Folia Microbiol. 55 (1), 47–52 (2010) http://www.biomed.cas.cz/mbu/folia/ Occurrence of Xanthomonas axonopodis pv. phaseoli, the Causal Agent of Common Bacterial Blight Disease, on Seeds of Common Bean (Phaseolus vulgaris L.) in Upper Egypt M.H. ABD-ALLA a , S.R. BASHANDY a , S. SCHNELL b a Botany Department, Faculty of Science, Assuit University, Assuit 71516, Egypt b Institute of Applied Microbiology, Interdisciplinary Research Center (IFZ), Justus-Liebig-Universität Giessen, D-35392 Giessen, Germany e-mail mabdalla@sci.mak.ac.ug Received 27 March 2009 Revised version 28 August 2009 ABSTRACT. 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–dextr- ose–calcium carbonate agar medium (YDC). Yellow, convex, mucoid colonies of Xanthomonas were con- sistently 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. Common beans (Phaseolus spp. L.) are one of the most ancient crops of the world. Beans are the most important grain legumes for direct human consumption in the world. Total production exceeds 23 Tg (23 × 10 6 metric tonnes) of which 7 Tg are produced in Latin America and Africa (Broughton et al. 2003). Common bean (Phaseolus vulgaris) is an important source of dietary protein and starch in Egypt. Consump- tion of beans in Africa represents a significant contribution to human nutrition. Phytopathogenic bacteria are responsible for a great variety of diseases in plants, causing important agricultural losses (Abd-Alla and Bashandy 2008). Among the numerous bean diseases, common bacterial blight (CBB) is one of the most economically important and widespread and is a major constraint to the realization of high yields all over the world (Opio et al. 1993; Coyne et al. 2003). The causal agent of common bacterial blight is Xanthomonas axonopodis pv. phaseoli (Vauterin et al. 1995). The disease causes both quantitative and qualitative yield losses ranging between 10 and 40 % depending on bean cultivar susceptibility and environmental conditions (Saettler 1989). Common bacterial blight is a serious seedborne disease of beans in both temperate and tropical production zones (Saettler et al. 1995). Contaminated seed is probably the major source of bacteria introduced into new bean crops. Common bean seed planted in Egypt normally is not tested for presence of X. axonopodis pv. phaseoli. The overall objective of this study was to determine the occurrence of X. axonopodis pv. phaseoli on common bean seed lots collected from different seed stores in Assuit and Menia Governorates, Upper Egypt, and to characterize the pathogenicity of these isolates. MATERIAL AND METHOD Samples collection. Seed samples (500 g seed of each) of common bean (Phaseolus vulgaris L.) used were collected from two seed dealers in Assuit City and one seed dealer in El Kossia town (Assuit Gover- norate). Three varieties (Nebraska, Bronco and Giza 3) and one commercial variety were collected from Agriculture Research Station and seed dealer, respectively, in Malawii town (Menia Governorate). From each sample were taken from bags by reaching to the bottom of the bag and pulling a subsample up through the bag. This was repeated several times until 500 g seed had been collected.