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 the cytotoxicity of phytonematicides on non-target entities. The aims of the study were to determine the cucurbitacin residue accumulation after the application of Nemarioc-AL and Nemafric-BL phytonematicides in tomato fruits and to determine their cytotoxic effects on a 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 six times. 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyl-2 H -tetrazolium bromide (MTT) viability assay was used to assess the cytotoxicity of Nemarioc-AL and Nemafric-BL phytonematicides, and the Annexin-V and DAPI apoptosis assay was performed on Raw 264.7 macrophage cells. 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 and then sandy soil with 21.7 ng/g, and dark soil showed the least at 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 IC 50 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 the 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 the toxicity of the products.
Mashela et al. (Thu,) studied this question.