THREELEAF ARROWHEAD (Sagittaria trifolia) with GROUP B/2 resistance: (INHIBITION OF ACETOLACTATE SYNTHASE ) Inhibition of Acetolactate Synthase
MUTATION: PROLINE 197 to SERINE
Threeleaf Arrowhead (Sagittaria trifolia) is a monocot plant in the alismataceae family. A single amino acid substitution from Proline 197 to Serine has led to resistance to Inhibition of Acetolactate Synthase as indicated in the table below.		Threeleaf Arrowhead

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

REFERENCES

Satoshi, I., H. Watanabe, T. Miura, H. Matsumoto, A. Uchino.. 2014. Occurrence of sulfonylurea resistance inSagittaria trifolia, a basal monocot species, based on target-site and non-target-site resistance. Weed Biology and Management 14 : 43 - 49.

Sagittaria trifolia L. is one of the most serious weeds in paddy fields in Japan. Since the late 1990s, severe infestations ofS. trifoliahave occurred following applications of sulfonylurea herbicides in Akita prefecture. In this study, two accessions ofS. trifolia, R1 and R2, were collected from paddy fields with severe infestations and their resistance profiles were determined in comparison to a susceptible accession, S1. R1 and R2 were highly resistant to bensulfuron-methyl. R1 was also highly resistant to pyrazosulfuron-ethyl, but R2 was susceptible. Relative to S1, R1 had an amino acid substitution at the Pro_{197 residue of acetolactate synthase (ALS), a well-known mutation that confers sulfonylurea resistance, suggesting that R1 has a target-site-based resistance (TSR) mechanism. The sequence of the ALS gene in R2 was identical to that in S1. A Southern blot analysis indicated that there was only one copy of the ALS gene in S1 and R2. These results suggest that R2 has a non-target-site-based resistance (NTSR) mechanism. R2 was moderately resistant to imazosulfuron but susceptible to thifensulfuron-methyl. R2 and S1 were susceptible to pretilachlor, benfuresate, MCPA-ethyl and bentazon. The results reveal the occurrence of two sulfonylurea-resistant biotypes ofS. trifoliathat show different mechanisms of cross-resistance to sulfonylureas related to TSR in R1 and NTSR in R2.}.

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

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