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Relationships of Xanthomonas pruni Bacteriophages to Bacterial Spot Disease in Prunus. E. L. Civerolo, Research Plant Pathologist, Fruit Laboratory, Agricultural Research Service, U.S. Department of Agriculture, Agricultural Research Center, Beltsville, Maryland 20705; Phytopathology 63:1279-1284. Accepted for publication 9 April 1973. DOI: 10.1094/Phyto-63-1279.

Xanthomonas pruni phage (Xp3-A) plates with approximately the same relative efficiency of plating (EOP) on seven susceptible X. pruni isolates from peach, apricot, plum, and sweet cherry. Relative EOP of phage Xp3-I on the same isolates was more variable, but consistently lower on the heterologous X. pruni hosts than on the homologous host. There is no apparent direct relationship between virulence of the seven phage-sensitive X. pruni isolates on ‘Sunhigh’ peach seedlings and the relative EOP of phages Xp3-A and Xp3-I on these isolates. Extensive lysis of peach, apricot, and plum isolates of X. pruni by phage Xp3-A occurred at 20 and 27 C but not at 35 C. Limited lysis of a sweet cherry isolate of X. pruni, which produces turbid plaques when incubated at 27 C with phage Xp3-A, also occurred at 20 and 27 C but not at 35 C. Leaf infection, as measured by disease symptoms, was significantly less on Sunhigh peach seedling foliage pre-treated with phage and when phage was mixed with X. pruni inoculum. X. pruni phages may have an epidemiological role in bacterial spot disease development.

Additional keywords: Prunus persica, peach bacterial disease, phage-bacterium interaction.