First report of Exserohilum leaf spot: a unique halophilic pathogen in Cucumis sativus in the South Bengal area of India

Cucumber ( Cucumis sativus L.) is a nutritious domesticated vegetable which belongs to Cucurbitaceae family. India ranks 30th in global cucumber production and its total output is 1,61,000 metric tons annually. In the investigation a different kind of leaf spot disease was observed on 2 months old c...

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Bibliographic Details
Published in:Australasian plant pathology 2020-05, Vol.49 (3), p.257-266
Main Authors: Dhara, Bikram, Maity, Amrita, Mondal, Poushali, Mitra, Arup Kumar
Format: Article
Language:English
Subjects:
Agriculture
Biomedical and Life Sciences
Blight
Conidia
Cucumis sativus
Defoliation
Ecology
Entomology
Exserohilum rostratum
Fungi
Immune system
Leafspot
Life Sciences
Mycelia
Necrosis
Original Paper
Pathogens
Plant Pathology
Plant Sciences
Signs and symptoms
Vegetables
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Summary:Cucumber ( Cucumis sativus L.) is a nutritious domesticated vegetable which belongs to Cucurbitaceae family. India ranks 30th in global cucumber production and its total output is 1,61,000 metric tons annually. In the investigation a different kind of leaf spot disease was observed on 2 months old cucumber leaves samples from cucumber fields in Baruipur, West Bengal, India (Latitude: N 22° 22.262′, Longitude: E 88° 24.5086′). The spots appeared were large, greyish brown in colour surrounded by a yellow to brownish halo, measuring 2 × 1 cm in average. These lesions expanded gradually from circular to angular spots ultimately resulting in necrosis and defoliation. The isolated fungus showed greyish black to dark olive mycelial growth. Microscopic characterization revealed straight to slightly curved conidia and distoseptate with a distinctly protruding basal hilum. Through microscopic observation and ITS sequencing the organism was identified to be Exserohilum rostratum. E. rostratum was previously known for causing blight disease in maize as well as human immune system diseases. E. rostratum, E. longirostratum and E. mcginnisii are identified as human pathogens. Koch’s postulates were carried out and distinct symptoms were observed in cucumber. As because there is no such record, this is the first time the host pathogen combination is separated in India.
ISSN:0815-3191
1448-6032
DOI:10.1007/s13313-020-00705-9