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A Semiselective Medium for Detecting Epiphytic and Systemic Populations of Pseudomonas savastanoi from Oleander. Hamid R. Azad, Department of Plant Pathology, University of California, Riverside 92521-0122; D. A. Cooksey, Department of Plant Pathology, University of California, Riverside 92521-0122. Phytopathology 85:740-745. Accepted for publication 11 April 1995. Copyright 1995 The American Phytopathological Society. DOI: 10.1094/Phyto-85-740.

A new medium, oleander knot agar (OKA), was developed for isolation of Pseudomonas savastanoi from oleander plants. OKA contained (in grams per liter) agar (14.0), l-serine (2.0), yeast extract (1.0), NH4H2PO4 (0.5), K2HPO43H2O (0.5), NaCl (5.0), MgSO47H2O (0.2), boric acid (1.0), vancomycin (0.15), cephalexin (0.05), bacitracin (0.05), ampicillin (0.015), novobiocin (0.02), and cycloheximide (100). All 39 strains of P. savastanoi from different geographical areas grew on OKA, and the quantitative recovery ranged from 5.7 to 93.6% (mean = 43.6%). OKA was more selective than other media tested, including BCBRVB, M-71, KBBC, MSP, proline agar, and PVF-1, and inhibited 89 to 96.7% of saprophytic bacterial strains recovered from oleander tissues. Forty-four percent of other plant-pathogenic bacteria tested did not grow on OKA, and 13% grew sparingly. OKA was used to detect epiphytic populations of P. savastanoi from galls, leaves, stems, and flowers and to detect systemic movement of the bacterium in oleander stems. The pathogen was present in wash water from 26 of 34 apparently healthy oleander plants. Thirty-one of these plants subsequently developed galls within 1 year. The bacterium was also capable of systemic movement up to 25 cm above and 20 cm below the site of inoculation.