Selection for glyphosate resistance in Conyza spp. occurring in the railway network of southern Spain

Abstract

Conyza spp. are broadleaf weeds that occur in many crops but are also common in non-crop systems such as roadsides and railways. Conyza have selected for glyphosate resistance along railway tracks in southern Spain due to the misuse of this herbicide and the high seed dispersal rate of these species. Twenty-three samples of the genus Conyza (11 Conyza canadensis and 12 Conyza bonariensis) were collected from the margins of railways in different routes of the Andalusia railway network running adjacent to nearby crop fields. The glyphosate resistance level of Conyza populations was evaluated through GR50 (herbicide rate causing 50% growth reduction) and resistance factor (RF) values in every population collected. The highest GR50 were 1851.2 g a.e. ha−1 (RF = 52.53) in C. canadensis (Malaga–Cordoba route) and 1972.4 g a.e. ha−1 (RF = 35.20) in C. bonariensis (Seville–Cordoba route), and the lowest were 46.9 g a.e. ha−1 (RF = 1.33) in C. canadensis (Seville–Cordoba route) and 23.2 g a.e. ha−1 (RF = 0.41) in C. bonariensis (Seville–Cordoba route). The results showed that, among all the C. canadensis populations collected, 18.2% were glyphosate-resistant (RF > 10), 45.5% showed a tendency to develop resistance (RF = 2.5–5), and 36.4% were susceptible (RF < 2.5). Of the 25% of C. bonariensis populations that had resistance to glyphosate, 16.7% had moderate resistance (RF = 5–10) and 58.3% were susceptible. This study found that there are already glyphosate-resistant Conyza spp. along the railway network in southern Spain. This could lead to possible seed exchange between the railway and adjacent places. Therefore, it is vital to consider the railway network when planning control measures against resistance.

Survival on railway tracks of Geranium robertianum—a glyphosate-tolerant plant

“…Until now, few plant biotypes have been found on railway tracks that tolerate or become resistant to glyphosate used there. These are such biotypes from railway tracks as: C. canadensis in Poland, the Czech Republic, Spain and Japan (Chodová et al 2009;Adamczewski et al 2011;Hamouzová et al 2009Hamouzová et al , 2012Adamczewski 2014;Nagai et al 2015;Amaro-Blanco et al 2019;Heap 2020), Conyza bonariensis in Spain (Amaro-Blanco et al 2019), Lolium rigidum in Australia (Malone et al 2012;Heap 2020), Brassica napus in Switzerland (Schoenenberger and D'Andrea 2012) and Parthenium hysterophorus in the USA (Fernandez et al 2015;Heap 2020). In Poland, individuals of C. canadensis found on railway tracks in the suburbs of the Poznań city, where the glyphosate is constantly used, were the resistant biotype.…”

Degradation and sorption of the herbicides 2,4-D and quizalofop-P-ethyl and their metabolites in soils from railway tracks

“…Results In these railway materials, the compounds were indeed degraded slower than in agricultural soils (mean half-lives differed by a factor of 1.4-26, depending on the substance) and mobility was higher (mean sorption coe cients differed by a factor of [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19]. Half-lives and sorption coe cients were also estimated by extrapolation of data from agricultural soils, considering the organic carbon content of railway soils and agricultural soils.…”

“…In many countries, weed control on railway tracks relies on glyphosate [1][2][3][4]. Glyphosate is a broad-spectrum herbicide with systemic properties [5] and, therefore, shows good activity not only against annual, but also most perennial weeds, including weeds with deep roots that are commonly present on railway tracks.…”

“…Some weeds are not su ciently controlled, for example, horsetails (Equisetum) with their acicular stems and extensive rhizomes [2,9]. Long-term use of glyphosate may also promote development of resistance [4,5].…”

Degradation and sorption of the herbicides 2,4-D and quizalofop-P-ethyl and their metabolites in soils from railway tracks

“…Some weeds are not sufficiently controlled, for example, horsetails (Equisetum) with their acicular stems and extensive rhizomes [2,9]. Long-term use of glyphosate may also promote development of resistance [4,5]. Moreover, there is an ongoing, controversial discussion about possible carcinogenicity of glyphosate [10][11][12].…”