Article ; Online: First Report of Cladosporium tenuissimum Causing Spot Diseases on Leaves and Fruits of Cucurbits in Brazil
Plant Disease. 2023 Aug. 01, v. 107, no. 8 p.2540-
2023
Abstract: Cucurbitaceae crops are widely cultivated in the northeast region of Brazil, which is the largest producer of melons and watermelons in the country (Oliveira et al. 2020). Between November and December 2020, leaves of pumpkin (Cucurbita maxima L.) and ... ...
| Abstract | Cucurbitaceae crops are widely cultivated in the northeast region of Brazil, which is the largest producer of melons and watermelons in the country (Oliveira et al. 2020). Between November and December 2020, leaves of pumpkin (Cucurbita maxima L.) and watermelon (Citrullus lanatus L.) plants and leaves and fruits of melon plants (Cucumis melo L.) with moderate to severe necrotic, irregular, and brown lesions were collected from farms in the state of Rio Grande do Norte, Brazil. Fragments of diseased tissues were cut into small pieces, surface disinfested in 70% ethanol for 30 s and then in 2% sodium hypochlorite for 1 min, and washed in sterile distilled water. The disinfested pieces were plated on potato dextrose agar and incubated for 7 days in the dark at 28 ± 2°C. A total of 12 fungal isolates (four from pumpkins, one from watermelons, and seven from melons) were isolated from symptomatic leaves and fruits. All isolates in this study shared similar morphological characteristics. The colonies were dark gray to olive green in color with a velvety texture and surrounded by gray-white hyphae. The conidiophores were erect, tall, dark, and irregularly branched at the apex, containing dark conidia, with 0 to 3 septa, variable in shape and size, forming chains that were often branched, globose or subglobose, and 3 to 4.5 μm in diameter. DNA from each isolate was extracted using the SDS method (Smith et al. 2001) and subjected to PCR amplification of the internal transcribed spacer (ITS) and translation elongation factor 1-α (TEF1-α) regions with the primers ITS1/ITS4 (White et al. 1990) and EF1-728F/EF1-986R (Carbone and Kohn 1999), respectively. The amplicons were sequenced and deposited in GenBank: OP493545 to OP493556 for ITS and OP536836 to OP536847 for TEF1-α. BLASTn analysis of the ITS and TEF1-α partial sequences revealed that all 12 isolates belong to the species Cladosporium tenuissimum, with 100% nucleotide similarity with sequences of many C. tenuissimum isolates deposited in GenBank. A phylogenetic tree was constructed using the maximum parsimony method, with the concatenated sequences (ITS–TEF1-α) on MEGA X software (version 11.0.8) (Tamura et al. 2021). All 12 isolates clustered in the same clade and were closely related to the isolates A2PP5, A3I1, and XCHK2 with the respective accession numbers KU605789.1, KU605790.1, and MG873071.1 from GenBank, with 99% bootstrap support. The pathogenicity of the 12 isolates was evaluated in pumpkin and melon plants in a greenhouse. Spore suspensions (10⁶ conidia/ml) were sprayed on the leaves of healthy seedlings until runoff, only water was sprayed on control plants as the mock treatment, and five seedlings of each crop (melon and pumpkin) were inoculated in each treatment. All plants were covered with plastic bags for 2 days. Spots similar to those observed on diseased plants in the field developed on the inoculated leaves (after 7 days from the inoculation; no symptoms were observed on plants from the mock treatment), and the fungal morphology was identical to that observed on the original diseased leaves, fulfilling Kochʼs postulates. The pathogenicity test was repeated and yielded the same results. The fact that all 12 isolates were pathogenic on pumpkin and melon leaves indicates that many cucurbits are susceptible to C. tenuissimum infection. Many growers in the region are reporting similar symptoms in their melon plantations, and thus it appears that the disease incidence is becoming more severe year after year. Therefore, more research needs to be conducted to determine the epidemiology and the extension of the economic impact caused by this pathogen on cucurbits to develop strategies for disease control. To the best of our knowledge, this is the first report of C. tenuissimum causing spot diseases in cucurbits in Brazil. |
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| Keywords | Citrullus lanatus ; Cladosporium ; Cucumis melo ; Cucurbita ; DNA ; color ; computer software ; conidia ; conidiophores ; culture media ; disease control ; disease incidence ; economic impact ; ethanol ; fungal morphology ; fungi ; greenhouses ; hyphae ; internal transcribed spacers ; pathogenicity ; pathogens ; peptide elongation factors ; phylogeny ; pumpkins ; runoff ; sodium hypochlorite ; texture ; watermelons ; Brazil ; Cladosporium tenuissimum ; cucurbits ; melon ; spot diseases | |||||
| Language | English | |||||
| Dates of publication | 2023-0801 | |||||
| Publishing place | The American Phytopathological Society | |||||
| Document type | Article ; Online | |||||
| ZDB-ID | 754182-x | |||||
| ISSN | 0191-2917 | |||||
| ISSN | 0191-2917 | |||||
| DOI | 10.1094/PDIS-10-22-2388-PDN | |||||
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| Database | NAL-Catalogue (AGRICOLA) |
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