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TALL WATERHEMP (Amaranthus tuberculatus (syn. rudis))
with GROUP B/2 resistance: (ALS INHIBITORS)
Inhibition of acetolactate synthase ALS (acetohydroxyacid synthase AHAS)

MUTATION: TRYPTOPHAN 574 to LEUCINE

Tall Waterhemp (Amaranthus tuberculatus (syn. rudis)) is a dicot plant in the amaranthaceae family. A single amino acid substitution from Tryptophan 574 to Leucine has led to resistance to ALS inhibitors as indicated in the table below.

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Tall Waterhemp

Chemistry	Example	Resistance
Imidazolinones	Imazethapyr	Resistant > 10 fold
Pyrimidinylthiobenzoates	Bispyribac-Na	Not Determined
Sulfonylureas	Chlorsulfuron	Resistant > 10 fold
Triazolopyrimidines	Chloransulam-methyl	Resistant > 10 fold
Sulfonylaminocarbonyltriazolinone	Flucarbazone-Na	Not Determined

NOTES

REFERENCES

Foes, M. J., Liu LiXin, P. Tranel J., L. Wax M., and E. Stoller W. (1998). A biotype of common waterhemp (Amaranthus rudis) resistant to triazine and ALS herbicides. Weed Science , 46 (5) : 514-520.

An A. rudis biotype resistant to triazine and acetolactate synthase (ALS)-inhibiting herbicides was isolated from Bond County, Illinois, USA, in Autumn 1996. In greenhouse experiments, the Bond County biotype required >1000 times the amount of imazethapyr needed by a susceptible biotype to reduce growth by 50%. Cross resistance to thifensulfuron (a sulfonylurea) and flumetsulam (a triazolopyrimidine sulfonanilide) was also detected. In vivo enzyme assays showed that ALS was 20-, >8-, and 68-fold less sensitive than the susceptible biotype ALS to imazethapyr, thifensulfuron and flumetsulam, respectively. The Bond County biotype required >20 kg ha-1 atrazine to inhibit growth by 50%. In chlorophyll fluorescence assays, 10 M did not affect photosynthesis in the Bond County biotype, whereas 100 nM was inhibitory in the susceptible control. Sequencing regions of the genes encoding ALS and D1 proteins identified a glycine for serine substitution at residue 264 of the D1 protein, and a leucine for tryptophan substitution at residue 569 of ALS. These substitutions are thought to be the molecular basis of triazine and ALS resistance.

Woodworth, A. R., B. Rosen A., and P. Bernasconi. (1996). Broad range resistance to herbicides targeting acetolactate synthase (ALS) in a field isolate of Amaranthus sp. is conferred by a Trp to Leu mutation in the ALS gene (Accession No. U55852) (PGR96-051). Plant Physiology , 111 () : 1353.