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QUIK STATS (last updated Apr 27, 2022 )
NOTES ABOUT THIS BIOTYPE
Pest Management Science - 2022 doi: 10.1002/ps.6940
A novel EPSPS Pro-106-His mutation confers the first case of glyphosate resistance in Digitaria sanguinalis
Marcos Yanniccari1, José Guadalupe Vázquez-García2, Ramón Gigón3, Candelario Palma- Bautista2, Martin Vila-Aiub4, and Rafael De Prado2 1 Chacra Experimental Integrada Barrow (MDA-INTA), National Scientific and Technical Research Council (CONICET), Faculty of Agronomy, National University of La Pampa, Argentina. 2Department of Agroforestry, Plant Biochemistry and Molecular Biology, University of Cordoba, Spain. 3Private Consultant in Weed Control, Argentina. 4 Department of Ecology, IFEVA-CONICET, Faculty of Agronomy, University of Buenos Aires (UBA), Argentina.
BACKGROUND: Digitaria sanguinalis has been identified as a species at high risk of evolving herbicide resistance, but thus far, there are no records of resistance to glyphosate. This species is one of the most common weeds of summer crops in extensive cropping areas in Argentina. This weed shows an extended period of seedling emergence with several overlapping cohorts during spring and summer, and it is commonly controlled with glyphosate. However, a D. sanguinalis population was implicated as a putative glyphosate-resistant biotype based on poor control at recommended glyphosate doses.
RESULTS: The field-collected D. sanguinalis population (Dgs R) from the Rolling Pampas has evolved glyphosate resistance. Differences in plant survival and shikimate levels after field recommended and higher glyphosate doses were evident between Dgs R and the known susceptible (Dgs S) population, and the resistance index was 5.1. No evidence of differential glyphosate absorption, translocation, metabolism, or basal EPSPS activity was found between Dgs S and Dgs R populations; however, a novel EPSPS Pro-106-His point substitution is likely the primary glyphosate resistance endowing mechanism. EPSPS in vitro enzymatic activity demonstrated that an 80-fold higher concentration of glyphosate is required in Dgs R to achieve similar EPSPS activity inhibition as in the Dgs S population.
CONCLUSION: This study reports the first global case of glyphosate resistance in D. sanguinalis. This yet novel transversion at the second position of the EPSPS 106 codon demonstrates the intensity of glyphosate pressure in selecting unexpected glyphosate resistance alleles if they retain EPSPS functionality.
CONTRIBUTING WEED SCIENTISTS
BACKGROUND Crabgrass (Digitaria sanguinalis) is an annual monocotyledonous weed. In recent years, field applications of nicosulfuron have been ineffective in controlling crabgrass populations in Shandong Province, China. To investigate the mechanisms of resistance to nicosulfuron in crabgrass populations, the acetolactate synthase (ALS) gene fragment covering known resistance-confering mutation sites was amplified and sequenced.
RESULTS Dose–response experiments suggested that the resistant population SD13 (R) was highly resistant to nicosulfuron (resistance index R/S = 43.7) compared with the sensitive population SD22 (S). ALS gene sequencing revealed a Trp574Arg substitution in the SD13 population, and no other known resistance-conferring mutations were found. In vitro ALS enzyme assays further confirmed that the SD13 population was resistant to all tested ALS-inhibiting herbicides. The resistance pattern experiments revealed that, compared with SD22, the SD13 population exhibited broad-spectrum resistance to nicosulfuron (43.7-fold), imazethapyr (11.4-fold) and flumetsulam (16.1-fold); however, it did not develop resistance to atrazine, mesotrione and topramezone.
CONCLUSIONS This study demonstrated that Trp574Arg substitution was the main reason for crabgrass resistance to ALS-inhibiting herbicides. To our knowledge, this is the first report of Trp574Arg substitution in a weed species, and is the first report of target-site mechanisms of herbicide resistance for crabgrass.