Elicitation of sunflower resistance to Meloidogyne incognita by ascorbic and glutamic acids: integrating direct nematicidal activity and defense enzyme induction

Abstract Root-knot nematode ( Meloidogyne incognita ) causes a significant reduction in the production of sunflower ( Helianthus annuus ) globally. The paper assessed the nematicidal activity of ascorbic acid and glutamic acid and their ability to trigger systemic resistance in sunflower within controlled conditions. Laboratory evaluations proved that both compounds significantly suppressed egg hatch to 29.5% (from 92.3% in control) and elevated juvenile mortality to 62.1% (from 6.0% in control) in a concentration-dependent manner, with ascorbic acid (2 mg/ml) showing the strongest effects. Experiments in greenhouses found that pre- and post-inoculation foliar application of these acids suppressed nematode root galling by up to 59% and population density by up to 57%, while boosting shoot fresh weight by 21.1% and root fresh weight by 24.8% compared to inoculated controls. Treated plants also showed increased the activities of major defense enzymes, such as peroxidase (POX), phenylalanine ammonia-lyase, (PAL), superoxide dismutase (SOD), and ascorbate peroxidase (APX). Pre-inoculation treatments were more efficient, which demonstrates the role of priming in the activation of defense. Our results indicate that ascorbic and glutamic acid have a combination of direct nematicidal activity with induction of host defense systems, which is promising as a safe means of managing nematode infestation in sunflower farming.