First Report of Fusarium incarnatum Causing Rhizome Rot of Curcuma amada in Meghalaya, India

Curcuma amada (Zingiberaceae) is closely related to ginger (Zingiber officinale) but has the distinctive flavour and aroma of raw mango, hence its common name of mango ginger. The plant has promising anti-obesity, antimicrobial, anticancer and antidiabetic activities (Sahoo et al. 2023). In December 2024, > 80% of C. amada rhizomes harvested from a farm in Krang, Meghalaya, India, were stricken with rhizome rot, exhibiting 75%–90% disease severity (percent diseased tissue). Diseased rhizomes had rot and decay at the tips, exposing underlying dead tissue (Figure 1). Infected rhizomes were surface sterilised with 70% ethanol for 1 min and 1% sodium hypochlorite for 2 min, followed by 70% ethanol for 20 s and rinsed three times with distilled water. A 5-mm diameter tissue sample was cut from each infected part and inoculated onto potato dextrose agar and incubated at 29°C for 7 days. A uniform fungal colony characterised by abundant dense aerial mycelia, initially off-white and ageing to yellowish brown (Figure 2). Macroconidia were elongated and slender, with a curved dorsal side and a straight ventral side, containing four to six septa. Microconidia were unicellular and ovoid. Chlamydospores were plentiful, globose to ellipsoid, mostly intercalary or terminal, hyaline, and smooth-walled (Figure 3). This morphology identified the pathogen as Fusarium incarnatum as described by Pongpisutta et al. (2023). Identification of the pathogen was confirmed through PCR amplification and sequencing of the nuclear rRNA internal transcribed spacer (ITS) region using ITS1 (5′-TCCGTAGGTGAACCTGCGG-3′) and ITS4 (5′-TCCTCCGCTTATTGATATGC-3′) primers (White et al. 1990). The sequence was deposited in GenBank with Accession No. PV169200. A phylogenetic tree was constructed using sequences of known F. incarnatum isolates (Figure 4). The pathogenicity of the isolate was confirmed following surface-sterilisation of healthy C. amada rhizomes and inoculation with 10 µL of a spore suspension (1 × 105 spores/mL) through 5 mm × 5 mm wounds. Disease symptoms identical to those observed in the field emerged within 2 weeks of incubation at 29°C (Figure 5). Fusarium incarnatum was successfully re-isolated from the inoculated rhizomes and verified microscopically. Rhizome rot in plant species in the Zingiberaceae family is mainly caused by Fusarium solani, Pythium aphanidermatum and Rhizoctonia solani (Ayodele et al. 2018; Chenniappan et al. 2019). However, F. incarnatum has been reported to cause rhizome rot in Z. officinale (Gurung et al. 2018). This is the first report of F. incarnatum causing rhizome rot in C. amada in India. This finding will help farmers in developing effective disease management practices to reduce losses caused by the pathogen. The first author sincerely thanks the Department of Botany, North-Eastern Hill University, Shillong, Meghalaya, India, for providing the necessary facilities and acknowledges the financial support received from the UGC Non-NET scheme.