Point Mutations as Main Resistance Mechanism Together With P450-Based Metabolism Confer Broad Resistance to Different ALS-Inhibiting Herbicides in Glebionis coronaria From Tunisia.

Zeineb Hada,Julio Menéndez,Antonia M. Rojano-Delgado,Thouraya Souissi,Rafael de Prado,Joel Torra,Candelario Palma-Bautista,Yosra Menchari

doi:10.3389/fpls.2021.626702

Abstract

Resistance to acetolactate synthase (ALS) inhibiting herbicides has recently been reported in Glebionis coronaria from wheat fields in northern Tunisia, where the weed is widespread. However, potential resistance mechanisms conferring resistance in these populations are unknown. The aim of this research was to study target-site resistance (TSR) and non-target-site resistance (NTSR) mechanisms present in two putative resistant (R) populations. Dose–response experiments, ALS enzyme activity assays, ALS gene sequencing, absorption and translocation experiments with radiolabeled herbicides, and metabolism experiments were carried out for this purpose. Whole plant trials confirmed high resistance levels to tribenuron and cross-resistance to florasulam and imazamox. ALS enzyme activity further confirmed cross-resistance to these three herbicides and also to bispyribac, but not to flucarbazone. Sequence analysis revealed the presence of amino acid substitutions in positions 197, 376, and 574 of the target enzyme. Among the NTSR mechanisms investigated, absorption or translocation did not contribute to resistance, while evidences of the presence of enhanced metabolism were provided. A pretreatment with the cytochrome P450 monooxygenase (P450) inhibitor malathion partially synergized with imazamox in post-emergence but not with tribenuron in dose–response experiments. Additionally, an imazamox hydroxyl metabolite was detected in both R populations in metabolism experiments, which disappeared with the pretreatment with malathion. This study confirms the evolution of cross-resistance to ALS inhibiting herbicides in G. coronaria from Tunisia through TSR and NTSR mechanisms. The presence of enhanced metabolism involving P450 is threatening the chemical management of this weed in Tunisian wheat fields, since it might confer cross-resistance to other sites of action.

Highlights

Glebionis coronaria (L.) Cass. ex Spach, formerly called Chrysanthemum coronarium L., is one of the most troublesome broadleaf annual weeds in cereal crops in northern Tunisia
A point mutation at the second base of the amino acid Trp (TGG), which resulted in the substitution by Leu (TTG), was found in one homozygous and one heterozygous plant from the R1 population (Table 4). These findings showed that most R plants sequenced contained at least one mutant-resistant allele, suggesting that the target-site resistance (TSR) mechanism is relevant in G. coronaria resistance to acetolactate synthase (ALS)-inhibiting herbicides
A previous survey, conducted in the same region, showed that florasulam was frequently used in a mixture with synthetic auxin herbicides (SAH) to control G. coronaria in cereal crops (Hada et al, 2020) while imazamox has never been applied on the weed to our knowledge

Summary

Introduction

Glebionis coronaria (L.) Cass. ex Spach, formerly called Chrysanthemum coronarium L., is one of the most troublesome broadleaf annual weeds in cereal crops in northern Tunisia. It has been estimated that wheat yield losses associated with high densities of G. coronaria is up to 75% (Hada et al, 2020). It has been proven that G. coronaria evolved resistance to sulfonylureas (SU), herbicides with potential crossresistance to triazolopyrimidines – Type 1 (TP) family (Hada et al, 2020). Both herbicide families target the ALS enzyme, which catalyzes the first common step in the biosynthesis of leucine, isoleucine, and valine in plants (Duggleby et al, 2008; Liu et al, 2015). ALS is the target of three other chemical families, namely, imidazolinones (IMI) (Shaner et al, 1984), sulfonanilides (BTP) (Stidham, 1991), and triazolinones (SCT) (Santel et al, 1999)

Objectives

Methods

Results

Discussion

Conclusion