Introduction
Cultural Practices
Causal Organism
Chemical Control
References
The first visible symptoms of CBR are the yellowing and
wilting of leaves on the erect, primary stem of a plant. Entire
plants may wilt and die at an alarming rate when prolonged periods of
high soil moisture are followed by a period of moisture stress. In
the absence of ideal conditions for disease development, plants may
develop only a yellow, stunted appearance. When CBR is seen for the
first time in a field, the diseased plants are usually observed in
one or more localized spots. (Fig. A).
Below-ground, plant parts are the first to show symptoms
of CBR. Hypocotyls, primary and secondary roots, and pods become
black and necrotic. (Fig B). Infected pods exhibit
dark brown to black necrotic spots, or may be totally blackened and
severely decayed. Infected kernels are usually reduced in size and
have a russet appearance. The taproot is often necrotic and severely
decayed in plants with aboveground symptoms. Wilted or dead plants
are easily pulled from soil due to the near total destruction of the
tap root.
A useful diagnostic sign of CBR is the occurrence of
small, reddish-orange perithecia of the pathogen in
dense clusters on stems (Fig. C) , pegs, and
occasionally pods. These fruiting bodies develop just above and
sometimes below the soil surface during periods of wet, humid
weather. If perithecia are not found on diseased plants, tissue
samples must be assayed in a laboratory to positively identify the
disease. These structures can be confused in the field with the
smaller and more round perithecia of Neocosmospora sp.,
which is a common saprophyte on dead tissue near the soil surface.
Introduction Cultural Practices Causal Organism Chemical Control References
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Last Updated on March 5, 1998 by Barron Britt Keeling