Nematicidal Activity of Aqueous and Ethanolic Leaf Extracts of Azadirachta indica (A. Juss.) and Senna alata (L.) Roxb. against Meloidogyne Species on Tomato

Abstract

Root-knot nematode (Meloidogyne spp.) is a serious constraint to tomato production, and reliance on chemical nematicides poses environmental and health concerns. This study investigated the phytochemical composition and nematicidal potential of Azadirachta indica and Senna alata leaf extracts against root-knot nematode second-stage juveniles (J2) under laboratory and field conditions. Though neem (Azadirachta indica) is widely studied, senna (Senna alata or related species) is less explored in nematode control. The fresh leaves of both plants were shade-dried, pulverized, and extracted using aqueous and ethanolic solvents by cold maceration. Phytochemical constituents were screened qualitatively; while nematicidal assays were carried out by exposing approximately 100 J2 to graded concentrations of extracts (0.625–5.0 mg/ml) using Complete Randomized Design (CRD). Mortality was recorded at 6-hours intervals up to 24 hours, with distilled water as control. Field trials were conducted on nematode-infested tomato plots laid out in a Randomized Complete Block Design (RCBD). Treatments consisted of different extract concentrations (1 ml) of 30 mg/ml, 45 mg/ml, and 60 mg/ml were applied to soil at transplanting. Parameters assessed included root gall index, J2 population density, and fruit yield. Data generated were subjected to ANOVA using Statistical package for social sciences (SPSS) and means separated at p ≤ 0.05. Phytochemical screening revealed variations in metabolite distribution. Azadirachta indica aqueous extracts contained abundant saponins, tannins, and phenols, whereas ethanolic extracts were rich in tannins, flavonoids, and glycosides. S. alata exhibited broader profiles, with high levels of alkaloids, flavonoids, tannins, phenols, anthraquinones, and steroids. Laboratory assays showed strong concentration- and time-dependent mortality, with S. alata extracts achieving 100 % mortality within 12–18 hours at 5 mg/ml, while A. indica required up to 18–24 hours. Field studies confirmed significant suppression of galling and J2 density, alongside improved yields. At 5 mg/ml, both species reduced gall index to below 1.0, suppressed J2 by over 90 %, and increased tomato yield above 31 t•ha⁻¹ compared to 18 t•ha⁻¹ in control. In conclusion, A. indica and S. alata possess potent nematicidal properties, with S. alata acting more rapidly. The field trial demonstrated the potential of Azadirachta indica and Senna alata as eco-friendly bio-nematicides for sustainable tomato production.