Jan 4, 2011

Glossary

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Apple scab

A plant disease caused by fungi

Apple scab Photo: www.obstbauseite.de

Apple scab is one of the most dangerous apple diseases in the world. Apple scab and all other scab diseases, e.g. potato scab, pear scab and firethorn scab, are caused by sac fungi.

Pale olive-green spots form on the leaves and fruit, which later turn brown or black. Although these spots are not toxic to humans, the infected apples are practically unmarketable.

The fungus overwinters in the dead leaves on the ground and causes the first infections in the spring when the winter spores are dispersed by rain. The summer spores then form at the sites of the infection, leading to further infections.

It has been possible to cross resistance genes from wild apples into susceptible apple varieties 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 certain enzymes (glucanases and chitinases) are transferred into the plants. These enzymes attack the fungal cell wall and destroy it. There are plans to use this concept for other plant diseases caused by fungi in the future.