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Effect of Glyphosate Application on Foliar Diseases in Glyphosate-Tolerant Alfalfa

August 2012 , Volume 96 , Number  8
Pages  1,104 - 1,110

Deborah A. Samac, United States Department of Agriculture–Agricultural Research Service, Plant Science Research Unit, and Department of Plant Pathology, University of Minnesota, St. Paul 55108; and Dawn Foster-Hartnett, Department of Plant Pathology, University of Minnesota

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Accepted for publication 27 February 2012.

Glyphosate, the active ingredient in Roundup herbicide, inhibits 5-enol-pyruvyl shikimate 3-phophate synthase (EPSPS), an enzyme found in plants, fungi, and bacteria. Plants engineered for glyphosate tolerance with a glyphosate-insensitive EPSPS take up and translocate the herbicide throughout the plant. In greenhouse experiments, we found that application of glyphosate at the recommended field application rate completely controlled alfalfa rust (Uromyces striatus) on 4-week-old plants inoculated with the fungus 3 days after glyphosate treatment. Control was effective in all seven cultivars tested. The level of protection declined with time after application, indicating that control transitory and protection declined with time after inoculation, suggesting that protective treatments have fungistatic activity. Complete control of rust was obtained when glyphosate was applied up to 10 days after inoculation with rust spores, indicating that the herbicide also has curative activity. Treatment increased protection from anthracnose, caused by Colletotrichum trifolii, a hemibiotrophic pathogen, and reduced symptom severity for spring black stem and leaf spot, caused by Phoma medicaginis, a necrotrophic pathogen. These results indicate that glyphosate could be used to help manage foliar diseases in glyphosate-tolerant alfalfa.

This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 2012.