Leaf Spot Disease Caused by Alternaria arborescens, A. tenuissima, and A. infectoria on Brassica rapa subsp. parachinensis in China

Abstract

HomePlant DiseaseVol. 103, No. 9Leaf Spot Disease Caused by Alternaria arborescens, A. tenuissima, and A. infectoria on Brassica rapa subsp. parachinensis in China PreviousNext DISEASE NOTES OPENOpen Access licenseLeaf Spot Disease Caused by Alternaria arborescens, A. tenuissima, and A. infectoria on Brassica rapa subsp. parachinensis in ChinaWaheed Akram, Guihua Li, Aqeel Ahmad, Tehmina Anjum, Basharat Ali, Wenlong Luo, Juxian Guo, Dasen Xie, and Qing WangWaheed Akramhttp://orcid.org/0000-0003-3811-6677Guangdong Key Laboratory for New Technology Research of Vegetables, Guangdong Academy of Agricultural Sciences, Guangzhou, 510640, ChinaVegetable Research Institute, Guangdong Academy of Agricultural Sciences, Guangzhou, 510640, ChinaSearch for more papers by this author, Guihua Li†Corresponding author: G. Li; E-mail Address: liguihua@gdaas.cnGuangdong Key Laboratory for New Technology Research of Vegetables, Guangdong Academy of Agricultural Sciences, Guangzhou, 510640, ChinaVegetable Research Institute, Guangdong Academy of Agricultural Sciences, Guangzhou, 510640, ChinaSearch for more papers by this author, Aqeel Ahmadhttp://orcid.org/0000-0001-9097-2628Guangdong Key Laboratory for New Technology Research of Vegetables, Guangdong Academy of Agricultural Sciences, Guangzhou, 510640, ChinaVegetable Research Institute, Guangdong Academy of Agricultural Sciences, Guangzhou, 510640, ChinaSearch for more papers by this author, Tehmina AnjumInstitute of Agricultural Sciences, University of the Punjab, Lahore, PakistanSearch for more papers by this author, Basharat AliDepartment of Microbiology and Molecular Genetics, University of the Punjab, Lahore, PakistanSearch for more papers by this author, Wenlong LuoGuangdong Key Laboratory for New Technology Research of Vegetables, Guangdong Academy of Agricultural Sciences, Guangzhou, 510640, ChinaVegetable Research Institute, Guangdong Academy of Agricultural Sciences, Guangzhou, 510640, ChinaSearch for more papers by this author, Juxian GuoGuangdong Key Laboratory for New Technology Research of Vegetables, Guangdong Academy of Agricultural Sciences, Guangzhou, 510640, ChinaVegetable Research Institute, Guangdong Academy of Agricultural Sciences, Guangzhou, 510640, ChinaSearch for more papers by this author, Dasen XieGuangdong Key Laboratory for New Technology Research of Vegetables, Guangdong Academy of Agricultural Sciences, Guangzhou, 510640, ChinaVegetable Research Institute, Guangdong Academy of Agricultural Sciences, Guangzhou, 510640, ChinaSearch for more papers by this author, and Qing WangGuangdong Key Laboratory for New Technology Research of Vegetables, Guangdong Academy of Agricultural Sciences, Guangzhou, 510640, ChinaVegetable Research Institute, Guangdong Academy of Agricultural Sciences, Guangzhou, 510640, ChinaSearch for more papers by this authorAffiliationsAuthors and Affiliations Waheed Akram1 2 Guihua Li1 2 † Aqeel Ahmad1 2 Tehmina Anjum3 Basharat Ali4 Wenlong Luo1 2 Juxian Guo1 2 Dasen Xie1 2 Qing Wang1 2 1Guangdong Key Laboratory for New Technology Research of Vegetables, Guangdong Academy of Agricultural Sciences, Guangzhou, 510640, China 2Vegetable Research Institute, Guangdong Academy of Agricultural Sciences, Guangzhou, 510640, China 3Institute of Agricultural Sciences, University of the Punjab, Lahore, Pakistan 4Department of Microbiology and Molecular Genetics, University of the Punjab, Lahore, Pakistan Published Online:25 Jul 2019https://doi.org/10.1094/PDIS-05-19-0951-PDNAboutSections ToolsAdd to favoritesDownload CitationsTrack Citations ShareShare onFacebookTwitterLinked InRedditEmailWechat A leaf spot disease on Chinese flowering cabbage plants (Brassica rapa L. subsp. parachinensis), locally known as caixin, was observed in different agricultural fields around the cities of Lianzhou and Guangzhou of Guangdong Province of China in January 2017 and January 2018. The