Investigations into glyphosate-resistant horseweed (Conyza canadensis): retention, uptake, translocation, and metabolism

Abstract

The mechanism of glyphosate resistance in horseweed was investigated. Eleven biotypes of putative sensitive (S) and resistant (R) horseweed were obtained from regions across the United States and examined for foliar retention, absorption, translocation, and metabolism of glyphosate. Initial studies used spray application of14C-glyphosate to simulate field application. When S and R biotypes were compared in the absence of toxicity at a sublethal dose, we observed comparable retention and absorption but reduced root translocation in the R biotypes. S and R biotypes from Delaware were further examined at field use rates and results confirmed similar retention and absorption but reduced root translocation in the R biotypes. Application of14C-glyphosate to a single leaf demonstrated reduced export out of the treated leaf and lower glyphosate import into other leaves, the roots, and the crown in R relative to S biotypes. Examination of the treated leaf by autoradiography showed that glyphosate loading into the apoplast and phloem was delayed and reduced in the R biotype. Our results consistently showed a strong correlation between impaired glyphosate translocation and resistance. Tissues from both S and R biotypes showed elevated levels of shikimate suggesting that 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) remained sensitive to glyphosate. Analysis of tissue shikimate levels demonstrated reduced efficiency in EPSPS inhibition in the R biotypes. Our results suggest that resistance is likely due to altered cellular distribution that impaired phloem loading and plastidic import of glyphosate resulting in reduced overall translocation as well as inhibition of EPSPS.

Herbicidas alternativos para controle de biótipos de Conyza bonariensis e C. canadensis resistentes ao glyphosate

“…Dois mecanismos de resistência já foram parcialmente definidos, sendo eles: a reduzida translocação do glyphosate para as zonas meristemáticas da planta e a alteração no sítio de ação do herbicida (Powles & Preston, 2006). Trabalhos desenvolvidos com populações resistentes de C. bonariensis e C. canadensis mostraram que essas plantas possuem menor taxa de translocação do glyphosate das zonas tratadas para outras partes da planta, o que não acontece com as plantas suscetíveis (Feng et al, 2004;Koger & Reddy, 2005;Ferreira et al, 2008). Entretanto, ainda não se sabe quais as características bioquímicas e moleculares que levam a essa translocação diferencial do herbicida Ainda, é importante ressaltar que, mesmo sabendo da importância da rotação de culturas no manejo integrado de plantas daninhas, nos experimentos realizados por Davis et al (2007), a densidade de sementes no banco de sementes de buva não foi afetada em nenhuma das rotações propostas.…”

CARACTERÍSTICAS ESTRUCTURALES Y FISIOLÓGICAS DE Petunia axillaris RELACIONADAS CON SU BAJA SENSIBILIDAD A GLIFOSATO

“…Además el hecho de P. axillaris presente altos valores de ED 50 y bajas concentraciones de ácido shikímico permite inferir que la ruta del shikimato no se encuentra alterada por la aplicación de glifosato, como ya fue demostrado para otras especies tolerantes o resistentes. (Feng et al, 2004).…”

“…hybridus, hecho que podría estar relacionado a la baja sensibilidad encontrada en la especie. Se ha descrito que las alteraciones en la retención foliar constituyen mecanismos potenciales de resistencia (Feng et al, 2004); en el género Conyza la menor sensibilidad encontrada, fue correlacionada con una baja retención foliar (Gonzalez-Torralva et al, 2010).…”

“…La resistencia a glifosato puede ser resultado de: mutaciones en el DNA (Powles & Yu, 2010), sobreexpresión de la enzima EPSPS (Gaines et al, 2011), tazas de absorción o translocación reducida (Feng et al, 2004), secuestración del herbicida en vacuolas (Ge et al, 2010), alteración de la enzima EPSPS (Baerson et al, 2002) o variaciones en el metabolismo del glifosato (Rojano-Delgado et al, 2012). Asociado a la baja eficacia del glifosato, independientemente de sus causas, entran en juego otros factores que determinan que las especies o los genotipos de una especie que sobreviven, se reproduzcan y aumenten su frecuencia dentro de una determinada área, resultando en un cambio en la composición y abundancia de poblaciones de malezas (Johnson et al, 2009).…”

Verification of the Mechanism of Glyphosate Resistance in Italian Ryegrass Biotypes

“…These mechanisms involve reduced absorption and/or translocation of herbicides, increased metabolism rates or the herbicide sequestration on metabolically inactive cellular organelles (Feng et al, 2004;PerezJones et al, 2007;Dinelli et al, 2008;Powles and Yu, 2010).…”