Abstract: Quinoa black stem disease is one of the common diseases found in quinoa production in recent years. In the previous study, a strain of Bacillus subtilis LS3 with good inhibitory effect on Ascochyta caulina was isolated from quinoa ear. In order to clarify its control effect and the composition of antifungal substances, the growth rate method was used to determine the inhibitory effect of volatile and non-volatile antifungal substances of strain LS3. The field control effect of LS3 strain fermentation broth was determined by randomized block design. The volatile antifungl substances were identified by GC-MS. The non-volatile antifungl substances of LS3 strain were isolated and purified by ammonium sulfate precipitation and ion exchange chromatography, and identified by HPLC-MS. The results showed that the inhibition rate of volatiles of strain LS3 was 43.47%, the inhibition rate of fermentation broth was 61.45%, and the inhibition rate of fermentation broth after high temperature sterilization was only 13.08%. Different concentrations of LS3 strain fermentation broth had different control effects on quinoa black stem disease. When the concentration was 2.0×10⁶ cfu/mL, the control effect was 66.81%. The main volatile components of LS3 were identified as 2-nonanol, phenol and tridecanol. Among them, 2-nonanol and phenol had better inhibitory effect on the pathogen, and the EC₅₀ values were 2.57 and 1.24 μg/mL, respectively. The crude antifungal protein of LS3 strain was separated and purified, and only one active peak was found. A clear band was found by polyacrylamide gel electrophoresis. After HPLC-MS detection, it was found that the protein was a flagellin with a molecular weight of about 32.6 kDa. LS3 strain showed good antifungal activity, and identification of antifungal substances was the basis for further development and utilization of LS3 strain.

Key words: Ascochyta caulina, Bacillus subtilis, antifungal effect, antifungal substances