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Observations by Scanning Electron and Bright-Field Microscopy on the Mode of Penetration of Soybean Seedlings by Phomopsis phaseoli. Martin M. Kulik, Research Plant Pathologist, U.S. Department of Agriculture, Agricultural Research Service, Beltsville, MD 20705. . Plant Dis. 72:115-118. Accepted for publication 15 July 1987. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1988. DOI: 10.1094/PD-72-0115.

Cotyledons, hypocotyls, and unifoliolate leaves of soybean seedlings at growth stage V1 grown in pots in the greenhouse were inoculated by spraying with an aqueous suspension of 100,000 alpha conidia of Phomopsis phaseoli per milliliter. Plants were incubated in a moist chamber at 2127 C for 24144 hr. Scanning electron and bright-field microscopy were used to examine plant material collected at 24-hr intervals beginning 24 hr after inoculation. Conidia produced germ tubes 2448 hr after inoculation. Germ tubes from conidia situated directly over or immediately adjacent to stomata sometimes produced appressoria. Germ tubes penetrated leaves and cotyledons via stomata but did not penetrate directly through the cuticle. Conidia were not observed on hypocotyls. A reticulum associated with conidia that may serve to anchor the conidium to the host surface also was observed.

Keyword(s): soybean pod and stem blight.