Studies on phylogenetic analyses and detection method of fire blight pathogen and its closely related bacteria

Fire blight, caused by Erwinia amylovora, is the world's most important bacterial disease of pear and apple. It was first reported in the eastern area of the United States of America (Hudson Valley, New York State) in the 1780s. Thereafter the disease spread south and westward in the USA. In early 1900s, the disease was confirmed all over the USA. Furthermore, the first occurrence of fire blight was mentioned as early as the 1840s in Canada. Since 1924, the disease has spread to all pear and apple growing areas of Canada. On the other hand, the reports of fire blight came from New Zealand in 1919, from England in 1958, and from Egypt in 1964. Fire blight has been spreading in European and Middle Eastern countries and occasionally causes severe damage. There are about 40 countries known with fire blight worldwide at present. Erwinia amylovora has not been isolated in Japan. However, bacterial shoot blight of pear with symptoms resembling fire blight was reported and the causal pathogen closely related to E. amylovora was assigned to Erwinia sp. This disease was eradicated by Japanese governmental emergency control measures and has not been reported since eradication. Erwinia amylovora also has not been isolated in South Korea. In 1999, a new disease with symptoms resembling fire blight was reported on Asian pears in South Korea. The causal agent was named E. pyrifoliae. In this study, the phylogenetic relationships among E. amylovora, Erwinia sp. (the pathogen of bacterial shoot blight of pear), and E. pyrifoliae were revealed on the basis of their common nucleotide sequences. For the detection and identification of each bacterium, PCR primers were designed using the nucleotide sequences. Epiphytic bacteria on Japanese pear flowers, which may cause misidentification in the diagnosis of fire blight using direct PCR, were investigated. The sensitivity and suitable sites for direct PCR were also investigated.