ALLELOPATHIC EFFECT OF NIGER PLANT (Guizotia abyssinica L.) ON WEEDS AND ITS INFLUENCE ON GROWTH AND DEVELOPMENT OF BEANS (Phaseolus vulgaris L.)

Abstract

Niger plant (Guizotia abyssinica), is an annual herbaceous plant that originated from Ethiopia. In Kenya, the plant is perceived as a weed whereas in Ethiopia and India, it is cultivated as an important oil crop. It has been observed that crops following a Niger plant infested field have fewer weeds leading to a hypothesis that Niger plant produces secondary metabolites known as allelochemicals that suppress weeds. Being environmentally friendly and with new sites of action, use of allelochemicals may be a solution to the current problems caused by herbicide use. This study was therefore carried out to determine the allelopathic effect of Niger plant on weeds and its influence on growth and development of beans in Moiben sub-county, Uasin Gishu, county. The study involved assessing the genetic diversity of Niger plant from Moiben sub-county using ISSR markers, determining secondary metabolites in Niger plant and evaluating the influence of Niger plant on growth and development of beans and weed abundance. Laboratory experiments included identifying genetic diversity of Niger plant and analysis for metabolites in Niger plant collected within Moiben sub-county. For genetic diversity experiment, plant samples were collected from every administrative ward within Moiben sub-county, DNA was extracted and Inter Simple Sequence Repeat (ISSR) markers used to assess genetic diversity. Assessment of secondary metabolites involved extraction and quantification of alkaloids, flavonoids, phenols, saponins and tannins from Niger plant samples. The field experiment involved four weed regimes and three bean varieties with three replicates. The experiment was a 4 x 3 factorial arranged in a Randomized Complete Block Design (RCBD). The four weed regimes were weed free, weedy, Niger plant intercrop and all weeds but no Niger plant. Bean varieties were Rosecoco, Mwitemania and Mwezi Mbili. Data were collected on genetic diversity of Niger plant, amount of secondary metabolites in Niger plant, stand count of beans at two weeks, plant height at 50% flowering, number of pods per plant, stand count at harvesting, number of seeds per plant and number of Field mustard (Brassica rapa), Broom weed (Guiterrezia sorothrae), Double thorn (Oxygonium sinuatum) Niger plant (Guizotia abyssinica) and couch grass (Cynodon dactylon). Quantitative data were subjected to ANOVA by Genstat version 14 and means separated by Duncan’s Multiple Range Test (DMRT). ISSR data were used to calculate the Squared Euclidean Distance matrix. Genetic analysis resulted into a dendogram with four main clusters hence showing that the Niger plant is genetically diverse. Alkaloids, flavonoids, phenols, tannins and saponins were found to occur in Niger plant in varying concentrations depending on the site of collection. Niger plant showed a negative allelopathy to the studied weeds. Bean growth and development was enhanced by the Niger plant. In conclusion therefore, Niger plant within Moiben sub-county is genetically diverse with varying levels of secondary metabolites. Niger plant can be used to control specific weeds without compromising on bean growth and development. It is recommended that further research be carried out on the agronomic issues surrounding allelopathy for proper understanding of this upcoming technology for weed management.