Refining a method for ascospore viability testing in overwintering chasmothecia of Erysiphe necator

The vital stain fluorescein diacetate (FDA) has long been used to assess the viability of Erysiphe necator ascospores in chasmothecia. To determine the viability of animal, plant and other cells, more complex staining procedures, for example simultaneous double-staining procedures based on the use of FDA and propidium iodide (PI), have also been widely used. This paper reports a refined, detailed version of this method and its limitations, where PI was replaced with ethidium bromide (EtBr), to be used in testing the viability of E. necator ascospores during overwintering in chasmothecia.