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The spores of Phytophthora: weapons of the plant destroyer

Subjects

Abstract

Members of the genus Phytophthora are among the most serious threats to agriculture and food production, causing devastating diseases in hundreds of plant hosts. These fungus-like eukaryotes, which are taxonomically classified as oomycetes, generate asexual and sexual spores with characteristics that greatly contribute to their pathogenic success. The spores include survival and dispersal structures, and potent infectious propagules capable of actively locating hosts. Genetic tools and genomic resources developed over the past decade are now allowing detailed analysis of these important stages in the Phytophthora life cycle.

Key Points

  • Although many researchers would consider oomycetes as fungi, officially oomycetes such as the genus Phytophthora are classified taxonomically in the Straminipilia kingdom, with diatoms and brown algae their nearest taxonomic neighbours.

  • The phytopathogenic Phytophthora are economically significant pathogens, with Phytophthora infestans, the causative agent of potato blight, responsible for an estimated US$5 billion of damage each year.

  • New techniques for genetic, genomic and proteomic analyses were initially applied to more tractable mycological systems such as the basidiomycetes and ascomycetes. However, in the past decade great advances have been made in developing these analytical tools for oomycetes, with Phytophthora leading the way.

  • In this article, the authors provide an overview of the results obtained in molecular studies on Phytophthora spores from the past 4 or 5 years. Several spore-specific genes have now been identified. Further analysis of the different stages of the Phytophthora life cycle might eventually lead to the development of effective strategies for controlling Phytophthora disease.

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Acknowledgements

We thank our colleagues that have helped to develop Phytophthora species into tractable experimental systems. Our work related to the topic has been supported by the US Department of Agriculture National Research Initiative, the National Science Foundation of the United States, Syngenta and the University of California Industry–University Cooperative Research Program.

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Competing interests

The authors declare no competing financial interests.

Correspondence to Howard S. Judelson.

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Glossary

SAPROPHYTE

An organism that feeds on dead organic matter.

SPORANGIUM

A sac-like structure that is capable of converting its cytoplasm into multiple spores.

ZOOSPORES

Motile, wall-less spores, specialized for dispersal.

OOSPORES

Non-motile, sexual spores.

CHLAMYDOSPORES

Thick-walled asexual reproductive structures that are found in many Phytophthora species, but not Phytophthora infestans.

SPORANGIOPHORE

A specialized hypha that has a sporangium.

CADUCOUS

In caducous species the sporangia can detach from the hypha for dispersal.

STOMATE

An epidermal pore on a leaf or stem that allows the passage of gases and water vapour.

LENTICEL

An opening in the corky skin of plants that enables gas and vapour to move to and from interior tissues.

COENOCYTIC

Non-septate, with nuclei residing in a common cytoplasm.

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Further reading

Figure 1: Course of infection by Phytophthora infestans.
Figure 2: Stages of the spore cycles of Phytophthora infestans.
Figure 3: Promoter activation during asexual sporulation and germination.
Figure 4: Sex in Phytophthora.