Potential of some Bacteria and Fungi as Biocontrol Agents of Cassava and Yam Tuber Rot Pathogens under Laboratory and Green House Conditions
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The potential of Bacterial isolates Pseudomonas sp., Xanthomonas sp., and Bacillus sp., and the fungi Trichoderma harzianum and Penicillium oxalicum as biocontrol agents of pathogens of cassava and yam tuber rot has been evaluated. The following assays were used (a) effect of the bacterial and fungal antagonists on fungal growth in the central disk with paired cultures (b) effect of the antagonists on the germination of fungal spores in the paired suspension assay (c) reduction of disease severity in green house experiments. The observed effects were specific for antagonistic- pathogen combination investigated .In the paired culture tests, the mycelial growth of most of the pathogens were inhibited by the bacterial antagonists. The mycelial growth of Sclerotium rolfsii was inhibited (90%) by all the bacterial antagonists. There was a significant difference among antagonists used against pathogens (P< 0.0001). T. harzianum showed the best results for controlling all pathogens. Penicillium oxalicum was very effective in controlling Fusarium only. Microscopic examination of excised pieces of fungal colony perimeters showed clear differ- ences among treatments and controls in hyphal morphology. There was inhibition in conidial germination of Botryodiplodia sp. and Fusarium on paired incubation with the antagonists. In the central disk test, Trichoderma showed necrosis of the pathogens and P. oxalicum showed the presence of inhibiton haloes. Bacillus sp. showed chemotaxis.