# Serial Coincubation Enrichment Technique (SCET): Rapid isolation of bacterial biocontrol agents

## TL;DR

The SCET method quickly isolates bacteria that fight plant fungal pathogens by mimicking natural interactions in the soil.

## Contribution

SCET offers a rapid, simplified technique for isolating biocontrol bacteria from rhizospheric soil.

## Key findings

- Bacteria with antagonistic activity against fungal pathogens can be enriched within 20 days using SCET.
- The technique mimics natural rhizomicrobiome interactions and allows for efficient screening of biocontrol agents.
- Serial dilution and nystatin-containing agar help isolate the enriched bacterial antagonists.

## Abstract

The Serial Coincubation Enrichment Technique (SCET) mimics the rhizomicrobiome interaction between antagonistic bacteria and the target fungal pathogen, and subsequent enrichment allows only the predominant bacteria with antagonistic activity to survive within 20 days or less. Here, soybean phytopathogens, Rhizoctonia Solani, Colletotrichum truncatum, and Sclerotium rolfsii, were taken separately. Their discs were placed in a 1:1 ratio of 100 ml nutrient broth and potato dextrose broth, grown for at least 24 h, and then incubated with a 1 g rhizospheric soil sample from healthy, disease-free soybean plants. The enrichment was performed by transferring 1 ml of the previous suspension to freshly prepared media containing the previously grown 24 h target pathogen for an additional 5 days, and this process was repeated twice. The final suspension was serially diluted and spread on nutrient agar containing nystatin.

• Coincubation of the targeted pathogen with the rhizospheric sample allows survival of bacteria with biocontrol properties against the target fungal pathogen within 20 days.

• SCET setup mimics the rhizomicrobiome or classical dual assay, where already existing pathogens interact with the antagonistic bacteria of the rhizosphere.

• Samples can be screened by comparing sole fungal growth in the medium against the fungal growth in a final enriched co-incubated setup.

Image, graphical abstractIsolation of bacterial antagonists against phytopathogens through Serial Coincubation Enrichment Technique (SCET)