Cleistothecium of Uncinula necator   -   Causal Agent of Powdery Mildew of Grapes

Images from MycoAlbum CD by George Barron

Left: The micrograph shows the fruitbody (= cleistothecium) that contains the spore mother cells (asci) of the fungus. The long appendages radiating from the ascoma (=ascocarp) are hooked at the end (=uncinate) and the fungus takes its genus name from this character. The cleistothecium is the persistent (overwintering stage ) of the fungus.  It  falls with the leaves to the ground in the autumn,  overwinters on the ground, and starts off a new cycle of disease in the new growing season. Right:   Micrograph shows a cleistothecium that has been split open by coverslip pressure to reveal the asci and ascospores.

The ‘powdery’ stage of the disease is caused by hyphae and conidia growing over the surfacwe of infected plants. Left: Powdery mildew of grape - photograph courtesy Catherine Gauthier BASF, France.  Right: micrograph of conidial state of Blumeria graminis (cause of powdery mildew of cereals) fruiting over the surface of a blue grass leaf.