Submitted to: Mycologia
Publication Type: Peer reviewed journal
Publication Acceptance Date: 1/14/2010
Publication Date: 2/28/2010
Citation: Balmas, V., Migheli, Q., Scherm, B., Garau, P., O Donnell, K., Ceccherelli, G., Kang, S., Geiser, D.M. 2010. Multilocus Phylogenetics Show High Levels of Endemic Fusaria Inhabiting Sardinian Soils (Tyrrhenian Islands). Mycologia. 102(4):803-812. Interpretive Summary: Although considerable knowledge exists concerning the distribution of the mycotoxigenic phytopathogen Fusarium within intensively cultivated soils, only a few studies have attempted to elucidate their genetic diversity in non-agricultural soils. Because the Mediterranean island of Sardinia is well known for high levels of vascular plant diversity and endemism, we postulated that similar levels of endemic fusaria might inhabit their soils. To test this hypothesis, 263 Fusarium isolates were recovered from soil in 10 ecologically distinct sites spanning the length and width of the island. All of the isolates were subjected to DNA typing schemes to identify them to species and species complex. Members of the vascular plant wilt complex (i.e., Fusarium oxysporum species complex) accounted for 76.8% (i.e., 202/263) of the isolates and included 37 genetically distinct multilocus sequence types (STs), of which 26 were novel. Similarly, all 11 STs within the F. solani species complex appeared to be endemic to Sardinia. The other fusaria identified comprised 25 STs which were distributed among 10 species, five of which appear to represent putatively novel, phylogenetically distinct species. Overall, these results indicate a high degree of novel Fusarium genetic diversity on multiple geographic scales within the island of Sardinia. All data are available for access and visualization using the FUSARIUM-ID database (http://www.fusariumdb.org/). The results of this study should benefit phytopathologists and mycotoxicologists who are engaged in studying fusarial diseases of agronomically important crops and fusarial toxins.
Technical Abstract: The Mediterranean island of Sardinia is well known for high levels of vascular plant diversity and endemism, but little is known about its microbial diversity. Under the hypothesis that Fusarium species would show similar patterns, we estimated variability in Fusarium species composition among ten sites located around the island. To this aim, we isolated 263 Fusarium isolates and multilocus DNA sequence haplotypes were determined for each isolate using markers previously adopted for multilocus sequence typing (MLST) of fusaria. Portions of the translation elongation factor 1-alpha and second largest RNA polymerase subunit genes were sequenced in all isolates. In addition, the intergenic spacer (IGS) region of the nuclear ribosomal RNA gene repeat was sequenced in members of the F. oxysporum species complex (FOSC), and a portion of the nuclear ribosomal RNA gene repeat comprising the internal transcribed spacer (ITS) and part of the large nuclear ribosomal RNA subunit was sequenced in members of the F. solani species complex (FSSC). Seventy-three multilocus haplotypes were identified among the 263 isolates typed, forty-eight of which were from the FOSC and FSSC. Thirty-seven out of 48 FOSC two-locus and FSSC three-locus haplotypes had not been previously observed. The 38 non-FOSC/FSSC fusaria identified comprised 25 haplotypes distributed among 10 species, five of which appear to represent putatively novel, phylogenetically distinct species. In general newly discovered haplotypes were restricted to one or a few sites. All FSSC isolates represented new haplotypes in phylogenetic species FSSC 5 and 9, which differ from the phylogenetic species known to dominate soils worldwide. No obvious correlations were found between haplotype diversity and geospatial or habitat distribution. Overall, these results indicate a high degree of novel Fusarium genetic diversity on multiple geographic scales within the island of Sardinia. These results contrast with recent work showing that common cosmopolitan species dominate Sardinia’s Trichoderma biodiversity. All data are available for access and visualization using the FUSARIUM-ID database.