Date of this Version
Crespo, R.J. 2015. Assessing Multiple-Herbicide Resistance in a 2,4-D Resistant Waterhemp (Amaranthus tuberculatus) Biotype from Nebraska – Student Research. University of Nebraska-Lincoln. Lincoln, NE, US.
A waterhemp biotype was recently reported resistant to 2,4-D in Nebraska. In addition to the repeated use of 2,4-D, atrazine and imazathapyr were reported to be frequently used to control broadleaf weeds. Greenhouse experiments were conducted to confirm 2,4-D resistance and test for resistance to growth regulator herbicides and other herbicide modes-of-action (MoA). A single dose-response experiment showed reduced sensitivity in all three waterhemp biotypes to atrazine, imazethapyr and lactofen; therefore, they were generally considered resistant to those three herbicide MoA. None of the biotypes contained the Ser264 target-site mutation. Since the ametryn dose-response experiment resulted in all susceptible biotypes, atrazine resistance is suspected to be metabolism based. Trp574Leu mutation conferring broad cross-resistance to ALS-inhibiting herbicides including imidazolinones and sulfonylureas was identified in the two 2,4-D susceptible waterhemp biotypes. Trp574Leu mutation was not found in the 2,4-D resistant biotype, but Ser653 mutation conferring resistance to imidazolinones was identified. However, dose-response experiments showed reduced sensitivity of the 2,4-D resistant biotype to chlorimuron-ethyl. Despite the 50% survival rate or higher of plants treated with lactofen, results from sequencing the PPX2L gene conferring resistance to PPO-inhibitor herbicides were not quite clear. The present manuscript confirms that the 2,4-D resistant biotype found in Nebraska is also resistant to herbicides belonging to PSII- and ALS-inhibitors. Additionally, the 2,4-D resistant biotype is resistant and has reduced susceptibility to some other growth regulator herbicides.