. Identification of antagonist isolates
Isolates that inhibited the growth of R. solanacearum strain To-udk2 under in vitro conditions were identified by gas chromatography-Fatty Acid Methyl Ester (GC-FAME) analysis using the MIDI system. Furthermore, isolates were characterized based on cultural, morphological and biochemical and physiological tests.
4. Screening of isolates for quorum sensing and quorum sensing inhibition activity
Bacterial isolates were screened for production of the quorum sensing signal molecule acyl-homoserine lactones (AHL). AHL production was detected in a cross-feeding assay by stabbing the selected antagonistic isolates onto LB agar plates seeded with Chromobacterium violaceum CV026. After an incubation of 24 h at 28 C, production of purple pigment violacein was evaluated as positive for the test.
Similarly, quorum sensing inhibition (QSI) activities of isolates were determined by adapting the method of McLean et al.(2004). The test strains were streaked onto the center of an NGApate and incubated overnight at 28 C.