Trop. Agric. (Trinidad) Vol 98 No. 4 October 2021 347 Toxicity of derivatized citrulline and extracts of water melon (Citrullus lanatus) rind on root knot nematode (Meloidogyne incognita) Oluwatoyin Adenike Fabiyi 1* and Gabriel Ademola Olatunji 2 1 Crop Protection Department University of Ilorin, Ilorin, Nigeria 2 Industrial Chemistry Department University of Ilorin, Ilorin, Nigeria *Corresponding author email: fabiyitoyinike@hotmail.com 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), 1 H/ 13 C-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%). 1 H-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. Keywords: Citrullus lanatus, citrulline, Meloidogyne incognita, hydroxycinnamic acid, bio-pesticide Significant economic losses are caused to a wide variety of crops by plant parasitic nematodes (Dong and Zhang 2006; Fabiyi et al. 2018; Fabiyi 2020; Fabiyi et al. 2020a). Root-knot nematodes (Meloidogyne spp) are serious pest of vegetables in Nigeria, where they cause yield loss in most vegetable production areas (Fabiyi and Atolani 2011; Fabiyi et al. 2012; Fabiyi 2021a; Fabiyi 2021b). The most destructive nematode responsible for enormous yield reduction in Corchorus olitorius is the root-knot nematode, Meloidogyne incognita (Sasser 1989; Fabiyi 2016). Root-knot nematode has been reported as one of the world’s most damaging agricultural pests (Curtis 2007). It causes about 5% of global crop loss and over 2000 plants have been indicated to be susceptible to M. incognita (Abad et al. 2003; Agrios 2005). The effect is characterized by numerous and pronounced galls on the roots of infected plants (Jain 1992). A highly toxic nematicide used in nematode control is carbofuran (2,3-dihydro-2, 2-dimethyl-benzofuran-7-yl methylcarbamate). Because of its high water solubility (351 ppm) and low adsorption coefficient, carbofuran is relatively mobile in soil and surface runoff (Lau et al. 2007). Consequently, carbofuran has the potential to contaminate lakes, streams, and groundwater (Goad et al. 2004). Environmental issues have increasingly limited the use of carbofuran (Rich et al. 2004). This study was initiated as a result of urgent concern for the enormous damage caused by nematode infection of crops, thereby reducing crop quality and yield. Also the environmental 0041–3216/2021/040347–355 © 2021 Trop. Agric. (Trinidad)