(Schoenoplectus juncoides)

Inhibition of Acetolactate Synthase HRAC Group 2 (Legacy B)

Japan, Hokkaido
Rock Bulrush (Schoenoplectus juncoides) is a monocot weed in the Cyperaceae family.  In Japan this weed first evolved resistance to Group 2 (Legacy B) herbicides in 1996 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, cyclosulfamuron, ethoxysulfuron, imazosulfuron, and pyrazosulfuron-ethyl 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.

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QUIK STATS (last updated Dec 28, 2013 )

Common NameRock Bulrush
SpeciesSchoenoplectus juncoides
GroupInhibition of Acetolactate Synthase HRAC Group 2 (Legacy B)
Herbicidesbensulfuron-methyl, cyclosulfamuron, ethoxysulfuron, imazosulfuron, and pyrazosulfuron-ethyl
LocationJapan, Hokkaido
Contributors - (Alphabetically)Kazuyuki Itoh 
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Tohru Tominaga
YAMADA Y, TOMINAGA T & OHSAKO T (2013). Microsatellite variability of sulfonylurea-resistant and susceptible populations of Schoenoplectus juncoides (Cyperaceae) in Kinki, Japan. Weed Research 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 (HS = 0.168) was lower than those for SU-S (HS = 0.256) and mixed (HS = 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.

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Toshiyuki Imaizumi

Genetic diversity within and between sulfonylurearesistant and susceptible populations of
Schoenoplectus juncoides (synonym - Scirpus juncoides) in Japan

To reveal the effects of herbicide selection on genetic diversity in the outcrossing weed species Schoenoplectus juncoides (synonym - Scirpus juncoides), six sulfonylurea-resistant (SU-R) and eight sulfonylurea-susceptible (SU-S) populations were analyzed 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 HS = 0.161, and the total genetic diversity was HT = 0.271. Although the HS of the SU-R populations (0.051) was lower than that of the SU-S populations, the HT 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.

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Confirmation Tests

Field, 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.

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

The mechanism of resistance for this biotype is either unknown or has not been entered in the database.  If you know anything about the mechanism of resistance for this biotype then please update the database.
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 Japan please update the database.
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Kobe University
Graduate School of Agricultural Science
1-1 Rokkodaicho
Kobe, 657-0013, Hyogo
Email Kazuyuki Itoh


The Herbicide Resistance Action Committee, The Weed Science Society of America, and weed scientists in Japan have been instrumental in providing you this information. Particular thanks is given to Kazuyuki Itoh for providing detailed information.
Herbicide Resistant Rock Bulrush Globally
(Schoenoplectus juncoides)
Herbicide Resistant Rock Bulrush Globally
(Schoenoplectus juncoides)
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Herbicide Resistant Rock Bulrush Globally
(Schoenoplectus juncoides)
#CountryFirstYearSituationActive IngredientsSite of Action
1 JapanJapan 1996 Rice bensulfuron-methyl, cyclosulfamuron, ethoxysulfuron, imazosulfuron, and pyrazosulfuron-ethyl 25 Inhibition of Acetolactate Synthase ( HRAC Group 2 (Legacy B)
196Schoenoplectus juncoidesRock Bulrush5131
2 South KoreaSouth Korea 2001 Rice azimsulfuron, bensulfuron-methyl, cyclosulfamuron, ethoxysulfuron, halosulfuron-methyl, imazosulfuron, and pyrazosulfuron-ethyl 27 Inhibition of Acetolactate Synthase ( HRAC Group 2 (Legacy B)
196Schoenoplectus juncoidesRock Bulrush5044
Literature about Similar Cases

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