Threats

Teratosphaeria stem canker (previously Coniothyrium)

Teratosphaeria stem canker (previously Coniothyrium)
Teratosphaeria gauchensis (M.-N. Cortinas, Crous & M.J. Wingf.) M.J. Wingf. & Crous and Teratosphaeria zuluensis (M.J. Wingf., Crous & T.A. Cout.) M.J. Wingf. & Crous
Canker

Teratosphaeria gauchensis and T. zuluensis cause indistinguishable disease symptoms (Aylward et al. 2019). Initial infections occur on young, green stem tissue and are first visible as small (2-5 mm) lesions on bark (Wingfield et al. 1996). Lesions become elliptical as their size increases, they penetrate the vascular cambium and eventually merge with neighbouring lesions to form cankers filled with gum, also known as kino pockets (Wingfield et al. 1996; Old et al. 2003). The bark covering these cankers often cracks vertically, creating a “cat-eye” appearance and causing the gum to exude (Cortinas et al. 2006). In the case of severe infections on susceptible clones, cankers girdle the stems, epicormic shoots develop and the tops of the trees die (Wingfield et al. 1996; Old et al. 2003).

Teratosphaeria zuluensis and T. gauchensis are visible on the surface of cankers as dark pycnidia, producing large numbers of dark, single-celled conidia (Wingfield et al. 1996). During moist conditions, black conidial tendrils extend from the canker surfaces (Cortinas et al. 2006). Sexual structures of T. zuluensis and T. gauchensis have never been observed in the field or in culture.

Morphological distinction between T. zuluensis and T. gauchensis is not possible with any reasonable level of confidence. Molecular data provide the only reliable means to identify and distinguish between the two species. See Aylward et al. (2019) for more information. 

Little is known about the biology of T. gauchensis and T. zuluensis, but evidence gathered during the course of the past two decades provides a likely scenario of their lifecycle in Eucalyptus plantations (Aylward et al. 2019).

Both T. gauchensis and T. zuluensis are present in Eucalyptus leaves (Pérez et al. 2009; Marsberg et al. 2014) and may also occur in the seeds and seed capsules of infected trees (Jimu et al. 2016). Seedlings that come into contact with contaminated plant debris are infected horizontally after they begin to grow. Infection of the green tissues of Eucalyptus trees most probably occurs from conidia produced on cankers and other plant tissues carrying asymptomatic infections.

Analysis of the available whole genome sequences of these species (Wingfield et al. 2019) has revealed that both follow a heterothallic mating strategy. Isolates of T. gauchensis and T. zuluensis will, therefore, have either the MAT1-1 or MAT1-2 mating type (Aylward et al. 2020). There is no physical evidence of sexual reproduction for either species and recombination is unlikely to form an important part of their life cycles in diseased Eucalyptus plantations.

 

Teratosphaeria zuluensis: 1996 (Wingfield et al. 1996).
Gauteng, KwaZulu-Natal
Unconfirmed. Currently believed to be Australia (Aylward et al. 2019).

Gallery

Proposed lifecycle of the Teratosphaeria stem canker pathogens
Lesions on Eucalyptus bark, caused by T. zuluensis
Gum-filled canker
Clones susceptible and resistant to infection by T. zuluense. Early KwaZulu-Natal infections.
E. grandis stem infection by T. zuluenis
Section through E. grandis stem infected by T. zuluense showing consecutive years of infection.
Stem of E. grandis ZG14 infected by T. zuluense when disease first appeared in SA threatening the clonal programme.
Eucalyptus stem infection by T. zuluensis
T. zuluensis
Canker produced by T. zuluensis

Aylward J, Havenga M, Dreyer LL, Roets F, Wingfield BD, Wingfield MJ. 2020. Genomic characterization of mating type loci and mating type distribution in two apparently asexual plantation tree pathogens. Plant Pathology 69: 28-37.

Aylward J, Roets F, Dreyer LL, Wingfield MJ. 2019. Teratosphaeria stem canker of Eucalyptus: two pathogens, one devastating disease. Molecular Plant Pathology 20: 8-19.

Cortinas MN, Crous PW, Wingfield BD, Wingfield MJ. 2006. Multi-gene phylogenies and phenotypic characters distinguish two species within the Colletogloeopsis zuluensis complex associated with Eucalyptus stem cankers. Studies in Mycology 55: 133-146.

Jimu L, Kemler M, Wingfield MJ, Mwenje E, Roux J. 2016. The Eucalyptus stem canker pathogen Teratosphaeria zuluensis detected in seed samples. Forestry 9: 316-324.

Marsberg A, Slippers B, Wingfield MJ, Gryzenhout M. 2014. Endophyte isolations from Syzygium cordatum and a Eucalyptus clone (Myrtaceae) reveal new host and geographical reports for the Mycosphaerellaceae and Teratosphaeriaceae. Australasian Plant Pathology 43: 503-512.

Old KM, Wingfield MJ, Yuan ZQ. 2003. A manual of diseases of Eucalypts in South-East Asia. Jakarta, Indonesia: CIFOR.

Pérez CA, Wingfield MJ, Altier NA, Blanchette RA. 2009. Mycosphaerellaceae and Teratosphaeriaceae associated with Eucalyptus leaf diseases and stem cankers in Uruguay. Forest Pathology 39: 349-360.

Wingfield BD, Fourie A, Simpson MC, Bushula-Njah VS, Aylward J, Barnes I, Coetzee MPA, Dreyer LL, Duong TA, Geiser DM, Roets F, Steenkamp ET, van der Nest MA, van Heerden CJ and Wingfield MJ. 2019. IMA Genome-F 11 Draft genome sequences of Fusarium xylarioides, Teratosphaeria gauchensis and T. zuluensis and genome annotation for Ceratocystis fimbriata. IMA Fungus 10: 13.

Wingfield MJ, Crous PW, Coutinho TA. 1996. A serious canker disease of Eucalyptus in South Africa caused by a new species of Coniothyrium. Mycopathologia 136: 139-145.