Physiological Response of Capsicum annuum L. to Aqueous Extracts of Allelopathic Plants: A Case of Tithonia rotundifolia and Murraya koenigii

The present study evaluated the allelopathic potential of fresh shoot aqueous extracts of Tithonia rotundifolia (FSET) and Murraya koenigii (FSEM) on the germination of seeds, growth, chlorophyll, ascorbic acid and percentage crude protein accumulation of Capsicum annuum. The laboratory experimental results showed that seed germination and juvenile seedling growth of C. annuum were significantly retarded by both FSEM and FSET. The radicle growth was more susceptible to the phytotoxicity of both extracts than the plumule growth. Both plants extract had a concentration-dependent inhibitory effect on the seedling growth of the recipient crop while the FSET was more phytotoxic than FSEM. However, this retardatory effect of aqueous extracts on growth observed in the laboratory was reversed in the soil-cultured experiments such that application of FSEM significantly enhanced all the studied growth parameters (shoot height, number of leaves, leaf area, leaf area ratio, shoot fresh and dry weight, root fresh and dry weight, chlorophyll a, chlorophyll b, total chlorophyll, ascorbic acid content in the shoot and percentage crude protein in the shoot and fruits). Likewise, FSET application significantly increased the leaf area, total chlorophyll and percentage crude protein accumulation in the shoot and fruits of the recipient crop at P<.05. This study then emphasizes the fact that T. rotundifolia and M. koenigii are allelopathic plants. The increased ascorbic acid and percentage crude protein accumulation in the aqueous extract-treated crop could, apart from enhancing the nutritional benefits of the test crop, be an adaptive mechanism evolved by the crop to overcome the allelopathic stress posed by the application of the aqueous extracts. These findings therefore suggest that allelochemicals in the aqueous extract of M. koenigii and T. rotundifolia could serve as biofertilizers for boosting the production of C. annuum.