First report of garden cucumber root rot caused by Globisporangium ultimum var. ultimum in Kyrgyzstan
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First report of garden cucumber root rot caused by Globisporangium ultimum var. ultimum in Kyrgyzstan Ismail Erper 1,2
&
Goksel Ozer 3 & Sezim Zholdoshbekova 1 & Muharrem Turkkan 4
Received: 26 February 2020 / Accepted: 21 August 2020 # Società Italiana di Patologia Vegetale (S.I.Pa.V.) 2020
Keywords Cucumis sativus . Pythium ultimum . Root rot . DNA sequencing
Garden cucumber (Cucumis sativus L.) has been commonly cultivated in a wide area in Kyrgyzstan. In 2019, wilting and yellowing symptoms were observed on cucumber plants in three fields planted in Lenin district, Bishkek, Kyrgyzstan, with a general incidence of 6%. Diseased plants showing root rot symptoms were subjected to pathogen isolation. Infected tissues were superficially disinfected in 1% NaOCl for 1 min and placed to Petri dishes containing water agar (agar 15 g/l) amended with 0.1 g/l streptomycin sulfate. Pythium-like isolates were purified to V8 medium (200 ml/l V8 vegetable juice, 3 g/l CaCO3, and 15 g/l agar) using the hyphal tip method and incubated at 20 °C for 7 days in the dark. The colonies were white and rapidly growing with hyaline and coenocytic hyphae (3.45–6.84 μm in diameter). Terminal and intercalary nearly globose sporangia (16.7 to 22.4 μm), thick-walled globose, smooth, and aplerotic oospores (18.7 to 25.6 μm), and globose terminal and intercalary hyphal swellings were observed on aerial mycelia. The antheridia were monoclinous and cystic in form. The pathogen was identified as Globisporangium sp. based on these morphological features (van der Plaats-Niterink 1981). The internal transcribed spacer (ITS) and the large subunit (LSU) regions of rDNA, and * Ismail Erper [email protected]; [email protected]
mitochondrial cytochrome oxidase II gene (cox II) of one representative isolate were sequenced with the primer pairs ITS1/ITS4, NL1/NL4, and FM58/FM66, respectively. The sequences were deposited in the GenBank database under accession numbers MT071197, MT071194, and MT075863, respectively, and comparisons with those of Globisporangium ultimum var. ultimum (Trow) Uzuhashi, Tojo & Kakish (syn. Pythium ultimum var. ultimum) strain CBS398.51 (AY598657 for ITS and LSU; GU138663 for cox II) showed 100% nucleotide identities. Pathogenicity assay was done as described by Zhang et al. (2018). Five two-week-old seedlings of garden cucumber cv. Orzu were cultivated in a mixture of mycelial mats of the pathogen and sterilized sandy soil (weight ratio 5:100), whereas additional five control plants were cultivated in sterilized sandy soil. After 14 days of incubation at 25 °C with a 14-h photoperiod, typical damping-off and root rot symptoms similar to those observed originally in the field occurred on all inoculated seedlings, while control seedlings remained symptomless. The pathogen was re-isolated from the roots of symptomatic seedlings to confirm Koch’s postulates. A reference isolate of Globisporangium ultimum var. ultimum (KG-Gu-8A) was deposited in the culture collection of the Mycology Laboratory of the Plan
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