Leaf blight in a Eucalyptus plantation caused by Calonectria spp. originating from both leaves and soils

Abstract

Abstract 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 soil samples collected from below the infected 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 soils. 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 (β-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 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 are specifically adapted to that niche and likewise those in the Ca. kyotensis species complex are better adapted to a soil habitat.