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A Detached-Leaf Bioassay for Xanthomonas campestris pv. pruni. 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 75:1060-1063. Accepted for publication 18 April 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, 1985. DOI: 10.1094/Phyto-75-1060.

Young leaves of peach seedlings were detached and surface sterilized with 70% ethanol. Inoculum (10⁶ colony-forming units [cfu] per milliliter) of Xanthomonas campestris pv. pruni was infiltrated with a needle-less syringe at several sites (approximately 70 cfu per site) on the abaxial side. The leaves were incubated on 0.5% water agar for 2 wk at 25 C under a 16-hr photoperiod. Leaves remained healthy and disease symptoms developed at the inoculation sites. The number of lesions produced at each site was directly proportional to the amount of inoculum infiltrated. Symptom expression and incubation time on detached leaves were similar to those on attached leaves. Symptoms specific for X.c. pv. pruni were not observed with 51 saprophytic bacterial strains tested at inoculum concentrations as high as 1 x 10⁸ cfu/ml. At inoculum concentration of 1 x 10⁶ cfu/ml, the detached leaf response distinguished the previously reported differential field resistance reactions of 21 of 22 peach cultivars.