<b>HRAC Group 2</b> <font size='2'> (Legacy B) </font> resistant Schoenoplectus juncoides from China

INTERNATIONAL HERBICIDE-RESISTANT WEED DATABASE

HRAC GROUP 2 (LEGACY B) RESISTANT ROCK BULRUSH
(Schoenoplectus juncoides)

Inhibition of Acetolactate Synthase HRAC Group 2 (Legacy B)

China, Liaoning

INTRODUCTION		ROCK BULRUSH
Rock Bulrush (Schoenoplectus juncoides) is a monocot weed in the Cyperaceae family. In China this weed first evolved resistance to Group 2 (Legacy B) herbicides in 2024 and infests Rice. Group 2 (Legacy B) herbicides are known as Inhibition of Acetolactate Synthase (Inhibition of Acetolactate Synthase ). Research has shown that these particular biotypes are resistant to bensulfuron-methyl and they may be cross-resistant to other Group 2 (Legacy B) herbicides. The 'Group' letters/numbers that you see throughout this web site refer to the classification of herbicides by their site of action. To see a full list of herbicides and HRAC herbicide classifications click here.

QUIK STATS (last updated Aug 11, 2024 )
Common Name	Rock Bulrush
Species	Schoenoplectus juncoides
Group	Inhibition of Acetolactate Synthase HRAC Group 2 (Legacy B)
Herbicides	bensulfuron-methyl
Location	China, Liaoning
Year	2024
Situation(s)	Rice
Contributors - (Alphabetically)	Mingshan Ji
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ACADEMIC ASPECTS

Confirmation Tests

Greenhouse, and Laboratory trials comparing a known susceptible Rock Bulrush biotype with this Rock Bulrush biotype have been used to confirm resistance. For further information on the tests conducted please contact the local weed scientists that provided this information.

Genetics

Genetic studies on HRAC Group 2 resistant Rock Bulrush have not been reported to the site. There may be a note below or an article discussing the genetics of this biotype in the Fact Sheets and Other Literature

Mechanism of Resistance

Studies on the mechanism of resistance of Group 2 (Legacy B) resistant Rock Bulrush from China indicate that resistance is due to an altered target site. There may be a note below or an article discussing the mechanism of resistance in the Fact Sheets and Other Literature

Relative Fitness

There is no record of differences in fitness or competitiveness of these resistant biotypes when compared to that of normal susceptible biotypes. If you have any information pertaining to the fitness of Group 2 (Legacy B) resistant Rock Bulrush from China please update the database.

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CONTRIBUTING WEED SCIENTISTS

MINGSHAN JI

Associate Professer Shenyang Agriculture University Plant Protection Argicultural Research and Extension Center 121 Northville Rd, Shenyang, 110161, Liaoning Province China Email Mingshan Ji

ACKNOWLEDGEMENTS
The Herbicide Resistance Action Committee, The Weed Science Society of America, and weed scientists in China have been instrumental in providing you this information. Particular thanks is given to Mingshan Ji for providing detailed information.

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Herbicide Resistant Rock Bulrush Globally
(Schoenoplectus juncoides)

Country

FirstYear

Situation

Active Ingredients

Site of Action

China

2024

Rice

bensulfuron-methyl

Inhibition of Acetolactate Synthase ( HRAC Group 2 (Legacy B)

Japan

1996

Rice

bensulfuron-methyl, cyclosulfamuron, ethoxysulfuron, imazosulfuron, and pyrazosulfuron-ethyl

Inhibition of Acetolactate Synthase ( HRAC Group 2 (Legacy B)

South Korea

2001

Rice

azimsulfuron, bensulfuron-methyl, cyclosulfamuron, ethoxysulfuron, halosulfuron-methyl, imazosulfuron, and pyrazosulfuron-ethyl

Inhibition of Acetolactate Synthase ( HRAC Group 2 (Legacy B)

Literature about Similar Cases

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Yamada, Y. ; Tominaga, T. ; Ohsako, T.. 2013. Microsatellite variability of sulfonylurea-resistant and susceptible populations of Schoenoplectus juncoides (Cyperaceae) in Kinki, Japan. Weed Research (Oxford) 53 : 429 - 439.

Schoenoplectus juncoides is one of the most harmful weeds found in East Asian paddy fields. Recent emergence of biotypes that are resistant to the herbicide sulfonylurea (SU) has made weed control difficult. To examine the effect of the evolution of this herbicide resistance on genetic diversity within local populations, we investigated microsatellite variability within and among paddy field populations of S. juncoides in Kinki, Japan. In vivo assay of acetolactate synthase activity and root elongation assay in the presence of SU revealed that of 21 populations, five were sulfonylurea-susceptible (SU-S) and eight were completely sulfonylurea-resistant (SU-R). The remaining eight populations were a mixture of SU-S and SU-R individuals. The average gene diversity for SU-R populations (H_S=0.168) was lower than those for SU-S (H_S=0.256) and mixed (H_S=0.209) populations, but the difference was not significant. This indicates that positive selection for SU-R phenotype did not cause a genome-wide reduction in genetic diversity. Genetic differentiation among S. juncoides populations was higher than that observed for most weed species studied previously. Although populations in neighbouring paddy fields showed a high level of differentiation, Bayesian clustering analyses suggested that some level of gene flow occurs among them and that the genetic exchange or colonisation between neighbouring populations could contribute to the geographical expansion of the resistant allele..

