Nematicidal and quantitative phytochemical analysis of the chromatographic fractions from the leaf and stem of Allamanda cathartica (L)

Abstract

The environmental pollution of synthetic nematicides is enormous, due to their residual effects and nondegradability. This study was conducted to investigate the possibility of a green alternative that will eventually replace the pollution problems of synthetic nematicides. The activity of plant  secondary metabolites against plant parasitic nematodes was tested in-vitro using chromatographic isolates from the stem and leaves of  Allamanda cathartica. Isolates from the extracted plant materials were tested at various concentrations (0 mg/mL, 0.06 mg/mL, 0.1 mg/mL and 0.2mg/mL) against Meloidogyne incognita juveniles and eggs. The effect was determined through testing the inhibition of egg hatch and larval mortality. The result showed that egg hatching was totally inhibited among all the isolates at different concentrations except in the control which had 48.39% on day 5. The isolates showed strong nematicidal effect, with percentage mortality of 16.87% at the first hour of exposure which  compared well with the commercial nematicide (oxamyl). However the leaves of A. cathartica proved more effective than the stem. Preliminary
phytochemical screening revealed that the quantities of secondary  metabolites are more in the leaves of A. carthatica than in the stems. Infra-red spectroscopic data of three of the isolates revealed the presence of alkanes (2930; 2923 and 1460 cm-1) aldehydes (2855; 2851 and 1733cm-1) and phenols at (3650; 1115cm-1). Aliphatic amines (3200; 1460 and 1600 cm-1) and non-cyclic ethers (1310; 1300; 1240  and 1000cm-1) are present in isolate four. This study showed that the leaves of A. cathartica could serve as a bio-pesticide to reduce environmental  pollution

Key words: Extraction, n-hexane, Isolation, Oxamyl, Nematodes, Chromatography.