SMALLFLOWER UMBRELLA SEDGE (Cyperus difformis) with GROUP B/2 resistance: (INHIBITION OF ACETOLACTATE SYNTHASE ) Inhibition of Acetolactate Synthase
MUTATION: PROLINE 197 to SERINE
Smallflower Umbrella Sedge (Cyperus difformis) is a monocot plant in the cyperaceae family. A single amino acid substitution from Proline 197 to Serine has led to resistance to Inhibition of Acetolactate Synthase as indicated in the table below.		Smallflower Umbrella Sedge

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

Ntoanidou, S., N. Kaloumenos, G. Diamantidis, P. Madesis, and I. Eleftherohorinos. 2016. Molecular basis of Cyperus difformis cross-resistance to ALS-inhibiting herbicides. . Pesticide Biochemistry and Physiology 127 : 38 - 45.

Applications of 64 times higher rates of azimsulfuron and halosulfuron-methyl failed to reduce by 50% growth of 10 putative resistant (R) Cyperus difformis (smallflower umbrella-sedge) populations collected from rice fields located in Northern Greece. However, the growth rate of the susceptible (S) population was reduced by 50% by 1/4 of the recommended rate of both herbicides. The als gene sequencing identified point mutations at Pro-197 position, leading to amino acid substitution by Ala or Ser of the ALS enzyme. The in vitro activity of the ALS enzyme indicated that the I₅₀ values (herbicide concentration required for 50% reduction of the ALS activity) ranged from 10.7 to 55.5 μM azimsulfuron and from 6.7 to 50.6 μM halosulfuron-methyl, whereas the respective values for the S population were 0.09 and 0.11 μM. These results strongly support that cross-resistance of 10 C. difformis populations was due to point mutations of the als gene, which resulted in a less-sensitive ALS enzyme. This study reports the presence of a 1240 bp intron in the C. difformis als gene with the Pro-197 point mutations near the splice junction..

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

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