Advances in diagnostics of downy mildews: Lessons learned from other oomycetes and future challenges

Authors: CRANDALL, S - California State University; RAHMAN, A - North Carolina State University; QUESADA-OCAMPO, LINA - North Carolina State University; Martin, Frank; BILODEAU, GUILLAUME - Canadian Food Inspection Agency; MILES, TIMOTHY - California State University

Submitted to: Plant Disease
Publication Type: Review Article
Publication Acceptance Date: 10/26/2017
Publication Date: 1/22/2018
Citation: Crandall, S.G., Rahman, A., Quesada-Ocampo, L.M., Martin, F.N., Bilodeau, G.J., Miles, T.D. 2018. Advances in diagnostics of downy mildews: Lessons learned from other oomycetes and future challenges. Plant Disease. 102(2):265-275. https://doi.org/10.1094/PDIS-09-17-1455-FE.
DOI: https://doi.org/10.1094/PDIS-09-17-1455-FE

Interpretive Summary: 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 a wide range of crops worldwide. Today, crops that are susceptible to downy mildews are worth at least $7.5 billion dollars 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 grow and accurately identify. This review will cover the current state of research and suggestions for future directions.

Technical Abstract: 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.