2017 Volume 62 Issue 3 Pages 126-133
Sulfonylurea-resistant biotypes of Schoenoplectus juncoides exhibit various patterns of cross-resistance to acetolactate synthase (ALS)-inhibiting herbicides depending on the amino acid substitutions in their ALSs. In this study, a seedling test was developed for diagnosing this cross-resistance to ALS-inhibiting herbicides. Seeds of S. juncoides were incubated in a solution containing an ALS-inhibiting herbicide at 30°C under light. The seedlings were established in the solution. A clear difference was observed between the resistant and susceptible biotypes with respect to the elongation of the 1st leaves at 5 days after incubation, although no or little difference was observed in the germination rate or the elongation of the coleoptile. Optimum concentrations for diagnosis were 75 ng a.i./mL and 600 ng a.i./mL of thifensulfuron-methyl and bensulfuron-methyl, respectively. In addition, 170 ng a.i./mL propyrisulfuron or 2700 ng a.i./mL pyrimisulfan distinguished two resistant biotypes with different amino acid substitutions, at Pro197 or Trp574. Then, we applied the seedling test to the biotypes collected from Akita Prefecture, Japan. The results were consistent with the whole plant response to herbicides in pot experiments and the amino acid substitutions of ALSs. As a result, resistant biotypes were found in the northern part of Akita Prefecture, suggesting that resistant biotypes occurred across Akita Prefecture.
