Isolation and Evaluation of Endophytic Bacteria Against Fusarium Oxysporum f. sp. Cucumerinum Infecting Cucumber Plants

The aim of this study was to isolate, within cucumber plants, Endophytic Bacterial (EB) isolates that can provide significant biological control of Fusarial wilt of cucumber caused by Fusarium Oxysporum f. sp. Cucumerinum (FOC) and enhance plant growth under in vitro conditions. The endophytic bacteria were isolated from the internal tissues of roots, leaves and stems of healthy cucumber plants. In this study, we isolated 112 EB strains from internal tissues of healthy cucumber plants grown in greenhouse and field conditions in Turkey. We determined several phenotypic properties of EB strains and found approximately equal numbers of Gram-negative and Gram-positive strains. These isolates were screened in vitro for their plant growth promoting traits such as production of Indol 3-Acetic Acid (IAA), Hydrogen Cyanide (HCN), siderophore, phosphate solubilization and antagonistic activity against FOC. More than 30% of the EB strains produced detectable levels (20-125 μg ml-1) of IAA in culture filtrates. 46 % of EB strains exhibited siderophore production ranging from 3 to 19 mm zones. HCN production was more common trait of Pseudomonas strains (16%). Solubilization of phosphate was detected by 29% in the EB isolates. More than 53% of the EB strains inhibited the mycelial growth of FOC on PDA plates. The strains CC29/3 and CC25/2 were more active compared to other against FOC. Majority of isolated endophytes were not only able to suppress pathogenic fungi, but could also improve seed germination and plant growth. Finally, these strains may be candidates for biological control and plant growth promotion.