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ARS Home » Northeast Area » Frederick, Maryland » Foreign Disease-Weed Science Research » Research » Publications at this Location » Publication #35808


item Schaad, Norman

Submitted to: International Seed Testing Association Handbook
Publication Type: Other
Publication Acceptance Date: 4/24/1995
Publication Date: N/A
Citation: N/A

Interpretive Summary: Routine methods to detect Xanthomonas campestris pv campestris, the causal agent of black rot of cabbage and other crucifers, are described. The methods were tested in a large scale comparative test (using naturally contaminated seeds) by the Bacteriology Working Group of Plant Disease Committee of International Seed Testing Association (ISTA) and shown to be reliable. For detection of contaminated seeds, washings from seeds are plated onto two different agar media that are semiselective for the pathogen. For detection of infected seeds, seeds are soaked in a 1:10 dilution of household bleach, rinsed in water, and plated, using a commercial vacuum seed planter, onto 15 cm diameter Petri plates containing a semiselective agar medium. Suspect colonies are removed, streaked onto YDC agar and the identification of all mucoid yellow colonies confirmed by pathogenicity tests. The methods are recommended by ISTA for routine seed health testing of Brassica seeds.

Technical Abstract: Results of an internationally organized comparative test on newly described methods for detecting Xanthomonas campestris pv campestris in commercial crucifer seeds are presented. For detection of contaminated seeds, samples from liquid washings of 10,000 seed soaked in saline, Tween 20 for 5 min. and 2.5 hr at room temperature are plated onto nutrient starch cycloheximide antibiotic agar and Fieldhouse-Sasser agar. Suspect colonies are removed and streaked onto yeast extract-dextrose calcium carbonate agar for presence of yellow, mucoid pigment. Identity is then confirmed by pathogenicity tests. Results showed that the numbers of viable cells of X. c. campestris recovered is increased by the longer wash in seed lots with few other bacteria and by the shorter wash time in lots with large numbers of other bacteria. For detection of infected seeds, samples are surface sterilized, and plated onto 15-cm diameter plates containing a modified starch medium for Xanthomonas (SX agar) using a 250- hole commercial vacuum seed planter. After 7-10 days seeds surrounded with a light green growth and starch hydrolysis are removed and tested for pathogenicity. The direct plating test should be used for assaying seeds treated to eradicate the pathogen. It is quantitative and, therefore, very useful for determining percentage infection