Antifungal Post-Infectional Compounds from Dioscorea Alata.
Phytoalexins were isolated from fungal infected discs of Dioscores alata Linn and their antimicrobial and phytotoxic activities studied. In order to determine the most probable biosynthetic pathway for the synthesis of these phytoalexins, the activities of some of the enzymes in the phenylpropanoid pathway were evaluated. Yam discs infected with mycelial suspension of Botrydiplodia theobromae and incubated in total darkness and 16 hours daylight respectively, was extracted with ethylacetate and diethylether respectively. Using different chromatographic and spectroscopic techniques, the phytoalexins isolated were characterised. These phytoalexins were assayed against the following human micro-organisms; Staphylococcus aureus NCTC 3251 and Escherichia coli NCTC 10418 using the cup-plate method and the extent of mycelial growth for assay against Aspergillus fumigatus at concentrations ranging from 10-100 µg/ml. They were also assayed against seeds and seedlings of Sorghum bicolor and Zeamays to determine their effects on seed germination and radicle elongation. The rate of accumulation of these phytoalexins in relation to the induction of phenylalanine ammonia lyase (PAL), tyrosine ammonia lyase (TAL) and shikimic acid dehydrogenase (SDH) were investigated in relation to the time of incubation of the yam discs in hours and distances from infected surface of the tubers.