Genetic recombination in Teratosphaeria destructans causing a new disease outbreak in Malaysia

The Eucalyptus foliar pathogen Teratosphaeria destructans causes severe and widespread damage in South-East Asian and South African plantations. In 2016, leaf blight symptoms resembling those caused by T. destructans were observed in a plantation of a Eucalyptus grandis x E. urophylla hybrid in Sabah, Malaysia. The aims of this study were to confirm the identity of the causal agent as T. destructans and to investigate the genetic structure of isolates associated with this newly detected disease outbreak. Using sequence data of three gene regions, the identity of the pathogen was confirmed as T. destructans. The mating type and microsatellite genotypes of 41 isolates from this Malaysian population were identified and compared with those from previously characterized populations in South-East Asia and South Africa. The Malaysian population had the highest genotypic diversity of any T. destructans population thus far investigated. Both the mating types were found in the collection of isolates, and these were in approximately equal proportions. Although structures linked to a sexual state of the fungus have not been found, sexual reproduction is theoretically possible and could explain the high genetic diversity in the pathogen that must have been accidentally introduced into Malaysia. This is the first record of T. destructans in Sabah and, to the best of our knowledge, in also other parts of Borneo.