First Report of <i>Ganoderma ellipsoideum</i> Causing Basal Stem Rot in Oil Palm in India

Oil palm (Elaeis guineensis) yields 4–6 t oil/ha/year, but basal stem rot (BSR), mainly due to Ganoderma spp., can reduce yield by up to 69% (Vijay et al., 2016). No prior Indian reports exist beyond G. lucidum and G. applanatum (Mandal et al., 2003). In Aug 2023, 18% BSR incidence was recorded in 10-year-old Dura palms at ICAR-IIOPR, Andhra Pradesh, showing leaf drooping, necrosis, basal basidiocarps, and internal rot. The basidiome was perennial, sessile, non-laccate, woody, applanate, flabelliform (18 × 12 × 3.5 cm), with a hard, concentrically sulcate upper surface and tuberculate bumps, greyish to yellowish brown. Hymenophore was white to yellowish white, pores round to sub-circular, turning brownish yellow. Basidiospores (n=20) were brownish-orange, double-walled, ellipsoidal (7.6–9.9 × 5.3–7.1 μm), with hyaline myxosporium and finely echinulate eusporium. Pileipellis was yellowish to brownish yellow, with dextrinoid, acanthus-like branched apical cells. Hyphal system was trimitic (n=20): thin-walled generative hyphae (5.2 μm), thick-walled skeletal hyphae (5.8 μm), and greyish-orange binding hyphae (2.3 μm). Five isolates were obtained on Ganoderma selective medium (Ariffin and Idris, 1991) from 10 samples. Cultures produced dense white mycelium with filamentous margins and concentric rings, reaching 4.5 cm radial growth on PDA and 0.87 g dry biomass in PDB within 10 days at 25 ± 2 °C. DNA extracted using HiPurA fungal kit was prescreened with GB4 primers (Hilmi et al., 2022). The internal transcribed spacer (ITS, primers ITS4/ITS5), partial sequences of the translation elongation factor 1-alpha (tef1-α, primers 983F/1567R) and RNA polymerase II second largest subunit (rpb2; primers 5F/7CR) regions were PCR-amplified, with their sequences deposited in GenBank (PP159047, PQ530059, PQ583322), and BLAST searches showed 99–100% identity to JFL 14080966 (ITS, MH106867), MFLU 19-2221 (tef1-α, MN423157), and Dai 20544 (rpb2, MZ245400). Maximum likelihood analysis with 1,000 bootstrap replicates using MEGA X (Kumar et al., 2018) grouped isolates within the G. ellipsoideum clade. A representative culture was deposited in ITCC (Accession No. ITCC9346). Pathogenicity was confirmed by inoculating 4-month-old seedlings (ICAR IIOPR accession IOPPVDD000001) via root immersion in 100 mL of 10⁵ mycelial fragments/mL (T1) and T1 plus 20 mL soil inoculation (T2). Controls included sterile water, PDB, and untreated seedlings (n=10 per treatment). Inoculated seedlings showed stunting, chlorosis, necrosis, mycelial mats, and basidiocarps after 15 days; controls remained asymptomatic. Re-isolated fungus matched original identity, completing Koch’s postulates. This first report of G. ellipsoideum causing BSR in Indian oil palm signals emergence of a more aggressive pathogen. Its presence threatens long-term productivity and highlights the need for improved surveillance, resistant cultivars, and region-specific management strategies.