Chemical residues in tomato plant tissue and in vitro Toxicology profiles of Nemarioc-AL and Nemafric-BL phytonematicides on Raw 264.7 macrophage cells

Ashwell Rungano Ndhlala^1*Tshepo Mashela²Esam Esamuldin Elgorashi³Raymond Makola²

• ¹University of Limpopo, Sovenga, South Africa
• ²University of Limpopo, Mankweng, South Africa
• ³Agricultural Research Council Onderstepoort Veterinary Research, Onderstepoort, South Africa

A shift from synthetic chemical nematicides to bionematicides in plant protection has led to the development of Nemarioc-AL and Nemafric-BL phytonematicides to manage plant parasitic nematodes. However, there is a lack of information on the accumulation of cucurbitacin residues and cytotoxicity of phytonematicides on non-target entities. The aims of the study were to determine the cucurbitacin residue accumulation after application of Nemarioc-AL and Nemafric-BL phytonematicides in tomato fruits and determine their cytotoxic effects on eukaryotic (Raw 264.7 cell line) model system. Two separate trials for Nemarioc-AL phytonematicide and Nemafric-BL phytonematicide each applied at 3% were conducted concurrently on sandy loam, dark soil, red soil, silt soil, sandy soil and sandy loam (+). Each trial was arranged in a randomized complete block design (RCBD) and replicated 6 times. MTT viability assay was used to assess the cytotoxicity of Nemarioc-AL and Nemafric-BL phytonematicides and the Annexin-V and Dapi apoptosis assay in macrophage cells on Raw 264.7. In Nemarioc-AL phytonematicide treated soil type, the highest accumulation of cucurbitacin B residues in fruits was observed on sandy loam (+) (37.1 ng/g), followed by red soil with 27.0 ng/g, then sandy soil with 21.7 ng/g and dark soil was the least with 20.3 ng/g. The phytonematicides were non-toxic at lower concentrations, ≤ 1.25 mg/mL. However, the higher concentrations (> 1.25 mg/mL) of phytonematicides exhibited cytotoxic effects on the Raw 264.7 cell line with 50% cell viability in comparison with curcumin (100 μM). The IC50 values for Nemarioc-AL and Nemafric-BL phytonematicides on Raw 264.7 cell lines were 0.55 and 1.6 mg/mL, respectively. Similar to MTT viability assay, the Annexin-V and Dapi apoptosis assay did show that the low concentrations of phytonematicides (0.313 mg/mL) had no signs of apoptosis or necrosis, however, high concentrations (10 mg/mL) had signs of apoptosis as opposed to necrosis. Therefore, the products can be used at lower concentrations to manage nematodes and avoid toxicity of the products.