Allelopathic effect of aqueous extracts of Tithonia Rotundifolia P.M. Blake And Murraya Koenigii L. on the growth and biochemical constituents of capsicum annuum L. and corchorus olitorius L.
The study was conducted to investigate the allelopathic effects of fresh shoot aqueous extracts of Murraya koenigii L. and Tithonia rotundifolia P.M. Blake on the growth and biochemical constituents of Capsicum annuum L. and Corchorus olitorius L. plants. Germination experiment was carried out by raising the seedlings of the two target crops in Petri-dishes lined with Whatman No 1 filter paper and moistened with 10 ml of different concentrations (50% and 100% representing half and full strength) of the aqueous extracts of M. koenigii and T. rotundifolia. For the growth parameters (shoot height, root length, number of leaves, leaf area, leaf area ratio ), yield parameters (fresh shoot and root weight, dry shoot and root weight) and quality parameters (chlorophyll, ascorbic acid and crude protein) analyses, potted plants were separated into the control and two other regimes namely: fresh shoot aqueous extract of T. rotundifolia (FSET) and fresh shoot aqueous extract of M. koenigii (FSEM). The pots were arranged in a completely randomized design. The control plants were supplied with 600 ml of tap water while the extract-treated plants were supplied with 600 ml of the appropriate aqueous extracts daily. Harvesting started at two weeks and continued thereafter on a weekly basis for six weeks. Chlorophyll accumulation, ascorbic acid, percentage nitrogen and crude protein content were determined using standard methods. The data were analyzed using Analysis of Variance (ANOVA) and Least Significance Difference (LSD p < 0.05). The extracts significantly inhibited the germination of the seeds and the plumule and radicle lengths of both target crops. This effect was extract concentration dependent (100% > 50% > Control). The applied extracts of M. koenigii plants significantly promoted virtually all the growth parameters such as shoot height, number of leaves, leaf area, leaf area ratio, fresh shoot weight, fresh root weight, dry shoot weight, dry root weight, chlorophyll a, chlorophyll b, total chlorophyll, ascorbic acid and protein accumulation of the two target crops. The aqueous extract of T. rotundifolia enhanced only the shoot height, leaf area, root fresh weight, chlorophyll a, chlorophyll b, total chlorophyll, ascorbic acid and protein accumulation in the shoot of C. annuum. The root length was however, significantly inhibited by both aqueous extracts. In the case of the potted plants, the effects of the extracts on the various parameters studied followed the order: FSEM > FSET > CONTROL and was target species dependent. The results presented in this work showed that FSEM had more pronounced stimulatory effects on the studied parameters than the FSET. It was evident that while the level of the allelochemicals in the extracts of the two donor plants was phytotoxic to and inhibited the germination and growth of the juvenile seedlings in the Petri-dishes, they, however, had a stimulatory effect on the growth of the matured potted plants as well as on the accumulation of the biochemical constituents studied.