(Glebionis segetum)

Inhibition of Acetolactate Synthase HRAC Group 2 (Legacy B)

Greece, Larisa region
Corn Marigold (Glebionis segetum) is a dicot weed in the Asteraceae family.  In Greece this weed first evolved resistance to Group 2 (Legacy B) herbicides in 2021 and infests Wheat, and Winter barley.   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 florasulam, imazamox, pyroxsulam, and tribenuron-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 May 19, 2024 )

Common NameCorn Marigold
SpeciesGlebionis segetum
GroupInhibition of Acetolactate Synthase HRAC Group 2 (Legacy B)
Herbicidesflorasulam, imazamox, pyroxsulam, and tribenuron-methyl
LocationGreece, Larisa region
Situation(s)Wheat, and Winter barley
Contributors - (Alphabetically)Ilias Eleftherohorinos 
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Papapanagiotou AP, Spanos T, Zarrougui NE, Livieratos IC, Eleftherohorinos IG (2023) Pro197 and Trp574 substitutions in the acetolactate synthase of corn marigold (Glebionis segetum) and their impact on competitive ability against barley. Weed Technol. 37: 165–173. doi: 10.1017/ wet.2023.17

Abstract Three suspected resistant (R1, R2, and R3) corn marigold populations collected from winter cereal fields located in central Greece were studied to confirm and elucidate the mechanisms of resistance to acetolactate synthase (ALS) inhibitors and their competitive ability against barley. Whole-plant dose–response assays proved that the three suspected R populations were highly cross-resistant to the ALS inhibitors tribenuron, pyroxsulam þ florasulam, and imazamox, whereas their control with synthetic auxin plus ALS inhibitors co-formulated mixtures was increased in the order of tritosulfuron þ dicamba < florasulam þ clopyralid < tribenuron þ mecoprop-P < florasulam þ aminopyralid. The ALS gene sequence revealed a point mutation in 11 plants of the R1, R2, and R3 populations, which resulted in the substitution of Pro-197-Thr or Trp-574-Leu. By contrast, all three sequenced plants of the susceptible (S) population were found with the wild-type allele encoding Pro-197 and Trp-574. This is the first report of ALS-inhibitor resistance in corn marigold. The competition study between barley and four densities of the S, R2, or R3 populations indicated similar biomass rates for all three populations, suggesting lack of association between the competitive ability of the R populations and the target-site resistance mechanism, which was also confirmed by the similar biomass reduction rates of barley grown in competition with S or R populations.

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Confirmation Tests

Greenhouse, and Laboratory trials comparing a known susceptible Corn Marigold biotype with this Corn Marigold 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 Corn Marigold 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 Corn Marigold from Greece 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 Corn Marigold from Greece please update the database.
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University Of Thessaloniki
Laboratory Of Agronomy
4033 Kensington Pl
Ghessaloniki, 54006
Email Ilias Eleftherohorinos


The Herbicide Resistance Action Committee, The Weed Science Society of America, and weed scientists in Greece have been instrumental in providing you this information. Particular thanks is given to Ilias Eleftherohorinos for providing detailed information.
Herbicide Resistant Corn Marigold Globally
(Glebionis segetum)
Herbicide Resistant Corn Marigold Globally
(Glebionis segetum)
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Herbicide Resistant Corn Marigold Globally
(Glebionis segetum)
#CountryFirstYearSituationActive IngredientsSite of Action
1 GreeceGreece 2021 Wheat, and Winter barley florasulam, imazamox, pyroxsulam, and tribenuron-methyl 19 Inhibition of Acetolactate Synthase ( HRAC Group 2 (Legacy B)
2358Glebionis segetumCorn Marigold28272
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PERMISSION MUST BE OBTAINED FIRST if you intend to base a significant portion of a scientific paper on data derived from this site. Citation:
Heap, I.  The International Herbicide-Resistant Weed Database.  Online.  Thursday, July 18, 2024 .  Available Copyright © 1993- 2024 All rights reserved. Fair use of this material is encouraged. Proper citation is requested.