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Selective Isolation of Xanthomonas campestris pv. campestris from Crucifer Seeds. P. S. Randhawa, Postdoctoral research associate, Department of Plant, Soil, and Entomological Sciences, University of Idaho, Moscow 83843; N. W. Schaad, associate professor, Department of Plant, Soil, and Entomological Sciences, University of Idaho, Moscow 83843. Phytopathology 74:268-272. Accepted for publication 12 September 1983. Copyright 1984 The American Phytopathological Society. DOI: 10.1094/Phyto-74-268.

Saprophytic and antagonistic bacteria associated with crucifer seeds often interfere with the isolation of Xanthomonas campestris pv. campestris (hereafter abbreviated to X. campestris) on general plating media such as nutrient starch cycloheximide agar (NSCA). The number of colonies of X. campestris recovered from various crucifer seed lots often depends upon the number of saprophytic and antagonistic bacteria present on NSCA plates. Up to 50% fewer colonies of X. campestris were recovered when antagonistic bacteria were present in the seed washings. Adding nitrofurantoin and vancomycin, respectively, at 10 and 0.5 μg/ml to NSCA (=NSCAA) and 2 and 0.1 μg/ml to basal starch cycloheximide agar (=BSCAA) significantly reduced the development of saprophytic and antagonistic bacteria recovered from washings of crucifer seeds. On NSCAA, 20 strains of X. campestris had plating efficiencies of 0.87 or more compared to 1.00 for NSCA. On BSCAA, 15 strains had plating efficiencies of 0.85 or greater, whereas those of five additional strains ranged from 0.54 to 0.72. On NSCAA or BSCAA, X. campestris was recovered from undiluted or 1:10 dilutions of seed washings, whereas on NSCA, dilutions of 1:100 were needed to reduce saprophytic and/or antagonistic bacteria. Twelve of 102 commercial seed lots assayed during a 2 mo period on NSCA, NSCAA, and BSCAA yielded X. campestris. In six of these seed lots X. campestris was not detected by using NSCA alone. X. campestris was detected in four lots on all three media, in four lots on BSCAA alone, and in one lot on NSCAA. Because of a zero tolerance for black rot and the natural variation in the bacterial flora of crucifer seeds, all three media should be used for assaying seeds for X. campestris.