VIEW ARTICLE

Ecology and Epidemiology

Interaction of Xanthomonas campestris pv. pruni with Pruniphage and Epiphytic Bacteria on Detached Peach Leaves. P. S. Randhawa, Fruit laboratory, U.S. Department of Agriculture, Beltsville Agricultural Research Center, Beltsville, MD 20705; E. L. Civerolo, Fruit laboratory, U.S. Department of Agriculture, Beltsville Agricultural Research Center, Beltsville, MD 20705. Phytopathology 76:549-553. Accepted for publication 7 November 1985. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1986. DOI: 10.1094/Phyto-76-549.

A bioassay for measuring the interaction of Xanthomonas campestris pv. pruni with pruniphage and epiphytic bacteria is described. Detached young peach leaves were surface-sterilized with 70% ethanol and placed on 0.5% water agar with their adaxial side up. Inoculum mixtures of X. c. pv. pruni and epiphytic bacteria (47 strains from stone fruit trees and two nonepiphytic strains from crucifer seeds and roots) or pruniphage were placed as 20 drops of 5 μl each on a leaf and incubated for 120 hr at 25 C under 16-hr photoperiods. Populations of X. c. pv. pruni were significantly reduced on the surface and within leaves by seven and 17 strains of epiphytic bacteria, respectively. Colonization of leaves depended upon the specific strain of epiphytic bacterium. Strains that had a higher degree of colonization caused stronger inhibition of X. c. pv. pruni. Inhibition of X. c. pv. pruni by epiphytic strains on nutrient glucose agar and leaves was not related. Coinoculation of pruniphage and X. c. pv. pruni resulted in reduction of X. c. pv. pruni on and within leaves. However, surviving X. c. pv. pruni developed pruniphage resistance especially at high ratios of plaque-forming units to colony-forming units. Approximately 50% of the pruniphage-resistant population was significantly less virulent than the parent strain.