First Report of Rot Disease Caused by Rhizopus microsporus var. chinensis on Leaf Mustard (Brassica juncea) in Guangzhou, China

Field: Agricultural and Biological Sciences (Life Sciences)

HomePlant DiseaseVol. 104, No. 7First Report of Rot Disease Caused by Rhizopus microsporus var. chinensis on Leaf Mustard (Brassica juncea) in Guangzhou, China PreviousNext DISEASE NOTES OPENOpen Access licenseFirst Report of Rot Disease Caused by Rhizopus microsporus var. chinensis on Leaf Mustard (Brassica juncea) in Guangzhou, ChinaR. Wang, A. Ahmad, H. Du, X. Xu, Y. Zhang, C. Yao, Y. Zhong, and T. WuR. WangVegetable Research Institute, Guangdong Academy of Agricultural Sciences, Guangzhou, 510640, ChinaGuangdong Key Laboratory for New Technology Research of Vegetables, Guangzhou, 510640, China, A. Ahmadhttp://orcid.org/0000-0001-9097-2628Vegetable Research Institute, Guangdong Academy of Agricultural Sciences, Guangzhou, 510640, ChinaGuangdong Key Laboratory for New Technology Research of Vegetables, Guangzhou, 510640, China, H. DuVegetable Research Institute, Guangdong Academy of Agricultural Sciences, Guangzhou, 510640, ChinaGuangdong Key Laboratory for New Technology Research of Vegetables, Guangzhou, 510640, China, X. XuVegetable Research Institute, Guangdong Academy of Agricultural Sciences, Guangzhou, 510640, ChinaGuangdong Key Laboratory for New Technology Research of Vegetables, Guangzhou, 510640, China, Y. ZhangVegetable Research Institute, Guangdong Academy of Agricultural Sciences, Guangzhou, 510640, ChinaGuangdong Key Laboratory for New Technology Research of Vegetables, Guangzhou, 510640, China, C. YaoVegetable Research Institute, Guangdong Academy of Agricultural Sciences, Guangzhou, 510640, ChinaGuangdong Key Laboratory for New Technology Research of Vegetables, Guangzhou, 510640, China, Y. ZhongVegetable Research Institute, Guangdong Academy of Agricultural Sciences, Guangzhou, 510640, ChinaGuangdong Key Laboratory for New Technology Research of Vegetables, Guangzhou, 510640, China, and T. Wu†Corresponding author: T. Wu; E-mail Address: tingquanwu@sina.comhttp://orcid.org/0000-0002-0869-4006Vegetable Research Institute, Guangdong Academy of Agricultural Sciences, Guangzhou, 510640, ChinaGuangdong Key Laboratory for New Technology Research of Vegetables, Guangzhou, 510640, China AffiliationsAuthors and Affiliations R. Wang1 2 A. Ahmad1 2 H. Du1 2 X. Xu1 2 Y. Zhang1 2 C. Yao1 2 Y. Zhong1 2 T. Wu1 2 † 1Vegetable Research Institute, Guangdong Academy of Agricultural Sciences, Guangzhou, 510640, China 2Guangdong Key Laboratory for New Technology Research of Vegetables, Guangzhou, 510640, China Published Online:12 May 2020https://doi.org/10.1094/PDIS-04-19-0736-PDNAboutSectionsSupplemental ToolsAdd to favoritesDownload CitationsTrack Citations ShareShare onFacebookTwitterLinked InRedditEmailWechat Leaf mustard (Brassica juncea [L.] Czern. et Coss.) is an important leaf vegetable species widely cultivated in China. Severe rot disease symptoms (water-soaked, puffy, and dark gray regions) were observed in the leaves of leaf mustard growing in the Baiyun Experimental Field, Guangzhou, China, during November 2018. Extensive decay of leaves and stems was observed, accompanied by white surface hyphae on the infected tissues. The disease outbreaks resulted in 30 to 100% disease incidence, and the diseased plants could not be harvested. The infected samples were collected from the field and brought to the Guangdong Academy of Agricultural Sciences, Guangzhou. Small pieces of leaf tissues were collected from the infection margins, surface sterilized with ethanol (70%, 30 s) and sodium hypochlorite (1%, 2 min), rinsed three times with sterile water, plated on potato dextrose agar (PDA) medium, and cultured in the dark at 28°C. Fungal colonies of similar morphological features were observed after 4 days of incubation, and they were transferred to separate PDA plates. The