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Significance

Erwinia amylovora is a native pathogen of wild, rosaceous hosts in eastern North America. These hosts include hawthorn, serviceberry, and mountain ash. Early European settlers introduced apple and pear to North America. The first report of fire blight as a disease of apple and pear occurred in 1780, in the Hudson Valley of New York. In California, the disease was first reported in 1887.

Early 19th and 20th century horticultural texts and bulletins recognized fire blight as a serious disease of pear, provided descriptions of symptoms, and outlined pruning practices for control (Figure 16). Nonetheless, in the eastern United States, fire blight proved to be destructively epidemic on pear, limiting the cultivation of this host. Even today, the threat of fire blight restricts commercial production of pear to semi-arid, desert areas west of the Rocky Mountains.

Figure 16

Erwinia amylovora has the distinction of being the first bacterium shown to be a pathogen of plants. Koch's postulates for E. amylovora were fulfilled by J.C. Arthur in 1885, but the genesis of the concept that bacteria can be plant pathogens required the contributions of many scientists (notably T.J. Burrill) and growers over a period extending from 1846 to 1901. E. amylovora is also one of the first plant pathogens to be associated with an insect vector. In the late 1890's, M.B. Waite linked blossom infection to the movement of the pathogen from flower-to-flower by pollinating insects.

During the 20th century, introductions of infested plant material served to establish E. amylovora in Europe, the Middle East, and New Zealand. In 1995, fire blight was first observed in the Po River Valley of northern Italy, which is the largest pear production area in the world. Since 1995, the Italian government has destroyed 500,000 pear trees in an attempt to eradicate E. amylovora.

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