Calonectria species associated with diseased leaves and soils in southern China Eucalyptus plantations

Calonectria leaf blight (CLB) is one of the most important diseases of Eucalyptus trees grown in plantations. This disease poses a serious threat to the sustainability of Eucalyptus plantations in southern China. To better understand the causal agents of CLB, we collected samples of diseased leaves and soil from Eucalyptus plantations from nine regions in Guangdong Province where the disease has become a serious problem. A total of 606 Calonectria isolates were purified from the samples, with 399 and 207 originating from diseased leaves and soils, respectively. Phylogenetic analyses utilizing six gene regions resolved 303 isolates in the C. kyotensis species complex and an equal number of isolates in the C. reteaudii species complex. These two complexes were represented by ten known Calonectria species, including C. aconidialis (12.0%), C. curvispora (0.3%), C. hongkongensis (24.8%), C. ilicicola (0.9%), and C. kyotensis (12.0%) in the C. kyotensis species complex, and C. crousiana (1.0%), C. Guangdongensis (0.3%), C. pseudoreteaudii (40.7%), C. queenslandica (7.3%), and C. reteaudii (0.7%) in the C. reteaudii species complex. Pathogenicity tests showed that all species were capable of causing disease on two tested Eucalyptus genotypes, albeit at varying degrees of aggressiveness. Most isolates (98.3%) in the C. reteaudii species complex were from the diseased leaves, indicating that species in this complex are the main causal agents of CLB outbreak. In addition, a significant number of the C. kyotensis species complex isolates (66.7%) from the soil samples could also cause the disease on Eucalyptus leaves.

Automated summary

Calonectria leaf blight (CLB) is a major threat to Eucalyptus plantations in southern China. Through sampling and analysis, it has been determined that the causal agents of CLB in Guangdong Province are primarily the species belonging to the C. kyotensis and C. reteaudii species complexes. These species have been found to be capable of causing disease on Eucalyptus leaves and are present in both diseased leaves and soil samples.