Application of borrelidin from Streptomyces candidus on biocontrol of tree seedling damping-off diseases

Streptomyces candidus Y21007-2(Sc), a naturally screened actinomycete, is antagonistic toward several damping-off disease pathogens of tree seedlings. The growth of Phytophthora cinnamomi was retarded in by diluted metabolites from S. candidus, with most retardation by undiluted metabolites. The complex antagonistic metabolites from S. candidus was further fermented and developed into commercial products (borrelidin from S. candidus, BA-Sc), and was applied in the integrated control of the damping-off pathogens such as Phytophthora cinnamomi (Pc) , Sclerotium rolfsii (Sr) and Rhizoctonia solani (Rs). When the seeds of Koelreuteria henryi Dummer and Cinnamomum camphora (L.) Prsil were coated with the produced biocontrol agent (BA-Sc), their germination rate and the sequential growth of seedlings were better than controls, in both the soil containing the damping-off pathogens and in control groups. After 3-month, germination rates of the seeds treated with BA-Sc were elevated 12%, 4% and 12% in the soil with Pc, Sr and Rs, respectively. The average height of the seedlings from BA-Sc-treated seeds also increased 13.8, 10.14 and 6.79 cm in the soil with Pc, Sr and Rs respectively. Interestingly, the BA-Sc treatment was somewhat helpful for the seed germination and seedling growth in the soil without those pathogens. Another experiment demonstrated that the infected seedlings planted in the BA-Sc treated soil were 5.04 cm higher than those in untreated soil after three months. In addition, the average height of uninfected seedlings grown in the BA-Sc treated soil also was 4.14 cm higher than the averages of those grown in untreated soil. Result showed that BA-Sc should be capable for control pathogens of damping-off diseases.