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Conidial Stage of Hypoxylon pruinatum: Factors Influencing Pillar Production and Conidial Germination. Davinderjit K. Bagga, Former Research Assistant, Department of Plant Pathology, University of Wisconsin, Madison 53706; Eugene B. Smalley(2), and J. G. Berbee(3). (2)(3)Professors, respectively, Department of Plant Pathology, University of Wisconsin, Madison 53706. Phytopathology 64:411-413. Accepted for publication 17 October 1973. DOI: 10.1094/Phyto-64-411.

Germinating conidia of Hypoxylon pruinatum occasionally developed into colonies on agar culture media. These colonies were always the “conidial”-type in contrast to the normal mycelial wild-type. Contact between colonies of different paired mycelial isolates was required for conidial development at merging colony margins. Conidia were always uninucleate. The optimum temp for conidial pillar development on naturally infected stem pieces of Populus tremuloides was between 20 and 24 C. Relative humidities lower than 95% resulted in inhibition of conidial pillar development. Mycelial macerates of certain isolates of the fungus, when mixed aseptically in warm oatmeal agar prior to gelation, produced conidial pillars in pure culture.