Black gram (Vigna mungo L.) is important pulse crop and is the third-most cultivated pulse in India (Swaminathan et al. 2023). In August 2022, pod rot symptoms were observed on a black gram crop with 80 to 92% disease incidence in the Crop Research Center, Govind Ballabh Pant University of Agriculture & Technology, Pantnagar (29.0222° N, 79.4908° E), Uttarakhand, India. Disease symptoms included white to salmon pink fungal-like growth over the pods. The symptoms were more severe initially at the tip of the pods, which expanded at later stages to cover the entire pod. Seeds present in the symptomatic pods were severely shrivelled and non-viable. Ten plants from the field were sampled to identify the causal agent. Symptomatic pods were cut into pieces, surface-disinfested with 70% ethanol for 1 min to reduce contaminants, rinsed with sterilized water three times, dried on sterilized filter paper, and aseptically placed on potato dextrose agar (PDA) amended with 30 mg/liter streptomycin sulphate. After 7 days of incubation at 25°C, three Fusarium-like (FUSEQ1, FUSEQ2, and FUSEQ3) isolates were purified by single spore transfer and subcultured on PDA. Fungal colonies on PDA were initially white to light pink, aerial, and floccose, and later on, colonies turned ochre yellowish to buff brown. After transfer to carnation leaf agar (Choi et al. 2014), isolates formed hyaline, 3 to 5 septate macroconidia, 20.4 to 55.6 × 3.0 to 5.0 µm (n = 50) with tapered, elongated apical cells and prominent foot-shaped basal cells. Chlamydospores were thick, intercalary, globose, and abundant in chains. No microconidia were observed. Based on morphological characters, the isolates were identified as belonging to the Fusarium incarnatum-equiseti species complex (FIESC) (Leslie and Summerell 2006). For molecular identification of the three isolates, total genomic DNA was extracted using the PureLink® Plant Total DNA Purification Kit (Invitrogen™, ThermoFisher Scientific, Waltham, Massachusetts, United States) and used for amplification and sequencing of a portion of the internal transcribed spacer (ITS) region, the translation elongation factor-1 alpha (EF-1α) gene, and the second largest subunit of RNA polymerase (RPB2) gene (White et al. 1990; O'Donnell 2000). The sequences were deposited in the GenBank database (ITS: OP784766, OP784777, and OP785092; EF-1α: OP802797, OP802798, and OP802799; RPB2: OP799667, OP799668, and OP799669). Polyphasic identification carried out in fusarium.org indicated 98.72 % and 100% similarity of FUSEQ1 and FUSEQ2 respectively to F. clavum and FUSEQ3 had 98.72 % similarity to F. ipomoeae. Both of the identified species are members of the FIESC (Xia et al. 2019). Pathogenicity tests were carried out on 45-day-old potted plants of V. mungo with seed pods, which were kept in a greenhouse. Plants were sprayed with 10 ml of a conidial suspension of each isolate (107 conidia/ml). Control plants were sprayed with sterile distilled water. The plants were covered with sterilized plastic bags after inoculation to maintain humidity and kept in a greenhouse at 25 ± 2°C. Within ten days, all the inoculated plants showed symptoms similar to those observed in the field, whereas control plants were symptomless. The pathogenicity test was repeated twice. Fungi consistently reisolated from the symptomatic pods were confirmed by morphological characterization and molecular assays as described above to belong to the FIESC, whereas no fungus was isolated from control pods. Fusarium spp. causing pod rot in green gram (V. radiata L.) has also been reported from India (Buttar et al. 2022). To our knowledge, this is the first report of FIESC as a causal agent of pod rot of V. mungo in India. The pathogen has the potential to cause considerable economic and production losses in black gram, and for that reason, disease management strategies should be implemented.
Keywords: Black gram; Fusarium; India; pod rot.