KOCHIA (Kochia scoparia) with GROUP B/2 resistance: (INHIBITION OF ACETOLACTATE SYNTHASE ) Inhibition of Acetolactate Synthase
MUTATION: ASPARTATE 376 to GLUTAMATE
Kochia (Kochia scoparia) is a dicot plant in the chenopodiaceae family. A single amino acid substitution from Aspartate 376 to Glutamate has led to resistance to Inhibition of Acetolactate Synthase as indicated in the table below.		Kochia

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

Warwick, S. I. ; Xu RenLin ; Sauder, C. ; Beckie, H. J.. 2008. Acetolactate synthase target-site mutations and single nucleotide polymorphism genotyping in ALS-resistant kochia (Kochia scoparia). Weed Science 56 : 797 - 806.

The molecular basis for acetolactate synthase (ALS)-inhibitor resistance was determined for 6 susceptible (HS) and 24 resistant (HR) kochia populations from western Canada. The latter included 3 HR populations from Alberta (AB), 3 from Manitoba (MB), and 18 from Saskatchewan (SK). HR plants survived application of the ALS-inhibitor herbicide thifensulfuron-tribenuron mixture in the greenhouse. Most of the HR populations were heterogeneous and contained both HR and HS individuals. The molecular basis for resistance was determined in 273 HR individuals by sequencing the ALS gene (2,270 base pair [bp]) or by conducting a TaqMan genotyping assay developed in this study using real-time polymerase chain reaction (PCR) for single nucleotide polymorphism (SNP) 1709, where a G to T substitution resulted in a Leu for Trp substitution at amino acid position 574 (Trp₅₇₄Leu mutation). A total of 16 SNPs were identified in the ALS gene sequences (0.7% polymorphism), 5 of which resulted in amino acid changes that confer resistance to ALS-inhibiting herbicides. The SNPs correspond to three target-site mutations: Pro₁₉₇ (SNPs 565 and 566), Asp₃₇₆ (SNP 1116), and Trp₅₇₄ (SNPs 1708 and 1709). The Trp₅₇₄Leu mutation was predominant (189 HR plants). The next most common mutation was the highly variable residue Pro₁₉₇ (44 HR plants) with substitution by one of nine amino acids. The least-frequent were Asp₃₇₆Glu (9 plants) and Trp₅₇₄Arg (3 plants) substitutions. The presence of two ALS target-site mutations was found in 30 individual kochia plants, the first report from field-selected weed populations. These include combinations Pro₁₉₇+Trp₅₇₄ (23 plants) and Pro₁₉₇+Asp₃₇₆ (7 plants). The detection of Pro₁₉₇, Asp₃₇₆, and Trp₅₇₄ mutations, as well as both combinations, from geographically separate regions suggests multiple origins of these mutations..

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

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