Intervention of bio-protective endophyte Bacillus tequilensis enhance physiological strength of tomato during Fusarium wilt infection

Abstract

The plants in their natural environment face various biotic stresses due to invading phytopathogens. Their control measures primarily involve large scale applications of chemical fungicides. The excessive use of chemicals leads to the contamination of the environment by entering the food web. To address the above concern, in the present study six antagonistic bacterial strains were screened from 344 isolates and identified through 16S rRNA sequencing. Out of these six antagonistic bacterial endophytes, Bacillus tequilensis (PBE1) (MTCC25188) was proven most effective and an eco-friendly substitute of chemical fungicides against Fusarium oxysporum for tomato wilt disease management. The antagonistic effect of PBE1 was well corroborated by dual culture plate assay and SEM micrographs. The PBE1 also showed efficient plant growth-promoting traits as it produced indole acetic acid (IAA) (31.89 μg ml−1), hydroxymate type siderophore (5.00 μg ml−1) along with phosphate solubilizing (9.09 μg ml−1) ability. The bio-protective intervention of PBE1 demonstrated 60.00% reduction of disease incidence in comparison to the pathogen infected plants. Simultaneously, enhanced physical parameters such as root length, shoot length, number of branches, fresh weight and dry weight by 1.73, 1.43, 1.71, 5.35 and 2.74 folds respectively. All the studies were performed under greenhouse conditions at 25 ± 2 °C for 30 days. Plants were grouped into six different treatments. The pathogen infection was given to 30 days old seedlings post-transplantation and PBE1 treatment was given at 7 days post-infection. The prevention of vascular bundle disruption and uniform thickness of parenchymatous cortical layer was observed in PBE1 treated plants. The changes were distinguished in transverse sections of the collar region of tomato stems. Moreover, PBE1 also enhanced various antioxidant and defense-related responses including superoxide dismutase, phenol peroxidase, peroxidase, and catalase enzymes estimated (77.22 U/mg of protein; 0.04 U/mg of protein, 0.003ΔOD/min/mg of FW and 1098.90 U/mg of protein respectively). The lipid peroxidation was found to decrease in PBE1+P treated plants (2.74 nM of TBARS/gm FW) as compared to all other groups. Whereas, the secondary metabolites including total phenolics and flavonoids content were higher in PBE1+P treated plants than all other treatments. By the virtue of obtained results, the study may provide an efficient eco-friendly bio-protective tool for the Fusarium wilt disease management by replacing widely used chemical fungicides.