In November 2023, a disease appeared in a field of Lablab purpureus (hyacinth bean) at Gazipur Agricultural University, Bangladesh (24° 2.12′ N; 90° 23.51′ E). This important winter vegetable was observed at the vegetative stage in a one-acre field with an 80%–90% disease incidence and 50%–60% severity by a random survey of 10 plants. Symptoms began as water-soaked lesions which expanded and coalesced into necrotic, scalded areas causing premature defoliation (Figure 1). A whitish mycelial growth was noticed on the leaves (Figure 1A) and the disease was identified as web blight, previously reported by Kader et al. (2022). For pathogen isolation, infected leaves were surface sterilised (70% alcohol for 30 s followed by 1% NaOCl for 2 min) (Kader et al. 2022), then rinsed in distilled water and dried with sterile filter paper before plating the tissues on water agar and incubating at 28°C ± 1°C for 48 h. Then the mycelium was sub-cultured onto potato dextrose agar (PDA). After 7 days, the white mycelia turned brown, forming whitish sclerotia (Figure 2A). Mature sclerotia were dark brown (1.3–5.3 × 0.7–4.2 mm). Microscopic analysis revealed hyaline mycelia (5.0–10 µm, mean 7.9 µm) that later turned brown, with right-angled branches (Figure 2B). Alkaline safranin staining (0.5% safranin, 3% KOH, glycerol and distilled water in a ratio of 0.5:10:5:79) was used to determine nuclei number (Sneh et al. 1991). Multinucleate hyphal cells and monilioid cell formation before sclerotia initiation were observed. These morphological and cultural features identified the pathogen as Rhizoctonia solani. Pathogen identity was confirmed by extracting genomic DNA, amplifying and sequencing the internal transcribed spacer (ITS) region of rDNA using the ITS-1/ITS-4 primers (White et al. 1990). ITS sequences of two typical isolates, SK1n (GenBank Accession No. PV653239) and SK5n (PV653241), showed 100% identity with R. solani AG-1 IA strains (KF907710, MG397058) (Figure 3). Pathogenicity was tested on L. purpureus (cv. IPSA Seem 2) plants at the 5–7 trifoliate leaf stage. Leaves were mechanically injured and inoculated with agar blocks from 1-week-old cultures of SK1n and SK5n. Non-inoculated PDA plugs served as a control. Tests involved three replications and the plants were kept in a humid chamber at 28°C ± 1°C. Water-soaked lesions appeared 3–5 days post-inoculation, expanding, progressing to extensive chlorosis, necrosis and blight with browning (Figure 4A–F), causing leaf defoliation similar to field symptoms. Disease incidence for SK1n and SK5n reached 83.33% and 76.92%, with a severity of 60% and 56.67% (Figure 4G,H), respectively. The pathogen was re-isolated and identified using the morphological and molecular methods described above as R. solani (PX453898 and PX453899). AG-1 IA has been reported on mung bean in China (Wang et al. 2025), soybean in the USA (Yang et al. 1990), common bean (Godoy-Lutz et al. 2008) and yard-long bean in Brazil (Quadros et al. 2021). This is the first report of R. solani AG-1 IA infecting L. purpureus in Bangladesh and globally. The authors gratefully acknowledge the support provided by the Research Management Wing of Gazipur Agricultural University, Bangladesh.
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