Ethnobotanical Leaflets 13: 343-50. 2009.
Allelopathic Effects of some Crop Residues on the Germination and Growth of Cowpea (Vigna unguiculata L. Walp.)
J. Kayode and J.M. Ayeni
Department of Plant Science, University of Ado-Ekiti,
The allelopathic effect of aqueous extracts from sorghum and rice husk on germination and growth of cowpea was investigated. The results showed that the extracts brought about considerable inhibition in the germination of cowpea seeds and in the growth of its radicle and plumule. The germination percentage in the extract-treated seeds decreased with the increase in the concentration of the extracts thus indicating that the degrees of inhibition were concentration dependent. It was apparent that sorghum extracts had more inhibitory effects on cowpea seeds than those from the rice husks. In sorghum extract- treated seeds, radicle growth was observed clearly at 48hrs of the experiment whereas radicle growth was recorded at 24hrs experimental time in the rice husks extracts. Also in sorghum extracts, plumule growth occurred at 72hrs of the experiment whereas plumule growth was recorded at 48hrs experimental time in the rice husks extracts treated seeds.
Key words: Allelopathy, allelochemicals, rice husk, sorghum, inhibition.
Allelopathy is the ability of plant to inhibit the germination of other plants through the production of allelochemcals (Rice 1984, Inderjirt 1966) which may be present in any parts of the plants, i.e. leaves, roots, fruits, stems, rhizomes and seeds, from where they are released to the soil through volatilization, root exudation, leaching and decomposition of plant residues (Rice 1984, Chou 1990).
A number of authors, such as Rice (1984), Rasmussen and Rice (1971) and Nelson (1996) had documented the interference effects of some plants on other crops, prominent of which is the inhibition of germination (Williamson et al 1992, Patil, (1992), Djurdjevic et al 2004), reduction in the growth lengths of plumule and radicle (Tobe and Omasa 2000), retardation of seedling growth (Bhatt and Todoria 1990) and poor seedling survival (Smitt 1990). Previous assertions had suggested that allelochemicals inhibit seed germination by blocking of nutrient reserve and cell division thereby caused significant reduction in the growth of plumule and radicle of many crops (Ogbe et al 1994, Tobe and Omasa (2000).
studies conducted in
rice husks were obtained from a rice mill in Ikere Ekiti, a town situated at about 25km from University Ado Ekiti
of 5g, 10g, 15g, 20g and 25g were measured out form rice husks and sorghum
residues. Each portion was soaked in 200ml of distilled water in 500ml
conical flasks. The mixtures were shaken intermittently and left over for
24hrs.The extracts were filtered using Whatman No 1
filter paper and the filtrates were used afresh, some portions were kept
inside the refrigerator for further usage. Two layers of Whatman
No 1 filter papers were put in each Petri dish of
9cm diameter and five maize seeds, obtained from the Department of Plant
Control experiment was also set up, also replicated ten times, with Petri dishes moistened with distilled water and replicated ten times. All the Petri dishes were kept in the growth chamber at room temperature. The seeds were considered germinated upon radicle emergence. The germination, radicle and plumule growth elongation measurements were recorded at 24hrs interval for six days. The results obtained from the extracts treated seeds were compared statistically to those obtained from the control experiments.
The allelopathic effects of aqueous water extracts derived from sorghum stem and rice husks in the germination of cowpea are shown in the Tables 1 and 2 respectively. It was obvious that the aqueous extracts from both extracts inhibited the germination of cowpea seeds. The degree of inhibition was concentration dependant as the proportion of the inhibition increased with the increase in the concentrations of the extracts.
The effects of the aqueous water extracts from sorghum stem and rice husks on the radicle lengths of cowpea were shown in Tables 3 and 4 respectively. The results showed that the radicle growth was retarded by both extracts but the effects were more pronounced in the sorghum extract treated seeds. Also the degree of retardation increased with the increase in the concentrations of the extracts. Statistical analyses at 5% levels (t-test) revealed that, apart from comparison between 5 and 25g extract concentrations, there were no significant differences in the growth length of radicles in the varying extract concentrations as well as those of the control in both extracts.
The aqueous extracts of the two extracts also retarded the plumule lengths of cowpea (Tables 5 and 6). The degree of retardation also increased with the increase in the concentrations of the extracts. The effects were also prominent in the sorghum extracts treated seeds than the rice husks extract treated seeds. While the plumule, with the exemption of the 5g extract concentration, germinated at 72hour period in the sorghum extract treated seeds, the plumule germinated at the 48hour period of the experiment in the rice husks extract treated seeds. Statistical analyses (t-test, 5% level) revealed that apart from the comparison of the growth lengths of plumule from the 25g sorghum extract concentration with those of the control, there were no significant differences in the growth lengths of the plumule in the varying extract concentrations and the control in both extracts.
Previous study by Nimbal et al (1996) had asserted that sorghum contained sorgoleone, an allelochemical substance. It was also reported that sorghum shoot produced higher amount of cynogenic glucoside whose phenolic products inhibit plant growth (Einhellig and Rasmussen 1989). The allelochemicals in mature sorghum, according to Cheema (1988) included benzoic acid, p-hydroxybenzoic acid, vannillic acid, m-comedic acid, p-coumaric acid, gallic acid, caffeic acid, ferulic acid and chlorogenic acid. Phenolic compounds such as p-hydroxybenzoic, vanillic, ferulic, p-coumeric and o-hydroxyphenylacetic acids are contained in the rice residues (Chou and Lin 1976). Previous assertion by Enhellig and Souza, (1992) had revealed that these phenolic derivatives are extremely phytotoxic. Hence they must have been responsible for the inhibition of seed germination and the retardation of seedling growths of radicle and plumule of the cowpea used in this study.
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Table 1. Effects of the aqueous extracts from sorghum stem on the germination of cowpea seeds.
* Figures in brackets represent the % decrease over control
Table 2. Effects of the aqueous extracts from rice husks on the germination of cowpea seeds.
Table 3. Effects of the aqueous extracts from sorghum stem on the radicle length (cm) of cowpea seeds.
Table 4. Effects of the aqueous extracts from rice husks on the radicle length (cm) of cowpea seeds.
Table 5. Effects of the aqueous extract from sorghum stem on the plumule length (cm) of cowpea seeds.
Table 6. Effects of the aqueous extracts from rice husk on the plumule length (cm) of cowpea seeds.