Department of Plant Pathology, University of Arkansas, Fayetteville 72701.
Yuma Agricultural Center, University of Arizona 85365.
Plant Dis. 2018 Mar;102(3):608-612. doi: 10.1094/PDIS-06-17-0859-RE. Epub 2018 Jan 18.
A unique foliar disease of spinach, determined to be caused by Pythium aphanidermatum, was observed on spinach in Yuma County, AZ and Imperial County, CA desert spinach production areas in both 2015 and 2016. The foliar symptoms of the disease included water-soaked foliage, rapid collapse of young plants, and white, aerial, cottony mycelia. The disease was associated with hot (27 to 42°C) and wet conditions associated with overhead irrigation under high-density plantings (>8.0 million seeds/ha). Isolations were performed on symptomatic tissue, and DNA was recovered from pure culture of the isolates recovered and sequenced using the internal transcribed spacer (ITS) ribosomal DNA (rDNA) primers ITS1/ITS4 and gene cytochrome oxidase I (COXI) primers FM55 and FM59. BLAST searches in GenBank indicated that the isolates were P. aphanidermatum based on 99 to 100% homology of ITS rDNA. Moreover, the DNA sequences of the ITS and COXI were identical for the five representative isolates. The objective of this research was to determine whether P. aphanidermatum recovered from symptomatic spinach tissue was able to cause foliar web blight and damping-off of spinach and other crops. In addition to spinach, other hosts evaluated included cotton, soybean, pepper, tomato, cucumber, melon, squash, lettuce, corn, wheat, and rice in greenhouse trials. Inoculations were performed by either foliar inoculations or infesting the soil with plugs of potato dextrose agar colonized by the P. aphanidermatum. Web blight symptoms were severe on spinach and all other dicotyledonous hosts tested, except lettuce. No web blight symptoms were observed on corn or rice, and only minor symptoms were observed on 10-day-old seedlings of wheat. P. aphanidermatum caused severe preemergence damping-off of all dicotyledonous plant species tested but only caused limited seedling size reduction in corn and wheat. Mefenoxam treatment of spinach seed provided complete protection against preemergence damping-off of spinach at both low (0.15 g a.i./kg of seed) and high (0.70 g a.i./kg of seed) rates of application, and the high rate of the application resulted in complete protection against web blight of spinach for 10 to 20 days after planting.
2015 年和 2016 年，在亚利桑那州尤马县和加利福尼亚州帝国县的沙漠菠菜生产区，观察到菠菜上有一种独特的菠菜叶病，确定该病由腐霉引起。该病的叶片症状包括水渍状叶片、幼苗迅速萎蔫以及白色、气生、棉花状菌丝。该病与热（27 至 42°C）和高密种植（>800 万粒/公顷）条件下的湿度过高有关，这种条件下采用头顶灌溉。对病组织进行分离，从分离物的纯培养物中回收 DNA，并使用内部转录间隔区（ITS）核糖体 DNA（rDNA）引物 ITS1/ITS4 和基因细胞色素氧化酶 I（COXI）引物 FM55 和 FM59 对其进行测序。在 GenBank 中的 BLAST 搜索表明，根据 ITS rDNA 的 99%至 100%同源性，分离株为腐霉。此外，5 个代表性分离株的 ITS 和 COXI 的 DNA 序列完全相同。本研究的目的是确定从症状菠菜组织中分离到的腐霉是否能够引起菠菜和其他作物的叶斑病和猝倒病。除了菠菜，在温室试验中还评估了其他宿主，包括棉花、大豆、辣椒、番茄、黄瓜、甜瓜、南瓜、生菜、玉米、小麦和水稻。通过叶片接种或用马铃薯葡萄糖琼脂塞污染腐霉的土壤进行接种。在所有测试的双子叶宿主中，除生菜外，菠菜和其他双子叶宿主上的网斑病症状都很严重。在玉米或水稻上未观察到网斑病症状，而在 10 天大的小麦幼苗上仅观察到轻微症状。腐霉引起所有测试的双子叶植物物种的严重幼苗猝倒，但仅在玉米和小麦上导致幼苗大小有限的减少。在菠菜种子中使用甲霜灵处理可在低（0.15 g a.i./kg 种子）和高（0.70 g a.i./kg 种子）施用量下完全防治菠菜的幼苗猝倒，高用量可在种植后 10 至 20 天内完全防治菠菜的网斑病。
