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Disease Note. Seedling Infection of Soybean by Rhizoctonia solani AG-1, Causal Agent of Aerial Blight. X. B. Yang, Department of Plant Pathology and Crop Physiology, Louisiana Agricultural Experiment Station, Louisiana State University Agricultural Center, Baton Rouge 70803. G. T. Berggren, Jr., 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. 72:644. Accepted for publication 2 March 1988. Copyright 1988 The American Phytopathological Society. DOI: 10.1094/PD-72-0644D.
Rhizoctonia aerial blight of soybean (Glycine max (L.) Merr.)
(RABS) is caused by Rhizoctonia solani Kuhn, anastomosis group I
(AG-I). Seedling infection by this pathogen before the V, stage has not
been confirmed previously (1). In 1987, natural seedling infection by R.
solani AG-I, which produced only sasaki i-type sclerotia, was observed.
The pathogen infected seeds before emergence, resulting in seed rot.
When infected seedlings emerged, circular lesions on the hypocotyls or
on the growing points were observed. Infection of the growing point
stopped further growth of the seedlings. Stem infections were observed
on small seedlings. Most stem infections occurred before the stems
turned green and were at or below the soil line. Stem lesions were
initially red, later turning brown and dry. Sasaki i-type sclerotia were
formed when the hypocotyl or stem lesions ceased expanding. Infected
seedlings served as one type of inoculum source for the formation of
disease foci. Isolation and anastomosis tests identified the pathogen as
R. solani AG-I, sasakii-type sclerotia form. Seedling infection and
RABS with the isolates were reproduced in both field and greenhouse
plantings. |