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Title: Anti-microbial properties of yam rhizosphere micro-organisms and their potential use for controlling yam tuber rots
Authors: Akrasi, Kwame Osei
Issue Date: 15-Nov-2005
Series/Report no.: 3894;
Abstract: The main purpose of this study was to screen some yam rhizobacteria for antagonism towards some yam tuber rot fungi and to control yam tuber rot caused by Aspergillus niger with the most promising rhizobacterium. Twenty- four rhizobacterial isolates were screened using the zone of inhibition test. Six bacterial isolates associated with rotten yam tubers were also studied. Three-day- old nutrient broth (NB) cultures of promising rhizobacterial isolates and their cell-free extracts were further tested for fungitoxicity. Nine rhizobacterial isolates, representing 30 % of all bacterial isolates screened, exhibited appreciable antifungal activity. They were all Gram-negative, catalase positive, aerobic and endospore-forming rods, suggesting that they could be Bacillus spp. None of the bacterial isolates from rotten yam tubers was inhibitory. Broth cultures and culture filtrates of the nine rhizobacterial isolates were fungitoxic when they were individually mixed with spores of three fungi and assayed. Fungitoxicity of the sterilized culture filtrate of the most promising rhizobacterium, ESI, was compared with two synthetic fungicides, Topsin-M (70 WP) and Ridomil Plus. Topsin-M completely inhibited the test fungus, A. niger, at 25% concentration and above whereas Ridomil Plus and the rhizobacterial culture filtrate completely suppressed the fungus at 75% concentration and above. These results suggest that the rhizobacterial extract is very potent and could be exploited as a bio-fungicide. The rhizobacterium, ESI, also inhibited all 22 fungal species from different phyla assayed against it, indicating its broad-spectrum fungitoxicity. £81 was further tested for ability to suppress yarn tuber rot caused by A. niger. When the tuber was inoculated with only A. niger, an average of 6 g of tuber with a volume of 6 cm3 was rotted. These were significantly higher (P> 0.05) than the 2.96 g (vol., 2.25 cm3) and 2.25 g (vol., 2.25 cm3) rotten tuber tissues, respectively, associated with the ESI and Topsin-M treatments. ESI and Topsin-M were equally effective in suppressing yam tuber rot. The rhizobacterium, £81, was consistently isolated from inoculation points on tubers, indicating its competitive survival, colonization and persistence on the tuber. The current study has clearly shown that certain rhizobacteria of yarn possess antifungal properties and should be investigated further for possible use in the control of yam tuber rot Curvularia lunata was identified in the current study as a new yam rot pathogen in Ghana.
Description: A thesis submitted to the Department of Crop Sciences in partial fulfilment of the requirements for the degree of Master of Science, 2005
URI: http://hdl.handle.net/123456789/1826
Appears in Collections:College of Agric and Natural Resources

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