Abstract
BackgroundSouth American leaf blight (SALB) of rubber has been the main constraint to production in its neotropical centre of origin since commercial plantations were first established. The fungal causal agent was identified and described more than a century ago but its precise placement within the Ascomycota still remains uncertain. Indeed, such is the ambiguity surrounding the pathogen that each of the spore morphs would, according to their present classification, be placed in different ascomycete families: the Microcyclus sexual morph in the Planistromellaceae and the two purported asexual morphs - Fusicladium and Aposphaeria – in the Venturiaceae and Lophiostomataceae, respectively. Given the historical importance of the fungus and the ever-menacing threat that it poses to rubber production in the Palaeotropics – and, thus to the rubber industry and to the global economy – its phylogeny, as well as its biology, should be resolved as a matter of urgency.Methods and ResultsHere, six genomic regions (LSU rRNA, mtSSU, MCM7, EF-1α, Act and ITS) were used for reconstructing the molecular phylogeny of the SALB fungus based on material collected throughout Brazil. The analyses support the classification of the fungus in the family Mycosphaerellaceae s. str. (Capnodiales, Dothideomycetes) and place it firmly within the clade Pseudocercospora s. str., now accepted as one of the distinct genera within Mycosphaerellaceae. The new combination Pseudocercospora ulei is proposed and the life cycle of the fungus is confirmed, based on both experimental and phylogenetic evidence, with the Aposphaeria morph shown to have a spermatial rather than an infective-dispersal function.ConclusionsBecause the phylogeny of the SALB fungus has now been clarified, new insights of its epidemiology and genomics can be gained following comparison with closely-related, better-researched crop pathogens.
Highlights
South American leaf blight (SALB) of the rubber tree Hevea brasiliensis
The magnitude of the threat represented by the SALB fungus is highlighted by Money [7] who described the relevance of natural rubber as an irreplaceable prime matter for the world’s industry in a plethora of applications besides tires, machinery belts and condoms and as an industry itself providing the livelihood of 30 million people, concluding that ‘‘Nothing else has the power to terminate the global flow of latex.’’ Because of the potential serious economic consequences, there are strict quarantine measures in place to prevent SALB from establishing in the rubber tree production areas in the Palaeotropics, especially in Southeast Asia, a SALB-free zone [3,8]
Phylogeny: LSU, mtSSU and MCM7 datasets Strongly supported clades provide molecular evidence of asexual-sexual morph connection between the three morphs of the SALB fungus and the holomorph belongs to the family Mycosphaerellaceae s. str., order Capnodiales (Figures 1–3)
Summary
South American leaf blight (SALB) of the rubber tree Hevea brasiliensis The magnitude of the threat represented by the SALB fungus is highlighted by Money [7] who described the relevance of natural rubber as an irreplaceable prime matter for the world’s industry in a plethora of applications besides tires, machinery belts and condoms and as an industry itself providing the livelihood of 30 million people, concluding that ‘‘Nothing else (but M. ulei) has the power to terminate the global flow of latex.’’ Because of the potential serious economic consequences, there are strict quarantine measures in place to prevent SALB from establishing in the rubber tree production areas in the Palaeotropics, especially in Southeast Asia, a SALB-free zone [3,8]. Given the historical importance of the fungus and the ever-menacing threat that it poses to rubber production in the Palaeotropics – and, to the rubber industry and to the global economy – its phylogeny, as well as its biology, should be resolved as a matter of urgency
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