Tomato (Solanum lycopersicum L.) is one of the most important vegetable worldwide, possessing not only high nutritional value but also playing a significant economic role in global agriculture. Root-knot nematode (Meloidogyne spp.) infestation poses a major challenge to sustainable tomato production, leading to a substantial reduction in growth parameters and crop yield. Providing appropriate management strategies, the utilization of environmentally friendly methods, and the development of suitable protocols for chemical nematicides against these nematodes appear to be of paramount importance.

1. Plant-parasitic nematodes are responsible for considerable economic losses in a wide range of agricultural crops. Among them, the root-knot nematode Meloidogyne javanica is regarded as one of the most destructive species worldwide. To manage plant-parasitic nematodes, which are major plant pathogens, several approaches are employed, including fallowing, crop rotation, the cultivation of resistant cultivars, biological control, and chemical nematicides. However, the extensive and indiscriminate use of agricultural pesticides has raised serious concerns regarding environmental safety and human health. The use of environmentally compatible approach and the development of suitable alternatives to chemical pesticides for controlling plant‑parasitic nematodes are essential.

2. Materials and Methods: In this study, the effect of the Heterorhabditis bacteriophora nematodes at concentrations of 10, 50, and 100 infective juveniles per milliliter, as well as the, Abamectin and Rugby nematicides at 5, 25, and 50 ppm, were evaluated separately against 50 second-stage juveniles (J2) of the root‑knot nematode (M. javanica) in vitro conditions by measuring larval mortality percentage at four exposure times: 48, 72, 96, and 120 hours. The experiment was conducted using 24-well tissue culture plates. Each treatment was prepared with three replicates. For each well, 50 J2 nematodes were introduced into the treatment solution. A negative control (containing only root-knot nematode (J2), without H. bacteriophora and nematicides) was also established with three replicates. The plates were incubated at 28 ± 2 °C. Mortality rates, including parasitized juveniles, were recorded at 48, 72, 96, and 120 hours post-exposure. To evaluate the antagonistic activity of H. bacteriophora and the efficacy of Abamectin and Rugby against M. javanica, a greenhouse experiment was conducted at the research greenhouse of the Faculty of Agriculture, Ilam University. The experiment consisted of nine treatments: Abamectin (17, 85, and 170 ppm), Rugby (20, 30, and 60 mg/kg), H. bacteriophora- applied as four infected cadavers of the greater wax moth larvae per pot, and two control treatments including; a control treatment infected with parasitic nematodes (tomatoes with root-knot nematode, without H. bactriophora, and without nematicides) and a sterile soil control treatment (tomatoes without root-knot nematode, without H. bactriophora, and without nematicides). Tomato seedlings (cv. Mobil) at the four-leaf stage were transplanted into 1-kg pots containing 900 g of sterilized soil. Plants were maintained under a photoperiod of 10–12 hours light. H. bacteriophora was applied by placing infected cadavers near the root zone. Ten days post-inoculation with the entomopathogenic nematode, a suspension of M. javanica eggs (2,000 eggs per pot) was inoculated by creating three holes (5 cm deep) at a distance of 2 cm from the root collar, using a pipette. Abamectin and Rugby treatments were applied via irrigation at the specified concentrations too. During the initial period, the temperature was maintained at 30–35 °C, and plants were watered regularly. Two months after inoculation, plant performance traits, including fresh and dry weights and lengths of shoots and roots and root knot nematode reproduction factor were recorded. The reproduction factor (RF) of the root-knot nematode was calculated using the formula, RF=Pf/Pi (Williamson and Kumar, 2006), where Pf represents the final population (total eggs and J2 in the soil) and Pi is the initial population (2,000 J2s). The experiments in vitro and greenhouse conditions were arranged in a completely randomized design (CRD). Data were subjected to analysis of variance (ANOVA), and treatment means were compared using Duncan’s test at the 5% probability level, using SAS software (version 9.4).

3. Results and Discussion: In vitro results showed that the highest larval mortality at all four time points occurred in the 100 IJs/mL treatment of the entomopathogenic nematode, while the lowest mortality was observed in the 5 ppm treatments of both Abamectin and Rugby at 48 hours.

Greenhouse data analysis revealed that the tested treatments had a significant effect on tomato growth parameters and the root-knot nematode reproduction factor (P<0.05). The sterile soil control exhibited the highest values for all growth parameters, including shoot fresh weight (241.2 g), shoot dry weight (74.8 g), shoot length (45.8 cm), root fresh weight (47.5 g), root dry weight (27 g), and root length (34.8 cm). Conversely, the nematode-infested control showed the lowest values for all these parameters. Among the experimental treatments, the 60 mg/kg Rugby treatment resulted in the highest shoot fresh weight (240.7 g). The 170 ppm Abamectin treatment demonstrated superiority in shoot dry weight (67.9 g), plant height (40.8 cm), root fresh weight (44.2 g), and root length (31.9 cm). Furthermore, for root dry weight, the 60 mg/kg Rugby treatment and the infested insect cadaver treatment ranked second with a value of 26.2 g. In terms of the reproduction factor, the highest value was recorded for the inoculated control (3.9), whereas the lowest reproduction factor (2.5) was observed in the Rugby (20 mg) and Abamectin (170 ppm) treatments, signifying the high efficacy of these treatments in nematode suppression.

4. Conclusions: This research demonstrated the efficacy of the entomopathogenic nematode H. bacteriophora and two nematicides, Abamectin and Rugby, in controlling tomato root-knot nematodes. Selected treatments, particularly 170 ppm Abamectin and 60 mg/kg Rugby, had a significant positive impact on plant growth and nematode suppression.