REDROOT PIGWEED (Amaranthus retroflexus) with GROUP B/2 resistance: (INHIBITION OF ACETOLACTATE SYNTHASE ) Inhibition of Acetolactate Synthase
MUTATION: SERINE 653 to THREONINE
Redroot Pigweed (Amaranthus retroflexus) 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.		Redroot Pigweed

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

REFERENCES

Chen, J., Z. Huang, C. Zhang, H. Huang, S. Wei, J. Chen, and X. Wang. 2015. Molecular basis of resistance to imazethapyr in redroot pigweed (Amaranthus retroflexus L.) populations from China. . Pesticide Biochemistry and Physiology 124 : 43 - 47.

Three putative resistant Amaranthus retroflexus L. populations were collected in Heilongjiang province in China. Whole plant bioassays indicated high resistance (RI > 10) to imazethapyr in the three populations. In vitro acetolactate synthase (ALS) assays revealed that ALS from populations H3, H17 and H39 was less sensitive to imazethapyr inhibition compared to the susceptible population H76. The half-maximal inhibitory concentration (I₅₀) values for H3, H17 and H39 were 14.83, 15.27 and 268 times greater, respectively, than that of the susceptible population H76. Three nucleotide mutations resulted in three known resistance-endowing amino acid substitutions, Ala-205-Val, Trp-574-Leu and Ser-653-Thr in the three resistant populations respectively. Therefore, ALS target-site mutations in resistant A. retroflexus could be responsible for imazethapyr resistance..

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

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