APS Abstracts of Presentations

Scanning electron microscope of Phymatotrichopsis omnivora and its infection of alfalfa roots
Presenter: H.-K. Lee, The Samuel Roberts Noble Foundation, Inc., 2510 Sam Noble Parkway, Ardmore, OK 73401
Co-Author(s): S. Marek, Oklahoma State University, Department of Entomology & Plant Pathology, 127 Noble Research Center, OSU, Stillwater, OK 74078; M. Sledge, The Samuel Roberts Noble Foundation, Inc., 2510 Sam Noble Parkway, Ardmore, OK 73401
Phytopathology 95:1112

Phymatotrichum or cotton root rot caused by fungus Phymatotrichopsis omnivora (Duggar) Hennebert, is one of the most important diseases of alfalfa (Medicago sativa L.) in southern Oklahoma and Texas. Two isolates of fungus, axenically cultured or infecting alfalfa seedlings, were examined using scanning electron microscopy (SEM). The vegetative mycelia grown on potato dextrose agar displayed characteristic septal constrictions. In agar co-culture, the roots and cotyledons of seedlings of several alfalfa cultivars were infected by the hyphae and mycelial strains of P. omnivore. The fungus penetrated cotyledons directly and through stomata whiles roots were penetrated directly and through natural openings. The fungus developed appressoria-like hypae on roots and hypae immersed in border cells of root hairs. Infected tissues appeared either asymptomatic or completely collapsed.

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