A Detached-Leaf Bioassay forXanthomonas campestrispv.pruni

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Abstract
Young leaves of peach seedlings very detached and surface sterilized with 70% ethanol. Inoculum (106 colony-forming units [cfu] per mililiter) of X. 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 .times. 106 cfu/ml. At inoculum concentration of 1 .times. 106 cfu/ml, the detached leaf response distinguished the previously reported differential field resistance reactions of 21 of 22 peach cultivars.