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Cytology and Histology

Histopathology of Soybean Seed and Seedling Infection by Macrophomina phaseolina. Indra K. Kunwar, Visiting research associate, Department of Plant Pathology, University of Illinois at Urbana-Champaign (UIUC), 1102 S. Goodwin Avenue, Urbana 61801; Tribhuwan Singh(2), C. C. Machado(3), and J. B. Sinclair(4). (2)(3)(4)Former visiting assistant professor of botany, graduate student, and professor, respectively, Department of Plant Pathology, University of Illinois at Urbana-Champaign (UIUC), 1102 S. Goodwin Avenue, Urbana 61801, (2)Present address: Department of Botany, University of Rajasthan, Jaipur, India 302004. Phytopathology 76:532-535. Accepted for publication 17 December 1985. Copyright 1986 The American Phytopathological Society. DOI: 10.1094/Phyto-76-532.

Soybean seeds infected by Macrophomina phaseolina, cause of charcoal rot of soybean (Glycine max), were used. Histological examination of symptomatic seeds showed that hyphae and sclerotia were ecto- and endophytic; hyphae were inter- and intracellular in tissues of the seed coat, endosperm, and embryo. Seed coats of severely infected seeds were fragmented. The fungus produced sclerotia in 4% of asymptomatic seeds after 2 days of incubation at 25 ± 2 C on acidified (pH 4.5) potato-dextrose agar. These sclerotia developed near or adjacent to the seed coat endosperm and hypodermis. The fungus apparently can penetrate and colonize soybean seeds without producing symptoms, but subsequently forms sclerotia in asymptomatic seeds when conditions are favorable for seed germination. After 3-4 days of incubation, sclerotia were formed in the cotyledons of asymptomatic seeds and after 4-5 days, in the hypocotyl-radicle axis. This is the first report of M. phaseolina being seedborne in field-grown soybeans in Illinois.