TALL WATERHEMP (Amaranthus tuberculatus (=A. rudis)) with GROUP B/2 resistance: (INHIBITION OF ACETOLACTATE SYNTHASE ) Inhibition of Acetolactate Synthase
MUTATION: SERINE 653 to THREONINE
Tall Waterhemp (Amaranthus tuberculatus (=A. rudis)) is a dicot plant in the amaranthaceae family. A single amino acid substitution from Serine 653 to Threonine has led to resistance to Inhibition of Acetolactate Synthase as indicated in the table below.		Tall Waterhemp

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

REFERENCES

Patzoldt, W. L. ; Tranel, P. J.. 2007. Multiple ALS mutations confer herbicide resistance in waterhemp (Amaranthus tuberculatus). Weed Science 55 : 421 - 428.

Herbicide responses among Illinois waterhemp half-sib populations were studied. Several of these populations exhibited varying responses to imazethapyr and thifensulfuron, two acetolactate synthase (ALS)-inhibiting herbicides. Plants from two waterhemp populations were identified to be resistant to imazethapyr but susceptible to chlorimuron using a nondestructive leaf-disc assay. Sequencing of the ALS gene revealed that imazethapyr-resistant waterhemp plants from both populations had inferred amino acid substitutions at position 653 of ALS. Depending on the population, serine at position 653 of ALS was substituted with either asparagine (S653N) or threonine (S653T). Waterhemp lines were derived from each population to create uniformly imidazolinone-resistant (IR) waterhemp biotypes, designated IR-62 and IR-101. The ALS-inhibitor responses of each IR biotype were compared with a previously identified ALS inhibitor-resistant biotype with a tryptophan to leucine substitution at position 574 (W574L) and a herbicide-susceptible control. Whole-plant rate-response experiments with waterhemp biotypes containing W574L, S653N or S653T mutations indicated that each biotype was resistant to imazethapyr, but only the biotype with a W574L mutation was resistant to thifensulfuron. In vitro ALS-activity assays revealed unique patterns of cross resistance among protein extracts derived from each biotype in response to imazethapyr, thifensulfuron, cloransulam and pyrithiobac. Three different forms of target-site-based resistance to ALS inhibitors were identified in waterhemp..

Patzoldt, W. L. And P. Tranel J.. 2001. ALS mutations conferring herbicide resistance in waterhemp. Proceedings of the North Central Weed Science Society 56 : 67.

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

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