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Collection, Viability, and Storage of Ascospores of Monilinia oxycocci. P. G. Sanderson, Department of Plant Pathology, University of Wisconsin, Madison 53706, Present address: Mid-Columbia Agricultural Research and Extension Center, Oregon State University, 3005 Experiment Station Drive, Hood River, OR 97031; S. N. Jeffers, Department of Plant Pathology, University of Wisconsin, Madison 53706. Phytopathology 82:160-163. Accepted for publication 16 July 1991. Copyright 1992 The American Phytopathological Society. DOI: 10.1094/Phyto-82-160.

Ascospores of Monilinia oxycocci were collected from apothecia onto membrane filters. Germination on potato-dextrose agar and fluorescence after staining with fluorescein diacetate were compared as methods for determining ascospore viability. Estimates of viability by the two methods were similar. Ascospores were stored for 24 mo with or without the desiccants CaCl₂ or CaSO₄ in four locations: a constant-temperature deep freezer at –20 C, a frost-free freezer at –20 C, a refrigerator at 4–6 C, and a laboratory drawer at room temperature (21–25 C). Ascospores survived best when stored desiccated in the deep freezer and did not survive at room temperature. A desiccant was necessary for ascospore survival in either of the freezers, but the type of desiccant made no difference. Viability of ascospores stored in the deep freezer over CaSO₄ was tested at 6, 12, and 24 mo and compared with that of freshly collected ascospores. The proportion of ascospores that was viable decreased by over 60% during the first 6 mo of storage; however, no further decrease was detected thereafter. Ascospores of M. oxycocci can be collected and preserved in a viable state for at least 24 mo if stored in a constant-temperature deep freezer at –20 C over a desiccant such as CaCl₂ or CaSO₄.