In-Vitro Evaluation of Microbial Isolates from Composted Farmyard Manure for Biological Control of Cocoyam (TARO: Colocasia spp.) LEAF Blight Diseases.

Production and yield of Cocoyam (Taro: Colocasia spp), a staple food crop in Nigeria is hampered as a result of attack by Taro leaf blight disease caused by Phytophtora colocasiae. Chemical control of this disease has caused some environmental problems. Microbial Isolates from composted manure, as biological control agents, were evaluated for their antagonistic activity on P. colocasiae. The research was carried out in the Laboratory of Department of Crop Science and Biotechnology, Imo State University, Owerri, Nigeria. Farmyard manure was composted for ninety (90) days, where samples were cultured in Nutrient Agar (NA) and Sabouraud Dextrose Agar (SDA) for 48 hours and 420 hours, respectively. Bacteria isolates were Pseudomonas spp., Bacillus spp. Escherichia coli, and Staphylococcus aureus; while fungi isolates were Penicillium spp., Aspergillus spp., Trichoderma viridae, Fusarium spp. and Mucor. These isolates were tested for their antagonism on P. colocasiae. Evidence of antagonism was measured by diameter (mm) of inhibition of growth of P. colocasiae in the culture. Data were analysed at 5% level of probability. Results showed that bacterial organisms; Pseudomonas spp., Bacillus spp., Escherichia coli and Staphylococcus aureus recorded mean diameter of P. colocasiae growth inhibition of 43.16mm, 40.35mm, 19.66mm and 17.33mm, respectively. No significant difference (p=0.05) was observed between Pseudmonas spp. and Bacillus spp. Similarly, the fungi organisms; Penicillum spp., Aspergillus spp., Trichoderma viridae, Fusarium spp. and mucor recorded mean diameter of P. colocasiae growth inhibition of 46.16mm, 42.66mm, 25.16mm, 22.16mm, and 6.66mm, respectively. Significant difference (P=0.05) was observed among all the fungi isolates. Pseudomonas spp and Bacillus spp (bacteria) and Penicillium spp (fungi) exhibited better antagonism properties on P. colocasiae than the others. These three organisms are currently being tried in field experiments for subsequent use as biological control agents for leaf blight disease pathogen in Cocoyam. Key Words: Cocoyam (Taro), P. colocasiae, biological control, bacteria, fungi, isolates.