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Soybeans
are susceptible to anthracnose pathogens at all stages of development.
Foliar symptoms that develop after prolonged periods of high humidity include
necrosis of laminar veins, leaf rolling, petiole cankering, and premature
defoliation. Symptoms typically appear in the early reproductive stages on
stems, petioles, and pods. In advanced stages of anthracnose, usually in the
late reproductive stages, infected tissues are covered with black fruiting
bodies (acervuli), that produce minute black spines (setae) that can be seen
with the unaided eye. Pre- and post- emergence damping-off may occur when
infected seeds are planted. Dark brown, sunken cankers often develop on the
cotyledons of emerging seedlings. The most common pathogen associated with
anthracnose is Colletotrichum truncatum.
C.
truncatum can overseason as mycelium in infected crop residue or in infected
seeds. Inoculums from infected seeds and residue may cause pre- and
post-emergence damping-off of seedlings. Mycelium may also become established in
infected seedlings without symptoms developing until the plants begin to mature.
Infected embryos fail to germinate. Stem and pod infections predominately occur
in the reproductive stages during warm, moist weather.
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