Blue and green LED light kills Meloidogyne javanica juveniles through cuticle damage and oxidative stress

Abstract Root-knot nematodes ( Meloidogyne javanica (Treub, 1885) Chitwood, 1949) cause severe global yield losses. Chemical nematicides are effective but raise environmental and health concerns. Light-emitting diodes (LEDs) offer a non-chemical alternative, but wavelength-dependent effects are poorly understood. This study investigated the lethal effect of visible LED light on second-stage juveniles (J2) in water and, to our knowledge, documented early cuticular changes using atomic force microscopy (AFM) at 1, 2 and 3 h. Blue (440 nm), green (510 nm), red (635 nm), yellow (580 nm) and white LEDs were applied for 1–4 h at irradiances of 2.6–2.9 mW/cm² (radiant exposure 36–42 J/cm² after 4 h). Blue light caused 20–27% mortality after 1–3 h, while all other wavelengths (including dark control) gave ≤ 20% mortality. After 4 h, blue and green both achieved 100% mortality, red caused 60%, and yellow or white remained ≤ 25% (Fig. 1). A sham control (opaque filter) and a thermal control (27 °C, dark) showed 0% mortality, ruling out heating or hypoxia. AFM images (Figs. 2, 3 and 4 and Supplementary Fig. S1) revealed progressive cuticular damage (increased roughness and pores) exclusively under blue and green light, occurring before death. Red light induced moderate roughness only from 3 h onward, while yellow and white caused no significant change. Pre-treatment with 5 mM N-acetylcysteine (NAC) reduced blue-light-induced mortality from 100% to < 15% ( p < 0.01), supporting the involvement of reactive oxygen species (ROS). Blue and green LED light (≥ 4 h) are highly nematicidal to M. javanica J2, with cuticle damage starting from the first hour as an early lethal event. The wavelength dependence and NAC rescue support an oxidative stress pathway. LED technology offers a promising non-chemical, residue-free alternative for nematode management in hydroponics and greenhouses, though effects on non-target organisms require further study.