Common bean seed lots collected from different seed dealers and Malawii agriculture station
were screened for the presence of Xanthomonas axonopodis pv. phaseoli. In the laboratory the pathogen was
isolated following the routine laboratory assay method, i.e. direct plating method using yeast extract–dextrose–
calcium carbonate agar medium (YDC). Yellow, convex, mucoid colonies of Xanthomonas were consistently
isolated on YDC from seed samples. The presumptive pathogen was confirmed by isolation on
semiselective medium, such as mTBM and MD5A. Further, the pathogen was confirmed by biochemical,
physiological and, finally, the pathogenicity tests. Five samples out of seven were positive for Xanthomonas.
The isolates were found to cause common blight of 3-week-old common bean plants by 7 d after inoculation.
Bacteria with the same characteristics as those inoculated were re-isolated from the infected plants.