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Chenopodium quinoa Wild, a pseudocereal food crop, has been cultivated for several thousand years in South America (Jacobsen S. E., et al. 2003), which has been accepted as a functional food in China and planted with increasing coverage recently. In November 2019, an ear rot disease was observed on Chenopodium quinoa in greenhouses from a farm located at Yuanping City (112.7° E; 38.73° N), and in 2020, about 5-50% of plants in greenhouses and fields were infected, yield loss was estimated to be 5-30% in Shanxi Province, north China. At first, an olive green spot-shaped mildew layer appeared on some glume shells, and then the color gradually deepened, turning brown to black-brown, the number of affected glume shells gradually increased, and spread to the whole spikelets, most of the infected spikelets became withered and moldy. Occasionally, a necrotic patch covering the mildew layer appeared on the young stem close to the ear, causing the upper part of the plant to wilt and even die. To identify the causal agent of the disease, fresh spikelets with symptoms of ear rot were collected from the diseased plants (n=7). Spores produced by the pathogen were picked with a sterilized inoculation needle in a sterilized airflow hood and were suspended in sterilized deionized water. Then dilution plate method was deployed to obtain the single-spore cultures on potato dextrose agar (PDA) plate, the colonies (n=14) had appeared in a round and flat in powder form, olive green, with folds and depresses in the center, and dark green at the backside of the colony, and cracks in the medium. Conidiophore grows from the side of hyphae, smooth or sometimes verruculose, with the size of 51.50 to 127.63 μm × 2.91 to 5.35μm (n = 50). Ramoconidia have 0-1 septa, mostly 2~3 conidial scars, and measured 6.51 to 15.73 μm × 2.4 to 4.47 μm (n=50). Conidia formed in long branched chains that were readily disarticulating, single-celled, colorless or brown, elliptic or rod-shaped, with blunt round ends, and measured 2.76 to 5.42 μm × 1.78 to 3.88 μm (n=50). The morphological characteristics of the isolates were First Report of Ear Rot of Chenopodium quinoa caused by Cladosporium cladosporioides in Shanxi, China Xinfeng Li, Tianchun Yu, Xiaodong Jiang, Chunlai Zhang, Xiaojun Zhao, and Jianmin Wang. Shanxi Agricultural University, Taigu, Shanxi Province 030801, China. Chenopodium quinoa Wild, a pseudocereal food crop, has been cultivated for several thousand years in South America(1), which has been accepted as a functional food in China and planted with increasing coverage recently. In November 2019, an ear rot disease was observed on Chenopodium quinoa in greenhouses from a farm located at Yuanping City (112.7° E; 38.73° N), and in 2020, about 5-50% of plants in greenhouses and fields were infected, yield loss was estimated to be 5-30% in Shanxi Province, north China. At first, an olive green spot-shaped mildew layer appeared on some glume shells, and then the color gradually deepened, turning brown to black-brown, the number of affected glume shells gradually increased, and spread to the whole spikelets, most of the infected spikelets became withered and moldy. Occasionally, a necrotic patch covering the mildew layer appeared on the young stem close to the ear, causing the upper part of the plant to wilt and even die. To identify the causal agent of the disease, fresh spikelets with symptoms of ear rot were collected from the diseased plants (n=7). Spores produced by the pathogen were picked with a sterilized inoculation needle in a sterilized airflow hood and were suspended in sterilized deionized water. Then dilution plate method was deployed to obtain the single-spore cultures on potato dextrose agar (PDA) plate, the colonies (n=14) had appeared in a round and flat in powder form, olive green, with folds and depresses in the center, and dark green at the backside of the colony, and cracks in the medium. Conidiophore grows from the side of hyphae, smooth or sometimes verruculose, with the size of 51.50 to 127.63 μm × 2.91 to 5.35μm (n = 50). Ramoconidia have 0-1 septa, mostly 2~3 conidial scars, and measured 6.51 to 15.73 μm × 2.4 to 4.47 μm (n=50). Conidia formed in long branched chains that were readily disarticulating, single-celled, colorless or brown, elliptic or rod-shaped, with blunt round ends, and measured 2.76 to 5.42 μm × 1.78 to 3.88 μm (n=50). The morphological characteristics of the isolates were consistent with those of Cladosporium cladosporioides(2). To further identify the causal agent, the actin (Act), translation elongation factor (TEF-1α), and rDNA internal transcribed spacer regions of ribosomal DNA (rDNA ITS) of the selected isolate 'YTC1' were amplified and sequenced. BLASTn analysis showed that Act (MW560123), TEF-1α(MW560124), and ITS (MZ674407) of the isolate 'YTC1' were 99 to 100% identical to C. cladosporioides (GenBank accession Nos. HM148504, HM148515, and HM148527 for ACT sequences; HM148258, HM148269, and HM148281 for TEF-1α sequences; HM148017, HM148028, and HM148040 for ITS sequences). The pathogenicity test was performed by injecting 10 μl of conidial suspending liquid (107 conidia/ml) into the inoculated ears (n=5), each of which had 8-10 spikelets, treatments without inoculation were the control(n=5), and all the treatments were maintained at 25°C and 90% relative humidity in an incubator. All inoculated ears showed the symptoms similar to those observed above after 5 days, but no symptoms were observed on the control, and C. cladosporioides isolates were re-isolated from plants and identified by the morphological and molecular traits described above, thus fulfilling Koch's postulates. Cladosporium cladosporioides are known to be on fading and decaying plant material, or a secondary invader on living plants(2). To our best knowledge, this is the first report of C.cladosporioides as the causal agent of ear rot of C. quinoa in China and perhaps the world. The new disease has impacted the yield and quality of C. quinoa and alerted scientists to investigate effective control strategies in the future. Xinfeng Li, Tianchun Yu, and Xiaodong Jiang contributed equally to this work. The authors are grateful to Mr. Xiangyun Wu, CEO of Jiaqi Seeds Ltd for his useful information. The author(s) declare no conflict of interest. Funding: Funding was provided by Shanxi Province Key Science and Technology Program on Agriculture (201803D221012-2, 201703D221006-3), the Sino-Pakistan aid project of Science and Technology Department of China （KY202002002）, and Shanxi Agriculture Valley Construction Program (SXNGJSKYZX201702, SXNGJSKYZX201704). References: [1] Jacobsen, S. E. 2003. Food Reviews International, 19:167-177. [2] Bensch K., Braun U., Groenewald J.Z., et al. 2012. Studies in Mycology, 72: 1- 401.