colonies were white colored and turned pale brown at the later stages. Microscopically, the hyphae emerged from the medium surface and were yellowish in color, with rhizoids. Numerous spherical sporangia of 60 to 100 µm in diameter were borne on the apices of the hyphae. The sporangia were yellow in color and formed yellowish-gray cysts with a diameter of 5 to 8 µm. These morphological characteristics were consistent with the characteristics described for Rhizopus microsporus var. chinensis (Zheng et al. 2007). The internal transcribed spacer region of rDNA was amplified with the primers ITS1/ITS4 (Bertini et al. 1999). The generated sequence was submitted to GenBank under the accession number MN204624. BLAST analysis showed 99.85% identity with the existing sequence of R. microsporus var. chinensis isolate ZJR-2 in GenBank (KM527221.1). Based on the morphological and molecular analyses, the pathogen was identified as R. microsporus var. chinensis. Pathogenicity tests were performed on 35-day-old leaf mustard plants grown in plastic pots (28 cm diameter). In the treatment group, leaves and leaf blades were inoculated with mycelium discs (diameter of 8 mm), whereas the control treatment was inoculated with PDA discs of identical diameters. The plant pots were incubated in a greenhouse under a 10-h/14-h (light/dark) regime at 26°C (light) and 24°C (dark) with 90% relative humidity. Visible lesions were observed 48 h postinoculation with identical morphological characteristics as noticed on the field-infected samples. The pathogen was reisolated from symptomatic leaves and reidentified as R. microsporus var. chinensis by both PCR and microscopic techniques. The pathogenicity of the reisolated pathogen was checked, and it fulfilled Koch's postulates. To our knowledge, this is the first report of rot disease caused by R. microsporus var. chinensis on leaf mustard (B. juncea) in China.The author(s) declare no conflict of interest.References:Bertini, L., et al. 1999. FEMS Microbiol. Lett. 173:239. https://doi.org/10.1111/j.1574-6968.1999.tb13508.x Crossref, ISI, Google ScholarZheng, R. Y., et al. 2007. Sydowia 59:273. ISI, Google ScholarThe author(s) declare no conflict of interest.Funding: This work was supported by Research and Development Projects in Guangdong Key Areas (grant no. 2018B020202010), Key Projects of Guangzhou Science and Technology Innovation Committee (grant no. 201804020047), the National Natural Science Foundation of China (grant no. 31701916), Public Welfare Research and Capacity Building Project of Guangdong Provincial Science and Technology Planning (2019B030316015), and the project "Construction of Guangdong Province Crop Germplasm Resource Bank (Nursery) and Collection, Preservation and Evaluation of Crop Germplasm Resources".DetailsFiguresLiterature CitedRelated Vol. 104, No. 7 July 2020SubscribeISSN:0191-2917e-ISSN:1943-7692 DownloadCaptionA cucumber plant with a light gray lesion of charcoal rot at the soil line and microsclerotia visible on the stem (D. S. Egel et al.). Photo credit: D. S. Egel. Rot and discolored sepals of persimmon fruit caused by Mucor inaequisporus (S.-Y. Lee and H.-Y. Jung). Photo credit: H.-Y. Jung. Metrics Downloaded 1,502 times Article History Issue Date: 2 Jul 2020Published: 12 May 2020First Look: 9 Mar 2020Accepted: 3 Mar 2020 Pages: 2029-2029 Information© 2020 The American Phytopathological SocietyFundingResearch and Development Projects in Guangdong Key AreasGrant/Award Number: 2018B020202010Key Projects of Guangzhou Science and Technology Innovation CommitteeGrant/Award Number: 201804020047National Natural Science Foundation of ChinaGrant/Award Number: 31701916Public Welfare Research and Capacity Building Project of Guangdong Provincial Science and Technology PlanningGrant/Award Number: 2019B030316015Keywordsrot diseaseRhizopus microsporus var. chinensisleaf mustardThe author(s) declare no conflict of interest.