Effect of leaf extracts of Cymbopogon Citratus, Chromolaena Odorata and Newbouldia Laevis on the Dioscorea Alata rot

Abstract

less than that of white yam. Water yam (D. alata L.) is grown widely in tropical and subtropical regions of the world. They are plants yielding tubers and contain starch between 70% and 80% of dry matter [9,10]. The tuber is the only economically important part of the crop and according to Sangoyomi [11], it is consumed roasted, fried, boiled, pounded or as flour which can be reconstituted with hot water. Yam tubers are of a very high value, as in food, where it is a major source of carbohydrate, minerals of calcium, phosphorus, iron and vitamins B and C [2,12]. According to Olayide and Heady [13], the demand for yam in Nigeria has always exceeded its supply. In spite of the importance of yams as major staple food and its socio-cultural value in the lives of the people of the West and Central Africa sub-region, research and documentation on this important staple food crop is very limited [11]. Abstract Fungitoxic effect of ethanol and cold-water extracts of Cymbopogon citratus, Chromolaena odorata, and Newbouldia laevis were determined in vitro on causative agents of water yam rot. The microbial pathogens obtained were Botryodiplodia theobromae, Aspergillus niger, Fusarium solani, Penicillium spp and Rhizopus stolonifer. Ethanol and cold-water extracts of the plants were prepared by adding separately 10 g, 20 g, 30 g, 40 g and 50 g of the leaf powder of Cymbopogon citratus, Chromolaena odorata and Newbouldia laevis into 100 ml of ethanol and cold water respectively. All extracts of the plant materials at varying concentrations showed antifungal activity against the fungal tested. The antimycotic effect of the plant extracts varied with the solvent of extraction, extraction concentration and the test organisms. Ethanol extracts of Cymbopogon citratus had between slightly (11.10-18.00%) and moderately effective (29.65-46.00%) inhibition on the mycelia growth of all the fungi tested. Also, cold water extracts of Cymbopogon citratus depicted slightly (4.00-19.92%) and moderately effective (37.7-39.00%) inhibition on all the fungi tested. Ethanol extracts of Chromolaena odorata had between slightly (11.18-15.03%) and moderately effective (29.65-41.00%) on all the fungal pathogens. Also, cold water extracts of Chromolaena odorata showed between slightly to moderately effective inhibition ranging from (8.00-19.05%) to (21.00-39.00%) respectively. Ethanol extracts of Newbouldia laevis showed between slightly (0.35-19.10%) and moderately effective (22.90-49.11%) inhibition on all the fungi tested. Cold water extracts of Newbouldia laevis showed between slightly to moderately effective inhibition ranging from (3.40-19.00%) to (22.00-44.01%) respectively. The most fungitoxic of all the extracts was observed with the 50% ethanol extract of Newbouldia laevis which showed significant (P<0.05) inhibition on all the test fungal pathogens. Ethanol plant extracts showed higher antifungal activity against the test pathogens than the cold-water plant extracts. Analysis of Variance (ANOVA) was employed and the Duncan's Multiple Range Test (DMRT) was also used to test the difference among treatments. Phytochemical screening of the leaf extracts revealed the presence of saponins, alkaloids, tannins and flavonoids in the extracts but at different concentrations. This study indicated that Cymbopogon citratus, Chromolaena odorata and Newbouldia laevis were able to suppress rot-causing fungi of water yam deterioration. The fungitoxic potentials of these extracts on water yam rots can provide an alternative to synthetic fungicides since it is less expensive, environmental friendly and easy to prepare.