Development and Application of a Plasmid DNA Probe for Detection of Bacteria Causing Common Bacterial Blight of Bean

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Abstract
Total plasmid DNA and cloned plasmid DNA fragments from Xanthomonas campestris pv. phaseoli were used as probes to detect X. c. phaseoli and X. c. phaseoli var. fuscans, causal agents of common bacterial blight of bean. Plasmid DNA hybridized extensively to total genomic DNA from 50 strains of X. c. phaseoli and X. c. phaseoli var. fuscans, less extensively to that from X. c. pvs. alfalfae, carotae, vesicatoria (races 1 and 2), and oryzae, and not at all to that from X. c. pvs. campestris, holcicola, or pelargonii, nonpathogenic xanthomonads from bean debris or other bacterial species. A 3.4-kb EcoRI fragment of plasmid DNA, which contains repetitive DNA, was more specific probe for X. c. phaseoli and X. c. phaseoli var. fuscans than total plasmid DNA. The limit of detection of these probes was 103 X. c. phaseoli colony-forming units (.apprx. 10 pg of DNA). A colony hybridization procedure was used to detect colonies of X. c. phaseoli recovered from bean leaves and debris, and squash and dot blot hybridization procedures were used to detect X. c. phaseoli in bean leaves. Our results indicate that DNA probes are a useful tool for detecting plant pathogenic xanthomonads and may be used in ecological and epidemiological studies.

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