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Erwinia amylovora

EPPO code

ERWIAM

Common names

English names: Fireblight
Nordic names: Ildsot (DK), Tulipolte (FI), Pærebrann (NO), päronpest (SE)

Estonian name: Viljapuu-bakterpõletik

Major host plants

The principal hosts to this bacterium are in the sub-family Pomoideae of the family Rosaceae. Genera which are considered as important hosts from both economic and epidemiological point of view include: Amelanchier, apples, Chaenomeles, Cotoneaster, Crataegus, Cydonia, pears, Pyracantha, Sorbus and Stranvaesia.

Symptoms

All aboveground parts of hosts can be infected by the pathogen. The most common and characteristic symptoms are:

  • Wilt and death of flower: The dead blossoms become dry and dark-brown to black in colour. They usually remain attached to the plant;
  • Death of shoots and twigs: Infected young, succulent shoots and twigs wither, turn brown and in most cases the tip of the shoot bends in a characteristic way forming the symptom known as “shepherd’s crook”;
  • Leaf blight: Infected leaves show either necrotic patches, which start from the margin of the leaf blade, or blackening of the petiole;
  • Fruit blight: Infected fruits turn brown to black, shrivel and remain attached to the spur, taking a mummified appearance;
  • Canker and trunk blight: From the infected blossoms, shoots or fruits, the disease spreads to larger twigs causing cankers and then may continue into branches and the trunk.

Cankers are slightly sunken, varying in size and surrounded by irregular cracks in the bark, and cause quick death of branches or the whole tree by girdling. Internally the tissues of the cankered area show a foxy red or brown discoloration which diffuses into the healthy tissues; they are often water-soaked in appearance. Under warm and wet conditions, whitish bacterial ooze may exude from infected tissues.

urtesy of EPPO: P.G. Psallidas, Benaki Institute, Athens (GR).

See more pictures on EPPO´s website

Distribution

E. amylovora is native to North America and was introduced into northern Europe several decades ago. It is now widespread in the EPPO region. roliferation has only been reported from the EPPO region. However, there are unconfirmed reports from India and South Africa.

A map can be downloaded from EPPO’s website. See instructions here.

Biology

The pathogen overwinters exclusively in infected host plants. Cankers are the most important source of primary inoculum for blossom infection in the spring. Bacteria enter the plant through blossoms, natural openings like stomata and lenticels or through wounds, carried by insects or by rain splash.

Major pathway(s)

Long distance spread is mainly by latently infested host plants, but is also considered possible by migrating birds and aerosols. Locally the disease spreads by insects, rain or by tools when pruning diseased plants.

Detection and inspection

Detection is done during the growing season, when symptoms are visible. Normally inspection should be done after flowering until late summer, when the symptoms are more obvious.

As the fireblight symptoms may be confused with those by other diseases, and considering the possibility of latent infection, detection of the disease should be confirmed by isolation and laboratory tests.

Pest status and importance

Fireblight is a major threat to pear industries as well as to apple production and the nursery trade.

Source of information

See further information here:

Author: Göran Kroeker
Editor: Elise T. Yamamoto Buch

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