New species, hyper-diversity and potential importance of <i>Calonectria</i> spp. from <i>Eucalyptus</i> in South China

<jats:p>Plantation forestry is expanding rapidly in China to meet an increasing demand for wood and pulp products globally. Fungal pathogens including species of <jats:italic>Calonectria</jats:italic> represent a serious threat to the growth and sustainability of this industry. Surveys were conducted in the Guangdong, Guangxi and Hainan Provinces of South China, where <jats:italic>Eucalyptus</jats:italic> trees in plantations or cuttings in nurseries displayed symptoms of leaf blight. Isolations from symptomatic leaves and soils collected close to infected trees resulted in a large collection of <jats:italic>Calonectria</jats:italic> isolates. These isolates were identified using the Consolidated Species Concept, employing morphological characters and DNA sequence comparisons for the β-tubulin, calmodulin, histone H3 and translation elongation factor 1-alpha gene regions. Twenty-one <jats:italic>Calonectria</jats:italic> species were identified of which 18 represented novel taxa. Of these, 12 novel taxa belonged to Sphaero-Naviculate Group and the remaining six to the Prolate Group. Southeast Asia appears to represent a centre of biodiversity for the Sphaero-Naviculate Group and this fact could be one of the important constraints to <jats:italic>Eucalyptus</jats:italic> forestry in China. The remarkable diversity of <jats:italic>Calonectria</jats:italic> species in a relatively small area of China and associated with a single tree species is surprising.</jats:p>