Interactions of Rhizobia Cultural Filtrates with Pseudomonas fluorescens on Bean Damping-off Control

Biotic as well as abiotic factors may influence the biocontrol activity and population density of pseudomonas fluorescens. however, limited studies have been carried out on the effects of extracellular metabolites of other competitor bacteria, especially on the biocontrol efficiency of p. fluorescens. a greenhouse experiment was conducted to evaluate the potential of the two p. fluorescens isolates utpf68 & utpf109 in the biocontrol of bean damping-off caused by rhizoctonia solani (ag-4), when applied individually or in combination with the culture filtrates of five rhizobia isolates (rh3 to rh7). although all treatments reduced bean damping-off severity in comparison with the untreated control, rh4 + utpf109 gave the lowest severity of damping-off (0.56 ,<1%). beside the effect on disease control, seeds treatment with both p. fluorescens isolates individually or in combined treatments especially rh4+utpf109 and rh6+utpf68 significantly improved bean growth factors such as shoot and root fresh/dry weights. on the other hand, all tested rhizobia and p. fluorescens isolates especially, rh4, proved to be siderophore, hcn, iaa, and exopolysaccharide producers. also, all tested bacteria except rh5 and rh7 produced chitinase. furthermore, our in vitro studies demonstrated that the filtrates of tested rhizobia isolates can effectively increase the population density of both p. fluorescens isolates as a biotic factor. thus, certain rhizobia seem to have a capacity to interact synergistically with p. fluorescens isolates having potential biocontrol activity.