Erasing the Past: A New Identity for the Damoclean Pathogen Causing South American Leaf Blight of Rubber

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.

Mycosphaerellaceae: Chaos or clarity?

“…(2013) placed the genus in Mycosphaerellaceae , and even though molecular data are lacking, this assumption seems likely. The genus Microcyclus includes an important pathogen on Hevea , Microcyclus ulei , that was recently recollected and transferred to Pseudocercospora based on morphological and molecular data ( Da Hora Júnior et al. 2014 ).…”

Genetic Determinism of Sensitivity to Corynespora cassiicola Exudates in Rubber Tree (Hevea brasiliensis)

“…Rubber tree is affected by several important cryptogamic diseases. In Latin America, from which Hevea originated, rubber cropping is severely hampered by the South American Leaf Blight, caused by Microcyclus ulei , alias Pseudocercospora ulei [ 1 ]. However, this disease remains so far confined to that continent.…”

Epidemiology and Management of South American Leaf Blight on Rubber in Brazil

“…This fungus has two types of infective spores in its life cycle, according to the type of reproduction: conidiospores (asexual reproduction or anamorphic phase), the anamorphic reclassification of which was recently described in the literature, e.g., Pseudocercospora ulei [4], with cycle varying between 6 and 10 days, depending on the clone, and ascospores (sexual reproduction or teleomorphic phase), with cycle varying from 100 to 150 days (Figure 1).…”