International Survey of Herbicide-Resistant Weeds

Countries Weeds Herbicides Mutations Graphs References Researchers
(Monochoria vaginalis)

Inhibition of Acetolactate Synthase HRAC Group 2 (Legacy B)

Japan, Ibaraki, Akita
Arrowleafed Monochoria (Monochoria vaginalis) is a monocot weed in the Pontederiaceae family.  In Japan this weed first evolved resistance to Group 2 (Legacy B) herbicides in 1998 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.

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QUIK STATS (last updated Jan 08, 2014 )

Common NameArrowleafed Monochoria
SpeciesMonochoria vaginalis
GroupInhibition of Acetolactate Synthase HRAC Group 2 (Legacy B)
LocationJapan, Ibaraki, Akita
Contributors - (Alphabetically)Satoshi Iwakami, Tohru Tominaga, and Akira Uchino 
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Tohru Tominaga
Takanori Ohsako and Tohru Tominaga.  Nucleotide substitutions in the acetolactate synthase genes of sulfonylurea-resistant biotypes of Monochoria vaginalis (Pontederiaceae). Genes Genet. Syst. (2007) 82, p. 207–215

Some point mutations in acetolactate synthase (ALS) confer resistance to ALSinhibiting herbicides in weeds. To clarify the evolution of the herbicide resistance of Monochoria vaginalis, a weed in rice fields in Japan, the nucleotide sequences of four genes encoding ALS were surveyed in five sulfonylurea-resistant (SU-R) and five sulfonylurea-susceptible (SU-S) biotypes. In the ALS1 gene, two SU-R biotypes showed nucleotide substitutions changing Pro197 to Ser and Leu, respectively. In a different gene, ALS3, three other SU-R biotypes showed either of the two nonsynonymous nucleotide substitutions seen in ALS1. Only two biotypes geographically located distantly from each other shared the same mutation conferring SU resistance in the same gene. These patterns of nucleotide substitutions indicate that the SU-R phenotype was acquired independently by different biotypes. Nucleotide diversity values of the genes showing SU-R mutations were higher than those of ALS2 lacking any SU-R mutation and of a putative pseudogene, ALS4. This result suggests that the maintenance of nucleotide variability within target genes provides an opportunity for the evolution of SU-R phenotypes by herbicide-driven selection for mutations conferring resistance.

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Confirmation Tests

Field, and Greenhouse trials comparing a known susceptible Arrowleafed Monochoria biotype with this Arrowleafed Monochoria 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 Arrowleafed Monochoria 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 Arrowleafed Monochoria from Japan please update the database.
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Weed Scientist
University of Tsukuba
Faculty of Life and Environmental Sciences
1-1-1 Tennoudai
Tsukuba, 305-8577, Ibaraki
Email Satoshi Iwakami
Kyoto University
Graduate School of Agriculture
Kyoto, 606-8502, Kyoto
Email Tohru Tominaga
Weed Scientist
NARO Agricultural Research Center
Graduate School of Agriculture
3-1-1 Kannondai
Tsukuba, 305-8666, Ibaraki
Email Akira Uchino


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 Satoshi Iwakami, Tohru Tominaga, and Akira Uchino for providing detailed information.
Herbicide Resistant Arrowleafed Monochoria Globally
(Monochoria vaginalis)
Herbicide Resistant Arrowleafed Monochoria Globally
(Monochoria vaginalis)
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Herbicide Resistant Arrowleafed Monochoria Globally
(Monochoria vaginalis)
#CountryFirstYearSituationActive IngredientsSite of Action
1 ChinaChina 2010 Rice bensulfuron-methyl 9 Inhibition of Acetolactate Synthase ( HRAC Group 2 (Legacy B)
202Monochoria vaginalisArrowleafed Monochoria5655
2 IndonesiaIndonesia 2022 Rice bensulfuron-methyl, bispyribac-sodium, and penoxsulam 22 Inhibition of Acetolactate Synthase ( HRAC Group 2 (Legacy B)
202Monochoria vaginalisArrowleafed Monochoria27274
3 JapanJapan 1998 Rice bensulfuron-methyl 25 Inhibition of Acetolactate Synthase ( HRAC Group 2 (Legacy B)
202Monochoria vaginalisArrowleafed Monochoria7764
4 South KoreaSouth Korea 1999 Rice bensulfuron-methyl 27 Inhibition of Acetolactate Synthase ( HRAC Group 2 (Legacy B)
202Monochoria vaginalisArrowleafed Monochoria151
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