Morphological and Phylogenetic Evidences Reveal Lasiodiplodia chonburiensis and L. theobromae Associated with Leaf Blight in Hevea brasiliensis in Southern 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-alpha, and beta 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.