Abstract
BackgroundEucalyptus bacterial wilt caused by Ralstonia solanacearum is an important eucalyptus disease. Endophytic fungi, an important source of natural active substances, provide a new breakthrough for the control of plant diseases.ResultsIn the present study, 80 endophytic fungal isolates were obtained from the healthy branches and fruits of Eucalyptus exserta. Fifteen distinct isolates (MK120854-MK120868) were selected for further taxonomic identification through morphological trait assessments and internal transcribed spacer (ITS) region-rRNA gene sequence analysis. Thirteen genera, namely, Phyllosticta, Penicillium, Eutypella, Purpureocillium, Talaromyces, Lophiostoma, Cladosporium, Pestalotiopsis, Chaetomium, Fusarium, Gongronella, Scedosporium and Pseudallescheria, were identified on the basis of their morphological characteristics. Members of the genus Phyllosticta were the primary isolates, with a colonization frequency (CF) of 27.5 %. Most of the fungal isolates displayed antibacterial activity. The crude extracts obtained from Lophiostoma sp. Eef-7, Pestalotiopsis sp. Eef-9 and Chaetomium sp. Eef-10 exhibited strong inhibition on the test bacteria, and Lophiostoma sp. Eef-7 was further cultured on a large scale. Three known compounds, scorpinone (1), 5-deoxybostrycoidin (2) and 4-methyl-5,6-dihydro-2 H-pyran-2-one (3), were isolated from the endophytic fungus Lophiostoma sp. Eef-7 associated with E. exserta. The structures of these compounds were elucidated by analysis of 1D and 2D NMR and HR-ESI-MS spectra and a comparison of their spectral data with published values. Compounds 1 and 2 showed weak antimicrobial activity against Ralstonia solanacearum.ConclusionsEndophytic fungi from Eucalyptus exserta may represent alternative sources of antimicrobial agents. Lophiostoma sp. Eef-7 can produce 2-azaanthraquinone derivatives and shows weak antibacterial activity against Ralstonia solanacearum.
Highlights
Eucalyptus bacterial wilt caused by Ralstonia solanacearum is an important eucalyptus disease
According to their morphological features, the isolates were preliminarily grouped through dereplication into fifteen different morphological taxa (Fig. 1) that were selected for DNA sequence analysis using the internal transcribed spacer (ITS) region
Based on the macro- and microscopic identification results, they were identified as members of thirteen genera, including Phyllosticta, Penicillium, Eutypella, Purpureocillium, Talaromyces, Lophiostoma, Cladosporium, Pestalotiopsis, Chaetomium, Fusarium, Gongronella, Scedosporium and Pseudallescheria (Table 1)
Summary
Eucalyptus bacterial wilt caused by Ralstonia solanacearum is an important eucalyptus disease. Eucalyptus bacterial wilt caused by Ralstonia solanacearum (Smith) Yabuuchi is a destructive, systemic vascular bundle disease referred to as cancer in eucalyptus. Plant diseases caused by pathogenic bacteria directly result in enormous losses in the agricultural economy each year and are significant issues that need to be resolved [2, 3]. Chemical pesticides such as antibiotics are some of the most efficient and cost-effective methods of controlling plant pathogenic bacteria. The search for antibacterial substances with novel structures and outstanding bioactivity from natural products and developing them into commercial pesticides has become a research hotspot in agriculture [5]
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