Jan 4, 2011

Glossary

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Apple powdery mildew (true mildew)

A plant disease caused by fungi

Apple powdery mildew Photo: www.obstbauseite.de

Powdery mildew is caused by sac fungi (ascomycetes). This group contains around 45 000 species, making it one of the world’s most serious plant pathogens. Each of these pathogens has its own host plant. They include apples, grapevines, barley, wheat, beet and roses.

Apple powdery mildew affects all plant parts above ground. Infected leaves have a powdery coating, curl upwards and become hard and brittle. Infected fruits are covered by a web-like structure. The fungi reproduce by producing spores that are dispersed by the wind. Since the fungus survives the winter in the leaf and flower buds, cutting back the affected plant parts is often the most effective control method. Pears and quinces are affected, as well as apples.

It has been possible to cross resistance genes from wild apples into susceptible apple varieties (Gala) using conventional breeding methods, but these new varieties have not yet gained acceptance on the market.

Genetic methods are also being used around the world to develop fungus-resistant plants. To do this, genes that produce e.g. glucanases or chitinases are transferred into the plants. These enzymes destroy the fungal cell wall, thereby conferring fungal resistance on the plants.