In September 2014, a high rate of bulb rot (5-15% depending on producer) was reported across all cultivars developing early in the storage season in the onion producing region of southwestern Idaho. Spanish yellow onion bulbs cv. Vaquero displaying tan to light brown necrotic rot were obtained. The bulb rot originated in the neck and spread to successive scales (Figure 1). In August 2015, onion cv. Redwing and Vaquero were observed to have wet necrotic lesions developing on leaves in the field (Figure 2). Margins of necrotic tissue, 1-2 cm3, were excised, surface sterilized, plated on water agar medium and incubated at 24°C. Hyphal growth was sub-cultured from eight strains (A- D in 2014; E-H in 2015) to fresh potato dextrose agar to obtain pure cultures. Cultures were characteristic of Fusarium species as described by Nelson et al. (1983) with the presence of microconidia formed on polyphialides with macroconidia present. Primers ITS4-A1 and ITS5 primers (White et al. 1990); EF-1 and EF-2 (O'Donnell et al. 1998); and fRPB2-5F and fRPB2-7cR (Liu et al. 1999) were used to amplify regions of the ITS, elongation factor 1-α and the second largest subunit of DNA-directed RNA polymerase II. Amplicons were sequenced and analyzed using BLAST (https://www.ncbi.nlm.nih.gov/) and in combination using Pairwise DNA Alignment and Polyphasic Identification (http://www.westerdijkinstitute.nl/Fusarium/DefaultInfo.aspx?Page=Home) as described by O'Donnell et al. 2015. Analysis indicated that these strains are Fusarium proliferatum, which is part of the F. fujikuroi species complex (O'Donnell et al. 1998). Similarity (99.5%) was observed in pairwise analyses and the polyphasic identification clustering to representative F. proliferatum strain NRRL 22944 and others. Sequences were submitted to Genbank and registered accession numbers are found in Table 1. To complete Koch's postulates, cv. Vaquero onion bulbs were surface sterilized and injected with 3 × 105 microconidia into the shoulder of each bulb. Five bulbs were inoculated for each isolate, placed in a mesh bag, and incubated at 30°C in the dark. Five bulbs injected with sterile water and five non-inoculated bulbs served as controls. After 14 days, each bulb was sliced vertically down the center and inspected for rot. All eight strains induced tan to light brown necrotic rot symptoms in each inoculated bulb. No symptoms were observed for the water inoculated and the non-inoculated onion bulbs. A fungus was isolated from the necrotic tissue and confirmed to be F. proliferatum as described above. Ten µl aliquots containing 1 × 105 microconidia of F. proliferatum strains (C, E-H) were applied to leaves in triplicate of 12-week-old onion plants (cv. Vaquero) wounded with a 21-gauge needle. Water controls were included. Within three days lesions, with light chlorosis, began to form and quickly spread on the leaves. A fungus was isolated and confirmed to be F. proliferatum as described above. This is the first extensive description and identification of F. proliferatum causing bulb rot in storage in Idaho (Mohan et al. 1997). In addition, this is the first report of the fungus causing leaf infection in the field. These findings confirm F. proliferatum as the causal agent of the high incidence of bulb rot observed in 2014 and 2015. This bulb rot continues to occur in southwestern Idaho and since the pathogen can cause leaf infections growers are encouraged to be vigilant for both leaf lesions during the growing season and bulb rot in storage.

中文翻译：

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关于Fusarium proliferatum引起坏死的叶片损害和西南爱达荷州的洋葱（洋葱头）的鳞茎腐烂的首次报道。

2014年9月，在爱达荷州西南部洋葱产区，在储藏季节早期发育的所有品种的鳞茎腐烂报告率很高（取决于生产者，为5-15％）。西班牙黄洋葱鳞茎简历。获得显示棕褐色至浅棕色坏死腐烂的Vaquero。鳞茎腐烂起源于颈部，并蔓延至连续鳞片（图1）。2015年8月，洋葱简历。观察到红翼和Vaquero在田间的叶子上出现了湿坏死性病变（图2）。切下1-2cm 3的坏死组织的边缘，表面灭菌，铺在水琼脂培养基上并在24℃下孵育。将菌丝生长从8个菌株（2014年A-D； 2015年EH）传代培养到新鲜马铃薯葡萄糖琼脂上，以获得纯培养物。如Nelson等人所述，培养是镰刀菌属物种的特征。（1983）与存在的大分生孢子的多phiideides上形成的分生孢子。ITS4-A1和ITS5引物（White等1990）; EF-1和EF-2（O'Donnell等，1998）；使用fRPB2-5F和fRPB2-5F和fRPB2-7cR（Liu等，1999）扩增ITS的区域，延伸因​​子1-α和DNA指导的RNA聚合酶II的第二大亚基。使用BLAST（https://www.ncbi.nlm.nih.gov/）以及结合使用成对DNA对齐和多相鉴定（http://www.westerdijkinstitute.nl/Fusarium/DefaultInfo.aspx？如O'Donnell等人所述。2015年。分析表明，这些菌株是镰刀菌（Fusarium proliferatum），它是F. fujikuroi物种复合体的一部分（O'Donnell等人，1998）。相似度（99。在成对分析中观察到5％（5％），多相鉴定聚类为代表性的F. proliferatum菌株NRRL 22944等。序列已提交Genbank，注册的登录号见表1。为完成Koch的假设，简历。对Vaquero洋葱鳞茎进行表面消毒，并向每个鳞茎的肩部注入3×105个微分生孢子。每个分离物接种五个球茎，放在网袋中，在黑暗中于30°C孵育。五个装有无菌水的球茎和五个未接种的球茎作为对照。14天后，将每个球茎垂直切下中心并检查是否腐烂。所有八个菌株在每个接种的球茎中均引起棕褐色至浅棕色的坏死性腐烂症状。接种水和未接种洋葱鳞茎均未观察到症状。如上所述，从坏死组织中分离出一种真菌，并证实是增殖小镰刀菌。将十个含有1×105微型分生孢子菌F. proliferatum菌株（C，EH）的等分试样，一式三份地用12号针头刺伤的12周龄洋葱植株（cv。Vaquero）的叶片上。包括水控制。在三天之内，开始出现萎黄病，开始形成病斑并迅速扩散到叶子上。分离出一种真菌，并证实是如上所述的F.proliferatum。这是对爱达荷州贮藏引起球茎腐烂的F. proliferatum的首次广泛描述和鉴定（Mohan等，1997）。另外，这是该真菌在田间引起叶片感染的首次报道。这些发现证实了F. proliferatum是2014年和2015年观察到的鳞茎腐烂高发的病因。