Biological management of vascular wilt of tomato caused by Fusarium oxysporum f.sp. lycospersici by plant growth-promoting rhizobacterial mixture

Abstract

Two plant growth promoting rhizobacterial (PGPR) strains, GIBC-Jamog ( Bacillus subtilis) and TEPF-Sungal ( Burkholderia cepacia) and PGPR strain mixtures, S2BC-1 ( B. subtilis)+GIBC-Jamog ( B. subtilis) and S2BC-2 ( Bacillus atrophaeus)+TEPF-Sungal ( Burkholderia cepacia) which inhibited the mycelial growth of vascular wilt fungus Fusarium oxysporum f.sp. lycopersici were selected for assessing vascular wilt control in tomato by localized and induced systemic resistance (ISR) experiments in the greenhouse. Seed bacterization and soil application of S2BC-1+GIBC-Jamog challenge-inoculated with F. oxysporum f.sp. lycopersici resulted in significantly lower incidence (54.9% and 53.8% reduction) relative to the non-bacterized pathogen control in localized and split-root experiments, respectively. In localized studies, the lower disease incidence coincided with increases in the plant vigor index and fresh weight of 44.1% and 183.4%, respectively, relative to the pathogen control. Analysis of root samples in localized and split-root experiments also indicated increased induction of chitinase (2.2- and 2.6-fold, respectively) and β-1,3-glucanase (1.4- and 1.1-fold, respectively). In native gel activity assay, S2BC-1+GIBC-Jamog with challenge-inoculation, expressed high intensity peroxidase isoforms in localized and ISR experiments. It is presumed that the induced chitinase, β-1,3-glucanase and peroxidase in localized and split-root experiments may be involved in the reduction of vascular wilt development in tomato. Reduced disease severity coupled with enhanced enzyme production elicited by S2BC-1+GIBC-Jamog in localized and split-root experiments indicate that its mode of action for vascular wilt suppression in tomato is through both direct biocontrol and ISR.