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1 May 2003 Glyphosate and shade effects on glyphosate-resistant soybean defense response to Sclerotinia sclerotiorum
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Application of glyphosate in combination with planting soybeans in narrow rows is an effective practice for management of weeds in glyphosate-resistant soybean. Farmers in Michigan reported higher levels of Sclerotinia stem rot (caused by Sclerotinia sclerotiorum) in fields of glyphosate-resistant soybean. Studies were conducted to determine if glyphosate or shading reduced the defense response of glyphosate-resistant soybean to S. sclerotiorum. Glyphosate caused shikimate accumulation in glyphosate-susceptible cultivar GL2415 but not in glyphosate-resistant cultivar GL2600RR. Ethylacetate extracts containing the plant defense compound glyceollin inhibited S. sclerotiorum hyphae in a rate-dependent manner. Glyphosate had no effect on either baseline or induced levels of glyceollin in glyphosate-resistant soybean, indicating that glyphosate did not impair plant defense responses to S. sclerotiorum. Shade levels of 60 and 90% in the greenhouse did not inhibit the induction of glyceollin synthesis. Glyphosate herbicide and shading did not affect the glyphosate-resistant soybean defense response to S. sclerotiorum.

Nomenclature: Glyphosate; lactofen; shikimate; soybean, Glycine max (L.) Merr. ‘Great Lakes GL2415′, ‘Great Lakes GL2600RR’, and ‘Pioneer 92B71′; Sclerotinia stem rot (white mold), Sclerotinia sclerotiorum (Lib.) de Bary.

Chad D. Lee, Donald Penner, and Ray Hammerschmidt "Glyphosate and shade effects on glyphosate-resistant soybean defense response to Sclerotinia sclerotiorum," Weed Science 51(3), 294-298, (1 May 2003).[0294:GASEOG]2.0.CO;2
Received: 12 February 2002; Accepted: 19 September 2002; Published: 1 May 2003

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