Chaenomeles speciosa fruit endophytic fungi isolation and characterization of their antimicrobial activity and the secondary metabolites composition

摘要

Background Endophytes promote the survival of the host plants affected by unfavorable environment. To confirm the endophytes role in Chaenomeles speciosa pathogenic resistance, fungal isolates were derived from both fruit peel and pulp, and presumptively identified using macroscopic and microscopic techniques. Antifungal potential of the isolates was assayed by dual culture method and agar disc method against Alternaria alternata, Fusarium culmorum, and Fusarium oxysporum strains. Two most active fungal isolates were cultured in Czapek's liquid medium to obtain metabolites. The crude ethyl acetate extracts of metabolites were characterized for antibacterial activity against Basillus subtilis and Erwinia dissolvens, and for component composition by GC-MS technique. Results Nine fungal endophytic isolates were derived from the peel and pulp of C. speciosa fruits and tentatively attributed to Penicillium spp. (seven isolates), Aspergillus spp. (one isolate), Mucor spp. (one isolate). Two fungal isolates, one each of the fruit peel and pulp, were designated as Penicillium sp. I and Penicillium sp. II respectively, and selected for further research. Both isolates showed similar activity against A. alternata; however, Penicillium sp. I activity against F. culmorum and F. oxysporum exceeded the activity of Penicillium sp. II. Cultural medium ethyl acetate extracts of both endophytes exhibited higher antibacterial activity against Gram-positive B. subtilis, while mycelium extracts were more active against Gram-negative E. dissolvens. In general, Penicillium sp. I antibacterial activity was higher in cultural medium extracts, while activity of Penicillium sp. II dominated in mycelium extracts. GC-MS analysis of the fungal metabolites component composition revealed the identity of 27 and 17 compounds, respectively in the ethyl acetate extracts of Penicillium sp. I and Penicillium sp. II cultural medium. Basic compounds produced by the first isolate, were represented by 3-Furanacetic acid, 4-hexyl-2,5-dihydro-2,5-dioxo, Diisooctyl phthalate, 11-Hexadecyn-1-ol, and Propanedioic acid, dihydroxy. At the same time, Phthalic acid diisooctyl ester and other phthalates constituted the main part of the second isolate metabolites, followed by Hexadecanoic acid, Eicosyl isopropyl ether, and 4-Butoxy-2-butanone at a lower content. Conclusions The findings showed that the antimicrobial potential of Chaenomeles fruits endophytic fungi is promising and deserves further investigation.