Abstract
Bromus catharticus Vahl. has been used as a valuable forage crop, but it has also been noted as a weed of winter crops and an invader in several countries. In Argentina, a putative glyphosate-resistant population of B. catharticus was identified as a consequence of the lack of effective control with glyphosate in the pre-sowing of wheat. Plant survival and shikimate accumulation analysis demonstrated a lower glyphosate-sensitivity of this population in comparison to a susceptible B. catharticus population. The resistant population was 4-fold more resistant to glyphosate than its susceptible counterpart. There was no evidence of target-site mechanisms of glyphosate resistance or an enhanced capacity to metabolize glyphosate in the resistant population. However, the resistant plants showed a lower foliar retention of glyphosate (138.34 μl solution g−1 dry weight vs. 390.79 μl solution g−1 dry weight), a reduced absorption of 14C-glyphosate (54.18 vs. 73.56%) and lower translocation of 14C-glyphosate from the labeled leaf (27.70 vs. 62.36%). As a result, susceptible plants accumulated a 4.1-fold higher concentration of 14C-glyphosate in the roots compared to resistant plants. The current work describes the first worldwide case of glyphosate resistance in B. catharticus. A reduced foliar retention of herbicide, a differential rate of glyphosate entry into leaves and an altered glyphosate translocation pattern would be the most likely mechanisms of glyphosate exclusion.
Highlights
The genus Bromus L. comprises approximately 150 species distributed across temperate and cool regions of both hemispheres (Planchuelo and Peterson, 2000)
Bromus catharticus originated in the Pampas of South America and was widely introduced into temperate regions worldwide (Planchuelo and Peterson, 2000; Planchuelo, 2006), but it escaped into the wild in four continents (Dastgheib et al, 2003; Di Tomaso and Healy, 2007; Verloove, 2012; Muzafar et al, 2016; Bromilow, 2018)
The aim of this work was to evaluate the magnitude of glyphosate resistance in the offspring of a putative glyphosate-resistant B. catharticus, and to determine the mechanisms associated with resistance to glyphosate in this weed species
Summary
The genus Bromus L. comprises approximately 150 species distributed across temperate and cool regions of both hemispheres (Planchuelo and Peterson, 2000). Bromus catharticus originated in the Pampas of South America and was widely introduced into temperate regions worldwide (Planchuelo and Peterson, 2000; Planchuelo, 2006), but it escaped into the wild in four continents (Dastgheib et al, 2003; Di Tomaso and Healy, 2007; Verloove, 2012; Muzafar et al, 2016; Bromilow, 2018) This is an annual, biennial, or perennial species and it shows two types of flowering, cleistogamic, and chasmogamic, but its reproductive behavior corresponds to that of an autogamous species with a low rate of allogamy (Naranjo, 1992; Gutierrez and Pensiero, 1998). Morphologic and reproductive traits have shown plastic responses to environmental variations, explaining the greater adaptability of B. catharticus (Aulicino and Arturi, 2002)
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