Rose apple (Syzygium samarangense, Myrthaceae) is considered one of the main tropical fruits native to Southeast Asia. In 2024, rose apples with fruit rot symptoms, characterized by dark, sunken circular lesions on ripening fruits, were observed in two locations in Perak, Malaysia. The identity of the pathogen that was responsible for the diseases was determined using morphological characteristics, DNA sequences, and phylogenetic analyses of internal transcribed spacer (ITS) and elongation translation factor 1-alpha (tef1-α). Morphological patterns of fungal isolates were observed on cultured potato dextrose agar (PDA) plates. The ITS and tef1-α of a fungal isolate were PCR amplified and sequenced, confirming the identity of Lasiodiplodia theobromae (GenBank accession nos. PQ584813 and PV155110, respectively). To fulfil Koch's postulates, the fungi were re-isolated and tested for pathogenicity on detached fruits. Symptoms similar to those observed in the market appeared on all inoculated fruits, while control fruits remained symptomless. To our knowledge, this is the first molecular-level report of L. theobromae infecting rose apples in Malaysia.

Keywords: fruit anthracnose, Lasiodiplodia theobromae, rose apple, Syzygium samarangense

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