STRAIN VARIATION AND OXALIC-ACID PRODUCTION BY CYTOSPORA-LEUCOSTOMA ISOLATED FROM SASKATOON (AMELANCHIER-ALNIFOLIA)

Leucostoma persoonii (anamorph = Cytospora leucostoma) is a pathogen t hat causes early dieback and canker disease on a variety of fruit tree s 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 stu died to determine the extent of strain variability and to investigate mechanisms of pathogenesis. Differences among isolates were found to b e significant with respect to cultural characteristics on various medi a, and growth responses of the isolates to a range of temperatures als o varied significantly. Oxalic acid production was observed in culture s of C. leucostoma. However, the amount of oxalic acid secreted by ind ividual isolates, as well as the time of onset, were significantly dif ferent. Bipyramidal crystals were isolated from cultures grown in pota to-dextrose broth supplemented with 0.1% (w/v) calcium carbonate. Ener gy dispersive X-ray microanalysis confirmed the presence of calcium in the crystals. This suggests that oxalic acid secretion and sequestrat ion of calcium from host tissue may be important factors in the pathog enesis by C. leucostoma.