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Etiology

Some Properties of Erwinia amylovora Bacteriophages. D. F. Ritchie, Department of Botany and Plant Pathology, Michigan State University, East Lansing 48824, Present address of senior author: Department of Plant Pathology, North Carolina State University, Raleigh 27650; E. J. Klos, Department of Botany and Plant Pathology, Michigan State University, East Lansing 48824. Phytopathology 69:1078-1083. Accepted for publication 3 April 1979. Copyright 1979 The American Phytopathological Society. DOI: 10.1094/Phyto-69-1078.

Eleven Erwinia amylovora bacteriophages isolated from aerial parts of apple trees in Michigan orchards during 1975 and 1976 were placed in two groups on the basis of morphology and serology. Group I phages produced two plaque types: (i) PEal(h) plaques were 23 mm in diameter surrounded by an expanding, translucent halo; (ii) PEal(nh) plaques were 12 mm in diameter without a halo. Group II phages, represented by PEa7, produced 0.51.0 mm diameter plaques with an expanding, translucent halo. Phage PEal(h) was polyhedral, 60 nm in diameter with a spikelike tail; PEa7 had an octahedral head, 75 nm in diameter with a rigid, striated tail 135 nm long. Phages PEal(h) and PEal(nh) had a buoyant density of 1.53 g/cc and a sedimentation coefficient of 566 S. Phage PEa7 had a buoyant density of 1.44 g/cc with a sedimentation coefficient of 1037 S. The latent period of PEal(h) was 45 min with a burst size of 50 plaque-forming units (pfu) per productive cell; that of PEa7 was 100 min with 8 pfu per productive cell. Phages PEal(h) and PEal(nh) required 10 min at 55 C for complete thermal inactivation; 10 min at 65 C were required for PEa7. Host ranges for the two phage groups were limited to E. amylovora and several Erwinia herbicola strains. Phage PEal(h) adsorbed more rapidly to encapsulated than to nonencapsulated strains of E. amylovora but PEa7 adsorbed more rapidly to nonencapsulated E. amylovora strains.

Additional keywords: K-phages, fire blight.