Pythium porphyrae
| Pythium porphyrae | |
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Not evaluated (IUCN 3.1)
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| Scientific classification | |
| Phylum: | Heterokontophyta |
| Class: | Oomycota |
| Order: | Peronosporales |
| Family: | Pythiaceae |
| Genus: | Pythium |
| Species: | P. porphyrae |
| Binomial name | |
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Pythium porphyrae M. Takah. & M. Sasaki, 1977 |
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| Synonyms | |
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Pythium porphyrae, is a parasitic species of oomycete in the Pythiaceae family. It is the cause of red rot disease or red wasting disease, also called akagusare (赤ぐされ) in Japanese. The specific epithet porphyrae (πορφυρα) stems from the genus of one of its common hosts, Porphyra, and the purple-red color of the lesions on the thallus of the host. However, many of its hosts have been moved from the Porphyra genus to Pyropia.
P. porphyrae can destroy an entire crop of nori within 3 weeks. It prefers low salinity and warm water (24-28 °C). It will only grow in the 15-35 °C range. Mild winters correlate with higher infestations and lower crop yields, possibly due to decreased temperatures inducing the development of sex organs in the oomycete. Losses can be combated by destroying diseased fronds and exposing thalli to the air for 3–4 hours daily. The oospores can be spread in contaminated organic matter and the sporangia can spread through the water.
P. porphyrae has a mycelial thallus that is eucarpic, meaning only part of the thallus turns into sporangia. It is primarily a facultative parasite of algae, but can also be saprobic.
Its hyphae can grow up to 4.5 µm wide, and are not septate. On algae, the hyphae will extend through the cell wall. It does not have haustoria not chlamydospores. The appressoria are club-shaped. It has sporangia that are unbranched, filamentous, and non-inflated, typically forming 6-17 zoospores per vesicle.Encysted zoospores are 8-12 µm in diameter. Hyphal swellings are and globose, from 12-28 µm in diameter.Oogonia average 17 µm in diameter and are also intercalary and globose, but rarely are terminal. In each oogonium are 1-2 diclinous antheridia coming out far away from the oogonial stalk. The antheridia's cells are clavate (club shaped) or globose. The antheridia will be apical to the oogonial wall. Sometimes there will be two antheridial cells on on stalk. The yellowish oospores average 15 µm in diameter, have thick (~2 µm) walls, and are plerotic (fill the whole oogonium).Conidia are spherical at 8.8-30.8 μm diameter, but rarely produced.
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