Antagonism of Bacillus subtilis Against Sclerotinia sclerotiorum on Lactuca sativa

Abstract

The objectives of this study were select and test the efficiency of the Bacillus subtilis strain and its metabolites against Sclerotinia sclerotiorum in all stages of its cycle. The bacterium was selected by performing antibiosis test against this and other pathogens, being selected that one who obtained the best result. For the assessment of radial mycelial growth under the influence of metabolite, this was added to PDA culture medium and the fungus was placed on its surface, being evaluated daily in the both directions. The test with volatiles was performed by using the two surfaces of the Petri dish, each containing culture medium, putting the fungus and the bacteria separately one on each surface without any contact between them, being measured every day the mycelial growth dimensions. For the evaluating the direct effect on the sclerotia was applied 1 mL of bacterial suspension (1.002 absorbance value at wavelength of 550 nm) to observe the possible presence of harmful substances to this structure. The test for the possible protection provided by the strain on lettuce (Lactuca sativa) was performed with four varieties grown up to 60 days after sowing, when was sprayed the bacterial suspension following the best incubation time tested. The antibiosis test showed a decreased by 16.33% compared to control. The metabolite, when mixed into the culture medium showed better inhibition results of the radial mycelial growth when concentration and incubation time were greater. The volatile test showed a reduction of 83.33% on mycelial growth. For the test with sclerotia, the mycelial and carpogenic germination were higher than the control. In vivo treatments with lettuces were observed differentiated levels of control, and some plants showed extremely sensitive to bacterial cells concentration used. This study show the B. subtilis as a biocontrol agent applying different strategies to control the pathogen and also the hipensensitive plant reaction in some cases.