DNA sequence incongruence and inconsistent morphology obscure species boundaries in the Teratosphaeria suttonii species complex

Abstract

Teratosphaeria suttonii (= Kirramyces epicoccoides) is a leaf pathogen that can cause premature defoliation, reduced growth and vigosr and subsequent tree death of many Eucalyptus species.Although the fungus primarily infects mature leaves in the lower canopy, infections can spread to younger leaves during continued epidemics or when trees are stressed. Teratosphaeria suttonii has a wide distribution in Australia and has been introduced to many other parts of the world, most probably with germplasm used to establish plantations. The aim of this study was to establish the phylogenetic relationships between T. suttonii isolates from different countries and to consider whether cryptic species exist in a species complex. DNA from parts of the nuclear ribosomal internal transcribed spacer (ITS), β-tubulin and elongation factor-1α genes was sequenced and analyzed for isolates from throughout the range of T. suttonii in Australia, and from six countries (China, Indonesia, South Africa, Uruguay, USA and Vietnam) where the pathogen is introduced.Morphometrics of conidia produced both in vivo and in vitro were also considered. Analysis of the sequence data resulted in incongruent genealogies. Furthermore, groups of isolates in the genealogies could not be linked to area of origin. Likewise differences in conidial morphology could not be linked to any of the phylogenetic groups. There was no evidence of distinct species 2 boundaries and isolates from Australia were closely related to those from other parts of the world.The results of this study support the treatment of T. suttonii as a morphologically and genetically diverse species in its natural range in Australia. The diversity is reflected in introduced populations.

Multiple introductions from multiple sources: invasion patterns for an important Eucalyptus leaf pathogen

“…are planted as non‐natives (Taole et al. ). Consequently, historical gene flow would have been out of Australia.…”

“…However, the application of a combination of multiple gene phylogeny and morphological assessment for collections from various parts of the world led to the recent conclusion that T. suttonii is a single but morphologically variable species (Taole et al. ).…”

“…; Taole et al. ) and plantations of exotic Eucalyptus spp. in other parts of the world including South Africa (Nichol et al.…”

Molecular markers delimit cryptic species in Ceratocystis sensu stricto

“…This was based on i) the number of species that could be (Cummings et al 2008), and iii) the congruence in tree topology as compared to a combined reference tree (Nye topological score) (Nye et al 2006). The gsi T is a statistical support value, in addition to BS and BI values, that indicates the exclusive ancestry of a group of organisms in a genealogy, and has proven informative in recent fungal phylogenetic studies (Sakalidis et al 2011;Taole et al 2012;Walker et al 2012a). The analysis produces a value on a scale from 0 to 1 for each identified group, with 0 indicating no exclusive ancestry from other groups in the genealogy and 1 representing monophyly.…”

Recommended names for pleomorphic genera in Dothideomycetes

“…This species causes a leaf spot and premature defoliation of Eucalyptus, as described by Taole et al (2012) and Walker et al (1992) who provide the synonyms listed here. Cercospora epicoccoides provides the oldest epithet for this species, which is now placed in Teratosphaeria.…”