Pest Management Science (2012) 68, 1164-1170

Heping Han, Qin Yu, Edison Purba, Mei Li, Michael Walsh, Shane Friesen and Stephen B. Powles (2012)
A novel amino acid substitution Ala-122-Tyr in ALS confers high-level and broad resistance across ALS-inhibiting herbicides
Pest Management Science 68 (8), 1164-1170
Abstract:
BACKGROUND: Wild radish, a problem weed worldwide, is a severe dicotyledonous weed in crops. In Australia, sustained reliance on ALS-inhibiting herbicides to control this species has led to the evolution of many resistant populations endowed by any of several ALS mutations. The molecular basis of ALS-inhibiting herbicide resistance in a novel resistant population was studied.
RESULTS: ALS gene sequencing revealed a previously unreported substitution of Tyr for Ala at amino acid position 122 in resistant individuals of a wild radish population (WARR30). A purified subpopulation individually homozygous for the Ala-122-Tyr mutation was generated and characterised in terms of its response to the different chemical classes of ALS-inhibiting herbicides. Whole-plant dose-response studies showed that the purified subpopulation was highly resistant to chlorsulfuron, metosulam and imazamox, with LD₅₀ or GR₅₀ R/S ratio of > 1024, > 512 and > 137 respectively. The resistance to imazypyr was found to be relatively moderate (but still substantial), with LD₅₀ and GR₅₀ R/S ratios of > 16 and > 7.8 respectively. In vitro ALS activity assays showed that Ala-122-Tyr ALS was highly resistant to all tested ALS-inhibiting herbicides.
CONCLUSION: The molecular basis of ALS-inhibiting herbicide resistance in wild radish population WARR30 was identified to be due to an Ala-122-Tyr mutation in the ALS gene. This is the first report of an amino acid substitution at Ala-122 in the plant ALS that confers high-level and broad-spectrum resistance to ALS-inhibiting herbicides, a remarkable contrast to the known mutation Ala-122-Thr endowing resistance to imidazolinone herbicide.
(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): Qin Yu, Stephen B. Powles, Michael J. Walsh

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.
	Raphanus raphanistrum (weed)