Erwinia amylovora is a Gram-negative enterobacterium bacterium that causes fireblight disease on Rosaceae family plants including apple (Malus spp.), pear (Pyrus spp.), quince (Chaenomeles spp.), strawberry (Fragaria spp.) and rose (Rosa spp.) (Zwet and Keil, 1979; Bradbury, 1986; van der Zwet et al., 2012; McNally, 2013).
[sup] The presence of Gram-negative bacteria such as Pseudomonas, Enterobacterium, Haemophilus and Klebsiella are rare, although the incidence of those species as agents of PTA has increased in recent decades.