AGRO 106 |
| Waterhemp (Amaranthus tuberculatus and A. rudis) is one of the most problematic weeds of agronomic crops in the Midwestern U.S. Illustrating waterhemp's adeptness at evolving herbicide resistance, this species has evolved two different mechanisms for resistance to Photosystem II (PSII) inhibitors, resistance to acetolactate synthase (ALS) inhibitors is now the norm rather than the exception, and waterhemp was the first weed species in the world to evolve resistance to protoporphyrinogen oxidase (PPO) inhibitors. For the latter, the resistance mechanism recently was identified as an amino acid codon deletion in a gene encoding a PPO that is dual-targeted to chloroplasts and mitochondria – a sophisticated mechanism that further illustrates waterhemp's resistance proclivity. Stacking of different resistances within a single biotype is also common; in an extreme case, a single biotype is resistant to ALS, PSII, and PPO inhibitors. Most recently, waterhemp populations were identified in Missouri that likely are resistant to glyphosate. Should this resistance be further stacked in an ALS/PSII/PPO-resistant biotype, selective control of waterhemp will be extremely difficult with current herbicide options. |
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Weed Resistance to Herbicides
1:30 PM-4:15 PM, Tuesday, 12 September 2006 San Francisco Marriott -- Salon 3, Oral
Division of Agrochemicals |