Abstract During the past few years, an unknown disease, which resulted in various degrees of chlorosis, mosaic and streaking of wheat leaves was commonly found in the irrigation wheat growing areas of South Africa (SA). The yellowing symptoms resembled a viral infection but were not consistent with previously reported wheat viruses in SA. The observed symptoms suggested that this disease was likely caused by soil-borne virus, which may be transmitted by soil inhabiting microorganisms such as Polymyxa graminis. Therefore, to identify any virus associated with leaves and determine the presence of P. graminis in roots, wheat plants exhibiting characteristic symptoms of the disease were collected during 2018 from farmers’ fields and/or experimental plots across major wheat growing regions of SA. While the roots of the samples were tested for P. graminis using light microscopy, polymerase chain reaction (PCR) and Sanger sequence analysis, the leaves were tested for the presence of viruses using Next generation sequencing (NGS), with the results being confirmed with reverse transcription (RT) PCR. Combined, the microscopic and PCR results confirmed P. graminis in 96% of the symptomatic samples tested. NGS analysis performed on a subset of 22 symptomatic leaf samples resulted in the identification of wheat stripe mosaic virus (WhSMV) in all the samples tested. RT-PCR confirmed the presence of WhSMV in similar samples suggesting that WhSMV is the most likely cause of the observed yellowing of wheat leaves. Twenty-one of the 22 samples which tested positive for WhSMV were also positive for P. graminis indicating that WhSMV is most probably transmitted by P. graminis. WhSMV is a novel virus that was recently described on wheat in Brazil and Paraguay. To our knowledge, this is the first report of WhSMV in South Africa and the third report in the world. As WhSMV has been detected only recently, information on the epidemiology and control of this disease is not yet available.

中文翻译：

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南非小麦上小麦条纹花叶病毒的检测与分子鉴定

摘要 近年来，在南非灌溉小麦产区普遍发现一种未知病害，导致小麦叶片出现不同程度的萎黄、花叶和条纹。变黄症状类似于病毒感染，但与之前报道的南澳小麦病毒不一致。观察到的症状表明，这种疾病很可能是由土壤传播的病毒引起的，这种病毒可能通过土壤中的微生物如禾本科多粘菌传播。因此，为了鉴定与叶子相关的任何病毒并确定根中是否存在禾本科青霉，2018 年期间从南澳主要小麦种植区的农田和/或试验田中收集了表现出该病害特征的小麦植株。虽然对样品的根进行了 P 测试。graminis 使用光学显微镜、聚合酶链反应 (PCR) 和 Sanger 序列分析，使用下一代测序 (NGS) 测试叶子是否存在病毒，结果通过逆转录 (RT) PCR 确认。结合起来，显微镜和 PCR 结果证实了 96% 的有症状样本中的禾本科。对 22 个有症状的叶子样本的子集进行的 NGS 分析导致在所有测试的样本中鉴定出小麦条纹花叶病毒 (WhSMV)。RT-PCR 证实了 WhSMV 在类似样品中的存在，表明 WhSMV 是观察到的小麦叶子变黄的最可能原因。在 WhSMV 检测呈阳性的 22 个样本中，有 21 个样本对禾本科青霉也呈阳性，表明 WhSMV 最有可能由禾本科禾本科传播。WhSMV 是一种新型病毒，最近在巴西和巴拉圭的小麦上进行了描述。据我们所知，这是 WhSMV 在南非的第一份报告，也是世界上的第三份报告。由于最近才检测到 WhSMV，因此尚无法获得有关该疾病的流行病学和控制的信息。