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Ecology and Epidemiology

Infection and Mycelial Colonization of Gramineous Hosts by Sclerophthora macrospora. Peter H. Dernoeden, Graduate research assistant, Department of Plant Pathology and Entomology, University of Rhode Island, Kingston 02881, Present address of senior author: Department of Agronomy, University of Maryland, College Park 20742; Noel Jackson, professor, Department of Plant Pathology and Entomology, University of Rhode Island, Kingston 02881. Phytopathology 70:1009-1013. Accepted for publication 12 April 1980. Copyright 1980 The American Phytopathological Society. DOI: 10.1094/Phyto-70-1009.

Seedlings of Lolium perenne were more susceptible to infection than were more mature plants following inoculation with zoospores of Sclerophthora macrospora. Repeated exposure of seedlings to high concentrations of zoospores resulted in higher infection and damping-off percentages than a single exposure to zoospores. The ratio of infected plants to inoculum levels tended to decrease as the amount of inoculum increased. The mesocotyl region of seedlings and the shoot apical meristem, axillary buds, and the intercalary meristem of mature plants were likely portals of entry. Following penetration, mycelium rapidly colonized developing leaf primordia. Mycelial growth was most extensive in older portions of the youngest leaves. Numbers of substomatal sporangiophoric pads were proportional to the percent leaf area colonized by secondary mycelium.