Biocontrol potential of Bacillus subtilis Sjb3 against Rosa chinensis and apple diseases

There are various diseases affecting Rosa chinensis, which significantly impact its ornamental value. This paper examines the inhibitory effect of the strain Bacillus subtilis Sjb3 on different pathogenic fungi and its biocontrol effects on anthracnose and black spot diseases. The plate confrontation method was employed to assess the antifungal activity of B. subtilis Sjb3. The results indicated that the strain exhibited inhibitory effects on the growth of seven pathogenic fungi, with an inhibitory rate ranging from 39.34 % to 47.50 %. By observing the mycelia of the seven types of pathogenic fungi that were inhibited by the fungus under an inverted fluorescence microscope, it was discovered that the fungus caused various distortions in the mycelia of these fungi, such as expansion, bending, and folding. With bubble-like structures, uneven thickness, and oval branch formations. In vitro inoculation experiments indicated that B. subtilis Sjb3 could effectively reduce anthracnose caused by Colletotrichum gloeosporioides, the black spot of R. chinensis caused by Alternaria tenuissima, and ring rot disease of apples caused by Botryosphaeria dothidea. The stability of the sterile filtrate from B. subtilis Sjb3 was determined using C. gloeosporioides as the test pathogen. The fermentation broth of B. subtilis Sjb3 exhibited strong thermal stability at 80 °C. It maintained good stability within a pH range of 6-9. UV irradiation time remained relatively stable for up to 60 min. It was not sensitive to protease K. Using BG medium as the base, the optimal culture conditions were identified. The results showed that the best inorganic salt was 0.1 % sodium chloride, the ideal nitrogen source was 1 % yeast extract, the preferred carbon source was 0.5 % glucose, and the optimal pH was 7. Thus, B. subtilis Sjb3 demonstrated broad-spectrum antagonism against various plant pathogenic fungi, effectively inhibiting the occurrence of anthracnose in R. chinensis and black spot diseases, along with high stability of antibacterial substances. This study provides a foundation for further applications of B. subtilis Sjb3 as a biocontrol agent.