Diversity of Calonectria species from leaves and soils in diseased southern China Eucalyptus plantation

Calonectria leaf blight (CLB) is one of the best-known diseases of Eucalyptus spp., particularly in Asia and South America. Recently, typical symptoms of leaf and shoot blight caused by Calonectria spp. Were observed in a Eucalyptus plantation in the YunNan Province of southwestern China. Isolations were made from diseased leaves and top soil collected below the diseased trees to determine the causal agent of the disease and to consider the distribution characteristics of the Calonectria species. This resulted in 417 isolates, of which 228 were from leaves and 189 were from soil. Based on comparisons of DNA sequences for the act (actin), cmdA (calmodulin), his3 (histone H3), rpb2 (the second largest subunit of RNA polymerase), tef1 (translation elongation factor 1-alpha) and tub2 (beta-tubulin) gene regions, as well as morphological characteristics, 11 Calonectria species were identified. These included Calonectria aciculata (0.7 %), Ca. colhounii (1.2 %), Ca. eucalypti (10.6 %) and Ca. honghensis (43.2 %) in the Ca. colhounii species complex, and Ca. aconidialis (15.3 %), Ca. asiatica (9.8 %), Ca. hongkongensis (1.0 %), Ca. ilicicola (6.0 %), Ca. kyotensis (0.5 %), and Ca. yunnanensis (11.3 %) in the Ca. kyotensis species complex. In addition, a novel species, accounting for 0.5 % of the isolates, was discovered and is described here as Ca. dianii sp. nov. in the Ca colhounii species complex. Most (99.1 %) of the isolates collected from the leaves resided in the Ca. colhounii species complex and a majority (95.8 %) of those from the soils were in Ca. kyotensis species complex. These results suggest that Calonectria spp. in the Ca. colhounii species complex infecting leaves might be adapted to that niche and that those in the Ca. kyotensis species complex are better adapted to a soil habitat.