Formulations of Bacillus subtilis BY-2 suppress Sclerotinia sclerotiorum on oilseed rape in the field

Abstract

We are developing a collection of Bacillus strains, isolated from different environments, for use in controlling Sclerotinia sclerotiorum on oilseed rape in China and elsewhere. Strain BY-2, isolated from internal tissues of an oilseed rape root, was demonstrated to be Bacillus subtilis based on biochemical and morphological characteristics and on 16S RNA gene sequence. Photographic evidence from gnotobiotic studies using the lacZ-tagged strain BY-2(pUC18) confirmed that this strain was capable of colonizing internal root tissues. Strain BY-2 did not effectively colonize the ectorhizosphere or the surface of the stems or leaves of oilseed rape when applied in pellet or wrap seed treatment formulations. Populations of BY-2 dropped from 108 CFU seed−1 to 104 CFUg root−1 and ⩽102 CFUg stem−1 or leaf−1 after 60days. Strain BY-2 was applied as a pellet seed treatment formulation alone, as a spray at flowering alone, and as the pellet seed treatment formulation combined with the spray application in two field trials at the Wuxue location conducted in two consecutive years. These three treatments containing BY-2 provided disease control (disease incidence) and mean seed yield that was similar to the chemical control treatment and significantly greater than the pellet without bacteria and non-treated control treatments. All three of these BY-2 treatments were similar to each other with regard to these two metrics and to treatments containing B. subtilis Tu-100, a genetically distinct strain previously shown to be effective against this disease. In two additional field trials, conducted in consecutive years at the Wuhan location, strain BY-2 applied as a wrap seed treatment formulation alone, as a spray at flowering alone, and as the wrap seed treatment combined with the spray application provided disease control (disease incidence) and mean seed yield that was similar to the chemical control treatment. These three BY-2 treatments also were significantly greater than the non-treated control treatments and compared favorably to treatments containing Tu-100. There was no evidence of BY-2 promoting growth of oilseed rape when applied in the pellet or wrap seed treatment formulations in field trials conducted at the Wuxue or at the Wuhan locations. We now have three Bacillus strains (B. subtilis strains BY-2 and Tu-100, B. megaterium A6) that control S. sclerotiorum on oilseed rape in the field that can be tested in strain combinations for enhanced disease control. We also have multiple methods for application of Bacillus strains as both seed treatment and foliar applications were effective.