Seasonal periodicity in the discharge of Pucciniastrum goeppertianum basidiospores
Discharge of Pucciniastrum goeppertianum (Kühn) Kleb. basidiospores from witches' brooms on lowbush blueberry (Vaccinium angustifolium Ait. and V. myrtilloides Michx.) in central New Brunswick occurred at irregular intervals from mid-May to late June in 1973 and 1974, but more than 75% of the total catch occurred in a 1-week period each year. Annual timings were related to spring weather variation so that discharge peaks each year coincided with shoot elongation of the aecial host, balsam fir (Abies balsamea (L.) Mill.). Measurable rainfall preceded all major discharge peaks; relative humidity and temperature were factors only as they affected the rate of drying of the hypertrophied twigs. Basidiospore concentration at 15, 90, and 150 cm above the ground level brooms decreased at a ratio of 7:2:1.