Biocontrol of Fusarium wilt and growth promotion of tomato plants using endophytic bacteria isolated from Nicotiana glauca organs

• Nicotiana glauca as potent source of bacterial biocontrol agents.
• Two isolates suppressed Fusarium wilt and enhanced plant growth.
• A. faecalis and B. cereus with antifungal potential towards F. o. lycopersici.
• Lytic enzymes, HCN, IAA production and phosphate solubilization are assessed.

Seven bacterial isolates, recovered from native Nicotiana glauca plants of the Tunisian Centre-East, and successfully colonizing the internal stem tissues of tomato cv. Rio Grande were screened for their ability to suppress tomato Fusarium wilt, caused by Fusaium oxysporum f. sp. lycopersici, and to enhance plant growth. S18 and S42 isolates were found to be the most effective in decreasing yellowing and wilt symptoms by 94 and 88% and the vascular browning extent by 95–97.5%, respectively, as compared to FOL-inoculated and untreated control. A significant enhancement in growth parameters of tomato plants inoculated with pathogen and treated with S18 and S42 isolates. These two bioactive isolates were characterized and identified using 16S rDNA sequencing genes as Alcaligenes faecalis S18 and Bacillus cereus S42, respectively. Pathogen mycelial growth was inhibited by 44.1 and 42.1% with S42 and S18 isolates, respectively. Using the disc diffusion method, S42 and S18 formed an inhibition zone against FOL of about 11.87–12.37 mm, respectively. The isolate S42 of B. cereus showed a proteolytic and chitinolytic activity. A. faecalis S18 exhibited only chitinolytic activity in chitin-agar medium. This isolate was also able to produce the volatile metabolite hydrogen cyanide. Indole-3-acetic acid production, phosphate solubilizing, and pectinase activity were assessed for these two bioactive isolates for elucidating their plant growth promoting traits and their endophytic colonization ability. This study clearly demonstrated that N. glauca is a potential source for the isolation of potent endophytic bacteria exhibiting Fusarium wilt-suppressive and plant growth-promoting effects on tomato.