Strain Variation and Oxalic Acid Production by Cytospora leucostoma solated from Saskatoon (A melanchier alnifolia). R. A. PLUIM, Former Graduate Student, Department of Plant Science, University of Alberta, Edmonton, Alberta, Canada T6G 2P5. J. P. TEWARI, Professor, and N. R. KNOWLES, Associate Professor, Department of Plant Science, University of Alberta, Edmonton, Alberta, Canada T6G 2P5; and R. J. HOWARD, Plant Pathologist and Head, Crop Protection and Utilization Section, Alberta Special Crops and Horticultural Research Center, Brooks, Alberta, Canada T1R 1E6. PIant Dis. 78:551-557. Accepted for publication 31 January 1994. Copyright 1994 The American Phytopathological Society. DOI: 10.1094/PD-78-0551.

Leucostoma persoonii (anamorph = Cytospora leucostoma) is a pathogen that causes early dieback and canker disease on a variety of fruit trees in North America. It has recently been recognized as an economically important disease of saskatoon (Amelanchier spp.) in Alberta, Canada. Isolates from infected bushes from five locations in Alberta were studied to determine the extent of strain variability and to investigate mechanisms of pathogenesis. Differences among isolates were found to be significant with respect to cultural characteristics on various media, and growth responses of the isolates to a range of temperatures also varied significantly. Oxalic acid production was observed in cultures of C. leucostoma. However, the amount of oxalic acid secreted by individual isolates, as well as the time of onset, were significantly different. Bipyramidal crystals were isolated from cultures grown in potato-dextrose broth supplemented with 0.1% (w/ v) calcium carbonate. Energy dispersive X-ray microanalysis confirmed the presence of calcium in the crystals. This suggests that oxalic acid secretion and sequestration of calcium [ from host tissue may be important factors in the pathogenesis by C. leucostoma.

Keyword(s): cation sequestration by plant pathogens