(Zea mays ssp. mexicana)

Inhibition of Acetyl CoA Carboxylase HRAC Group 1 (Legacy A)

Mexican teosinte (Zea mays ssp. mexicana) is a monocot weed in the Poaceae family.  In France this weed first evolved resistance to Group 1 (Legacy A) herbicides in 2020 and infests Corn (maize), Soybean, and Sunflower.   Group 1 (Legacy A) herbicides are known as Inhibition of Acetyl CoA Carboxylase (Inhibition of Acetyl CoA Carboxylase ).  Research has shown that these particular biotypes are resistant to cycloxydim and they may be cross-resistant to other Group 1 (Legacy A) 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 Oct 08, 2021 )

Common NameMexican teosinte
SpeciesZea mays ssp. mexicana
GroupInhibition of Acetyl CoA Carboxylase HRAC Group 1 (Legacy A)
Situation(s)Corn (maize), Soybean, and Sunflower
Contributors - (Alphabetically)Christophe Délye 
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Christophe Délye

Adaptive introgression from maize has facilitated the establishment of teosinte as a noxious weed in Europe. Valérie Le Corre, Mathieu Siol, Yves Vigouroux, Maud I. Tenaillon, and Christophe Délye

PNAS October 13, 2020 117 (41) 25618-25627; first published September 28, 2020;

Global trade has considerably accelerated biological invasions. The annual tropical teosintes, the closest wild relatives of maize, were recently reported as new agricultural weeds in two European countries, Spain and France. Their prompt settlement under climatic conditions differing drastically from that of their native range indicates rapid genetic evolution. We performed a phenotypic comparison of French and Mexican teosintes under European conditions and showed that only the former could complete their life cycle during maize cropping season. To test the hypothesis that crop-to-wild introgression triggered such rapid adaptation, we used single nucleotide polymorphisms to characterize patterns of genetic variation in French, Spanish, and Mexican teosintes as well as in maize germplasm. We showed that both Spanish and French teosintes originated from Zea mays ssp. mexicana race “Chalco,” a weedy teosinte from the Mexican highlands. However, introduced teosintes differed markedly from their Mexican source by elevated levels of genetic introgression from the high latitude Dent maize grown in Europe. We identified a clear signature of divergent selection in a region of chromosome 8 introgressed from maize and encompassing ZCN8, a major flowering time gene associated with adaptation to high latitudes. Moreover, herbicide assays and sequencing revealed that French teosintes have acquired herbicide resistance via the introgression of a mutant herbicide-target gene (ACC1) present in herbicide-resistant maize cultivars. Altogether, our results demonstrate that adaptive crop-to-wild introgression has triggered both rapid adaptation to a new climatic niche and acquisition of herbicide resistance, thereby fostering the establishment of an emerging noxious weed.

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Christophe Délye
Mexican teosinte is non-indigenous in Europe. It has been accidentally introduced in France, and has introgressed the herbicide-resistant ACC1 ACCase allele from herbicide-resistant Duo System® maize. Resistance is present in the field since the end of the 1990s.

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Confirmation Tests

Greenhouse, and Laboratory trials comparing a known susceptible Mexican teosinte biotype with this Mexican teosinte 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 1 resistant Mexican teosinte 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 1 (Legacy A) resistant Mexican teosinte from France 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 1 (Legacy A) resistant Mexican teosinte from France please update the database.
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The Herbicide Resistance Action Committee, The Weed Science Society of America, and weed scientists in France have been instrumental in providing you this information. Particular thanks is given to Christophe Délye for providing detailed information.
Herbicide Resistant Mexican teosinte Globally
(Zea mays ssp. mexicana)
Herbicide Resistant Mexican teosinte Globally
(Zea mays ssp. mexicana)
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Herbicide Resistant Mexican teosinte Globally
(Zea mays ssp. mexicana)
#CountryFirstYearSituationActive IngredientsSite of Action
1 FranceFrance 2020 Corn (maize), Soybean, and Sunflower cycloxydim 17 Inhibition of Acetyl CoA Carboxylase ( HRAC Group 1 (Legacy A)
354Zea mays ssp. mexicanaMexican teosinte21231
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