Erwinia amylovora causing fire blight of pear in the Guilan province of Iran [Pyrus communis L.; Malus pumila Mill.]

Fire blight, caused by Erwinia amylovora, is one of the important bacterial diseases of pear trees. It causes blight of different organs of the tree (blossoms, shoots, leaves, fruits and limbs) and production of exudates. During a survey of pear orchards in different areas of the Iranian province of Guilan (Astaneh, Ashrafieh, Lahijan and Kiashahr), necrotic shoots and exudates were observed in apple and pear trees. Samples taken from infected tissues were crushed in peptone water and aliquots of 100 micronl of the extract were cultured on nutrient agar (NA) and LB containing cycloheximide (50 microng mlE-1). A rod-shaped, gram negative, facultative anaerobic bacterium was consistently isolated, which produced levan in sucrose media, but not fluorescent pigment in King's B medium. All isolates induced hypersensitive reaction (HR) in tobacco and geranium leaves, were oxidase-, nitrate-, urease-, and indole-negative, could not rot potato tuber slices, produced H2S and grew at 36 deg C. The isolates could utilize citrate, arabinose, sorbitol, galactose and trehalose as carbon source and their gelatin test was positive. Based on morphological, biochemical and physiological characters and PCR amplification with specific primers, most bacterial isolates were identified as E. amylovora. Some isolates from spear orchards were identified as Pseudomonas syringae pv. syringae. This is the first report of the occurrence of E. amylovora on pear trees in the province of Guilan [Il colpo di fuoco, causato da Erwinia amylovora, è una delle malattie batteriche più importanti del pero. Essa determina avvizzimenti, imbrunimenti e necrosi di organi diversi della pianta (boccioli, germogli, foglie frutti e rami) e la produzione di essudati. Nel corso di un'indagine sugli impianti di pero in aree diverse della provincia iraniana di Guilan (Astaneh, Ashrafieh, Lahijan e Kiashahr), sono stati osservati germogli necrotici ed essudati su piante di pero e di melo. Campioni prelevati da tessuti infetti sono stati omogeneizzati in acqua peptonata e aliquote di 100 micronl dell'estratto sono state coltivate su agar nutritivo (NA) e su LB contenenti cicloesimide (50 microng mlE-1). E' stato costantemente isolato un bacillo Gram negativo, anaerobico facoltativo, che produceva levano in substrati con glucosio, ma non pigmento fluorescente in substrato B di King. Tutti gli isolati inducevano una reazione di ipersensibilità (HR) nelle foglie di tabacco e geranio, erano ossidasi-, nitrato-,