Biological Control of Post-harvest Rot in Water Yam (Dioscorea alata L.) Using Antagonistic Fungi

Water yam tubers are staple food consumed in the South-Eastern Nigeria and are susceptible to microbial contamination in storage. This investigation focused on antagonistic potentials of saprophytic fungi, Cryptococcus nemorosus, Rhodotorula toruloides and Nakaseomyces glabratus against the spoilage fungi of water yam tubers in storage. The diseased tissues from the water yam samples were inoculated on PDA plates. The microbial pathogens obtained were; Botryodiplodia theobromae, Aspergillus niger, Rhizopus stolonifer, Fusarium solani and Penicillium spp. Analysis of Variance (ANOVA) was employed and the Duncan’s New Multiple Range Test (DNMRT) was used to test the difference among treatments. The results of the in vitro assessment of fungal pathogens on water yam samples revealed that Cryptococcus nemorosus showed the highest zone of inhibition (13.50 + 0.12 mm) on Botryodiplodia theobromae while the least zone of inhibition (9.14 + 0.26 mm) was recorded for Fusarium solani after 48 hours of incubation. Rhodotorula toruloides recorded the highest zone of inhibition (22.10 + 0.45 mm) on Rhizopus stolonifer whereas the least zone of inhibition (9.05 + 0.36 mm) was observed on Botryodiplodia theobromae after 48 hours of incubation. Nakaseomyces glabratus showed the highest zone of inhibition (27.80 + 0.13 mm) on Botryodiplodia theobromae while the least zone of inhibition (14.84 + 0. 20 mm) was recorded against Fusarium solani after 48 hours of incubation. The results of the in vivo mean mycelia radial growth of the fungal pathogens revealed that Cryptococcus nemorosus showed the highest growth (73.75 + 0.11 mm) against Aspergillus niger while the least growth (64.80 + 0.15 mm) was observed on Rhizopus stolonifer after 48 hours of incubation. Rhodotorula toruloides had the highest growth (68.45 + 0.50 mm) on Aspergillus niger while the least growth (55.50 + 0.09 mm) was recorded against Rhizopus stolonifer after 48 hours of incubation. Nakaseomyces glabratus showed the highest growth (67.00 + 0.12 mm) on Rhizopus stolonifer whereas the least growth (51.90 + 0.12 mm) was recorded against Botryodiplodia theobromae after 48 hours of incubation. The fungitoxic potentials of these biological antagonists on water yam rot can provide an alternative to synthetic fungicides since it is less expensive, environmentally friendly and easy to prepare.