CHARACTERISTICS OF PERIDERMIUM-HARKNESSII IN AXENIC CULTURE

Axenic cultures of Peridermium harknessii J.P. Moore developed white a erial hyphae, orange callus-like growth, and white mycelium colonies a s successive vegetative forms when isolated from explants from infecte d mature field-grown Pinus ponderosa Dougl. ex. P. Laws & C. Laws. Exp lants (small cubes of gall phloem tissue) were collected from March th rough August 1988 and 1989 in eastern Nebraska and northern and wester n North Dakota. By 20 days after plating, white hyphae appeared to ori ginate from immature aeciospores. By 45 days, friable orange callus-li ke growth appeared on many explants from beneath the white hyphae and eventually overgrew the latter. Orange callus colonies consisted mostl y of single-celled vesicular cells, which seemed to originate from aec iospore initials. The larger vesicular cells were similar in size to a eciospores, contained orange subcellular globules, and occasionally ha d surface ornamentation similar to that of aeciospores. After 60 days, white mycelium colonies grew as sectors within and at the edges of ma ny orange callus cultures. The colonies appeared to originate as appen dages of thick-walled hyphal strands of orange callus and macroscopica lly consisted of compact masses of thin-walled hyaline hyphae arising from a stroma. If not transferred to fresh medium, orange callus would frequently convert to white mycelium colonies. No change in the morph ology of white mycelium colonies was observed. Only mineral salt media supplemented with peptone, soytone, or a mixture of yeast extract, su crose, and glucose sustained fungal growth apart from the host tissue. Both orange callus and white mycelium colonies grew over a temperatur e range of 5-35-degrees-C, and revealed similar staining patterns in 1 2 of 14 isozymes to those of Peridermium harknessii aeciospores when a nalyzed with starch gel electrophoresis.