Morphology and Ultrastructure of a Snowmold Fungus on Sagebrush (Artemisia Tridentata)

ABSTRACT

Morphology and ultrastructure of a fungus causing a snowmold disease of Artemisia tridentata are compared when the fungus is grown in vitro at -4, 1, and 20 C and on its sagebrush host. Whether grown on the host or in vitro at -4 and 1 C, external hyphal walls of the fungus are covered with numerous knob-like projections or tubercles, and prominent deposition vesicles and numerous multimembrane organelles are present and may be related to tubercle and thick wall formation. The presence of abundant glycogen could account for the ability of the fungus to grow below 0 C. Hyphae have typical ascomycetous septa with conspicuous Woronin bodies. Striated fibers permeate the cytoplasm, and are also frequently adjacent to the cell wall. When the fungus is cultured at 20 C external cell wall depositions are modified significantly and no longer appear as tubercles. Cell walls and septa become greatly thickened, glycogen is aggregated, and lipid bodies become more prominent. The unusual nature of the cell wall structure may be an adaptation for surviving over-summer desiccation on plant foliage.

Key Words:

• low temperature fungi
• plant disease
• range plant