Glyphosate-resistant sugar beets became more susceptible to root rot when
sprayed with glyphosate.
Sugar Beet (Beta vulgaris).
CP4 EPSPS gene from Agrobacterium, which produces an
herbicide-resistant version of the enzyme targeted by the herbicide
Goal of This Study:
Although glyphosate-resistant (GR) crops are not killed by glyphosate,
application of the herbicide to GR soybeans has exacerbated certain fungal
diseases. To investigate this problem with two GR sugar beet varieties
(B4 and H16), researchers exposed plants to different pathogenic strains
in a greenhouse setting.
Results of This Study:
"Increases in Rhizoctonia root rot could increase the soil pathogen
population and affect other susceptible crops in rotation with GR
sugar beet, such as dry bean, soybean and corn" (p. 1190).
The GR beet cultivar B4 showed significantly more injury (such as leaf
discoloration and ultimately death) from the soil fungus Rhizoctonia
solani isolate R-9 when sprayed with glyphosate using a surfactant
spray as a control. Disease severity was not visibly altered by glyphosate
for infection with R. solani isolate R-1411.
Both GR beet cultivars showed significantly more injury from the soil
fungus Fusarium oxysporum isolate FOB13 when sprayed with
glyphosate. Disease severity was not visibly altered by glyphosate for
infection with F. oxysporum isolate F-19.
In both GR varieties, there was a significant increase in shikimic acid
when 3-4 week old plants were sprayed with glyphosate, indicating only
partial resistance to the herbicide. The authors suggest this
might explain the disease observations because "[i]nhibition of the
shikimic acid pathway could result in reduced defensive capabilities of
sugar beet" (p. 1189).
Larson, R. L., A. L. Hill, A. Fenwick, A. R. Kniss et al. (2006).
"Influence of Glyphosate on Rhizoctonia and Fusarium Root Rot in
Sugar Beet," Pest Management Science vol. 62, pp. 1182-92.
USDA Agricultural Research Service, Fort Collins, CO; Department of Plant
Sciences, University of Wyoming.
U.S. commercial production of GR sugar beets began in 2008.
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