Yamato, S. ; Sada, Y. ; Ikeda, H.. 2013. Characterization of acetolactate synthase from sulfonylurea herbicide-resistant Schoenoplectus juncoides. Weed Biology and Management 13 : 104 - 113.

Ten accessions of sulfonylurea-resistant Schoenoplectus juncoides were collected from paddy fields in Japan. In order to characterize acetolactate synthase from sulfonylurea-resistant S. juncoides, acetolactate synthase amino acid substitutions, whole-plant growth inhibition and acetolactate synthase enzyme inhibition were examined. Schoenoplectus juncoides has two acetolactate synthase genes (ALS1 and ALS2). The sulfonylurea-resistant accessions harbored amino acid substitutions at Pro197 or Trp574 in either ALS1 or ALS2 (the amino acid number is standardized to the Arabidopsis thaliana sequence). The whole plants of all the sulfonylurea-resistant accessions showed resistance to imazosulfuron. The resistance level depended on the altered amino acid residues in acetolactate synthase. The acetolactate synthase enzyme that was partially purified from all the sulfonylurea-resistant accessions was less sensitive to imazosulfuron, compared to the susceptible accession, suggesting that the resistance is related to the altered acetolactate synthase enzyme. In addition, the concentration-response inhibition of acetolactate synthase activity by imazosulfuron in the sulfonylurea-resistant accessions was remarkably different with the presence of an amino acid substitution in either ALS1 or ALS2. Furthermore, the concentration-response inhibition of acetolactate synthase activity in the sulfonylurea-resistant accessions with a P197S, P197T or W574L mutation showed a double-sigmoid curve. The regression analysis of enzyme inhibition suggested that the abundance ratio of ALS1 to ALS2 enzymes was approximately 70:30%, with a range of±15%. Taken together, these results suggest that the resistance of sulfonylurea-resistant accessions of S. juncoides is related to altered acetolactate synthase in either ALS1 or ALS2, although the abundance of the altered acetolactate synthase in the plants is different among the sulfonylurea-resistant accessions..

Imaizumi, T. ; Kataoka, Y. ; Ogata, S. ; Uchino, A.. 2013. Genetic diversity within and between sulfonylurea-resistant and susceptible populations of Schoenoplectus juncoides in Japan. Weed Research (Oxford) 53 : 290 - 298.

To reveal the effects of herbicide selection on genetic diversity in the outcrossing weed species Schoenoplectus juncoides, six sulfonylurea-resistant (SU-R) and eight sulfonylurea-susceptible (SU-S) populations were analysed using 40 polymorphic inter-simple sequence repeat loci. The plants were collected from three widely separated regions: the Tohoku, Kanto and Kyushu districts of Japan. Genetic diversity values (Nei's gene diversity, h) within each SU-S population ranged from h=0.125 to h=0.235. The average genetic diversity within the SU-S populations was H_S=0.161, and the total genetic diversity was H_T=0.271. Although the H_S of the SU-R populations (0.051) was lower than that of the SU-S populations, the H_T of the SU-R populations (0.202) was comparable with that of the SU-S populations. Most of the genetic variation was found within the region for both the SU-S and SU-R populations (88% of the genetic variation respectively). Two of the SU-R populations showed relatively high genetic diversity (h=0.117 and 0.161), which were comparable with those of the SU-S populations. In contrast, the genetic diversity within four SU-R populations was much lower (from h=0 to 0.018) than in the SU-S populations. The results suggest that selection by sulfonylurea herbicides has decreased genetic diversity within some SU-R populations of S. juncoides. The different level of genetic diversity in the SU-R populations is most likely due to different levels of inbreeding in the populations..

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..

Sada, Y., H. Ikeda, and S. Kizawa. 2013. Resistance levels of sulfonylurea-resistant Schoenoplectus juncoides (Roxb.) Palla with various Pro197 mutations in acetolactate synthase to imazosulfuron, bensulfuron-methyl, metsulfuron-methyl and imazaquin-ammonium.. Weed Biology and Management 13 : 53 - 61.

An investigation, using herbicidal pot tests in a greenhouse condition, was conducted to determine the whole-plant dose–response relationships to several acetolactate synthase (ALS)- inhibiting herbicides of sulfonylurea (SU)-resistant Schoenoplectus juncoides with various Pro197 mutations in ALS that was collected from Japanese rice paddy fields.All the tested SU-resistant accessions with a Pro197 mutation were highly resistant to two commonly used SU herbicides (imazosulfuron and bensulfuron-methyl), but were much less resistant to another SU herbicide, metsulfuron-methyl, and were substantially not resistant to imazaquin-ammonium. These cross-resistance patterns have been known previously in fragments of S. juncoides and other weed species and were comprehensively confirmed in this study with a whole set of Pro197 mutations.The analyses of resistance levels, based on ED90 values, newly showed that different accessions with a common amino acid substitution in ALS1 showed similar responses to these herbicides (confirmed with four amino acid substitutions), that the rankings of resistance levels that were conferred by various Pro197 mutations in ALS1 differed among the SU herbicides and that the resistance levels of the ALS2-mutated accessions were higher than, lower than or similar to those of the corresponding ALS1-mutated accessions, depending on the compared pair, but the deviation patterns were generally similar among the SU herbicides in each compared pair.The final finding might suggest that the abundance of ALS2 is not as stable as that of ALS1. In addition, as a result of these new findings, together with expected further research, a suggested possibility is that substituting amino acids at Pro197 generally could be estimated by plotting each accession’s ED90 values of imazosulfuron and bensulfuron-methyl in a two-dimensional graph..

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