Submitted to: Biological Control
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/9/2013
Publication Date: 1/3/2014
Citation: Hu, X., Roberts, D.P., Xie, L., Maul, J.E., Yu, C., Li, Y., Jing, M., Liao, X., Che, Z., Liao, X. 2014. Formulations of Bacillus subtilis BY-2 suppress Sclerotinia sclerotiorum on oilseed rape in the field. Biological Control. 70:54-64. Interpretive Summary: The fungal pathogen Sclerotinia sclerotiorum can cause serious yield losses in oilseed crops in the United States and worldwide. Chemical control measures for diseases caused by this pathogen are often ineffective and can be hazardous to man and the environment. Other control measures such as plant breeding have met with limited success. Biological control measures for these diseases need to be developed due to environmental problems associated with existing chemical controls and the limited effectiveness of other traditional control measures. In this study we show that two different formulations of oilseed rape seed containing the beneficial bacterium Bacillus subtilis BY-2 significantly suppressed disease caused by S. sclerotiorum on oilseed rape in field trials conducted at two locations that differed in soil type. Oilseed rape seed yield was significantly increased in treatments containing this bacterium at both locations as well. Performance by B. subtilis BY-2 and by another biocontrol bacterium, B. subtilis Tu-100, was comparable to that obtained with the chemical pesticide recommended for use on this disease. It was also shown that BY-2 colonizes the internal tissues of oilseed rape roots. Experiments can now be conducted with formulations containing both strains BY-2 and Tu-100 to determine if these formulations perform better than formulations containing only one of these strains. This information will be useful to scientists devising strategies for biological control of diseases on oilseed crops caused by S. sclerotiorum.
Technical 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 per seed to 104 CFU per gram root and < 102 per gram of stem or leaf after 60 days. In two field trials at the Wuxue location, conducted in two consecutive years, strain BY-2 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 provided disease control (disease incidence) and mean seed yield per pot 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 per pot that was similar to the chemical control treatment and significantly greater than the non-treated control treatments. These three BY-2 treatments also compared favorably to treatments containing Tu-100 at the Wuhan site. 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.