Compatible Consortium of Endophytic Bacillus halotolerans Strains Cal.l.30 and Cal.f.4 Promotes Plant Growth and Induces Systemic Resistance against Botrytis cinerea

Microbial consortium mediated acceleration of the defense response in potato against Alternaria solani through prodigious inflation in phenylpropanoid derivatives and redox homeostasis

The present study was carried out in a pot experiment to examine the bioefficacy of three biocontrol agents, viz., Trichoderma viride, Bacillus subtilis, and Pseudomonas fluorescens, either alone or in consortium, on plant growth promotion and activation of defense responses in potato against the early blight pathogen Alternaria solani. The results demonstrate significant enhancement in growth parameters in plants bioprimed with the triple-microbe consortium compared to other treatments. In potato, the disease incidence percentage was significantly reduced in plants treated with the triple-microbe consortium compared to untreated control plants challenged with A. solani. Potato tubers treated with the consortium and challenged with pathogen showed significant activation of defense-related enzymes such as peroxidase (PO) at 96 h after pathogen inoculation (hapi) while, both polyphenol oxidase (PPO), and phenylalanine ammonia-lyase (PAL) at 72 hapi, compared to the individual and dual microbial consortia-treated plants. The expression of antioxidant enzymes like superoxide dismutase (SOD) and catalase (CAT) and the accumulation of pathogenesis-related proteins such as chitinase and β-1,3-glucanase were observed to be highest at 72 hapi in the triple microbe consortium as compared to other treatments. HPLC analysis revealed significant induction in polyphenolic compounds in triple-consortium bioprimed plants compared to the control at 72 hapi. Histochemical analysis of hydrogen peroxide (H2O2) clearly showed maximum accumulation of H2O2 in pathogen-inoculated control plants, while the lowest was observed in triple-microbe consortium at 72 hapi. The findings of this study suggest that biopriming with a microbial consortium improved plant growth and triggered defense responses against A. solani through the induction of systemic resistance via modulation of the phenylpropanoid pathway and antioxidative network.

Modulation of ethylene and ROS-scavenging enzymes by multifarious plant growth-promoting endophytes in tomato (Solanum lycopersicum) plants to combat Xanthomonas -induced stress

The purpose of the current study was to explore root endophytes- Priestia megaterium T3 and Bacillus cereus T4 from Moringa olefiera for the suppression of leaf spot disease in tomato plants challenged with Xanthomonas vesicatoria. Both strains had plant growth-stimulating characteristics including auxin production, solubilization of inorganic phosphate and zinc complexes, and production of ammonia, siderophore, as well as hydrolytic enzymes. An agar well diffusion and fluorescence viability assay have validated the antibacterial effect of the cell-free culture supernatant of strains T3 and T4. Liquid chromatography-mass spectrometry (LC-MS) profiling has identified the secondary metabolites in the cell-free supernatant of strains T3 and T4. The bio-priming of tomato seeds with a consortium of T3 and T4 strains has significantly declined ethylene (by 0.61-fold) and hydrogen peroxide (H2O2, 0.64-fold) concentration thus, maintaining a lower content of ROS-induced malondialdehyde (MDA, 0.91-fold) as compared to control counterparts. Consequently, the leaf spot disease severity was reduced by ∼70% in consortium-treated tomato plants in contrast to their pathogen-challenged control. The consortia (T3+T4) treatment has facilitated induced systemic resistance by enhancing enzymatic activities of phenylalanine ammonia-lyase (PAL), peroxidase (PO), polyphenol oxidase (PPO), catalase (CAT), and ascorbate oxidase (AO) to detoxify the excessive Xanthomonas-induced ROS accumulation in tomato plants. Conclusively, bacterial endophytes modulate X. vesicatoria-induced ROS response and ethylene levels in tomato plants. The current findings indicate that plant growth-promoting endophytic bacterial strains hold the potential to sustainably enhance plant growth and suppress bacterial leaf spot disease in tomato plants.