Morphological and Molecular Characterization of Calonectria foliicola Associated with Leaf Blight on Rubber Tree (Hevea brasiliensis) in Thailand

Leaf blight is commonly observed in rubber trees (Hevea brasiliensis) and can be caused by several fungal species. From October to December 2021, the emergence rubber tree disease was observed in Krabi province, southern Thailand. Small brown to dark brown spots developed on the leaves of rubber trees and later expanded into most parts of the leaves. Fungal isolates were isolated from infected tissues and a total of 15 Calonectria-like isolates were recovered from 10 infected leaf samples. Pathogenicity testing using the agar plug method revealed that four isolates caused leaf blight on rubber tree, similar to the situation in natural infections. Based on morphological study and the molecular properties of internal transcribed spacer (ITS), calmodulin (cal), translation elongation factor 1-α (tef1-α), and β-tubulin 2 (tub2) sequences, the four fungal isolates were identified as Calonectria foliicola. To the best of our knowledge, this is the first report of rubber trees pas a new host for C. foliicola in Thailand and elsewhere. This study reports on an emerging disease affecting rubber trees in Thailand, and the results are of benefit for the development of an appropriate method to manage this emerging disease in Thailand.