Poster: Integrative plant physiology
Abs #
32: Characterizing the Mechanism of Glyphosate Resistance in Horseweed (Conyza canadensis)
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Presenter: |
Sammons, R. D., r.douglas.sammons@monsanto.com |
Authors | Sammons, R. D. (A) Heck, Greg (A) Feng, Paul (A) Bunkers, Greg (A) Tran, Minhtien (A) Alibhai, Murtaza (A) Qi, Youlin (A) Flasinski, Stanislaw (A) Malven, Marianne (A) Hubmeier, Chris (A) | | Affiliations: |
(A): Monsanto, Roundup Ready Stewardship and Discovery
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Conyza canadensis (horseweed) is a winter or summer annual indigenous to North America that is readily dispersed and is in a variety of agricultural systems. The appearance of glyphosate resistant horseweed in Delaware in 2001 represented the first dicot species to be resistant to glyphosate. The resistance is due to a single dominant gene and is not metabolism of glyphosate. Horseweed has three EPSPS genes; all equivalent in sensitive and resistant biotypes. EPSPS1 and EPSPS2 are sensitive to glyphosate. EPSPS3 is inactive and a psuedogene. This confirms that glyphosate resistance is not target site based in horseweed. Studies evaluating the third resistance category, exclusion of the herbicide from the target site, have been carried out. Glyphosate uptake is similar between sensitive and resistant biotypes, but there is reduced glyphosate translocation in the resistant biotypes. A number of studies have been carried out in vivo and in vitro to establish the nature of this reduced translocation. A lower shikimate:glyphosate ratio in the resistant biotype, indicates a mechanism that functions to “shield” the EPSPS target from the full glyphosate dose. The genetic relationship between the geographically distinct susceptible and resistant horseweed accessions was examined by inter-MITE polymorphisms. Broad geographical and known genetic relationships were associated by this technique. At this point, we cannot determine if resistant populations potentially spread from a common source population or arose by independent origin. Cloning and sequencing of the resistance locus will be needed to resolve the origins of resistance in these populations.
