Endophytic Bacillus subtilis SR22 Triggers Defense Responses in Tomato against Rhizoctonia Root Rot

Abstract

Rhizoctonia root rot is one of the most destructive diseases of tomato and other crops. The biocontrol of plant diseases using endophytic bacteria has gained significant attention due to their distinct advantages compared with the free-living ones, as well as their new unexplored and unique properties. Endophytic Bacillus subtilis SR22 represents a promising and more effective biocontrol and growth-promoting agent for tomato plants than the free-living agents, being an ecofriendly and sustainable tool in modern agriculture. In this study, the direct antagonistic activity of B. subtilis SR22 was investigated against Rhizoctonia solani in vitro. The biocontrol activity of B. subtilis SR22 against Rhizoctonia root rot of tomato was also investigated. Effects on the level of the transcriptional expression of defense-related genes, biochemical responses, and the vegetative growth of tomato plants were also studied. The dual culture test showed 51% inhibition in the mycelial growth of R. solani due to B. subtilis SR22, indicating its potent antagonistic behavior. Using a GC-MS analysis, twenty bioactive compounds were detected to be produced by B. subtilis SR22, including chlorogenic acid, pyrrolo [1,2-a]pyrazine-1,4-dione, hexahydro, propyl thioglycolic acid, phthalic acid, and 2,3-butanediol. Under greenhouse conditions, the application of B. subtilis SR22 led to a reduction (up to 51%) in Rhizoctonia root rot of tomato. Furthermore, an upregulation in the expression of the responsive factor JERF3 (10.9-fold) and the defense-related genes POD (9.1-fold) and PR1 (4.5-fold) in tomato plants was recorded due to the application of B. subtilis SR22. In addition, this treatment enhanced the total phenolic content (76.8%) and activity of the antioxidant enzymes POD (56%) and PPO (29.2%) in tomato roots, indicating its resistance-inducing effect on tomato plants. Moreover, this treatment enhanced most of the evaluated growth parameters in tomato plants (up to 35%). We can conclude that B. subtilis SR22 is a promising biocontrol agent and growth promoter in tomato plants against Rhizoctonia root rot. An evaluation of the formulation and field application of this bio-agent is necessary in future studies.

Biological Control of Pseudomonas syringae in Tomato Using Filtrates and Extracts Produced by Alternaria leptinellae

“…In our case, although the results presented demonstrate a lack of phytotoxicity when used on tomato plants, further studies including a wider range of crops and employing different application conditions could allow for evaluating the actual potential of this product for future commercial use. The prospects are promising based on previous findings that have demonstrated the ability of endophytic extracts and microbial inoculants to enhance plant growth and confer resistance to pathogens [83][84][85].…”

A Biocontrol Strain of Serratia plymuthica MM Promotes Growth and Controls Fusarium Wilt in Watermelon

“…These compounds inhibit the synthesis of functional proteins by down-regulating specific functional protein coding genes [31,57,58]. 2,5-Piperazinedione, 3-methyl-6-(1-methylethyl)-and 2,5-Piperazinedione, 3,6-bis(2-methylpropyl)are found in many strains of Bacillus and have been reported to exhibit strong antifungal activity against various phytopathogenic fungi [31,[59][60][61][62]. Additionally, 9-octadecenamide, (Z) has also been reported to possess antimicrobial properties [63,64].…”

Bacillus Species: Excellent Biocontrol Agents against Tomato Diseases

“…Biocontrol agent B. subtilis SR22 efficiently suppressed the R. solani growth and root rot disease under in vitro and greenhouse conditions due to the production of numerous bioactive compounds, including phthalic acid, pyrrolo[1,2-a]pyrazine-1,4-dione, hexahydro, chlorogenic acid, propyl thioglycolic acid, and 2,3-butanediol [ 135 ]. Moreover, this strain improved tomato growth parameters as well as total phenolic content and antioxidant enzyme activity in tomato roots, indicating its ISR effect [ 135 ]. The application of Bacillus subtilis MBI600 on tomato plants significantly improved plant growth and had a strong biocontrol effect against three tomato pathogens, namely, R. solani , Pythium ultimum , and F. oxysporum f. sp.…”