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Substrate Effects on Helminthosporium maydis Race T Conidium and Germ Tube Morphology. Jean Marie Potter, Department of Plant Pathology, Seed and Weed Sciences, Iowa State University, Ames, IA 50011; Lois H. Tiffany(2), and C. A. Martinson(3). (2)(3)Department of Plant Pathology, Seed and Weed Sciences, Iowa State University, Ames, IA 50011. Phytopathology 70:715-719. Accepted for publication 17 January 1980. Copyright 1980 The American Phytopathological Society. DOI: 10.1094/Phyto-70-715.

Conidia of Helminthosporium maydis race T were produced on glucose asparagine agar and ground maize-leaf agar media, and on maize leaf lesions. Comparisons by light microscopy revealed that conidia produced on the glucose asparagine agar were shorter, had fewer septations, and germinated more slowly than conidia from maize-leaf agar or maize leaf lesions. Observations with scanning electron microscopy showed that conidia from the glucose asparagine agar have an almost-smooth wall surface and become flattened in response to vacuum while conidia from the other two substrates have rougher walls and become wrinkled in response to vacuum. Substrate effects on conidial morphology and germ tube response indicate that fungus nutrition should be considered in morphological, taxonomic, and epidemiological studies of H. maydis. Germ tubes of conidia from all three substrates formed a sheath-fibril complex when the conidia were inoculated onto maize leaves. The complex also was observed on germ tubes from conidia germinating on cellulose triacetate membrane filters resting on either moist filter paper or maize leaves. The sheath-fibril complex may function to attach germ tubes and appressoria to a substrate.