WILD MUSTARD (Sinapis arvensis) with GROUP B/2 resistance: (INHIBITION OF ACETOLACTATE SYNTHASE ) Inhibition of Acetolactate Synthase
MUTATION: PROLINE 197 to SERINE
Wild Mustard (Sinapis arvensis) is a dicot plant in the brassicaceae 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.		Wild Mustard

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

Warwick, S. I. ; Sauder, C. ; Beckie, H. J.. 2005. Resistance in Canadian biotypes of wild mustard (Sinapis arvensis) to acetolactate synthase inhibiting herbicides. Weed Science 53 : 631 - 639.

Multiple cases of ALS inhibitor-resistant weed biotypes are reported for many species, including wild mustard. The physiological extent and molecular basis of resistance to ALS inhibitors was compared in 4 wild mustard biotypes from western Canada: a sulfonylurea (SU)-resistant (R) biotype from Manitoba detected in 1992; an SU (ethametsulfuron)-R biotype from Alberta detected in 1993 (metabolism-based resistance); an SU-R biotype from Manitoba detected in 2002; and a SU- and imidazolinone (IMI)-R biotype from Saskatchewan detected in 2002. Herbicide dose-response experiments confirmed that the 2 Manitoba biotypes were resistant to the SU herbicides ethametsulfuron and tribenuron:thifensulfuron mixture, whereas the Saskatchewan biotype was resistant to both SU herbicides and to imazethapyr, an IMI herbicide. Sequence analysis of the ALS gene detected target site mutations in 3 of the 4 R biotypes, with amino acid substitutions Pro₁₉₇ to Ser (Domain A of the gene) in the 2 SU-R Manitoba biotypes and Trp₅₇₄ to Leu (Domain B) in the Saskatchewan biotype. The Alberta SU-R biotype had the same ALS nucleotide and amino acid sequence as the susceptible population at these 2 positions. Two heterozygous individuals [Trp₅₇₄ (Tt/gG)] were detected in the Saskatchewan biotype, and genetic segregation for nucleotide bases and resistance phenotype was consistent with single gene control. Nucleotide variation in neutral regions of the ALS gene varied with biotype, with no variation in the 2 Manitoba biotypes, 2 variants in the Saskatchewan biotype and 16 neutral nucleotide polymorphisms (0.9%) in the Alberta biotype. The occurrence of at least 3 different ALS inhibitor-R biotypes in this important weed species is likely to impact negatively on the use of ALS inhibitors, such as the IMIs, and serves as a warning for strict implementation of herbicide rotations to prevent or delay the evolution and spread of such populations..

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

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