黄芩（学名：Scutellaria baicalensis Georgi）是唇形科的多年生草本植物，分布在中国的10个以上省份。目前，中国的黄芩种植面积超过5.8万公顷，年产量接近2.8万吨。作为一种传统的中药材，黄芩的根部具有抗炎、抗神经炎症和神经保护、抗癌、抗病毒、抗菌和抗氧化活性，并且对治疗结肠炎、肝炎、肺炎、呼吸道感染和过敏性疾病有效（Jang et al. 2023; Liu et al. 2023）。自2022年8月至9月，中国北京市中药研究所（40.04°N，116.28°E）发现丝孢叶斑病症状，经过两周以上的连续调查，该病在田间的发病率高达20%。根据观察，叶片初期症状为小的深褐色斑点（0.5至2.0毫米），随后扩展为中央呈灰白色圆心，外围为黑环和深褐色边缘的不规则病斑，并带有浅褐色光晕（图1A1-A3）。严重病例中的植株会出现叶片脱落和枯萎。从三个实验点的12株患病植株的36片叶子中，我们将症状叶片切成5×5毫米的块状，先用75%乙醇浸泡30秒，然后用5%次氯酸钠溶液浸泡45秒，用无菌水冲洗三次，用无菌滤纸擦干，然后在马铃薯葡萄糖琼脂（PDA）培养基上培养，并在25°C下暗存放两天。通过将菌丝端切移到新的PDA平板上培养，在25°C下暗培养，最终得到8个具有相似的菌落形态特征的分离株（A1、B3、D1、F2、E2、a4、e4和f1）。在PDA上，菌落呈现密集、绒毛状，以及白色到灰绿色的菌丝，菌落的背面中心呈现深褐色，边缘为灰色（图1D，E）。分生孢子是单生或连锁状，淡褐色，柱状至圆柱状，顶端钝（图1B，C）。通过观察100个分生孢子（每个分离株的50个），将这些分离物分为两类，代表分离株D1和e4。D1的分生孢子大小为5.4至75.8 μm × 2.1至6.8 μm，平均为26.9 × 4.4 μm，在88%的分生孢子中观察到0至3个假隔膜。e4的分生孢子大小为20.3至103.4 μm × 2.0至7.9 μm，平均为41.9 × 4.8 μm，在90%的分生孢子中观察到2至5个假隔膜。根据形态学（Ellis 1971），这些分离株被鉴定为核杆菌属（Corynespora cassiicola）。我们采用溴化十六烷基三甲基铵（CTAB）法提取了两株分离物（D1和e4）的DNA，并通过引物ITS1/ITS4（Bandi et al. 2022）、EF1-728F/EF-986R（Wang et al. 2021）和Bt2a/Bt2b（Glass and Donaldson 1995）扩增rDNA内部转录间隔区（ITS）和翻译延长因子1α（TEF1-α）、β-管蛋白（TUB2）基因的片段。ITS序列OQ991339（524 bp）和OR044050（533 bp）与C. cassiicola具有99.8%的同源性，在GenBank中与MT228951（536 bp）和OQ991340（546 bp）的覆盖率达到99%。TEF1-α序列OR047441（304 bp）和OR047443（306 bp）与C. cassiicola具有99.3%的同源性，在GenBank中与ON381927（300 bp）和ON381933（301 bp）的覆盖率分别达到98%和99%。TUB2序列OR047449（427 bp）和OR047451（427 bp）与C. cassiicola具有99.53%的同源性，在GenBank中与MN604075（442 bp）的覆盖率分别达到99%和98%。我们利用MEGA 11软件中的Neighbor-Joining（NJ）方法，基于ITS、TEF1-α和TUB2序列构建了系统发育树（图2）。结果显示，这两株分离物为C. cassiicola，分支支持率超过90%（进行了1000次重复实验）。我们使用9株2年生的黄芩苗进行了致病性测定。每株植株的三片叶子分别用经过火焰灼烧消毒的针刺孔，接种D1和e4的菌丝块（直径为5毫米）。接种无菌PDA菌块的植株作为对照。所有接种的苗木均在25°C和90%相对湿度下培养。接种后约3至4天，接种D1和e4的叶片上出现了田间观察到的类似症状，而未接种的对照苗木上则没有观察到任何症状（附图1）。从接种D1和e4后出现病状的叶片中再次分离出具有强大、绒毛状、白色至灰绿色菌丝的分离物，并通过DNA测序确认为C. cassiicola，符合科克氏原则。基于形态学和多位点系统发育结果，这些分离株被确定为C. cassiicola，这是一种危害一些重要作物的病原体（Dixon et al. 2009; Zhang et al. 2018; Xie et al. 2021）。据我们所知，这是C. cassiicola首次被报告为中国黄芩丝孢叶斑病的病原菌，对黄芩的产量构成潜在威胁。

Scutellaria baicalensis Georgi. is a perennial herb in the Lamiaceae family, with a distribution in more than 10 provinces in China. At the current time, the cultivation area of S. baicalensis in China exceeds 58,000 hectares, with annual production approaching 28,000 tons. As a traditional Chinese herbal medicine, the root of S. baicalensis has many applications, such as anti-inflammatory, anti-neuroinflammatory and neuroprotective, anticancer, antiviral, antibacterial, and antioxidant activities, and is effective in treatment of colitis, hepatitis, pneumonia, respiratory infections, and allergic diseases. (Jang et al. 2023; Liu et al. 2023). From August to September 2022, septoria leaf spot symptoms were observed at the Institute of Medicinal Plant Development (40.04°N, 116.28°E), Beijing, China, and the incidence of this disease was up to 20% in the field through more than two weeks of continuous investigation. Initial symptoms on leaves were observed as small, dark-brown spots (0.5 to 2.0 mm), which then expanded to irregular lesions with a pale gray center surrounded by a black ring with a dark-brown edge and light brown halo (Fig. 1A1-A3). Plants were defoliated and withered in severe cases. Thirty-six symptomatic leaves of 12 diseased plants from three experimental sites were cut into 5 × 5 mm pieces, and surface sterilized with 75% ethanol for 30 s followed by 5% NaClO solution for 45 s, rinsed with sterile water three times, dried with sterile filter paper, and subsequently placed on