COMMON RAGWEED (Ambrosia artemisiifolia) with GROUP B/2 resistance: (INHIBITION OF ACETOLACTATE SYNTHASE ) Inhibition of Acetolactate Synthase
MUTATION: TRYPTOPHAN 574 to LEUCINE
Common Ragweed (Ambrosia artemisiifolia) is a dicot plant in the asteraceae family. A single amino acid substitution from Tryptophan 574 to Leucine has led to resistance to Inhibition of Acetolactate Synthase as indicated in the table below.		Common Ragweed

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

REFERENCES

Patzoldt, W. L. ; Tranel, P. J. ; Alexander, A. L. ; Schmitzer, P. R.. 2001. A common ragweed population resistant to cloransulam-methyl. Weed Science 49 : 485 - 490.

A population of common ragweed (Ambrosia artemisiifolia) not controlled by an acetolactate synthase (ALS)-inhibiting herbicide, cloransulam-methyl, was sampled near Dunkirk, Indiana, USA, the first year of the herbicide's commercialization in 1998. Resistance in the Dunkirk population was confirmed by treating greenhouse-grown seedlings with cloransulam-methyl. ALS activity assays and DNA sequencing were used to identify the resistance mechanism. ALS isolated from plants of the Dunkirk population exhibited a resistant/sensitive (R/S) ratio for cloransulam-methyl of >5000 when compared to ALS activity of populations from Claire City, South Dakota, and V & J Seed Farms. R/S ratios of 4100 and 110 were observed for two other ALS-inhibiting herbicides, chlorimuron and imazaquin, respectively. DNA sequencing revealed that an inferred leucine for tryptophan substitution at amino acid position 574 in ALS was responsible for the observed herbicide resistance. Additionally, DNA sequencing revealed significant variability among common ragweed ALS alleles. Two fragments of ALS were sequenced from three plants each of the Claire City and Dunkirk populations, totaling 688 nucleotide base pairs, of which 72 were polymorphic..

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

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