First Report of Leaf Sheath Rot of Arecanut ( <i>Areca catechu</i> ) Caused by <i>Marasmiellus palmivorus</i> in China

In June 2024, a leaf sheath rot disease was observed on arecanut (Areca catechu L.) in Wenchang, Hainan Province, China, affecting approximately 35% of trees in a 1-hectare plantation. Symptoms included brown to black discoloration of the leaf sheath, necrosis extending to the base of the petiole, and occasional wilting of affected fronds. Severely affected trees exhibited reduced nut yield, posing a potential threat to arecanut production, a key economic crop in the region. Diseased leaf sheath samples were collected, surface-sterilized with 1% sodium hypochlorite for 1 min, rinsed in sterile water, and plated on potato dextrose agar (PDA). Fungal colonies with white, cottony mycelium and small, cream-colored basidiocarps were consistently isolated from diseased leaf sheath. Microscopic examination revealed hyphae with clamp connections and a total of 50 basidiospores were randomly selected and measured [5-7 µm × 2-3 µm], consistent with Marasmiellus palmivorus (Sharples) Desjardin &amp; E. Horak (Gorea, et al. 2023). DNA was extracted from pure cultures, and the internal transcribed spacer (ITS) region was amplified using primers ITS1/ITS4 (White et al. 1990) and for large subunit rRNA (LSU) LR0R/LR7 (Vilgalys and Hester, 1990) respectively. The resulting sequences of the two strains BLQF2 and BLQF3 for LSU and ITS, GENBANK accession numbers PV926755, PV926756, and PV929698, PV929699 respectively, showed 99% identity to M. palmivorus in BLAST searches against peer-reviewed sequences. For phylogenetic analysis, ITS sequences were aligned with those of closely related species retrieved from GenBank using BLAST search (http://www.ncbi.nih.gov/BLAST/) with the default options of MUSCLE implemented using online tool NGPhylogeny (https://ngphylogeny.fr/), without manual editing (Supplementary Figure S1). Pathogenicity was confirmed by re-inoculating six healthy, 1-year-old arecanut seedlings with a mycelial patch applied to the leaf sheath base and kept at 25°C and 80% relative humidity. Controlled plants were treated with PDA patches. Ten days after inoculation (dai), inoculated plants developed symptoms and 30-60 dai, the symptoms were identical to those observed in the field, while controls remained healthy (Supplementary Figure S2). The pathogen was reisolated from inoculated plants, and its identity was re-confirmed via morphology and ITS sequencing, fulfilling Koch’s postulates. M. palmivorus has been reported on arecanut in India and other tropical regions, causing significant yield losses. This is the first report of M. palmivorus causing leaf sheath rot of arecanut in China. The disease’s emergence in Wenchang county threatens arecanut production, necessitating further research into management strategies.