The pitch canker pathogen Fusarium circinatum has caused devastation to Pinus spp. in natural forests and non-natives in commercially managed plantations. This has drawn attention to the potential importance of Fusarium species as pathogens of forest trees. In this study, we explored the diversity of Fusarium species associated with diseased Pinus patula, P. tecunumanii, P. kesiya and P. maximinoi in Colombian plantations and nurseries. Plants displaying symptoms associated with a F. circinatum-like infection (i.e., stem cankers and branch die-back on trees in plantations and root or collar rot of seedlings) were sampled. A total of 57 isolates were collected and characterised based on DNA sequence data for the translation elongation factor 1-α and β-tubulin gene regions. Phylogenetic analyses of these data allowed for the identification of more than 10 Fusarium species. These included F. circinatum, F. oxysporum, species within the Fusarium solani species complex and seven novel species in the Fusarium fujikuroi species complex (formerly the Gibberella fujikuroi species complex), five of which are described here as new. Selected isolates of the new species were tested for their pathogenicity on Pinus patula and compared with that of F. circinatum. Of these, F. marasasianum, F. parvisorum and F. sororula displayed levels of pathogenicity to P. patula that were comparable with that of F. circinatum. These apparently emerging pathogens thus pose a significant risk to forestry in Colombia and other parts of the world.
Some of the most significant breakthroughs in the biological sciences this century will emerge from the development of next generation sequencing technologies. The ease of availability of DNA sequence made possible through these new technologies has given researchers opportunities to study organisms in a manner that was not possible with Sanger sequencing. Scientists will, therefore, need to embrace genomics, as well as develop and nurture the human capacity to sequence genomes and utilise the 'tsunami' of data that emerge from genome sequencing. In response to these challenges, we sequenced the genome of Fusarium circinatum, a fungal pathogen of pine that causes pitch canker, a disease of great concern to the South African forestry industry. The sequencing work was conducted in South Africa, making F. circinatum the first eukaryotic organism for which the complete genome has been sequenced locally. Here we report on the process that was followed to sequence, assemble and perform a preliminary characterisation of the genome. Furthermore, details of the computer annotation and manual curation of this genome are presented. The F. circinatum genome was found to be nearly 44 million bases in size, which is similar to that of four other Fusarium genomes that have been sequenced elsewhere. The genome contains just over 15 000 open reading frames, which is less than that of the related species, Fusarium oxysporum, but more than that for Fusarium verticillioides. Amongst the various putative gene clusters identified in F. circinatum, those encoding the secondary metabolites fumosin and fusarin appeared to harbour evidence of gene translocation. It is anticipated that similar comparisons of other loci will provide insights into the genetic basis for pathogenicity of the pitch canker pathogen. Perhaps more importantly, this project has engaged a relatively large group of scientists including students in a significant genome project that is certain to provide a platform for growth in this important area of research in the future.
Fusarium circinatum is an important pathogen in countries that grow and manage Pinus species. Approximately 50% or 600,000 ha of South Africa's commercial plantations are planted to Pinus spp. and some of these are threatened by this fungus. Contaminated plants, planting trays, soil and water can all act as sources of inoculum.In this study, we considered the role of grasses as a possible source of inoculum for F. circinatum-associated disease of Pinus in South Africa. Isolates of F. circinatum were collected from grasses in the understories of pitch-canker affected stands of P. radiata and P. patula in the Western Cape and Limpopo provinces, respectively. The mating type and microsatellite-based genotypes of the isolates were then compared with those in collections of this pathogen associated with pitch-canker on P. radiata and P. patula in the respective regions. The results showed that the F. circinatum isolates from grass originated from inoculum produced from stem and branch cankers on the trees above the grasses. The discovery of F. circinatum from five grass species in Limpopo increases the total number of known grasses associated with the fungus to nine in South Africa and seventeen globally. All of the F. circinatum isolates recovered from grass in South Africa displayed levels of aggressiveness to P. patula seedlings that were comparable with that of an isolate used for routine screening of 1 commercial planting stock. The data also suggest that grass might influence the expression of disease caused by F. circinatum on Pinus. This was because a specific genotype of the pathogen originating from grass was less aggressive on P. patula seedlings than its counterpart from diseased Pinus. Taken collectively, the results indicate that phytosanitary practices for the management of F. circinatum should include grass as a significant source of inoculum, and this should be an important quarantine consideration, both nationally and internationally.
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