Biological control of root rot of groundnut with antagonistic Pseudomonas fluorescens strains

The potential of Pseudomonas fluorescens for the management of groundnut (A rachis hypogaea) root rot caused by Macrophomina phaseolina was evaluated u nder greenhouse and field conditions. Various strains of P. fluorescens iso lated from the rhizosphere of groundnut were screened for their ability to inhibit mycelial growth of M. phaseolina. Among the various strains tested in vitro, five strains were found to inhibit the mycelial growth of M. phas eolina. Talc-based powder formulations of the effective strains of P. fluor escens were developed and evaluated for their efficacy in the management of groundnut root rot under greenhouse conditions. Seed treatment or soil app lication of powder formulation of P. fluorescens strain Pf1 effectively red uced groundnut root rot when compared to other strains. Seed treatment with Pf1 powder formulation exhibited a similar level of control to the soil ap plication with A fluorescens or soil drenching with carbendazim. Seed treat ment with P. fluorescens reduced the root rot incidence from 88.8 % (with n on-bacterized seeds) to 33.3 %. Four Field trials were conducted over a 2-y ear period to determine the efficacy of seed treatment with powder formulat ion of Pf1 in checking groundnut root rot. Seed treatment with powder formu lation of Pf1 resulted in significant reduction in root rot incidence and i ncrease in pod yield in all field trials. Ten strains of P. fluorescens wer e tested for their ability to produce HCN, salicylic acid, siderophore and lytic enzymes. The strain Pf1 that showed maximum in vitro antagonism produ ced more HCN, salicylic acid, siderophore and beta -1,3-glucanase in vitro when compared to other strains. The results suggest that more than one mech anism might be involved in suppression of M. phaseolina by P. fluorescens.