Evaluation of Partial Substitution of Cocoyam Starch as Alternative Gelling Agent in Culture Media for Cultivation of Fungi

Aim: In view of high cost of agar in Nigeria, the study evaluated the suitability of cocoyam starch and cocoyam starch-agar blends as alternative gelling agents in mycological culture media.

Methodology: Media characteristics and ability of the media to support growth and sporulation of the test fungi A. niger and A. flavus were determined using standard procedures. Potato dextrose agar (PDA) served as the control medium.

Results: Addition of cocoyam starch to the media did not significantly affect media clarity, viscosity, and ease of pouring. Media in which cocoyam starch made up 57% or less of the gelling agent solidified while those with higher contents of starch were either semi solid or watery. Mean radial growth ranges were 75.00 ± 0.70 – 84.00 ± 1.00 mm and 77.50 ± 0.50 – 86.50 ± 0.50 mm for A. niger and A. flavus respectively. Cocoyam starch-agar blend (4:3) medium produced significantly higher mean radial growth (84.00 ± 1.00 mm and 86.00 ± 0.50 mm for A. niger and A. flavus respectively) than all the other treatments (P = .05). Mean spore counts per mycelial disc of the various media ranged from 8.6×103 to 9.3×103 for A. niger and 7.9×103 to 9.5×103 for A. flavus. Though both fungi sporulated well on all the media, the PDA medium and the 2 g of cocoyam starch + 4 g of agar medium had significantly higher mean spore counts compared to the other media.

Conclusion: The findings show that cocoyam starch can partially substitute agar as gelling agent in mycological culture media.