Characterisation of <i>Chrysoporthe cubensis</i> and <i>Chrysoporthe deuterocubensis</i>, the Stem Canker Diseases of <i>Eucalyptus</i> spp. in a Forest Plantation in Malaysia

Commercial plantations of <i>Eucalyptus</i> species have been established in Malaysia, especially during the past 10 years, with the aim of sustaining the supply of wood and timber products for industrial use in Malaysia. As part of an assessment of fungal diseases affecting <i>Eucalyptus</i> species in four regions in Malaysia, including Kelantan, Pahang, Sabah, and Selangor, stem canker disease was discovered to be a widespread disease infecting <i>Eucalyptus</i> species in Malaysia. This study aimed to identify the fungus-causing stem canker disease, test its pathogenicity in Eucalyptus, and determine the mating type of isolates from the infected trees. The fungi were identified based on morphology and through comparisons of DNA sequence data from the <i>ITS</i>, <i>β</i>-<i>tubulin 2</i> gene, and <i>TEF-1α</i> gene regions. Phylogenetic analyses showed that the causal agent of the stem canker was <i>Chrysoporthe cubensis</i> infecting <i>Eucalyptus</i> plantations in Pahang and <i>Chrysoporthe deuterocubensis</i> infecting <i>Eucalyptus</i> plantations in Kelantan, Sabah, and Selangor. We believe this is the first report of <i>Chrysoporthe cubensis</i>-infected <i>Eucalyptus</i> in Malaysia and Southeast Asia, while <i>Chrysoporthe deuterocubensis</i> is the first-reported species infecting <i>Eucalyptus pellita</i> in Malaysia. Moreover, the fact that the mating-type <i>MAT1-1</i> and <i>MAT1-2</i> genes and the pheromone genes <i>ppg1</i>, <i>ppg2</i>, <i>pre1</i>, and <i>pre2</i> were identified in all isolates indicates that <i>Chrysoporthe cubensis</i> and <i>Chrysoporthe deuterocubensis</i> are homothallic mating systems. Pathogenicity was tested on a 3-year-old standing tree, 1-year-old seedling, and detached healthy leaves, which were re-isolated for fulfilling Koch’s postulates. In pathogenicity trials, both <i>Chrysoporthe cubensis</i> and <i>Chrysoporthe deuterocubensis</i> gave rise to lesions on wounded <i>Eucalyptus.</i> Both <i>Chrysoporthe</i> spp. were equally pathogenic to <i>Eucalyptus urograndis</i> and <i>Eucalyptus pellita</i> and should be regarded as a biosecurity concern in Malaysia’s forest plantation industry.