Phylogeny, Morphology, Distribution, and Pathogenicity of Seven Calonectria Species from Leaf Blighted Eucalyptus in HaiNan Island, China

Leaf blight caused by Calonectria species constrains Eucalyptus trees in China. Calonectria leaf disease on Eucalyptus in China was first reported in HaiNan Island in 1985. No systematic investigation of Calonectria species associated with diseased Eucalyptus in HaiNan has been performed. To understand the species diversity, distribution, and pathogenicity of these Calonectria, 400 Calonectria isolates were obtained from 278 diseased Eucalyptus planted in 17 sites in five regions. All 400 isolates were identified by DNA sequences of translation elongation factor 1-alpha, β-tubulin, calmodulin, and histone H3 gene regions and on morphology. Seven species, C. acaciicola (198 isolates), C. pseudoreteaudii (161 isolates), C. reteaudii (29 isolates), C. hawksworthii (6 isolates), C. hongkongensis (4 isolates), C. auriculiformis (1 isolate), and C. chinensis (1 isolate), were identified. This is the first report of C. acaciicola in China. C. acaciicola, C. pseudoreteaudii, and C. reteaudii belong to the C. reteaudii species complex and accounted for 97% of all isolates. The three species overlapped in vesicle shape, macroconidia size, and macroconidia septa number. Region significantly influenced C. acaciicola and C. pseudoreteaudii distribution. Representative isolates of C. acaciicola, C. pseudoreteaudii, C. reteaudii, and C. hawksworthii producing abundant macroconidia were used in conidial suspension inoculation on Eucalyptus seedlings; all were highly pathogenic to the two tested genotypes. The tolerances of two Eucalyptus genotypes were significantly different. This first systematic investigation of Calonectria species associated with Eucalyptus leaf blight in HaiNan will aid selection of disease-resistant genotypes for managing Eucalyptus leaf blight caused by Calonectria species in China.