Investigation on biosuppression of Fusarium crown and root rot of tomato (Solanum lycopersicum L.) and growth promotion using fungi naturally associated to Solanum linnaeanum L.

Fusarium crown and root rot (FCRR) is a serious tomato disease in Tunisia which is difficult to control due to its soilborne nature and to the luck of genetic resistance. In the current study, native Solanum linnaeanum was explored as potential source of effective fungal agents for disease biocontrol. Eight fungal isolates, recovered from S. linnaeanum plants growing in the Tunisian Centre-East and shown able to colonize roots, crowns and stems of tomato (Solanum lycopersicum L.) seedlings, were tested for their ability to inhibit Fusarium oxysporum f. sp. radicis-lycopersici (FORL), the causal agent of this disease, and to promote plant growth. Tomato seedlings inoculated or not with FORL and treated using tested fungal isolates, exhibited significant increments in their growth parameters. Tested as conidial suspensions or cell-free culture filtrates, I74 and I92 isolates were the most active leading to 92.8% decrease in FCRR severity and 89.3 to 95.2% lowered vascular browning extent as compared to FORL-inoculated and untreated controls. These two isolates were microscopically and macroscopically described and identified using rDNA sequencing gene as being Penicillium crustosum I74 (MF188258) and Fusarium proliferatum I92 (MF188256). Pathogen mycelial growth was inhibited by 29.4 to 78.1% using their conidial suspensions and by 67.5 to 82% with their cell-free culture filtrates. P. crustosum I74 and F. proliferatum I92 showed chitinolytic, proteolytic and amylase activities. Only I92 isolate exhibited a lipolytic activity. Our study clearly demonstrated that I74 and I92 isolates were promising candidates for suppressing FCRR severity and promoting tomato growth. Further investigations are required for elucidating their mechanisms of action involved in disease suppression and plant growth promotion.