Fusarium head blight (FHB) is one of the most troublesome fungal diseases challenging US wheat (Triticum aestivum L.) production (Savary et al. 2019). Harmful mycotoxin contamination, primarily due to deoxynivalenol (DON) in the Fusarium-damaged kernels (FDK), can negatively impact human and livestock health (McMullen et al. 1997). Although Fusarium graminearum is the primary causal agent of FHB, several other species including F. poae could pose a risk by producing dangerous mycotoxins such as nivalenol, DON, HT-2, and T-2 (Stenglein 2009). Severe FHB epidemics on wheat have occurred in recent years along with increased corn acreage across the southeast US specifically in Georgia (Ghimire et al. 2020). Five symptomatic wheat heads displaying bleaching symptoms were randomly collected from 19 different fields across 13 counties of Georgia in late spring of 2018. Infected kernels were dipped in 6% sodium hypochlorite for 10 min and rinsed three times with sterilized water. Blot dried kernels were placed on potato dextrose agar (PDA) and incubated for 7 days at 25°C under 12-h photoperiod. Three isolates (GA18W-2.1.6, GA18W-6.1.4, and GA18W-10.2.3) from Terrell, Peach, and Sumter counties exhibited dense, whitish mycelium colony typical of F. poae (Leslie and Summerell 2006). When grown in carboxymethylcellulose broth, isolates produced globose to piriform microconidia (5.1 to 12.4 µm by 4.4 to 11.2 µm) that were aseptate or had a single septation. The morphological identification was further confirmed by DNA sequencing. Single hyphal tip isolates were grown on cellophane overlain on PDA for 10 days. Fungal DNA was extracted using a Qiagen DNeasy Plant Mini Kit. Genomic DNA was sequenced using TEF1 and TEF2 primer pairs that target the translation elongation factor 1-α (EF1-α) locus (O'Donnell et al. 1998). BLASTn query of the obtained sequences of GA18W-2.1.6 (accession no. MT856907) and GA18W-10.2.3 (accession no. MT856909) were identified as F. poae with a 99% sequence homology with GenBank reference accession MK629641, while GA18W-6.1.4 (accession no. MT856908) displayed 100% similarity with F. poae accession KJ947343. Koch's postulates were performed under greenhouse conditions. Three seeds of the FHB susceptible wheat cultivar 'SS8641' were planted in individual cone-tainers with three replications (two cone-tainers/replicate). Wheat plants were vernalized for six weeks and then moved back to the greenhouse. Each F. poae isolate was spray inoculated (50,000 spores/ml) at the flowering stage onto 18-24 wheat heads. A field isolate of F. graminearum was included as a positive control whereas heads mock-inoculated with water were used as a negative control. Inoculated wheat heads were incubated in black plastic bags for 48 hours. Disease severity and FDK were recorded three weeks post inoculation. Disease severities were 6.7% (GA18W-2.1.6), 8.3% (GA18W-10.2.3), and 15.2% (GA18W-6.1.4) compared to 90.0% in the positive control similar to Arrúa et al (2019). No symptoms were observed in the negative control. FDK was 18% (GA18W-2.1.6), 28% (GA18W-10.2.3) and 44% (GA18W-6.1.4). F. poae was re-isolated from the infected heads and found to be morphologically identical to the isolates used for inoculation. To our knowledge, this is the first report of F. poae associated with FHB of wheat in the state of Georgia, USA. F. poae isolates from Georgia might produce mycotoxins in addition to reducing grain yield which needs further study.

中文翻译：

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美国佐治亚州首次报道由早熟禾镰刀菌引起小麦赤霉病。


赤霉病 (FHB) 是挑战美国小麦 (Triticum aestivum L.) 生产的最棘手的真菌病害之一（Savary 等人，2019）。有害的霉菌毒素污染，主要是由镰刀菌损坏的籽粒 (FDK) 中的脱氧雪腐镰刀菌烯醇 (DON) 造成的，会对人类和牲畜的健康产生负面影响（McMullen 等，1997）。虽然禾谷镰刀菌是 FHB 的主要致病菌，但包括早熟禾镰刀菌在内的其他几种物种也可能产生危险的霉菌毒素，如雪腐镰刀菌烯醇、DON、HT-2 和 T-2（Stenglein 2009）。近年来，随着美国东南部地区（特别是佐治亚州）玉米种植面积的增加，小麦上出现了严重的 FHB 流行病（Ghimire 等，2020）。 2018年春末，从佐治亚州13个县的19个不同田地中随机收集了5个出现白化症状的麦穗。将受感染的麦粒浸入6%次氯酸钠中10分钟，并用消毒水冲洗3次。将印迹干燥的籽粒置于马铃薯葡萄糖琼脂 (PDA) 上，并在 25°C、12 小时光周期下孵育 7 天。来自特雷尔县、桃县和萨姆特县的三个分离株（GA18W-2.1.6、GA18W-6.1.4 和 GA18W-10.2.3）表现出典型的早熟禾镰刀菌密集的白色菌丝体菌落（Leslie 和 Summerell 2006）。当在羧甲基纤维素肉汤中生长时，分离株产生球形至梨状小分生孢子（5.1至12.4微米×4.4至11.2微米），无隔膜或具有单一隔膜。通过DNA测序进一步证实了形态学鉴定。单个菌丝尖端分离物在覆盖在PDA上的玻璃纸上生长10天。使用 Qiagen DNeasy Plant Mini Kit 提取真菌 DNA。 使用针对翻译延伸因子 1-α (EF1-α) 基因座的 TEF1 和 TEF2 引物对对基因组 DNA 进行测序（O'Donnell 等人，1998）。对获得的GA18W-2.1.6（登录号MT856907）和GA18W-10.2.3（登录号MT856909）序列进行BLASTn查询，鉴定为早熟禾镰刀菌，与GenBank参考登录号MK629641有99%的序列同源性，而GA18W -6.1.4（登记号MT856908）与早熟禾登记号KJ947343显示100%相似性。科赫假设是在温室条件下进行的。将 FHB 易感小麦品种“SS8641”的三颗种子种植在单独的锥形容器中，并进行三次重复（两个锥形容器/重复）。小麦植株经过六周的春化处理，然后移回温室。在开花阶段将每个早熟禾镰刀菌分离物（50,000个孢子/ml）喷雾接种到18-24个小麦头上。禾谷镰刀菌的田间分离株作为阳性对照，而用水模拟接种的头作为阴性对照。接种的小麦头在黑色塑料袋中孵育48小时。接种后三周记录疾病严重程度和FDK。疾病严重程度分别为 6.7% (GA18W-2.1.6)、8.3% (GA18W-10.2.3) 和 15.2% (GA18W-6.1.4)，而阳性对照的疾病严重程度为 90.0%，与 Arrúa 等人 (2019) 类似。阴性对照中未观察到任何症状。 FDK为18%(GA18W-2.1.6)、28%(GA18W-10.2.3)和44%(GA18W-6.1.4)。从受感染的头部重新分离出早熟禾镰刀菌，发现其形态与用于接种的分离株相同。据我们所知，这是美国乔治亚州首次报道与小麦 FHB 相关的早熟禾镰刀菌 (F. poae)。 F。 来自格鲁吉亚的早熟禾分离物除了降低谷物产量外，还可能产生霉菌毒素，这需要进一步研究。