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Disease Note. First Report of Phytophthora megasperma f. sp. glycinea on Soybean in Virginia. M. A. Hansen, Virginia Polytechnic Institute and State University, Blacksburg 24061. R. L. Wick, and E. L. Stromberg. University of Massachusetts, Waltham 02154; and Virginia Polytechnic Institute and State University, Blacksburg 24061. Plant Dis. 74:183. Accepted for publication 29 November 1989. Copyright 1990 The American Phytopathological Society. DOI: 10.1094/PD-74-0183D. Patches of dead or dying soybeans (Glycine max (L.) Merr. 'Bay')
were observed in a field in Amelia County, Virginia, in August 1988.
Roots of affected plants were necrotic, and numerous oospores were
observed within the pith of stems. A homothallic oomycete with
non papillate, internally proliferating sporangia and mostly paragynous
(occasionally amphigynous) antheridia was isolated from pith tissue
of affected plants. Oospores were 45 µm or less in diameter; the
length:breadth ratio of sporangia averaged 2.0. The fungus was
identified as Phytophthora megasperma (Drechs.) f. sp. glycinea Kuan
& Erwin. Inoculum produced from pure cultures of the isolate,
according to the methods of Mircetich and Matheron (I), induced
damping-off and root rot of 3-day-old soybean seedlings (cv. Essex)
within 5 days after inoculation. The fungus was reisolated from both
roots and hypocotyls of affected plants. This is the first known report
of P. m. f. sp. glycinea on soybeans in Virginia. Fields with similar
symptoms were observed in Mecklenburg County in 1982 and Essex
County in 1984. |