Ascospore germination and appressorium formation in vitro of Polystigma amygdalinum and its survival period

Ascospore germination was examined in Polystigma amygdalinum, incitant of red leaf blotch of almond with the goal of more detailed study of the biology and disease phases of this biotroph. Appressorium development is described for a species of Polystigma for the first time. Temperature had marked effect on ascospore germination and appressorium formation process. Germination and appressorium formation occurred in a temperature range of 5 to 20°C. Germination percentages were highest at 5 to 10°C. Ascospores at 25°C showed abnormal swellings and distortion of the cell content. Light had no effect on ascospore germination. The highest germination of ascospores was obtained on potato dextrose agar medium.