ROCK BULRUSH (Schoenoplectus juncoides) with GROUP B/2 resistance: (INHIBITION OF ACETOLACTATE SYNTHASE ) Inhibition of Acetolactate Synthase
MUTATION: PROLINE 197 to THREONINE
Rock Bulrush (Schoenoplectus juncoides) is a monocot plant in the cyperaceae family. A single amino acid substitution from Proline 197 to Threonine has led to resistance to Inhibition of Acetolactate Synthase as indicated in the table below.		Rock Bulrush

Chemical Family	Example Herbicide	Resistance Level
Imidazolinones	Imazethapyr	Susceptible
Pyrimidinyl benzoates	Bispyribac-Na	Not Determined
Sulfonylureas	Chlorsulfuron	Resistant > 10 fold
Triazolopyrimidine - Type 1	Chloransulam-methyl	Not Determined
Triazolinones	Flucarbazone-Na	Not Determined

REFERENCES

Sada, Y., H. Ikeda, and S. Kizawa. 2013. Resistance levels of sulfonylurea-resistant Schoenoplectus juncoides (Roxb.) Palla with various Pro197 mutations in acetolactate synthase to imazosulfuron, bensulfuron-methyl, metsulfuron-methyl and imazaquin-ammonium.. Weed Biology and Management 13 : 53 - 61.

An investigation, using herbicidal pot tests in a greenhouse condition, was conducted to determine the whole-plant dose–response relationships to several acetolactate synthase (ALS)- inhibiting herbicides of sulfonylurea (SU)-resistant Schoenoplectus juncoides  with various Pro197  mutations in ALS that was collected from Japanese rice paddy fields.All the tested SU-resistant accessions with a Pro197  mutation were highly resistant to two commonly used SU herbicides (imazosulfuron and bensulfuron-methyl), but were much less resistant to another SU herbicide, metsulfuron-methyl, and were substantially not resistant to imazaquin-ammonium. These cross-resistance patterns have been known previously in fragments of S. juncoides  and other weed species and were comprehensively confirmed in this study with a whole set of Pro197  mutations.The analyses of resistance levels, based on ED90  values, newly showed that different accessions with a common amino acid substitution in ALS1 showed similar responses to these herbicides (confirmed with four amino acid substitutions), that the rankings of resistance levels that were conferred by various Pro197  mutations in ALS1 differed among the SU herbicides and that the resistance levels of the ALS2-mutated accessions were higher than, lower than or similar to those of the corresponding ALS1-mutated accessions, depending on the compared pair, but the deviation patterns were generally similar among the SU herbicides in each compared pair.The final finding might suggest that the abundance of ALS2 is not as stable as that of ALS1. In addition, as a result of these new findings, together with expected further research, a suggested possibility is that substituting amino acids at Pro197  generally could be estimated by plotting each accession’s ED90  values of imazosulfuron and bensulfuron-methyl in a two-dimensional graph..

This case was entered by Patrick Tranel Email: tranel@illinois.edu

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