MATURATION AND SEASONAL DISCHARGE PATTERN OF ASCOSPORES OF ANISOGRAMMA-ANOMALA

Maturation and release of ascospores of Anisogramma anomala were monit ored over a 6-year period (1988 to 1995) in European hazelnut orchards located in western Oregon. Perithecia of A. anomala were dissected fr om stromata collected monthly from September to May to determine spore maturation. Spore maturation began in late summer; by January, >90% o f the spores were morphologically mature. Similarly, both the number o f mature ascospores per perithecium and the proportion of ascospores t hat germinated increased through autumn. After January, the number of spores per perithecium declined until May, when few viable spores rema ined. Each of the 6 years, rain catch-type spore traps were placed und er cankers in diseased trees from 15 September to 30 June. Based on sp ore collection periods of 1 to 4 weeks, three patterns for the seasona l release of A, anomala ascospores were observed: in the 1988-1989 sea son, >80% of the seasonal ascospore release occurred between September and January; in the 1989-1990 season, 32 to 42% of the seasonal ascos pore release occurred after mid-April; and in the other 4 years, month ly releases of ascospores were relatively uniform over the 9-month sea sonal period. Timing and amount of precipitation were the most importa nt variables accounting for the differences among the yearly patterns of ascospore release. Over all years and sites, the cumulative proport ion of total ascospores collected in each orchard was highly correlate d (R-2 = 0.90) With cumulative precipitation. This relationship was co nfirmed in mist chamber experiments. A regression model was developed relating cumulative ascospore release to cumulative hours of precipita tion. The model provides an estimate of the proportion of ascospores r emaining to be released after budbreak, which coincides with the perio d of highest susceptibility to infection.