Rania Aydi Ben Abdallah, Boutheina Mejdoub-Trabelsi, Ahlem Nefzi, Hayfa Jabnoun-Khiareddine and Mejda Daami-Remadi
Four nonpathogenic and putative endophytic bacterial isolates, recovered from Withania somnifera fruits (S7, S8 and S9) and stems (S15), were evaluated for their in vivo and in vitro antifungal activity against Fusarium oxysporum f. sp. lycopersici (FOL), and their plant-growth promoting ability. Tomato plants challenged and/or not with FOL and treated using these bacterial isolates exhibited a significant increment in their growth parameters (plant height, aerial part fresh weight, maximum root length, and root fresh weight). The strong suppressive effect against Fusarium wilt was achieved using two isolates (namely S15 and S8) leading to 92-96% lower disease severity compared to pathogen-inoculated and untreated control. Both isolates were characterized and only the isolate S8 was identified as Alcaligenes faecalis subsp. faecalis str. S8 (KR818077) using 16S rDNA gene sequencing. The unidentified bacterial isolate S15 had improved germination of bacterized tomato seeds relative to the untreated ones. Tested using streak and sealed plates methods, diffusible and volatile compounds from S15 and S8 isolates inhibited FOL by 10.7-16.8% and 53.8-20.7%, respectively. Moreover, an inhibition zone (8.5-8.25 mm) was formed around FOL colonies using the disc diffusion method. Alcaligenes faecalis subsp. faecalis str. S8 and the unidentified bacterium str. S15 were shown able to produce chitinolytic, proteolytic and pectinolytic enzymes and hydrogen cyanide. Production of indole-3-acetic acid and phosphate solubilizing ability were also investigated for elucidation of their plant growth-promoting traits.