Effect of Indole-3-Acetic Acid (IAA) Produced by Pseudomonas aeruginosa in Suppression of Charcoal Rot Disease of Chickpea

The production of indole-3-acetic acid (IAA), by rhizobacteria, has been associated with plant growth promotion, especially root initiation and elongation. Isolate TO3 selected from 103 fluorescent pseudomonads, identified as Pseudomonas aeruginosa, showed maximum production of IAA. Isolate TO3 having biocontrol activity against Macrophomina phaseolina also showed production of siderophore and HCN was used to screen the role of bacterial IAA in reducing the level of charcoal rot disease occurrence in chickpea. Four IAA defective stable mutants of isolate TO3 having biocontrol activity against M. phaseolina were developed through 5-bromouracil mutagenesis. Mutant TO₅₂ showed 76.47% reduction in production of IAA. Standard IAA was used in similar concentration as present in cell-free culture supernatant of wild isolate TO3 and its mutant TO₅₂. The in vitro and in vivo study showed that IAA-defective mutant TO₅₂ caused reduced biocontrol and plant growth promotory activity than wild isolate TO3. Standard IAA showed comparable biocontrol activity to the culture supernatant. To some extent better biocontrol and growth promotory activity in supernatant than standard IAA indicates the synergistic role of siderophore and HCN. The study clearly reports the role of bacterial IAA in suppression of charcoal rot disease of chickpea.