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A marine isolate of fluorescent Pseudomonassp. having the ability to produce the pyoverdine type of siderophores under low iron stress (up to 10 µMiron in the succinate medium) was identified as Pseudomonas aeruginosaby using BIOLOG Breathprint and siderotyping. Pyoverdine production was optimum at 0.2% (w/v) succinate, pH 6.0, in an iron-deficient medium. Studies carried out in vitro revealed that purified siderophores and Pseudomonasculture have good antifungal activity against the plant deleterious fungi, namely, Aspergillus niger, Aspergillus flavus, Aspergillus oryzae, Fusarium oxysporum, and Sclerotium rolfsii. Siderophore-based maximum inhibition was observed against A. niger. These in vitro antagonistic actions of marine Pseudomonasagainst phytopathogens suggest the potential of the organism to serve as a biocontrol agent.

After screening for siderophore (microbial iron chelator) production, of seven available cultures of soybean (Glycine maxL.) root nodule bradyrhizobia, one strain, Bradyrhizobium japonicumNCIM 2746, was selected to confirm its phytopathogenic suppression and soybean growth promotion. Based on chromatographic and spectrophotometric studies, two different siderophores, a hydroxamate type (MW 734) and another catecholate type (MW 1000), were observed. Randomized block design (RBD) analysis of sickpot studies (soil inoculated with phytopathogens) with an MACS 124 variety of soybean, bacterized with siderophoregenic B. japonicum, showed a marked increase in the percentage of germination, nodulation, chlorophyll, oil, protein content, and number of pods. Field trial study confirmed these pot results, which were evident from enhancement in shoot length, number of branches, chlorophyll content, number of nodules, root length, and number of pods. These results suggest the possibility of exploiting B. japonicumNCIM 2746 as a potential bioinoculant.