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.

The rubber tree is an important economic tree in Thailand. Recently, the cultivation of rubber trees in Thailand has suffered from a novel leaf fall disease with diverse symptoms, including leaf spot and leaf blight, resulting in severe leaf defoliation. Fungi from the Lasiodiplodia genus, which causes leaf disease in rubber trees, have not been reported in Thailand. Our research aimed to identify Lasiodiplodia associated with leaf blight disease in Thailand by examining morphological characteristics and completing a multi-gene sequence analysis and pathogenicity test to fulfill Koch’s postulates. The internal transcribed spacer regions, translation elongation factor 1-α, and β tubulin 2 were sequenced for the multi-gene sequence analysis. In total, we recovered 14 isolates with 6 of those isolates. Of the six pathogenetic isolates, LST001, LST002, LYT003, LSrt001, and LSrt002 were determined to be Lasiodiplodia chonburiensis, and isolate LYL005 was determined to be L. theobromae. To the best of our knowledge, this is the first report of L. chonburiensis and L. theobromae being associated with leaf blight disease in rubber trees in Thailand or elsewhere.