Biological control of take-all of wheat in the Pacific Northwest of the USA using hypovirulent Gaeumannomyces graminis var. tritici and fluorescent pseudomonads

Hypovirulent Gaeumannomyces graminis var. tritici strain L108hv, five strains of Pseudomonas spp., and a mixture of four of these bacterial strains were used individually and in combination for the suppression of take-all of wheat. In the growth chamber, L108hv and all five individual bacterial strains provided a significant reduction in take-all severity compared with an untreated control. Combination of L108hv and the bacteria did not significantly enhance the suppressiveness of either agent. In the field at Pullman, WA, 108hv significantly reduced crown root infection of winter wheat but not seminal root infection, while the reverse was true for a mixture of bacterial strains suggesting these agents may be more effective at different stages in disease development. In a second field trial at Pullman, yield of spring wheat was increased by 20.8%. In contrast, in two field trials at Mt. Vernon, WA, L108hv had no effect on take-all of spring wheat. We conclude that specific biocontrol agents may be better suited for certain environments and that biocontrol treatments should be customized for the target site.