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

Abstract

Leaf blight caused by Calonectria species is a major constraint to Eucalyptus trees in China. Calonectria leaf disease on Eucalyptus planted in China was first reported in HaiNan Island in 1985. No systematic investigation or identification of Calonectria species associated with diseased Eucalyptus in HaiNan Island have been performed to date. In order to comprehensively understand the species diversity, distribution, and pathogenicity of Calonectria associated with diseased Eucalyptus trees in HaiNan Island, 400 Calonectria isolates were obtained from 278 diseased Eucalyptus trees planted in 17 sites in five counties/regions. All 400 isolates were identified based on DNA sequence comparisons of the translation elongation factor 1-alpha (tef1), β-tubulin (tub2), calmodulin (cmdA), and histone H3 (his3) gene regions as well as a combination of morphological characteristics. Seven species, namely C. acaciicola (198 isolates, 49.5%), C. pseudoreteaudii (161 isolates, 40.25%), C. reteaudii (29 isolates, 7.25%), C. hawksworthii (6 isolates, 1.5%), C. hongkongensis (4 isolates, 1%), C. auriculiformis (1 isolate, 0.25%) and C. chinensis (1 isolate, 0.25%), were identified. This is the first report of C. acaciicola in China. Calonectria acaciicola, C. pseudoreteaudii, and C. reteaudii belong to the C. reteaudii species complex and were the dominant species collected, accounting for 97% of all the isolates obtained. Overlap in vesicle shape, macroconidia size, and macroconidia septa number existed among these three species in the C. reteaudii species complex. The geographical regions significantly influenced the distribution of C. acaciicola and C. pseudoreteaudii. Representative isolates of C. acaciicola, C. pseudoreteaudii, C. reteaudii and C. hawksworthii produced abundant macroconidia were used in conidial suspension inoculation on Eucalyptus seedlings. Inoculation showed that all four of the tested Calonectria species were highly pathogenic to the two tested Eucalyptus genotypes. The tolerances of two Eucalyptus genotypes were significantly different. This study conducted the first systematic investigation and identification of Calonectria species associated with Eucalyptus leaf blight in HaiNan Island and advanced the concept of selection of disease resistant Eucalyptus genotypes for managing Eucalyptus leaf blight caused by Calonectria species in China.