Authors: K O Akrasi, R T Awuah, E Moses, E Otoo, R Asiedu
Journal: Ghana Journal of Horticulture
Fungitoxicity of sterilized nutrient broth (NB) culture filtrate of a yam rhizosphere bacterium (designated ESI) with proven anti-fungal activity was compared with two synthetic fungicides, Topsin-M (70 WP) and Ridomil plus. Five concentrations (0, 25, 50, 75 and 100 %) of the culture filtrate and the fungicides were tested for activity towards Aspergillus niger, a major yam rot fungus. Each concentration was established by mixing the filtrate or the fungicide with the requisite amount NB in 25 cc-capped vials. Vials containing the various filtrate/fungicide concentrations were seeded with a conidial suspension (106 conidia/ml) of A. niger (50 Jul /vial) and mycelial mats of the fungus, if any, harvested after 7 days, oven-dried and weighed. The ESI culture filtrate was also autoclaved up to 80 min and similarly assayed to determine its thermo stability. In the absence of fungicides or ESI culture filtrate in the NB, an average mycelial mat weight of 107.10 mg was obtained after 7 days. Topsin-M completely inhibited the fungus at concentrations of 25 % and above whereas Ridomil plus and the rhizobacterial filtrate completely inhibited the fungus at 75 % concentration and above. In vials where mycelial growth observed in the presence of Ridomil virus and the ESI filtrate, conidial production by the test fungus was poor. Repeat of the experiment gave similar results. The ESI filtrate was fungitoxic after 80 min of autoclaving, indicating its thermo stability stability. These results suggest that the culture filtrate of the rhizobacterium, ESI, is highly fungitoxic and could be exploited as a stable bio-fungicide.