Allelopathic Activities of Ethylacetatate and N-Hexane Extracts of Calotropis Procera on the Germination of Maize Seeds

The alarming rate of residual toxicities of several herbicides and insecticides in agricultural produce calls for urgent attention. Calotropis procera leaf is one of the natural insecticides that is generally used on various crops at various stages. Many of these natural insecticides have positive or negative effects on plant growth. Therefore, this study determined the phytochemical constituents and the allelopathic effects of Calotropis procera leaf extract on Maize seed germination and seedling growth using standard method. The allelopathic activities of N-hexane and ethylacetate extracts of C. procera leaf was determined on maize seed using concentration of 2.5%, 5.0% and 10% for 12 days. On days 3, 6, 9 and 12, the root and shoot development, germination percentage, and seedling vigour of maize seeds were determined. N-hexane and ethylacetate extracts contained calotropin, calotoxin, calactin, caffeic acid, thioacetate, alpha-amyrin, beta-sitosterol, stigmasterol, isoquercitrin, quercetin, kaempferol, rhamnetin, luteolin, lineolone, voruscharin, uscharin and uscharidin, while azeleatin, tyranton were present in only the ethylacetate extract.The inhibition of plumules and radicles growth were observed to be concentration-dependent with the highest percentage of inhibition in 10% of n-hexane and ethylacetate extracts of Calotropis procera. Germination percentage also decreased with higher concentration, with a maximum of 100% germination in the control group, and 20% each at 10% concentrations of n-hexane and ethylacetate extracts. Similarly, Seedling vigour index was drastically reduced at higher concentrations, with a value of 14.4 and 8.0 at 10% concentration of n-hexane and ethylacetate extracts, respectively as compared to 423 in the control group. These findings suggests that high concentration of n-hexane and ethylacetate of C. procera (10% and 5%) extracts could inhibit maize germination and seedling growth. Therefore, high concentrations of these extracts should be avoided when using C. procera leaf extract as insecticide during germination stage of maize.