Inhibitory effects of solanum nigrum L.extracts on four phytopathogenic species of colletotrichum corda.

Abstract

In this study Solanum nigrum extracts were evaluated for their potential as a source of a biologically based fungicide. The extracts were tested in vitro against four phytopathogenic species of Colletotrichum Cda. The fungi included C. coffeanum Noack, C. lindemuthianum (Sacc. and Magn.) Schribner, C. musae Berk. and M.A Curtis and C. gloeosporioides (Penzig.) Sacco These were isolated from coffee berries, bean pods, ripe bananas arid mango fruits respectively. The pathogens were isolated from their hosts and cultured in potato dextrose agar (PDA). Solanum nigrum plants were grown in October, 1990 from seeds collected from gardens around Nairobi. The plants were harvested at four week intervals and taken to the laboratory where they were separated into different parts viz: roots, stems, leaves and fruits. Water extracts were made from the different plant organs and tested on the four species of Colletotrichum. Some of the extracts were kept in the freezer for later use. -, . The effect of different concentrations of extracts was determined by diluting the extracts using sterile distilled water. Each aqeous extract ~as mixed with sterilized PDA cooled to 40°C, and this was then dispensed into petri dishes. Each extract and every concentration level had four replicates. Sterile distilled water was used in place of the extract for the control. Colony diameters were measured daily for a period of 9 days. The colony diameters on the treated plates compared to that on the control was taken as a relative measure of fungitoxicity. Mycelial growth and sporulation of the pathogens was less in media treated with S. nigrum extract than on the control plates. Extracts from different plant parts had different inhibitory effects. Leaf extracts were found to have the highest inhibitory effects as compared to extracts from other plant parts. Higher concentrations of the extract were found to be more effective than the lower ones. This was true for stem, root and fruit extracts. Inhibition by leaf extracts did not vary with dilution upto the level used in this study. Extracts from plants at different ages had varying inhibitory effects whereby extracts from three months old plants were found to be most inhibitive. However, inhibition by leaf extracts did not vary with plant age. Extracts from fruits at different sfages of development had varying inhibitory properties. The green fruit extracts had higher inhibition than those from the red ripe fruits. The differences in response to Solanum nigrum extracts by the four species of Colletotrichum were not statistically significant (p>O.05). From this study, there is sufficient grounds for the conclusion that Solanum nigrum may be a potential source of a fungicide against crop diseases caused by the four species of Colletotrichum.