onset of rains increased disease incidence, which reached up to 70% in severely infected fields. Early disease symptoms observed were small necrotic spots of light to dark brown color. The spots were uniformly distributed on leaves and often coalesced afterward and turned into large blight areas. Under severe infection, 100% of leaves of plants became infected. Ten symptomatic leaf tissues were surface sterilized with 1% NaOCl, cut into small pieces (5 × 5 mm), and plated onto potato dextrose agar (PDA) medium. A total of 19 pathogen isolates were purified by successively subculturing on PDA medium using the single-spore technique. Conidia were produced by growing these purified isolates on potato carrot agar and V8 agar media under 12-h dark/12-h light cycles at 25 ± 2°C. Pathogen isolates were identified as Alternaria spp. on the basis of morphological characterization (Simmons 2007). Conidia were golden brown to brown, ellipsoid to ovoid, obclavate to pyriform (17.4 to 39.2 × 7.5 to 13.6 μm), having a short to long beak. Conidia had three to five transverse septa and zero to two longitudinal septa. Small-spored Alternaria spp. cannot be identified based on morphology because of overlapping characteristics (Woudenberg et al. 2015; Zhu and Xiao 2015). Therefore, the molecular identification of all isolates was performed using a multilocus gene sequencing technique. Genomic DNA was extracted using the Dzup Fungal DNA isolation kit (Sangon Biotech, Shanghai, China). Sequences of the internal transcribed spacer (ITS) region of rDNA and the plasma membrane ATPase (ATP) genes were obtained after PCR amplification using primer pairs ITS1/ITS4 (White et al. 1990) and ATPDF1/ATPDR1 (Lawrence et al. 2013). BLAST analysis of consensus sequences showed 99 to 100% similarity with previously submitted sequences of Alternaria arborescens E.G. Simmons (AF404667; JQ811991), Alternaria infectoria (Fuckel) Barr et Simmons (AF081456; MG740622), and Alternaria tenuissima (Nees) Wiltshire (KX664408; MG740659). ITS sequences of two representative isolates from all three species were deposited in GenBank under accession numbers MK530946 and MK788285 for A. arborescens, MK530947 and MK788286 for A. infectoria, and MK530948 and MK790641 for A. tenuissima. Similarly, ATP gene sequences of two representative isolates from all three species were deposited in GenBank under accession numbers MK531521 and MK792936 for A. arborescens, MK792937 and MK792938 for A. infectoria, and MK792939 and MK792940 for A. tenuissima. Pathogenicity tests were performed by spraying conidial suspensions (1 × 105 conidia/ml in 0.1% Tween 20 in sterilized distilled water) of two representative pathogen isolates from each species under separate treatments on leaves of 40-day-old B. rapa plants of variety ‘Lianzhou’. Control plants were treated with sterilized distilled water containing 0.1% Tween 20. The plants were incubated in an artificial climate chamber with a 16-h photoperiod at 25 ± 2°C and 90% relative humidity. Five plants were included in each treatment, and two independent trials were conducted. The same leaf spots were observed on the leaves of all inoculated plants after 1 week of inoculation. No symptoms were seen on control plants. Pathogen isolates of all three species were reisolated consistently from inoculated leaves. All three species were found to be pathogenic and caused disease symptoms. The species identity was reconfirmed by both morphological and molecular characteristics, thus fulfilling Koch’s postulates. Previously, multiple Alternaria species have been reported to cause leaf spot disease on apple in Chile (Elfar et al. 2018) and the Netherlands (Wenneker et al. 2018). To our knowledge, this is the first report of leaf spot on caixin plants caused by multiple Alternaria species. This disease can cause severe economic losses, because leaves are mainly sold in the market and used in salads or cooked dishes. Timely measures must be taken to manage this disease.The author(s) declare no conflict of interest.