Efficacy of Plant Extracts on Management of Anthracnose Disease of Yam (Dioscorea spp.) in Bamenda, Cameroon

Anthracnose is a devastating disease in yam (Dioscorea spp)-growing regions, causing heavy yield losses. This study evaluated the efficacy of plant extracts as alternatives to chemical fungicides used to control yam anthracnose. Yam varieties in five species were used to establish an experiment in a split plot randomized block design at the Research Farm of College of Technology, University of Bamenda from March to September 2023. Scent leaf (Ocimum gratissimum) infusion, neem (Azadirachta indica) seed oil and chemical fungicide (mancozeb) were used to treat yam varieties at 2-weekly interval for four months. Yams were assessed for anthracnose incidence, severity and yield. Fungal isolates from infected plants were identified using morphological traits and pathogenicity tested. Mycelia fragments were inoculated on potato dextrose agar (PDA) media, pre-treated with plants extracts and mancozeb, to test in-vitro mycelia growth inhibition. Incidence of anthracnose was significantly higher (p≤0.05) on untreated plants (40 to 80%) than treated plants (0 to 50%) among yam varieties. Severity of anthracnose was not significantly different (p≤0.05) amongst yam varieties treated with O. gratissimum infusion (25±0.07%, D. rotundata) and mancozeb (20±0.07%, D. rotundata). Tuber yield was lowest among untreated plants (1.8±0.8 kg, D. alata) and highest among plants treated with O. gratissimum infusion (5.3±0.25 kg, D. alata) in all yam species. Fungal isolates were identified as Colletotrichum gloeosporioides and its pathogenicity for anthracnose confirmed. Plant extracts at 100% concentration inhibited mycelia growth (92%, D. dumetorum) with similar (p≤0.05) efficacy to mancozeb (100%, D. dumetorum). This study suggests O. gratissimum infusion and A. indica seed oil as good alternatives of chemical fungicides in integrated management of yam anthracnose, with broader implications in global yam-growing areas.