Erwinia amylovora

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apple tree with fire blight (Erwinia amylovora)
Author: Sebastian Stabinger
Source: Wikimedia Commons

Erwinia amylovora (Burrill 1882) Winslow et al. 1920 - (fire blight)

The bacterium is a wide-spread pathogen of pear, apple and quince. Other plants of Roseaceae may also become infected. It is of North American origin, but was accidentally introduced into Europe (first record 1957). Apart from North America, it is now found in Europe, the Mediterranean region and parts of Asia and the Pacific. Yearly losses due to the disease have been estimated at around US$ 100 million in the United States alone.

The bacterium is Gram-negative, rod-shaped and motile. Plants often die due to the infection and losses have been severe in Europe, especially during the initial epidemics after the disease reached a new area. For example, in Italy more than 1 million pear trees were destroyed between 1994 and 2004.

The disease spreads mainly through human activity like the shipment of bud wood. Control involves a combination of sanitation, resistant cultivars and the application of streptomycin sprays on blossoms. However, streptomycin resistant strains have appeared in some regions. Further, winter pruning of infected branches is also recommended. Quarantine is very important for preventing the introduction of the bacterium into new areas.

Vernacular names
• Deutsch: Feuerbrand
Feuerbrand der Kernobstgehölze
• English: fire blight
fireblight of apple and pear
• Español: fuego bacteriano
niebla del peral y del manzano
• Français: feu bactérien

The disease is very contagious. A common route of infection appears to be through the flowers, carried by pollinating insects. Infections can also start through wounds when the bacterium spreads by rain splashes or with contaminated tools. Typically, flowers are infected first (blossom blight) in spring.

Subsequently, young shoots and leaves wilt, die off and appear scorched. The bacterium colonizes the xylem system which spreads it within the tree. Later cankers develop on branches and the trunk. The rootstock can also become infected. Further, bacterial ooze is also produced. The bacterium overwinters in cankers on the trunk and the disease develops faster during warm temperatures.

For a review on the epidemiology and control of the disease in Israel see Shtienberg et al., 2015.