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Comparative Relationships between Two Xanthomonas pruni Bacteriophages and Their Bacterial Host. E. L. Civerolo, Research Plant Pathologist, Crops Research Division, ARS, USDA, Beltsville, Maryland 20705. Phytopathology 60:1385-1386. Accepted for publication 8 April 1970. DOI: 10.1094/Phyto-60-1385.

The comparative relationships between two virulent Xanthomonas pruni bacteriophages (Xp3-A, Xp3-I) that produce morphologically distinct plaques and their bacterial host are described. Adsorption rate constants are 1.1 × 10^–9 and 1.8 × 10^–9 ml/min for Xp3-A and Xp3-I, respectively. For Xp3-A, the latent period is 30-45 min; the eclipse period is between 15-30 min; and the burst size is 42-49 plaque-forming units (PFU). All phage particles are completed and released rapidly, reaching a maximum about 25 min after end of the adsorption period. For Xp3-I, the latent period is 60-75 min, the eclipse period is between 15-30 min, and the burst size is 176-296 PFU. Infectious Xp3-I phage particles are released slowly from infected cells over a period of 120 min. The infectivity of both phages in nutrient broth containing 1-2 × 10³ PFU/ml is stable up to 55 C for 10 min but decreases markedly between 60-70 C. The relative roles of these relationships in the development of bacterial spot of peach are discussed.