Effectiveness of Plant-Induced Resistance Against Root-Knot Nematode Depends on the Policy of Using Inducer on the Host Plant.

This research was conducted to determine the relationship between plant defense responses and the extent of treatment applied to either the aerial parts or roots of the plant. The experimental treatments included different methods of application (spraying versus soil drenching), varying treatment areas (one-sixth, one-third, half, or all of the plant's aerial parts and roots) with SA, and infecting the plants with root-knot nematodes. Evaluation of plant growth and nematode pathogenicity indices in the greenhouse section, H₂O₂ accumulation rate, and phenylalanine ammonia lyase enzyme activity (in aerial parts and roots) were carried out in biochemical experiments. The results showed that treating less than one-third of the aerial parts with salicylic acid (SA) did not significantly impact plant growth or nematode pathogenicity indices. However, it did lead to a notable increase in hydrogen peroxide (H₂O₂) accumulation, while phenylalanine ammonia lyase (PAL) enzyme activity remained unchanged. In contrast, treating more than one-third of the aerial parts resulted in decreased nematode pathogenicity and enhanced production of defense compounds. Notably, treatments targeting the roots consistently demonstrated a more pronounced effect on nematode suppression and increased defense compound levels, emphasizing the importance of root treatment, as this is where nematodes are primarily present. Overall, the study highlights the differential impact of treatment location and extent on plant defense mechanisms and suggests that strategic targeting of either aerial or root tissues can optimize plant responses against nematode attacks.