Non-Target Site Mechanisms Endow Resistance to Glyphosate in Saltmarsh Aster (Aster squamatus).

José Alfredo Domínguez-Valenzuela,Candelario Palma-Bautista,Rafael De Prado,Ricardo Alcántara-De La Cruz,José Guadalupe Vázquez-García,Hugo E Cruz-Hipolito

doi:10.3390/plants10091970

José Alfredo Domínguez-Valenzuela, Candelario Palma-Bautista + Show 4 more

Open Access

https://doi.org/10.3390/plants10091970

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Abstract

Of the six-glyphosate resistant weed species reported in Mexico, five were found in citrus groves. Here, the glyphosate susceptibility level and resistance mechanisms were evaluated in saltmarsh aster (Aster squamatus), a weed that also occurs in Mexican citrus groves. The R population accumulated 4.5-fold less shikimic acid than S population. S plants hardly survived at 125 g ae ha−1 while most of the R plants that were treated with 1000 g ae ha−1, which suffered a strong growth arrest, showed a vigorous regrowth from the third week after treatment. Further, 5-enolpyruvylshikimate-3-phosphate basal and enzymatic activities did not diverge between populations, suggesting the absence of target-site resistance mechanisms. At 96 h after treatment, R plants absorbed ~18% less glyphosate and maintained 63% of the 14C-glyphsoate absorbed in the treated leaf in comparison to S plants. R plants metabolized twice as much (72%) glyphosate to amino methyl phosphonic acid and glyoxylate as the S plants. Three non-target mechanisms, reduced absorption and translocation and increased metabolism, confer glyphosate resistance saltmarsh aster. This is the first case of glyphosate resistance recorded for A. squamatus in the world.

Highlights

Glyphosate is the active ingredient in numerous trade formulation herbicides for nonselective postemergence control of both annual and perennial weeds [1]
LD50 of 2078.1 g ae ha−1, which exceeded the field dose used in citrus groves (720 g ae ha−1 ), while all S plants died from glyphosate doses of 250 g ae ha−1
S population of another Asteraceae weed species found in citrus groves in the same area of the Gulf Coast of Mexico, such as Bidens pilosa and Parthenium hysterophorus, were greatly sensitive to glyphosate (GR50 values of 52 and 43 g ae ha−1, respectively), while some R plants of both species survived at doses higher that 2000 g ae ha−1 [19,20]

Summary

Introduction

Glyphosate is the active ingredient in numerous trade formulation herbicides for nonselective postemergence control of both annual and perennial weeds [1]. This herbicide disrupts the biosynthesis of tryptophan, phenylalanine and tyrosine by interrupting the activity of the enzyme 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) [2]. Glyphosate is used to control all types of annual and perennial weeds [3], being the main weed control tool in citrus groves in Veracruz, Mexico [4]. In the Gulf of Mexico, are subject to a heavy use of glyphosate [8], since rarely preemergent herbicides are used and other postemergence ingredients increase weed control costs [4]. Of the six weed species reported to be resistant to glyphosate in Mexico, five were found in citrus groves [9]

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