New paper in Proceedings B released last Wednesday

Restoration of seagrass beds threatened by family member potato blight

We discovered that two family members of the potato blight – Phytophthora gemini and Halophytophthora sp. Zostera – strongly reduce germination of seagrass seeds. These two pathogens are new to seagrasses and discovered as a result of disappointing results in seagrass restoration experiments in the Dutch Wadden Sea. Additional research showed that these pathogens not only inhabit Dutch waters, but are also present in many other seagrass beds throughout Europe and even in the US. This means that seagrass restoration by seeds is threatened on a global scale.

 Potato Blight

The most infamous member of the Phytophthora-family, Phytophthora infestans causes late blight in potatoes. This vigorous pathogen causes billions of euros of damage to European agricultural crops and affected 1million Irish due during the great famine in 19th century Ireland. Other family members also affect natural ecosystems, such as Californian oak forests and Australian heathland. In total, about 100 species are known from this family, mostly pathogenic to terrestrial plants. Surprisingly little is known about Phytophthora species in seawater, although marine plants such as seagrasses, mangroves and salt marsh plants form the foundation of many coastal ecosystems. Today, an international team, led by us published a study showing the danger of marine Phytophthora species to seagrasses. The study is published in a renowned journal, Proceedings of the Royal Society B.

 Infected seagrass seeds

Researchers collected seagrass seed material from five European countries (the Netherlands, Germany, Denmark, Sweden, France) and from Chesapeake Bay in the US. Seed from all locations appeared to be infected by either a Phytophthora species or related Halophytophthora species, which, up to now, were only known as a plant decomposer on dead mangrove leaves. Principal Investigator, Laura Govers (Radboud University, University of Groningen) explains: “In a lab experiment we subsequently tested germination of infected seeds. Infected seeds showed 6x reduced germination and only 3-4% of all infected seeds germinated.”

Seagrass restoration

Vegetated coastal ecosystems are rapidly disappearing on a global scale. The Dutch Wadden Sea once harbored vast subtidal seagrass meadows (150 km2) that have completely disappeared after the 1930s and have never recovered. These meadows highly contributed to local biodiversity and functioned as nurseries for herring and anchovies. They also provided coastal protection by wave attenuation and by preventing sediment erosion through root mat formation. Therefore, restoration efforts are trying to restore Dutch seagrass beds. Currently, seed material from the German barrier island Sylt is being used for restoration and almost 100% of all seeds is infected by Phytophthora. Thus, researchers are now looking for a solution to reduce infection in order to improve restoration success.

This study is the result of a collaboration between Radboud University, University of Groningen, Royal Netherlands Institute for Sea Research (NIOZ), the Dutch Food and Safety Authority (NVWA), the Fieldwork Company and the Virginia Institute of Marine Science. The study was funded by Natuurmonumenten, Rijkswaterstaat and the Dutch Food and Safety authority (NVWA).


Halophytophthora sp. Kers (c) Johan Meffert
Halophytophthora isolated from seagrass seed



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