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Biological control of onion basal rot disease using phosphate solubilising rhizobacteria

ABSTRACT Onion basal rot is the most destructive disease caused by Fusarium oxysporum f. sp. cepae (FOC) for onion growing regions of the world. To control this disease, biological control agents 287 phosphate solubilising bacteria (PSB) were isolated from 43 onion rhizosphere soil samples. The value on the phosphate solubilisation index (SI) of the PSB was calculated to be in the range of 1.2–5.5, and a quantitative estimation of P solubilisation was investigated in liquid medium and found to be in the range of 15.2–382.5 mg/l. Furthermore, all tested organisms solubilised rock phosphates (RP) by lowering the medium’s pH. These isolates were tested for their effect on the mycelial growth of FOC in dual cultures. Eight isolates were determined to inhibit mycelial growth of FOC at rates from 71.5 to 75.7%. For the pot experiments, 15 rhizobacteria (12 isolates highest P-solubilising and 3 isolates P-solubilising and effective antagonist) were selected through 287 PSB. In the pot experiments, onion seeds (sensitive and resistant) coated with PSB were sown in soil which was infected with FOC and RP. Seed treatment with the isolates was found to suppress disease severity in ratios varying from 10.9 to 77.8%. At the same time, these PSB isolates significantly reduced disease, similar in degree to a chemical fungicide (Antrachol) (p < 0.05). The results of the in vitro and in vivo research demonstrated that the isolated PSB are potential biological control agents and need to be further researched for the biochemical basis of their activity against FOC.