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Disease Note. Choanephora Leaf Blight of Soybeans in Louisiana. K. V. Subba Rao, Department of Plant Pathology and Crop Physiology, Louisiana Agricultural Experiment Station, Louisiana State University Agricultural Center, Baton Rouge 70803. G. B. Padgett, D. K. Berner, G. T. Berggren, and J. P. Snow. Department of Plant Pathology and Crop Physiology, Louisiana Agricultural Experiment Station, Louisiana State University Agricultural Center, Baton Rouge 70803. Plant Dis. 74:614. Accepted for publication 29 April 1990. Copyright 1990 The American Phytopathological Society. DOI: 10.1094/PD-74-0614B. During the summer of 1989, to study the dispersal of the soybean
stem canker pathogen, soybean (Glycine max (L.) Merr. 'Bedford,)
plants, grown in 30-cm-diameter clay potS at the R1 growth stage
(1), were placed weekly in a field at the Burden Research Farm in
Baton Rouge. Plants placed during the week of 26 August-2 September
and removed to the greenhouse developed grayish areas on leaves
on 3 September; the areas became necrotic 5 days later. There was
heavy and frequent rainfall on all days during the exposure period.
Symptoms were more prominent on older leaves. Characteristic sporangiophores
and sporangioles were observed on all blighted leaves
and were dense along the edges of necrotic areas. Sporangiospores were obovoid, with typical tufts of polar appendages. The fungus
Choanephora infundibulifera Sacco was isolated from all infected
plants on potato-dextrose and water agars. The fungus produced
sporangioles after 2 days in culture. Koch's postulates were carried
out using cv. Bedford plants (growth stages V4 and V6) in a greenhouse.
The plants were inoculated by spraying to runoff with an aqueous
spore suspension obtained from culture, then were incubated first in
a dew chamber for 20 hr at 20 C and then on greenhouse benches
at 26 C. Symptoms similar to those on the field-exposed plants were
observed 7 days after inoculation. C. infundibulifera was reisolated
from inoculated plants. This may have been an opportunistic infection
of soybeans, since the field in which the plants were placed is usually
planted with horticultural crops, on which this fungus is a common
pathogen. This is the first report of Choanephora blight of soybeans
in Louisiana. |