First report of stem and pod blight of hyacinth bean caused by Sclerotinia sclerotiorum in Bangladesh.

Abstract

Hyacinth bean (Lablab purpureus) is an almost year round vegetable crop in Bangladesh. During January 2011, while surveying hyacinth bean fields in the Gazipur district, plants with light tan to brown blighted stems and pods were observed. Within the pod pith, large dark irregular sclerotia embedded in a white fluffy mycelium were found. Symptomatic tissues were excised, surface-sterilized in 0.5% sodium hypochlorite and placed on potato dextrose agar (PDA). Isolated fungal colonies consistently yielded white mycelium and produced a ring of large sclerotia near the edge of PDA plates. Under microscope, the hyphae were hyaline, branched and multinucleate. Sclerotia were induced to produce apothecia, asci and ascospores following a conditioning process (Smith and Boland, 1989). Based on morphology, the fungus was assumed to be Sclerotinia sclerotiorum. Pathogenicity of the fungal isolate was proven by placing seven-day-old PDA mycelial plugs (5 mm) on hyacinth bean stems. Seven days post inoculation, all inoculated plants started wilting and stem breakage were also observed for some dead plants. Dark sclerotia were found after splitting the dead stems of all inoculated plants. Identification of the fungus was confirmed by comparing the sequences generated from the internal transcribed spacer (ITS) region of the ribosomal DNA (ITS1 and ITS4 primers) (White et al., 1990). The nucleotide sequence was deposited in GenBank as accession No. KF791510. These sequences shared 100% nucleotide similarity with those of S. sclerotiorum. This pathogen has previously been reported on different crops (Huang et al., 2005). To our knowledge, this is the first report of S. sclerotiorum on hyacinth bean in Bangladesh.