Plant Growth Promotion and Biocontrol Potentiality of Endophytes Isolated from Root Nodules of Sulla flexuosa L. Plants

Legumes, native to the Mediterranean, harbor reservoirs of endophytes that help plants adapt to various environmental stresses. The current study was carried out to evaluate the plant growth characteristics and antifungal activity of root nodule endophytes as biocontrol agents and plant growth promoters. Eleven bacterial endophytes isolated from root nodules of Sulla flexuosa L. grown in Northwest Morocco were assessed for their plant growth-promoting (PGP), and antifungal properties. Four endophytic bacteria were selected for their efficiency in solubilizing inorganic phosphate. The selected strains were positive for more than 2 PGP traits, including indole acetic acid, ACC deaminase, siderophore, and ammonia production. The screening for lytic enzyme production revealed that all strains were capable of producing chitinase, cellulase, catalase, and protease, while the secretion of amylase and urease was not detected. The HFB11 was the only strain incapable of producing pectinase. In vitro experiments revealed the strains’ potential to withstand salt and drought stresses by being able to grow in high concentrations of NaCl and PEG. Based on 16S rRNA gene sequencing, the strains were identified as Enterobacter and Serratia. The antagonistic activity of the strains against Botrytis cinerea, Aspergillus ochraceus, and Fusarium oxysporum was detected and they were shown to inhibit the fungal growth with various percentages. The highest percentage of inhibition was observed for HFB3 against B. cinerea with 50% inhibition followed by HFB8 which was able to inhibit 47% of F. oxysporum’s growth. In contrast, a weak inhibition was observed against A. ochraceus. All these findings indicate that the chosen endophytes, halotolerant Serratia inhibens HFB8 and Enterobacter hormaechei HFB11, might be used as candidates for effective biocontrol and growth promotion of legumes.