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1 April 2011 Detection of Sourgrass (Digitaria insularis) Biotypes Resistant to Glyphosate in Brazil
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Sourgrass is a perennial weed infesting annual and perennial crops in Brazil. Three biotypes (R1, R2, and R3) of sourgrass suspected to be glyphosate-resistant (R) and another one (S) from a natural area without glyphosate application, in Brazil, were tested for resistance to glyphosate based on screening, dose-response, and shikimic acid assays. Both screening and dose-response assays confirmed glyphosate resistance in the three sourgrass biotypes. Dose-response assay indicated a resistance factor of 2.3 for biotype R1 and 3.9 for biotypes R2 and R3. The hypothesis of a glyphosate resistance was corroborated on the basis of shikimic acid accumulation, where the S biotype accumulated 3.3, 5.0, and 5.7 times more shikimic acid than biotypes R1, R2, and R3, respectively, 168 h after treatment with 157.50 g ae ha−1 of glyphosate. There were no differences in contact angle of spray droplets on leaves and spray retention, indicating that differential capture of herbicide by leaves was not responsible for resistance in these biotypes. The results confirmed resistance of sourgrass to glyphosate in Brazil.

Nomenclature: Glyphosate; sourgrass, Digitaria insularis (L.) Mez ex Ekman, TRCIN

Weed Science Society of America
Leonardo Bianco de Carvalho, Hugo Cruz-Hipolito, Fidel González-Torralva, Pedro Luis da Costa Aguiar Alves, Pedro Jacob Christoffoleti, and Rafael De Prado "Detection of Sourgrass (Digitaria insularis) Biotypes Resistant to Glyphosate in Brazil," Weed Science 59(2), 171-176, (1 April 2011).
Received: 6 August 2010; Accepted: 1 November 2010; Published: 1 April 2011

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