7 research outputs found
Weed resistance to synthetic auxin herbicides
Herbicides classified as synthetic auxins have been most commonly used to control broadleaf weeds in a variety of crops and in non-cropland areas since the first synthetic auxin herbicide (SAH), 2,4-D, was introduced to the market in the mid-1940s. The incidence of weed species resistant to SAHs is relatively low considering their long-term global application with 29 broadleaf weed species confirmed resistant to date. An understanding of the context and mechanisms of SAH resistance evolution can inform management practices to sustain the longevity and utility of this important class of herbicides. A symposium was convened during the 2nd Global Herbicide Resistance Challenge (May 2017 in Denver, CO, USA) to provide an overview of the current state of knowledge of SAH resistance mechanisms including case studies of weed species resistant to SAHs and perspectives on mitigating resistance development in SAH-tolerant crops
Understanding the Differential Response of <i>Setaria viridis</i> L. (green foxtail) and <i>Setaria pumila</i> Poir. (yellow foxtail) to Pyroxsulam
Green
foxtail [<i>Setaria viridis</i> (L) Beauv.] and
yellow foxtail [<i>Setaria pumila</i> (Poir.) Roem. &
Schult.] are among the most abundant and troublesome annual grass
weeds in cereal crops in the Northern Plains of the United States
and the Prairie Provinces of Canada. Greenhouse and laboratory experiments
were conducted to examine the differential responses of both weed
species to foliar applications of the new triazolopyrimidine sulfonamide
acetolactate synthase-inhibiting herbicide, pyroxsulam, and to determine
the mechanism(s) of differential weed control. Foliar applications
of pyroxsulam resulted in >90% control of yellow foxtail at rates
between 7.5 and 15 g ai ha<sup>–1</sup>, whereas the same rates
resulted in a reduced efficacy on green foxtail (≤81%). The
absorption and translocation of [<sup>14</sup>C]Âpyroxsulam in green
and yellow foxtail were similar and could not explain the differential
whole-plant efficacy. Studies with [<sup>14</sup>C]Âpyroxsulam revealed
a higher percentage of absorbed pyroxsulam was metabolized into an
inactive metabolite in the treated leaf of green foxtail than in the
treated leaf of yellow foxtail. Metabolism studies demonstrated that,
48 h after application, 50 and 35% of pyroxsulam in the treated leaf
was converted to 5-hydroxy-pyroxsulam in green and yellow foxtail,
respectively. The acetolactate synthase (ALS) inhibition assay showed
that ALS extracted from green foxtail was more tolerant to pyroxsulam
than the enzyme extracted from yellow foxtail was. The in vitro ALS
assay showed IC<sub>50</sub> values of 8.39 and 0.26 ÎĽM pyroxsulam
for green and yellow foxtail, respectively. The ALS genes from both
green and yellow foxtail were sequenced and revealed amino acid differences;
however, the changes are not associated with known resistance-inducing
mutations. The differential control of green and yellow foxtail following
foliar applications of pyroxsulam was attributed to differences in
both metabolism and ALS sensitivity