A study on the antimicrobal activity of 7 strains Sarcandra glabra endophytes including Lasiodiplodia pseudotheobromae.

  Object  Endophytic Sarcandra glabra fungi exhibiting an antimicrobial activity were isolated and studied for application as potential resource of natural disease control agents.

  Method   The in vitro methods based on pathogen mycelial growth rate and minimum inhibitory concentration of extracts of various solvents from the fermentation broths of 7 species of S. glabra known to have antimicrobial activities were applied to determine their potential for disease control on plants.

  Result   Of the 7 strains of endophytic fungi, J-10, which was subsequently identified as Lasiodiplodia pseudotheobromae, showed a broad-spectrum antimicrobial activity against tested pathogens. For instance, at the concentration of 2 mg·mL⁻¹, the methanol and ethyl acetate extracts from the J-10 fermentation broth displayed a bacteriostasis rate of 84.84-88.51% against Ceratocystis paradoxa and Fusarium solani. The ethyl acetate extract had the most significant antifungal activity with an EC₅₀ against 8 pathogenic fungi ranging from 0.199 5 mg·mL⁻¹ to 1.172 2 mg·mL⁻¹, and the highest toxicity to Exserohilum turcicum but the lowest to Fusarium solani. The methanol extracts had EC₅₀ against the same 8 pathogens ranging from 0.108 8 mg·mL⁻¹ to 9.468 7 mg·mL⁻¹ with the highest toxicity to Athelia rolfsii and the lowest to Fusarium solani. Furthermore, the ethyl acetate extract was more effective against Proteus vulgaris, Micrococcus lyssodeikticus, Staphyloccocusaureus, Escherichia coli, Salmonella typhi, Bacillus cereus, Bacillus megaterium, Bacillussubtilis, Bacillus anthraci, Micrococcus luteus (Schroeter) Cohn, Ralstonia solanacearum than either the methanol or n-butanol extract and rendered an MIC between 0.125 5 mg·mL⁻¹ and 2.5 mg·mL⁻¹ after 24 h of treatment on the pathogens.

  Conclusion  L. pseudotheobromae showed a broad-spectrum antimicrobial activity against a variety of pathogens. The active components in the fermentation broth were of medium polarity and ethyl acetate soluble.