Abstract
Constituents of watermelon (Citrullus lanatus) rind were extracted in ethanol and derivatized to produce white water soluble crystals designated as derivatized citrulline. The derivatized citrulline, chromatographic fractions and ethanolic crude extracts from Citrullus lanatus (Thunb.) were assessed in the laboratory and screenhouse on possible toxicity to Meloidogyne incognita (Kofoid & Chitwood). The structure elucidation of the citrulline derivative (CTRL/DRVT) and chromatographic fractions (CMTG/FRCT) were established with spectral data from infrared (FTIR), 1H/13C-NMR spectroscopy as well as gas chromatography mass spectrometry (GCMS). The infrared spectral data of the derivatized citrulline revealed a prominent absorption bands at 3431 cm-1 which is characteristic of N-H stretching vibration of primary amides. The bands at 1506 and 1456 cm-1 further support the presence of an amide group. The major compounds identified from GC-MS analysis of fractions include hydroxycinnamic acid (17.16%) p-anisic acid (16.10%) and chlorogenic acid (16.22%). 1H-NMR data showed chemical shifts at δ 0.85, 0.88, 1.26, 1.33, 1.37, 1.60, 4.6, 4.6 ppm. The resonance at 0.8 - 1.37ppm is attributed to methyl and methylene protons. The down field signals at 4.6 ppm are ascribed to olefinic protons. The derivatized citrulline, had a significant action on percentage mortality of M. incognita juveniles. 19.10% mortality was achieved after 24 hours of juvenile exposure as opposed to 5.57% and 6.13% noted in the fractions and carbofuran (CBFN) respectively. At day six, percentage juvenile mortality in derivatized citrulline was remarkably similar to the observed value in carbofuran. Egg hatch in derivatized citrulline, fractions and carbofuran was inhibited maximally, while hatches were recorded in crude extract and control. In the screenhouse, vegetative growth of Corchorus olitorius (L) plants treated with derivatized citrulline, was appreciable and nematode population was significantly (P ≤ 0.05) reduced in C. olitorius plants treated with chromatographic fractions and derivatized citrulline. The derivatized citrulline prepared in this study by semi-synthetic method can serve as an alternative to environmentally hazardous synthetic nematicides.
