is a cause for concern because it may provide widespread resistance to other modes of action and compromise crop productivity; its management may require more diversification than rotating the herbicide’s mode of action

Summary

Introduction

The genus Phalaris L. has a complicated taxonomic history. This genus comprises 22 species of annual and perennial grasses found in open habitats of temperate regions around the world, affecting cereal, pasture fodder, and vegetable crops [1]. Phalaris spp. are among the most frequent annual winter weeds in Iran, and they are represented mainly by Phalaris minor Retz., Phalaris paradoxa L., and Phalaris brachystachys Link. These species are distributed in various regions of the country, invading mainly wheat fields and other arable crops [3,4]. In Iran, wheat is the most important crop, while weeds, mainly Avena spp., Lolium spp., and Phalaris spp. grasses, can reduce the annual yield by ~23% [5]. Phalaris spp. are highly competitive plants with high seed production [6–8]; managing these grasses is essential to avoid compromising crop yields

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