ROCK BULRUSH (Schoenoplectus juncoides) with GROUP B/2 resistance: (INHIBITION OF ACETOLACTATE SYNTHASE ) Inhibition of Acetolactate Synthase
MUTATION: ASPARTATE 376 to GLUTAMATE
Rock Bulrush (Schoenoplectus juncoides) is a monocot plant in the cyperaceae family. A single amino acid substitution from Aspartate 376 to Glutamate has led to resistance to Inhibition of Acetolactate Synthase as indicated in the table below.		Rock Bulrush

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

REFERENCES

Sada, Y., H. Ikeda, S. Yamato, and S. Kizawa. 2013. Characterization of sulfonylurea-resistant Schoenoplectus juncoides having a target-site Asp₃₇₆Glu mutation in the acetolactate synthase.. Pesticide Biochemistry and Physiology 107 : 106 - 111.

Schoenoplectus juncoides, a noxious weed for paddy rice, is known to become resistant to sulfonylurea (SU) herbicides by a target-site mutation in either of the two acetolactate synthase (ALS) genes (ALS1 and ALS2). SU-resistant S. juncoides plants having an Asp₃₇₆Glu mutation in ALS2 were found from a paddy rice field in Japan, but their resistance profile has not been quantitatively investigated. In this study, dose–response of the SU-resistant accession was compared with that of a SU-susceptible accession at in vivo whole-plant level as well as at in vitro enzymatic level.In whole-plant tests, resistance factors (RFs) based on 50% growth reduction (GR₅₀) for imazosulfuron (ISF), bensulfuron-methyl (BSM), metsulfuron-methyl (MSM), bispyribac-sodium (BPS), and imazaquin (IMQ) were 176, 40, 14, 5.2 and 1.5, respectively. Thus, the accession having an Asp₃₇₆Glu mutation in ALS2 was highly resistant to the three SU herbicides and moderately resistant to BPS, but was not substantially resistant to IMQ. This is slightly different from the earlier results reported from other weeds with an Asp₃₇₆Glu mutation, in which the mutation confers resistance to broadly all the chemical classes of ALS-inhibiting herbicides.In enzymatic tests, ALS2 of S. juncoides was expressed in E. coli; the resultant ALS2 was subjected to an in vitro assay. RFs of the mutated ALS2 based on 50% enzymatic inhibition (I₅₀) for ISF, BSM, MSM, BPS, and IMQ were 3699, 2438, 322, 80, and 4.8, respectively. The RFs of ALS2 were highly correlated with those of the whole-plant; this suggests that the Asp₃₇₆Glu mutation in ALS2 is a molecular basis for the whole-plant resistance. The presence of two ALS genes in S. juncoides can at least partially explain why the whole-plant RFs were less than those of the expressed ALS2 enzymes..

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

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