Relationship between suppression of plant defence systems by Meloidogyne javanica with the distance of different parts of the plant from the nematode establishment site

Abstract

Suppression of plant defence systems by plant-parasitic nematodes is an important aspect of research on resistance induction in plants. The present work aimed to address the question of whether this suppressive ability by nematodes can be spread systemically and equally to other parts of the plant. The root-knot nematode, Meloidogyne javanica, and the host plant, tomato, was used with salicylic acid (SA) as a potent inducer of the plant defence systems. SA was sprayed on the second and fifth leaves, as near and far from the nematode establishment site, respectively. The results of hydrogen peroxide and phenylalanine ammonia lyase enzyme evaluation in the root (site of nematode establishment), crown, second and fifth leaves showed that, firstly, the amount of defence compounds induced by SA in the leaves was not equal in all parts of the plant and gradually decreased from the aerial parts (treatment site) towards the roots. Furthermore, the synthesis and accumulation of the evaluated compounds in the younger parts of the plant (fifth leaf) was more than the older parts (second leaf), and the crown and root. Although the suppression of the plant defence systems by the nematode was transferred to other parts of the plant, the amount of this suppression gradually decreased in the parts farthest from the site of the nematode establishment. Based on the results, it is inferred that the success of a resistance induction strategy in plant disease management depends on the type of pathogen, type of inducer, place of application of the inducer on the plant and the induction area.