amylovora

Erwinia amylovora is a Gram-negative, rod-shaped bacterium in the family Erwiniaceae that causes fire blight, a destructive disease of apple and pear trees and other members of the Rosaceae. It is the causal agent of fire blight and is widely distributed in temperate regions around the world.

Hosts and symptoms: The primary hosts are Malus (apple) and Pyrus (pear), with other Rosaceae such as quince and crabapple occasionally affected. Symptoms begin at blossoms (blossom blight) and shoot tips, progressing to wilted shoots that turn brown or black. Infected shoots may develop characteristic shepherd’s crook shapes. Cankers form on limbs and trunks, and a light brown to amber bacterial ooze can exude from cankers under warm, humid conditions. Fruit lesions are sunken and corky, reducing market quality and tree vigor.

Biology and virulence: E. amylovora relies on amylovoran, an exopolysaccharide essential for virulence, and a type III secretion system that injects effector proteins (such as DspA/E) into plant cells. The bacterium is typically more active in warm, wet weather and can be disseminated by wind-driven rain, insects, and contaminated pruning tools.

Life cycle and spread: The pathogen overwinters in cankers; in spring it produces an ooze that contains large numbers of bacteria. Inoculum spreads to blossoms and young tissue, initiating infections that can lead to systemic colonization and canker development.

Management: Approaches include orchard sanitation to remove and destroy cankers, use of resistant cultivars when available, and protective chemical treatments (copper compounds and antibiotics such as streptomycin in regions where permitted). Biological controls and integrated pest management strategies are also used to reduce spread and inoculum.

Distribution and impact: Fire blight occurs in many temperate regions of North America, Europe, Asia, and the Middle East. It can cause substantial yield losses and tree mortality in commercial orchards if unmanaged.