Characterisation of antagonistic Bacillus and Pseudomonas strains for biocontrol potential and suppression of damping‐off and root rot diseases

Abstract

Novel strains of rhizobacteria, Pseudomonas fluorescens Pf 9A-14, Pseudomonas sp. Psp. 8D-45 and Bacillus subtilis Bs 8B-1, showed broad-spectrum antagonistic activity and provided suppression of Pythium damping-off and root rot of cucumber. Their biocontrol potential was further investigated for suppression of additional seedling diseases of cucumber (Phytophthora capsici) and radish (Rhizoctonia solani). Bacterial strains were also characterised for production of antibiotics, metabolites, volatiles, phytohormones and lytic enzymes. Seed and pre-plant applications of all three antagonistic bacteria as cell suspension and talc or irradiated peat formulations to the infested potting mix provided overall high level of suppression of Phytophthora damping-off and root rot of cucumber (66-85% healthy seedlings) and relatively low level of suppression of Rhizoctonia damping-off of radish (18-38% healthy seedlings). Bacterial treatments also resulted in higher plant fresh masses. Seed coating with irradiated peat formulation of a mixture of three bacteria resulted in superior control of Phytophthora damping-off and root rot of cucumber and much higher plant fresh masses. The presence of genes for biosynthesis of phenazine-1-carboxylic acid, 2,4-diacetylphloroglucinol, pyrrolnitrin and pyoluteorin was confirmed in Pseudomonas strains, and that of fengycin, bacillomycin, bacilysin, surfactin and iturin A in B. subtilis Bs 8B-1. All three strains produced HCN, salicylic acid, indole-3-acetic acid, protease and -1,3-glucanase. Both Pseudomonas strains produced siderophores and only P. fluorescens Pf 9A-14 showed phosphate solubilisation and chitinase activity. All three strains inhibited pathogen growth by producing volatiles, and gas chromatography-mass spectrometry analysis revealed eight compounds in Pf 9A-14, 10 in Bs 8B-1 and 4 in Psp 8D-45, some with known antifungal activity. The antagonistic and plant-growth promotion activities of these strains might be due to production of antibiotics, metabolites, lytic enzymes or phytohormones.

Isolation and characterization of Bacillus altitudinis JSCX-1 as a new potential biocontrol agent against Phytophthora sojae in soybean [Glycine max (L.) Merr.]

“…Different lowercase letters above the bars indicate significant difference between the treatments at P < 0.05 level by ttest Many studies reported that the application of Bacillus spp., such as B. subtilis, B. cereus, Bacillus licheniformis, could manage diseases caused by Phytophthora species, such as Phytophthora capsici, P. sojae, Phytophthora fragariae var. fragariae, Phytophthora infestans, and Phytophthora cactorum on pepper, soybean, potato, cucumber, alfalfa, strawberry and apple (Utkhede 1984;Handelsman et al 1990;Osburn et al 1995;Anandhakumar and Zeller 2008;Özyilmaz and Benlioglu 2013;Maksimov et al 2014;Khabbaz et al 2015).…”

Assaying the potential autotoxins and microbial community associated with Rehmannia glutinosa replant problems based on its ‘autotoxic circle’

“…However, some species belong to the same genus as our identified species were confirmed to have positive effect on plant growth. For instance, some species of Bacillus, Pseudomonas, Acremonium and Humicola could promote plant growth due to their antagonistic activity, the production of IAA or specific substance to activate resistance for control of diseases (Dharni et al 2014;Hassan et al 2015;Khabbaz et al 2015;Wenhsiung 2009;Yang et al 2014). On the other side, some species of these genera showed negative effect on plant growth due to their broadspectrum pathogenic activity (Elbanna et al 2014;Furuya et al 2005;Iakovleva et al 2013;Racedo et al 2013;Zhang et al 2014).…”

Plant-Microbe Interactions: A Molecular Approach

“…This exudate causes an increase in bacterial propagation of both pseudomonads and other benefi cial bacteria. Within the bacterial cells, there is an upregulation of the expression of phzI gene, resulting in an increased activity of N -acyl-Lhomoserine lactone or generally referred to as HSL (Khabbaz et al 2015 ;Schenk et al 2014 ). This ultimately leads to an increase in the production of PCA which inhibits the further colonization and propagation of the fungus on roots.…”