California State University Monterey Bay, School of Natural Sciences, Seaside, CA, 93955.
North Carolina State University, Department of Plant Pathology, Raleigh, NC, 27695.
Plant Dis. 2018 Feb;102(2):265-275. doi: 10.1094/PDIS-09-17-1455-FE. Epub 2018 Jan 5.
Downy mildews are plant pathogens that damage crop quality and yield worldwide. Among the most severe and notorious crop epidemics of downy mildew occurred on grapes in the mid-1880s, which almost destroyed the wine industry in France. Since then, there have been multiple outbreaks on sorghum and millet in Africa, tobacco in Europe, and recent widespread epidemics on lettuce, basil, cucurbits, and spinach throughout North America. In the mid-1970s, loss of corn to downy mildew in the Philippines was estimated at US$23 million. Today, crops that are susceptible to downy mildews are worth at least $7.5 billion of the United States' economy. Although downy mildews cause devastating economic losses in the United States and globally, this pathogen group remains understudied because they are difficult to culture and accurately identify. Early detection of downy mildews in the environment is critical to establish pathogen presence and identity, determine fungicide resistance, and understand how pathogen populations disperse. Knowing when and where pathogens emerge is also important for identifying critical control points to restrict movement and to contain populations. Reducing the spread of pathogens also decreases the likelihood of sexual recombination events and discourages the emergence of novel virulent strains. A major challenge in detecting downy mildews is that they are obligate pathogens and thus cannot be cultured in artificial media to identify and maintain specimens. However, advances in molecular detection techniques hold promise for rapid and in some cases, relatively inexpensive diagnosis. In this article, we discuss recent advances in diagnostic tools that can be used to detect downy mildews. First, we briefly describe downy mildew taxonomy and genetic loci used for detection. Next, we review issues encountered when identifying loci and compare various traditional and novel platforms for diagnostics. We discuss diagnosis of downy mildew traits and issues to consider when detecting this group of organisms in different environments. We conclude with challenges and future directions for successful downy mildew detection.
霜霉病是一种植物病原体，会在全球范围内损害作物的质量和产量。19 世纪 80 年代中期，葡萄霜霉病在世界范围内爆发，这是最严重和最臭名昭著的作物疫病之一，几乎摧毁了法国的葡萄酒行业。此后，非洲的高粱和小米、欧洲的烟草以及最近北美的生菜、罗勒、瓜类和菠菜都爆发了多次此类疫病。20 世纪 70 年代，菲律宾因霜霉病而损失的玉米估计价值 2300 万美元。如今，易感染霜霉病的作物至少为美国经济带来了 75 亿美元的价值。尽管在美国和全球范围内，霜霉病会造成毁灭性的经济损失，但由于该病原体难以培养和准确鉴定，该病原体群仍未得到充分研究。早期在环境中检测到霜霉病对于确定病原体的存在和身份、确定杀菌剂抗性以及了解病原体种群的扩散方式至关重要。了解病原体何时何地出现也对于确定关键控制节点以限制其传播和遏制其种群非常重要。减少病原体的传播还可以降低性重组事件的可能性，并阻止新的毒力菌株的出现。检测霜霉病的一个主要挑战是，它们是专性病原体，因此无法在人工培养基中进行培养以鉴定和保存标本。然而，分子检测技术的进步为快速且在某些情况下相对廉价的诊断提供了希望。在本文中，我们讨论了可用于检测霜霉病的最新诊断工具。首先，我们简要描述了霜霉病的分类学和用于检测的遗传基因座。接下来，我们综述了在鉴定基因座时遇到的问题，并比较了各种传统和新型诊断平台。我们讨论了霜霉病特征的诊断以及在不同环境中检测该病原体时需要考虑的问题。最后，我们总结了成功检测霜霉病的挑战和未来方向。
