Citrus Endophytic Bacteria Ys45 Antibacterial Substances And Bacteria On The Biological Control Of Sclerotinia Sclerotiorum

YS45 strain was an endophytic bacterial strain isolated from the xylem of branches in healthy citrus plants. Its antibiotic activity against Sclerotinia sclerotiorum (pathogen of sclerotinia stem rot of rapeseed) was remarkable. The strain was identified as a Bacillus subtilis strain by morphological, biochemical, physiological and 16SrDNA sequence analysis.The stability of the antibiotic activity of YS45 culture broth was tested under different conditions. A thermal stability test showed the antibiotic activity was not sensitive to high temperature. A pH stability test showed the antibiotic activity of the culture broth was the highest in neutral conditions (pH 6.0-8.0), and it was stable when the pH ranged from 6.0 to 2.0. But the activity had weak stability in alkaline conditions. The antibiotic activity was reduced when the culture broth was treated with papain. Furthermore, the antibiotic activity was changing with the culture time and its curve was similar to the growth curve of YS45 strain.Solubility of the antibiotic compounds produced by YS45 strain was very limited in acidic conditions. The precipitation at pH 3.0 showed the highest antibiotic activity comparing with the precipitation in other acidic conditions. The precipitation was collected and extracted twice with methanol. Then the antibiotic compounds were separated and purified by multiple-chromatography approaches, including ion exchange chromatography, gel filtration chromatography and reverse phase HPLC. MALDI-TOF MS analysis of the isolated antibiotic compounds showed that YS45 strain produced a cluster of fengycin homologues.Biocontrol experiments were conducted in vitro, in pots and in a field. Results from these experiments showed YS45 strongly inhibited leaf lesions caused by S. sclerotiorum. Its control effect was almost comparable with that of quintozene suspension.