Rhizobacteria-mediated Induction of Systemic Resistance (ISR) in Tomato against Meloidogyne javanica

The two rhizobacteria Pseudomonas aeruginosa strain IE-6Sþ and P. fluorescens strain CHA0 used as bare root-dip treatment or as soil drench substantially reduced Meloidogyne javanica juvenile penetration into tomato roots under glasshouse conditions. To better understand the basis of antagonism, the mode of action of the bacterial antagonists was investigated. The ability of bacterial inoculants to stimulate induced systemic resistance against the nematode was demonstrated in split-root-trials, where the root system of a single tomato plant was spatially divided into two separate parts. Application of IE-6Sþ to one half of the split-root system caused a significant (42%) systemic reduction in nematode penetration in the other half of the split-root system. CHA0 applied in the same manner reduced nematode infection similarly, by 29% over the controls. The population sizes of the strains IE-6Sþ and CHA0 were compared in order to determine if low degree of ISR by CHA0 could be attributed to a reduction in root population size. Populations of the strain CHA0 in the rhizosphere was higher during early growth stages of tomato while IE-6Sþ colonized relatively heavily during the later growth stages. Only strain IE-6Sþ was reisolated from the inner root tissues. Neither of the bacterium was isolated from the rhizosphere and inner root tissues of tomato from the non-bacterized halves. Bacteria with systemic nature (IE-6Sþ) induce systemic resistance in plant to a relatively higher degree against root-knot nematode compared to the rhizosphere colonizer (CHA0).