Staged microbial succession in Acacia mangium dieback
Dieback disease in Acacia mangium plantations has long been attributed principally to infection by Ceratocystis species, yet its aetiology remains incompletely resolved in many tropical plantation systems. Here, we combined Illumina MiSeq amplicon sequencing of fungal ITS1 and bacterial 16S rRNA regions with culture-dependent fungal isolation to characterise sapwood-associated microbial assemblages in diseased and asymptomatic trees from a Malaysian plantation. Fungal profiling revealed more than 50 taxa, including Ceratocystis fimbriata, Lasiodiplodia, Fusarium, and several wood-decay fungi, but no single taxon was consistently dominant across diseased samples. Notably, the Ceratocystis species was detected in both diseased and externally asymptomatic trees. beta-Diversity analysis separated diseased from non-diseased fungal assemblages, while one asymptomatic tree displayed a diseased-like fungal profile despite retaining a bacterial community characteristic of healthy trees. Bacterial assemblages showed a secondary but coherent shift during host decline. Collectively, these observations indicate that A. mangium dieback reflects staged microbial succession, in which fungal destabilisation may precede visible symptom development and bacterial restructuring may follow during later tissue deterioration, rather than invasion by a single primary pathogen.