The resistance mechanism of a glyphosate-resistant Lolium multiflorum Lam. biotype collected in Córdoba (Southern Spain) was examined. Resistance Factor values at three different growth stages ranged between 4.77 and 4.91. At 96 hours after treatment (HAT) the S biotype had accumulated seven times more shikimic acid than the R biotype. There were significant differences in translocation of 14C-glyphosate between biotypes, i.e. at 96 HAT, the R biotype accumulated in the treated leaf more than 70% of the absorbed herbicide, in comparison with 59.21% of the S biotype; the R biotype translocated only 14.79% of the absorbed 14C-glyphosate to roots, while in the S population this value was 24.79%. Visualization of 14C-glyphosate by phosphor imaging showed a reduced distribution in the R biotype compared with the S. Glyphosate metabolism was not involved in the resistance mechanism due to both biotypes showing similar values of glyphosate at 96 HAT. Comparison of the EPSPS gene sequences between biotypes indicated that the R biotype has a proline 182 to serine amino acid substitution. In short, the resistance mechanism of the L. multiflorum Lam. biotype is due to an impaired translocation of the herbicide and an altered target site.
Bibliographical noteFunding Information:
The authors are grateful to Rafael Roldán-Gómez and Isabel M. Algaba García for their technical assistance during the conducting of this research. This research was funded by the firm Monsanto and by Spain's MICINN (Project AGL2010-16774). Javier Gil-Humanes acknowledges financial support from the I3P Program from the Consejo Superior de Investigaciones Científicas, which is co-financed by the European Social Fund.
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- Lolium multiflorum Lam.
- Resistance mechanism