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First Report of Sclerotinia Sclerotiorum Causing Pod Rot Disease on Okra in Bangladesh

Ananya Prova
Department of Plant Pathology, EXIM Bank Agricultural University Bangladesh, Chapainawabganj 6300, Bangladesh

Abdul Mannan Akanda
Department of Plant Pathology, Bangabandhu Sheikh Mujibur Rahman Agricultural University, Gazipur, 1706, Bangladesh

Shaikhul Islam
Department of Plant Pathology, EXIM Bank Agricultural University Bangladesh, Chapainawabganj 6300, Bangladesh

Md. Motaher Hossain
Department of Plant Pathology, Bangabandhu Sheikh Mujibur Rahman Agricultural University, Gazipur, 1706, Bangladesh

Abstract/ Executive Summary:

Pods of okra(Abelmoschus esculentusL Moench)‘BARI Dherosh-1 cultivated in a farmer’s field in Gazipur District, Bangladesh, were found rotted in December 2014. A fungus having fluffy mycelium and large sclerotia was isolated from affected pods. Combined results of morphological, molecular and pathological analyses identified the fungus as Sclerotinia sclerotiorum (Lib) de Bary. Inoculating the fungus on healthy okra pods reproduced the symptoms previously observed in the field. This is the first report of S. sclerotiorum causing the disease of okra in Bangladesh.

Keywords: Abelmoschus esculentus, Apothecia, pod rot, Sclerotia, Sclerotinia sclerotiorum

Location:

Start Date:

End Date:

Program Area: Pest Management

Commodity: Diseases, Okra

Objectives:

The objectives of the present study were to identify the pathogen involved in the okra pod rot in Bangladesh using morphological and molecular characterization and to verify the pathogenicity of this fungus.

Methodology:

Isolation and characterization of the pathogen: Ten infected pods were collected from a farmer’s field in Gazipur District. They were washed in tap water and dried on sterile blotter paper. Symptomatic pod tissues were cut into 2–3-mm pieces, surface-sterilized with70% ethanol for 30 s and then with 0.1% mercuricchloride solution for 3 min. After rinsing in sterile distilled water three times and subsequent drying on blotter paper, 30 tissue pieces were placed in Petridishes containing potato dextrose agar (PDA) made from peeled potato infusion and amended with strep to-mycinsulphate (1.0gL⁻¹). Petri dishes were incubated at 25ºC in the dark for 5 days. For the morphological identification of the isolated fungus, single hyphal tips were transferred onto new PDA dishes. No signs of asexual spore formation were found on any of the fungal isolates while all the isolates produced largesclerotia. Morphological characteristics of the teleomorph stages of 20 isolates were examined. Surface-sterilizedsclerotia were placed in 9 cm diameter Petri dishes filled with sterile, wet sand and incubated at 4ºC for5–6 weeks. Then the Petri dishes were transferred to another incubator and illuminated for 3–4 days at 20ºC under scattered fluorescent irradiation (260 μmol m−2s−1) until apothecial discs were formed (Huang et al.2005). Fifteen apothecia and the ascospores produced from sclerotia were examined under the microscope (40× and 100×) for morphological features. Molecular identification Total genomic DNA was extracted as described by Toda et al. (1999). Polymerase chain reaction (PCR)with forward primer ITS-1 (5-TCC GTA GGT GAACCT GCG G-3) and reverse primer ITS-4 (5-TCCTCCGCTTATTGATATGC-3) was used to amplifyr DNA-ITS regions of the fungal isolate PSLF1 (White et al.1990) and was conducted following the method described by Hayakawa et al. (2006). At least two complete sequences were obtained for each ITS regionand the BLAST search program was used to search for nucleotide sequence homology in GenBank. Highly homologous sequences were aligned using Clustal-Xversion 2.0.11 and manually adjusted as required. Neighbor-joining trees were generated using MEGAversion 6.06 (Tamura et al.2013; Islam et al. 2016). Bootstrap replication (1000 replications) was used as statistical support for the nodes in the phylogenetic trees. The adjusted alignment consisted of eight taxa including Magnapor the oryzaeAr2 (KJ850437) as an out group taxon. Pathogenicity tests Pathogenicity of isolate PSLF1 used in the molecular analysis was tested. The okra variety‘BARI Dherosh-1?was used throughout the study. PDA plugs excised from actively growing margins of fungal colonies were placed in wounds made with a sterile blade in the outer tissue layer of okra pods and sealed with moistened cheesecloth. Wounded pods inoculated with sterile PDA plugs served as controls. The inoculated pods were subsequently covered with plastic bags and maintained in a growth chamber in dark for 48 h at 23–25°C. Twenty pods were inoculated with isolate PSLF1, and 20 pods were included as controls. Pathogenicity of the isolate was also tested on 4-week-old whole plants by placing a mycelial plug of the fungus onto an incised stem surface in a similar manner. Re-isolation of the fungus was done from symptomatic tissues to compare and confirm that the original and the re-isolated fungus were the same.

Source of Information: Can. J. Plant Pathol., 2017

Article Link (Online Journal): http://dx.doi.org/10.1080/07060661.2017.1278723

Funding Source:

Budget:

Total Budget (Tk.) :

Achievement/Findings:

To our knowledge, this is the first report of the occurrence of a disease caused by S. sclerotiorum on okra pod in Bangladesh, and it is the first detection using molecular data of this fungal pathogen in Bangladesh. The disease has previously been reported to occur on okra pods in Mie Prefecture in Japan (Kubota & Misawa2014).

Knowledge Management: Journal