In the present study, a collection of 235 Bacillus strains, which had been isolated from the potato rhizosphere, was screened with the aim of controlling Pectobacterium carotovorum subsp. carotovorum (Pcc), a dominant potato pathogen known for causing soft rot in Iran. Fifteen strains inhibited the known Pcc strains in vitro and these were chosen for further studies. The maceration capacity of Pcc strains was decreased by the antagonistic strains in the range of 1.6 to 4 times. Based on 16S rRNA sequencing, five Bacillus species were characterized. Conducting various supplementary tests, the current work evaluated all antagonistic strains for biosurfactant production, mobility, enzymatic activities, production and inactivation of acyl-homoserine lactones, and the ability to produce auxin. Among the five antimicrobial peptide biosynthetic genes tested, bmyB was the less frequent gene while three genes, namely srfAA, fenD, and ituC, were the most distributed genes. In addition, the interaction of four promising Bacillus species in the potato-Pcc system was studied. Along with its discussion of the potency for the biocontrol of Pcc by B. pumilus IrB8 and B. amyloliquefaciens IrB12, the present study's test results also indicated these two suppressed tuber maceration by 63.7 and 47.8 % respectively. The high levels of phenylalanine ammonia-lyase, polyphenol oxidase, peroxidase and total phenols were obtained in a single application of IrB8 or IrB12 after 8 h. In addition, the discontinuous usage of Bacillus and Pcc strains was achieved in comparison to other treatments. Consequently, the current work's findings show that IrB8 and IrB12 strains have the potential to be used for potato soft rot control.

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