Isolation of sweet potato rhizobacteria with growth-promoting and antifungal activity against Fusarium oxysporum

The application of plant growth-promoting rhizobacteria (PGPR) offers great potential to enhance crop production. This study aimed to isolate and screen PGPR associated with sweet potato (Ipomoea batatas (L.) Lam). A total of 258 potential PGPR isolates were obtained from sweet potato fields and were screened for plant growth-promoting traits and biocontrol activity against the soil-borne pathogen, Fusarium oxysporum. A subset of isolates was subsequently evaluated for growth promotion under greenhouse conditions. The results showed that 24.8% of the tested isolates produced siderophores, three isolates solubilised phosphate, and all isolates produced indole-3-acetic acid (IAA) with concentrations ranging between 9 and 131 μg ml−1. Forty-three isolates reduced the mycelial growth of F. oxysporum. Molecular identification was conducted on the 50 best-performing isolates and revealed that the selected isolates belonged to the genera Achromobacter, Bacillus, Pantoea, Priestia, Pseudomonas, Rahnella and Staphylococcus. In greenhouse trials, 5.7% of isolates significantly enhanced root length in the first trial. In the second trial, 4.2% of isolates increased root length, 14.3% enhanced shoot wet mass, and one isolate improved root wet mass. These findings highlight the potential of PGPR in improving sweet potato productivity and thus promoting food security.