Jan 4, 2011

Glossary

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Fire blight

A notifiable bacterial disease of fruit plants and woody ornamentals

Fire blight Photo: www.obstbauseite.de

Fire blight is caused by the Erwinia amylovora bacterium. It mainly affects plants of the Rosaceae family, to which a large proportion of our native fruit trees (apples, pears and quince) and woody ornamentals like cotoneaster belong. Stone fruit like cherries and plums are not host plants. The disease first appeared in Germany in 1971 and has been spreading towards the southwest ever since. In 2004 nearly the whole of Germany was affected.

Infestation with the bacterium leads to brown flowers, leaves or fruit that shrivel, but do not fall. This gives the plants the appearance of having been burnt. The only remedy for infected plants is radical pruning. In Belgium, Greece and Holland, pesticides containing antibiotics (e.g. streptomycin) are used, but these are not permitted in Germany.

Commercial apple varieties (Braeburn, Gala, Fuji) are susceptible or very susceptible to fire blight. It has been possible to obtain fruit plants with increased resistance using classic breeding methods, but these new breeds have not yet gained acceptance on the market.

Genetic methods insert genes that produce proteins inside the apple trees. The proteins have a negative effect on the fire blight pathogen. For instance, a gene has been introduced into apple plants that triggers the production of lysozyme, an enzyme with antibacterial properties. However, a planned field trial of these genetically modified apple trees in 2003 was refused.