potato dextrose agar (PDA) medium and incubated at 25°C in dark for two days. Isolates were purified by transferring hyphal tips to new PDA plates and incubated at 25°C in dark. Finally, eight isolates (A1, B3, D1, F2, E2, a4, e4 and f1) with similar colonial morphological characteristics were obtained. Colonies on PDA exhibited dense, downy, and white to grayish-green aerial mycelia and the reverse of colonies showed dark-brown in the center and grayish on the edge (Fig. 1D, E). Conidia were solitary or catenate, pale brown, obclavate to cylindrical, apex obtuse (Fig. 1B, C). The isolates were divided into two categories by examining 100 conidia (50 of each isolate), represented by isolates D1 and e4. Conidia of D1 measured 5.4 to 75.8 μm × 2.1 to 6.8 μm, mean 26.9 × 4.4 μm, had 0 to 6 pseudosepta, with 0 to 3 pseudosepta observed in 88% of conidia. Conidia of e4 measured 20.3 to 103.4 μm × 2.0 to 7.9 μm, mean 41.9 × 4.8 μm, had 0 to 6 pseudosepta, with 2 to 5 pseudosepta observed in 90% of conidia. These isolates were identified as Corynespora cassiicola based on morphology (Ellis 1971). DNA of the two isolates (D1 and e4) was extracted by the cetyltrimethylammonium bromide (CTAB) method, and internal transcribed spacer (ITS) region of rDNA, translation elongation factor 1 alpha (TEF1-α), and beta-tubulin (TUB2) gene were amplified, using the primers ITS1/ITS4 (Bandi et al. 2022), EF1-728F/EF-986R (Wang et al. 2021), and Bt2a/Bt2b (Glass and Donaldson 1995), respectively. Sequences of ITS OQ991339 (524 bp) and OR044050 (533 bp) shared 99.8% identity to C. cassiicola, with a 99% coverage to MT228951 (536 bp) and OQ991340 (546 bp) in GenBank. Sequences of TEF1-α OR047441 (304 bp) and OR047443 (306 bp) shared 99.3% identity to C. cassiicola, with a 98% and 99% coverage to ON381927 (300 bp) and ON381933 (301 bp) in GenBank, respectively. Sequences of TUB2 OR047449 (427 bp) and OR047451 (427 bp) shared 99.53% identity to C. cassiicola, with a 99% and 98% coverage to MN604075 (442 bp) in GenBank, respectively. Phylogenetic trees were computed with ITS, TEF1-α, and TUB2 sequences in MEGA 11 using the Neighbor-Joining (NJ) method (Fig. 2). The results showed that the two isolates were C. cassiicola with more than 90% bootstrap support (1000 replicates). Nine 2-year-old seedlings of S. baicalensis were used for the pathogenicity assay. Three leaves from each plant were punctured with flame-sterilized needles, and inoculated with mycelial plugs (5 mm in diameter) of D1 and e4. Plants inoculated with sterile PDA plugs were used as control. All the inoculated seedlings were incubated at 25 oC and 90% relative humidity. About 3 to 4 days after inoculation, similar symptoms to those observed in the field were present on leaves inoculated with D1 and e4, while no symptoms were observed in the uninoculated control seedlings (Supplementary Fig. 1). Isolates with vigorous, downy, and white to grayish-green aerial mycelia were reisolated from the diseased leaves inoculated with D1 and e4 and identified as C. cassiicola by DNA sequencing, fulfilling Koch's postulates. Based on morphological and multilocus phylogenetic results, these isolates were identified as C. cassiicola, a pathogen that threatens several important crops (Dixon et al. 2009; Zhang et al. 2018; Xie et al. 2021). To our knowledge, this is the first report of C. cassiicola as the causal pathogen of septoria leaf spot on S. baicalensis in China, which poses a potential threat to the production of S. baicalensis.