Abstract

Cases of weed resistant to herbicides have changed the dynamics of agricultural areas in Brazil, and in recent years, Erigeron species have caused major problems to farmers in the country, mainly in relation to the ineffectiveness of herbicide treatments used. The objective of this study was to confirm the cross-resistance to ALS inhibitors in populations of Erigeron sumatrensis as well as to investigate the existence of mutations in the site of action of ALS-inhibiting herbicides. To do this, 30 populations collected in the 2016/2017 crop season were grown in a greenhouse. Dose–response (chlorimuron-ethyl and cloransulam-methyl), inhibition of cytochrome P-450 with malathion, and ALS gene sequencing experiments were carried out in the F1 generations of two fleabane populations. The results proved the cross-resistance to chlorimuron-ethyl and cloransulam-methyl herbicides applied in the post-emergence of the resistant population of E. sumatrensis. The higher activity of P450 enzymes is unlikely responsible for the resistance of the population studied. The resistance mechanism found in R was the target site mutation Pro197Ser at the ALS gene. This is the first study in Brazil to identify a target-site change as a survival mechanism in E. sumatrensis for the resistance to ALS-inhibiting herbicides.

Highlights

  • Weeds known as horseweed or fleabane belong to the genus Erigeron

  • Three Erigeron species are commonly found across South America territories: Erigeron bonariensis (L.) Cronquist, Erigeron sumatrensis (L.) Cronquist, and Erigeron canadensis (L.) Cronquist [1]

  • The collection sites were agricultural properties where soybean was cultivated, and failures in the control of E. sumatrensis were observed after the application of glyphosate and chlorimuron-ethyl herbicides in the 2016/2017 season

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Summary

Introduction

Weeds known as horseweed or fleabane belong to the genus Erigeron (synonym Conyza). Many studies in the literature report Sumatran fleabane (Erigeron sumatrensis) as the most frequent species infesting soybean fields in Southern Brazil [1,2,3]. Sumatran fleabane plants can reach up to 2 m, produce more than 60,000 seeds and grow exponentially for 30 days after emergence [4,5]. These species have been considered as troublesome weeds in Brazilian agricultural environments due to their potential to reduce yield in many crops. Densities of one plant m−2 of hairy fleabane may result in yield losses of approximately 25%, depending on the soybean cultivar [6]

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