Reduced translocation is involved in resistance to glyphosate and paraquat in Conyza bonariensis and Conyza canadensis from California

Abstract

Resistance to glyphosate and paraquat has evolved in some populations of Conyza spp. from California, USA. This study evaluated whether herbicide absorption and translocation were involved in the mechanism of resistance to both herbicides. Three lines of each species were used: glyphosate-paraquat-susceptible (GPS), glyphosate-resistant (GR) and glyphosate-paraquatresistant (GPR). Radiolabelled herbicide was applied to a fully expanded leaf, and absorption and movement out of the treated leaf were monitored for up to 24 h for paraquat and 72 h for glyphosate. Plants treated with paraquat were incubated in darkness for the first 16 h and then subjected to light conditions. More glyphosate was absorbed in C. bonariensis (52.9-58.3%) compared with C. canadensis (28.5-37.6%), but no differences in absorption were observed among lines within a species. However, in both species, the GR and GPR lines translocated less glyphosate out of the treated leaf when compared with their respective GPS lines. Paraquat absorption was similar among lines and across species (71.3-77.6%). Only a fraction of paraquat was translocated in the GPR lines (3% or less) when compared with their respective GPS or GR lines (20% or more) in both species. Taken together, these results indicate that reduced translocation is involved in the mechanism of resistance to glyphosate and paraquat in C. bonariensis and C. canadensis.

First evidence of multiple resistance of Sumatran Fleabane (Conyza sumatrensis (Retz.) E.Walker) to five- mode-of-action herbicides

“…Some reports of Conyza spp. exhibit the level of paraquat resistance values ranging from 9 to 352.5-fold, when compared with S populations (Van Gessel et al, 2006;Eubank et al, 2012;Moretti et al, 2017). In the present study, the R biotype showed resistant index of 25.51 and 51.83-fold based on LD 50 and GR 50 , respectively.…”

Mechanisms of glyphosate resistance and response to alternative herbicide‐based management in populations of the three Conyza species introduced in southern Spain

“…GR 50 and LD 50 values found in this study were in line with previous research on Conyza spp . The similar results between R populations could be because the three species are so close, as indicated by the molecular markers.…”

“…GR 50 and LD 50 values found in this study were in line with previous research on Conyza spp. 5,7,29 The similar results between R populations could be because the three species are so close, as indicated by the molecular markers. However, at the species level, this analysis indicates that the North-American native C. canadensis is a taxonomic entity separate from C. bonariensis and C. sumatrensis, of South American origin, which appear to be more closely related species.…”

Multiple target site resistance to glyphosate in junglerice (Echinochloa colona) lines from California orchards

“…Absorption and movement of glyphosate within the plant was similar among resistant and susceptible plants in this study and, thus, was not considered a primary mechanism of resistance in these E. colona lines. Altered translocation of glyphosate has not been observed as a mechanism of resistance in Echinochloa species to date, despite being identified in other weed genera including Conyza , Lolium and Chloris …”

“…30 Absorption and movement of glyphosate within the plant was similar among resistant and susceptible plants in this study and, thus, was not considered a primary mechanism of resistance in these E. colona lines. Altered translocation of glyphosate has not been observed as a mechanism of resistance in Echinochloa species to date, despite being identified in other weed genera including Conyza, 21 Lolium 33 and Chloris. 15 The accumulation of shikimic acid in all E. colona lines following treatment with glyphosate suggests that glyphosate is successfully reaching the chloroplast and that at least some portion of the EPSPS enzyme present is sensitive to the herbicide.…”