Allelopathic Potentials of Tithonia diversifolia (Hemsl) A. Gray: Effect on the Germination, Growth and Chlorophyll Accumulation of Capsicum annum L. and Lycopersicon esculentum Mill.

The study was carried out to evaluate the allelopathic effect of the fresh shoot aqueous extract (FSE) and water soluble root exudate (WRE) of Tithonia diversifolia (Hemsl) A. Gray on the germination, growth and chlorophyll content of pepper (Capsicum annum L. ) and tomato (Lycopersicon esculentum Mill.). The aqueous extract of the fresh shoot (FSE) of T. diversifolia did not affect the germination of L. esculentum seeds but significantly retarded germination of C. annum seeds at p<0.05. The plumule length of both crops and radicle length of C. annum were not affected while the latter parameter was significantly reduced at p<0.05 for L. esculentum. The water soluble root exudate of Tithonia diversifolia plants did not have any significant effect on the growth parameters of both test crops. However, chlorophyll b of C. annum was significantly inhibited at p<0.05 especially in the older plants while chlorophyll b and total chlorophyll of L. esculentum were significantly enhanced at p<0.05. Evidently, the concentration of allelochemicals in the T. diversifolia exudate and extract that was inhibitory to germination and chlorophyll b accumulation in C. annum was ineffective on germination of L. esculentum and stimulatory to its chlorophyll accumulation. The allelochemicals in T. diversifolia are therefore capable of performing a dual role. Their mode of actions differing depending on the associated plant species.