Antifungal Efficacy of Plant Extracts against Fungal Pathogens Associated with Postharvest Rot in Cocoyam

Fungal pathogens affecting stored cocoyam are estimated to result in over 40% post-harvest and financial losses for cocoyam farmers in Sub-Saharan Africa. A study was conducted to isolate and identify fungal organisms responsible for postharvest rot of cocoyam corms during storage, as well as to assess the fungicidal efficacy and mycelia growth inhibitory effects in vitro of plant extracts from Black pepper (Piper nigrum), Neem (Azadirachta indica), and Alligator pepper (Aframomum melegueta) against fungi associated with cocoyam rot in storage. Cocoyam corms exhibiting signs of rot were retrieved from storage to isolate fungal pathogens. Fresh, healthy cocoyam corms were also used to assess the pathogenicity of the isolated fungi. The fungicidal capacity of the aqueous plant extracts was assessed using three extract concentrations (10% w/v, 20% w/v, and 30% w/v). Means were separated using Duncan Multiple Range Test, and analysis of variance was utilized for analysing the data at the 95% confidence level. All fungal pathogens isolated caused rot in both varieties of healthy cocoyam corms following a 14-day inoculation period. Rhizopus stolonifer and Bipolaris sp caused 73.33% rot severity each, followed by Aspergillus flavus (60.0%), Colletotrichum gloeosporioides (33.33%) and Botryodiplodia theobromae (26.67%). The highest radial growth inhibition (90.0%) was recorded for 30% w/v Alligator pepper on Rhizopus stolonifer and 30% w/v black pepper on Bipolaris spp. Alkaloids, tannins, phenols, saponins, flavonoids, cardiac glycosides terpenoids, and Phytosterols were found in the crude aqueous plant extracts. Aqueous extracts of Alligator pepper, Black pepper, and Neem significantly (P ≤ 0.05) inhibited the mycelia growth of fungal pathogens in vitro and can also be used as a substitute for conventional fungicides.