Seed treatment containing Bacillus subtilis BY-2 in combination with other Bacillus isolates for control of Sclerotinia sclerotiorum on oilseed rape

Abstract Biological control treatments for soil-borne plant pathogens must provide enhanced levels of disease suppression and consistency of control over diverse soils before they enjoy wide-spread use. Bacillus megaterium A6 and two genetically distinct B. subtilis isolates, BY-2 and Tu-100, were applied individually and in combinations as seed treatments and tested in field trials conducted at four locations with different soils for control of Sclerotinia sclerotiorum on oilseed rape. The treatment containing isolate BY-2 resulted in significant reductions in disease relative to the non-treated and formulation-only controls at all four locations. Treatments containing isolate A-6 or Tu-100 resulted in a significant decrease in disease at two locations only. There were no significant reductions in disease with treatments containing combinations of these strains relative to treatments containing strains applied individually. In plant growth promotion studies conducted in pots, the seed treatment containing isolate BY-2 combined with A6 and Tu-100 resulted in seed yield greater than the non-treated control in four of the five soils tested. The seed treatment containing isolate A-6 combined with Tu-100 significantly increased yield in one soil. No other treatment containing a single isolate, or combination of two isolates, significantly increased yield in these pot studies. Field experiments reported here indicated that seed treatment with isolate BY-2 provided consistent reduction of disease at four field locations with different soil types. Pot studies suggested that combining other Bacillus isolates with BY-2 provided the added benefit of plant growth promotion.