EVALUATION OF BOTANICALS FOR THE CONTROL OF ANTHRACNOSE (Colletotrichum gloeosporioides Penz) OF YAM (Dioscorea rotundata POIR)

Abstract

Anthracnose is the most serious leaf and vine epiphytotic disease of yam that causes yield loss. Severe infection results in vine dieback, defoliation, and tuber rot. Aqueous extracts of Azadirachta indica A Jus seed (Neem tree seed), Jatropha curcas ( L) seed (Jatropha plant seed) and Nicotiana tabacum (L) leaf (Tobacco plant leaf) extracts were evaluated for the control of anthracnose disease of yam (Dioscorea rotundata Poir). The pathogen was isolated, identified and its growth was determined in vitro. The Potato Dextose Agar (PDA) was amended with the mother extract to make 35, 45, 55, 65 and 75% concentrations in the Petri dishes. Each Petri dish contained 2 ml of an extract and 20 ml of sterilized PDA. The solidified PDA plates were inoculated at the centre with 5 mm diameter mycelial disc of C. gloeosporioides Penz and incubated at 27 0C for 7 days (Nene and Thapliyal, 1979). PDA plates without extract served as negative controls whiles those with the thiophanate methyl (2 ml) served as positive controls. It was observed that 75 % of each plant extract recorded the least mycelial growth compared to the negative control. Percentage mycelial growth in PDA plates treated with A. indica seed extract, N. tabacum (L) leaf extract and J. curcas (L) seed extract were 15, 19.33 and 26.33 % respectively compared to the untreated control (100 %). Generally, the higher the concentration of each plant extract, the higher the inhibitory action against the fungus. Pathogenicity tests carried out showed that C. gloeosporioides Penz was the cause of the anthracnose symptoms observed. Each plant extract at 75 % concentration applied in vivo reduced the incidence and severity of the anthracnose disease. The plants extracts also promoted vegetative growth. Uninfected plants produced higher chlorophyll content than infected plants. The plant extracts at 75 % concentration also produced higher yield. Farmers may use 75 % concentration of A. indica A Jus seed, J. curcas (L) seed and N. tabacum (L) leaf extracts as an alternative to synthetic fungicides for the control of yam anthracnose diseases.