1 research outputs found
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 μM 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