The role of the Bacterial Filtrate of Bacillus subtilis S20 in Limiting the Growth and Development of Halo blight Disease of beans Pseudomonas syringae pv. phaseolicola and in Enhancing Defensive Responses in the Host Plant

Abstract

Biological control of plant pathogens represents a new approach within the strategy of conservation and sustainable development. In this study, the biological control of the bacterium Pseudomonas syringae pv. phaseolicola, (PsPh) causing halo blight disease of beans, was investigated using a bacterial filtrate, cell-free culture filtrate produced by B. subtilis S20. The results obtained showed that the bacterial filtrate and its dilutions were able to inhibit the growth of halo blight bacteria. The 100% full filtrate and the 80% dilution (filtrate: distilled water) gave the highest effectiveness, as it led to 100% mortality of the bacterial pathogen, 72 hours after incubation. As for the other dilutions (5, 10, 20 and 40%), the inhibition rate 72 hours after incubation reached 13.9, 30.6, 84.4, 97.8%, respectively. The results obtained also showed that the minimum inhibitory concentration (MIC) for bacterial growth was the 20% filtrate dilution. On the other hand, the results showed that spraying the leaves with the 100% full filtrate or the 50% dilution led to a logarithmically reduced disease development in plant tissues (3.48 and 2.11) compared to the control treated with sterile distilled water. The results revealed a significant increase in peroxidase enzyme levels in the first true leaves of bean plants treated with either full filtrate soaking or 50% dilution, reaching approximately 97.89 and 73.23 nanokatal/mg, respectively, compared to the control (41.5 nanokatal/mg). These findings suggest the ability of the bacterial filtrate to induce systemic resistance in the host plant, in addition to its ability to inhibit the growth of the bacterial pathogen Pseudomonas syringae pv. phaseolicola.

Keywords:

Bacillus subtilis S20, bacterial filtrate, Pseudomonas syringae pv. phaseolicola, biological control, acquired systemic resistance.