Bacteria from necrotic branches of Asian pear trees (Pyrus pyrifolia) in Korea were consistently isolated as white colonies on nutrient agar and formed mucoid, slightly yellow colonies on a minimal medium with copper sulphate. Isolates with this colony morphology were studied in a series of microbiological, molecular and pathological tests. Most isolates allowed the verification of Koch's postulate on P. pyrifolia seedlings and on slices from immature pear (Pyrus communis) fruits and were also positive in hypersensitivity tests on tobacco leaves. They showed characteristics common to species in the genus Erwinia, but were different from Erwinia amylovora, the agent of fire blight. A relationship between the novel pathogen and E. amylovora was found in microbiological and serological tests. Both organisms had similar but not identical protein patterns in 2‐D gel electrophoresis, and in growth morphology the new pathogen produced colonies on MM2 Cu medium that were mucoid and slightly yellow, compared with the clearly yellow colonies of E. amylovora. No similarity was found in the plasmid profiles, and consequently no PCR signal was obtained with primers from the E. amylovora plasmid pEA29. REP‐PCR also produced bands differing for the two organisms.
Biosynthesis of the repeating units of the exopolysaccharides amylovoran from Erwinia amylovora and stewartan from Pantoea stewartii (2011) Physiological and Molecular Plant Pathology, 75 (4), pp. 163-169.
The fire blight pathogen Erwinia amylovora was assayed for survival under unfavourable conditions such as on nitrocellulose filters, in non-host plants as well as in inoculated mature apples and in infested apple stem sections. In a sterile dry environment, an E. amylovora EPS (exopolysaccharide) mutant, and to a lesser extent its parental wild-type strain decreased within 3 weeks to a low titre. However, under moist conditions the decrease of viable cells occurred only partially for both strains. Very low cell titres were recovered after application of E. amylovora onto the surface of tobacco leaves, whereas infiltration into the leaves produced lesions (hypersensitive response, HR), in which the bacteria survived in significant amounts. A similar effect was found for the necrotic zones of HR in tobacco leaves caused by E. pyrifoliae, by Pseudomonas syringae pathovars and HR-deficient E. amylovora mutants or mutants deficient in EPS synthesis and disease-specific genes. During 7 years of storage, the viability of E. amylovora in wood sections from fire blight-infested apple trees declined to a low titre. In tissue of mature apples, E. amylovora cells slowly dispersed and could still be recovered after several weeks of storage at room temperature. A minimal risk of accidental dissemination of E. amylovora apart from infested host plants can experimentally not be excluded, but other data confirm a very low incidence of any long distance distribution.
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