Submitted to: European Journal of Plant Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/1/2014
Publication Date: 9/11/2014
Publication URL: http://doi 10/1007/s10658-014-0497-3
Citation: Kebede, M., Timilsina, S., Ayalew, A., Admassu, B., Potnis, N., Minsavage, G.V., Goss, E.M., Hong, J.C., Strayer, A., Paret, M., Jones, J.B., Vallad, G.E. 2014. Molecular characterization of Xanthomonas strains responsible for bacterial leaf spot of tomato in Ethiopia. European Journal of Plant Pathology. online. Interpretive Summary: Bacterial spot of tomato is found throughout Ethiopia and central Africa, yet a formal study has not been performed to identify the causal agent. In this study, strains were collected throughout Ethiopia and were characterized using pathogenicity tests, pesticide resistance, and phylogenetically using six housekeeping genes. The Ethiopian strains were closely related to either Xanthomonas vesicatoria, X. perforans or X. gardneri.
Technical Abstract: Bacterial spot of tomato (BST) is a major constraint to tomato production in Ethiopia and many other countries leading to significant crop losses. In the present study, using pathogenicity tests, sensitivity to copper and streptomycin, and multilocus sequence analysis, a diverse group of Xanthomonas strains from central Ethiopia was isolated and characterized. None of the strains was sensitive to copper or streptomycin. Multilocus sequence analysis was used to compare Ethiopian strains with representative Xanthomonas strains from a worldwide collection based on DNA sequences of six housekeeping genes (lacF, lepA, gyrB, fusA, gltA and gapA) and hrpB genes. Phylogenetic analysis of the concatenated sequences showed that X. gardneri, X. vesicatoria and X. perforans were associated with BST in Ethiopia, whereas X. euvesicatoria was absent from the Ethiopian sample. There was no genetic diversity among the isolated strains belonging to X. gardneri and X. perforans. However, two X. vesicatoria haplotypes were identified indicating at least two different sources of introduction of X. vesicatoria to Ethiopia. All of the X. perforans strains were only pathogenic on tomato and were T3 strains with the exception of one identified as tomato race 4 (T4). The X. gardneri and X. vesicatoria strains were tomato race 2 (T2), but were variable in pepper race determinations indicating variation in effectors among strains.