Siderophore production of antagonists was assessed under iron deprivation, at 30C for 72 h. To achieve iron deprivation, all media and glassware were treated according to Cox (1994). Chrome azurol S (CAS) medium was prepared according to Schwyn and Neilands (1987). The cell free supernatant (0.5 ll) of each strain was obtained after centrifugation of exponential phase culture at 10,0009g for 30 min followed by filter sterilization (0.22 l, Millipore). This supernatant was inoculated on overlay chrome azurol S (O-CAS) medium plates and incubated for 48 h to observe the colour change (from blue green media colour to orange haloes).