Physiological Studies on Xanthomonas axonopodis Pv Manihotis (Xam) Strains Isolated in Nigeria

Xanthomonas axonopodis pv manihotis (Xam) is the causal agent of cassava bacterial blight (CBB) worldwide. To develop a well-organized disease management policy in a country, the diversity of pathogens population must be known. The bacterial populations of Xanthomonas axonopodis pv manihotis (Xam) obtained as flora cassava leaves and stems, in Nigeria were characterized by their biochemical and the physiological reactions with basic routine microbiological techniques which were subjected to cluster analysis. A total of 75 bacteria strains were studied, made up of sixty eight (68) Xanthomonas axonopodis pv manihotis (Xam), four (4) Xanthomonas axonopodis pv cassavae (Xac) and three (3) unidentified species. The isolates were similar to one another in most of the cultural and physiological characteristics. They were all able to hydrolyze aesculin and showed a positive reaction to catalase, citrate and oxidase tests. They were indole, methyl-red, Voges-Proskauer and urease negative. The analysis carried out on the biochemical data clustered the Xam and Xac together at 94.5 %; the unidentified strains were separated. The dendrogram generated from the data obtained from the oxidative metabolism of various sugars clustered the pathogens together at 94 %, also exempting the unidentified bacterial flora. We conclude that cultural and physiological reactions could not differentiate the yellow strains from the white strains of the pathogen of cassava bacterial blight from the result obtained in this study. Although there are variations in the reaction of the pathogen to some tests conducted, these could not be used to segregate the bacteria into different pathogenic group since they are not consistent within the white strains of the bacteria.