Webster C G, Kousik C S, Roberts P D, Rosskopf E N, Turechek W W, Adkins S
USDA-ARS-USHRL, Fort Pierce FL 34945.
USDA-ARS-USVL, Charleston, SC 29414.
Plant Dis. 2011 Mar;95(3):360. doi: 10.1094/PDIS-11-10-0813.
Pigweeds (genus Amaranthus) are problematic weeds in crop production throughout the world and are responsible for significant yield losses in many crops (2). Members of this genus can produce hundreds of thousands of seeds per plant and are also capable of supporting populations of important crop pathogens including viruses, nematodes, fungi, and oomycetes. Thirty-one pigweed samples (tentatively identified as Amaranthus lividus L. based on leaf notch and growth habit) were collected in November and December of 2009 from a watermelon field near Immokalee, FL, previously found to contain watermelon plants infected with three whitefly-transmitted viruses: Cucurbit yellow stunting disorder virus (CYSDV), Cucurbit leaf crumple virus (CuLCrV), and Squash vein yellowing virus (SqVYV). Although no obvious virus symptoms were observed on any of the pigweed plants, whiteflies (Bemisia tabaci), a known vector of CYSDV, CuLCrV, and SqVYV, were observed on leaves. Consequently, replica tissue blots were made from all pigweed samples and tested independently by tissue blot nucleic acid hybridization assay for CYSDV, CuLCrV, or SqVYV (3). Tissue blots indicated CYSDV infection in six pigweed samples. Neither CuLCrV nor SqVYV was detected. Three of the tissue blot-positive pigweed samples were further tested by reverse transcription (RT)-PCR amplification from total RNA (extracted from leaf tissue with TRIzol Reagent [Invitrogen, Carlsbad, CA]) with HSP70 and coat protein (CP) gene primers (1). HSP70 and CP gene RT-PCR products of the expected sizes (175 and 707 nt, respectively) were amplified, sequenced, and found to be 100% identical for all three pigweed samples. The partial HSP70 gene sequence from pigweed shared 98.3 to 100% nucleotide identity with CYSDV isolates from Arizona, California, and Spain (GenBank Accession Nos. FJ492808, EU596530, and NC_004810, respectively). The partial CP gene sequence from pigweed shared 88.8 to 100% nucleotide identity with CYSDV isolates from Arizona, Saudi Arabia, Texas, and Spain (GenBank Accession Nos. EF210558, AF312811, AF312806, and AF312808, respectively). To our knowledge, this is the first report of CYSDV infection of pigweed in Florida. Infection of redroot pigweed (A. retroflexus) was recently reported in California (4). These results collectively indicate that control of noncucurbit weeds may be important for effective management of CYSDV in cucurbit crops. References: (1) S. Adkins et al. Online publication. doi:10.1094/PHP-2009-1118-01-BR. Plant Health Progress, 2009. (2) L. Holm et al. World's Weeds: Natural Histories and Distributions. John Wiley and Sons, Inc. New York, NY, 1997. (3) W. W. Turechek et al. Phytopathology 100:1194, 2010. (4) W. M. Wintermantel et al. Plant Dis. 93:685, 2009.
苋属杂草是全球作物生产中的问题杂草，会导致许多作物严重减产（2）。该属植物每株可产生数十万粒种子，还能滋生包括病毒、线虫、真菌和卵菌在内的重要作物病原体。2009年11月和12月，从佛罗里达州伊莫卡利附近的一块西瓜田采集了31份苋属杂草样本（根据叶裂和生长习性初步鉴定为凹头苋），此前发现该西瓜田的西瓜植株感染了三种由粉虱传播的病毒：葫芦科黄化矮缩病毒（CYSDV）、葫芦科叶片皱缩病毒（CuLCrV）和南瓜脉黄化病毒（SqVYV）。尽管在任何苋属杂草植株上均未观察到明显的病毒症状，但在叶片上发现了粉虱（烟粉虱），已知其为CYSDV、CuLCrV和SqVYV的传播媒介。因此，对所有苋属杂草样本制作了复制组织印迹，并通过组织印迹核酸杂交试验分别检测CYSDV、CuLCrV或SqVYV（3）。组织印迹显示6份苋属杂草样本感染了CYSDV。未检测到CuLCrV和SqVYV。对3份组织印迹呈阳性的苋属杂草样本，用HSP70和外壳蛋白（CP）基因引物从总RNA（用TRIzol试剂[Invitrogen，卡尔斯巴德，加利福尼亚州]从叶片组织中提取）进行逆转录（RT）-PCR扩增进一步检测（1）。扩增出预期大小（分别为175和707 nt）的HSP70和CP基因RT-PCR产物，进行测序，发现这3份苋属杂草样本的序列完全相同。苋属杂草的部分HSP70基因序列与来自亚利桑那州、加利福尼亚州和西班牙的CYSDV分离株（GenBank登录号分别为FJ492808、EU596530和NC_004810）的核苷酸同一性为98.3%至100%。苋属杂草的部分CP基因序列与来自亚利桑那州、沙特阿拉伯、得克萨斯州和西班牙的CYSDV分离株（GenBank登录号分别为EF210558、AF312811、AF312806和AF312808）的核苷酸同一性为88.8%至100%。据我们所知，这是佛罗里达州苋属杂草感染CYSDV的首次报道。最近在加利福尼亚州报道了红根苋（反枝苋）的感染情况（4）。这些结果共同表明，控制非葫芦科杂草对于有效管理葫芦科作物中的CYSDV可能很重要。参考文献：（1）S. Adkins等人。在线发表。doi:10.1094/PHP - 2009 - 1118 - 01 - BR。《植物健康进展》，2009年。（2）L. Holm等人。《世界杂草：自然史与分布》。约翰·威利父子公司，纽约，纽约州，1997年。（3）W. W. Turechek等人。《植物病理学》100:1194，2010年。（4）W. M. Wintermantel等人。《植物病害》93:685，2009年。
