Weed Science (2015) 63, 561-568

Parsa Tehranchian, Dilpreet S. Riar, Jason K. Norsworthy, Vijay Nandula, Scott McElroy, Shu Chen and Robert C. Scott (2015)
ALS-resistant smallflower umbrella sedge (Cyperus difformis) in Arkansas rice: Physiological and molecular basis of resistance
Weed Science 63 (3), 561-568
Abstract: Smallflower umbrella sedge is a problematic weed in direct-seeded rice in the midsouthern United States. It recently has evolved resistance to the acetolactate synthase (ALS) –inhibiting herbicide halosulfuron in Arkansas rice. Studies were conducted (1) to determine if the resistant biotype is cross resistant to other ALS-inhibiting herbicides, (2) to evaluate alternative herbicide control options, and (3) to determine the mechanism of resistance. Whole-plant bioassay revealed that halosulfuron-resistant plants were not controlled by bispyribac–sodium, imazamox, and penoxsulam at the labeled field rate of each herbicide. The level of resistance to these herbicides, based on the lethal dose needed to kill 50% of plants (LD₅₀) was > 15-fold compared to a susceptible biotype. Both biotypes were controlled >96% with bentazon and propanil and < 23% with quinclorac, thiobencarb, and 2,4-D. Hence, effective control measures exist albeit, the number of herbicide options appear limited. Based on in vitro ALS enzyme assays, altered target site is the mechanism of resistance to halosulfuron and imazamox. Massively parallel sequencing with the use of the Illumina HiSeq detected an amino acid substitution of Pro₁₉₇-to-His in the resistant biotype that is consistent with ALS-inhibiting herbicide resistance in other weed species.
(The abstract is excluded from the Creative Commons licence and has been copied with permission by the publisher.)
Link to article at publishers website
Database assignments for author(s): Vijay K. Nandula, Dilpreet S. Riar

Research topic(s) for pests/diseases/weeds:
pesticide resistance of pest

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Pest and/or beneficial records:

Beneficial	Pest/Disease/Weed	Crop/Product	Country	Quarant.
	Cyperus difformis (weed)	Rice (Oryza)	U.S.A. (mid S)