Application of formulated rhizobacteria against root rot of field pea.

Formulations of bacterial biocontrol agents were evaluated for the control of pea root-rot caused primarily by Pythium ultimum and Rhyzoctonia solani, at different levels of disease severity in field trials. Pseudomonas fluorescens (strain PRA25) in a peat-based formulation increased yield by 17% over the untreated, in a trial with light disease infection, and by 120% in another with moderate infection. Other bacteria including P. cepacia (strain AMMD) and fluorescent pseudomonads increased seedling emergence, and decreased disease incidence and severity, but with variable effects on yield when disease level was light to moderate. Biocontrol agents resulted in only limited control when disease was severe. Control with Captan did not differ significantly from that obtained with bacterial biocontrol agents. The application of Rhizobium granular inoculum together with PRA25 granules did not differ from other treatments in disease control, indicating that Rhizobium is compatible with biocontrol agents. The population dynamics of a fluorescent pseudomonad introduced into the rhizosphere in peat or granular formulation was monitored using an antibiotic-resistant mutant marker strain. The bacterium in peat formulation established a considerably higher population than that in granular formulation in 1993 trials, and a slightly higher population in 1994 trials. The higher population may have been responsible for the efficiency of root colonization and the effectiveness of disease control. [ABSTRACT FROM AUTHOR]