Pythium porphyrae, is a parasitic species of oomycete in the family Pythiaceae.[5] It is the cause of red rot disease or red wasting disease, also called akagusare (赤ぐされ) in Japanese.[1][6] The specific epithetporphyrae (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.[7] However, many of its hosts have been moved from the genus Porphyra to Pyropia.
Economic impact
Pythium porphyrae can destroy an entire crop of nori within three weeks.[8][9][6] It prefers low salinity and warm water (24-28 °C).[10][11][12][6] It will only grow in the 15-35 °C range.[13] Mild winters correlate with higher infestations and lower crop yields,[14] possibly due to decreased temperatures inducing the development of sex organs in the oomycete.[1] Losses can be combated by destroying diseased fronds and exposing thalli to the air for 3–4 hours daily.[6] The oospores can be spread in contaminated organic matter and the sporangia can spread through the water.[15]
Its hyphae can grow up to 4.5 μm wide,[13][15] and are not septate.[1] On algae, the hyphae will extend through the cell wall.[1] It does not have haustoria not chlamydospores.[15] The appressoria are club-shaped.[15] It has sporangia that are unbranched, filamentous,[1][3] and non-inflated,[3] typically forming 6-17 zoospores per vesicle.[1][13][15]Encysted zoospores are 8-12 μm in diameter.[15] Hyphal swellings are intercalary and globose, from 12-28 μm in diameter.[15]Oogonia average 17 μm in diameter and are also intercalary and globose, but rarely are terminal.[13][15] In each oogonium are 1-2 diclinousantheridia[3][15][1] coming out far away from the oogonial stalk.[13] The antheridia's cells are clavate (club shaped) or globose.[1][13][15] The antheridia will be apical to the oogonial wall.[15] Sometimes there will be two antheridial cells on one stalk.[13] The yellowishoospores average 15 μm in diameter, have thick (~2 μm) walls, and are plerotic (fill the whole oogonium).[13][15]Conidia are spherical at 8.8-30.8 μm diameter, but rarely produced.[1]
Pythium porphyrae shares many physical traits with P. marinum and P. monospermum,[13] and appears to be most closely related to P. adhaerens.[2][3] However it has up to four diclinous antheridia and sometimes two antheridial cells per stalk; P. monospermum has 1-4 either diclinous or monoclinous antheridia and P. marinum has only a single diclinous antheridium.[13]P. monospermum and P. marinum also have oogonia terminally on short branches, yet in P. porphyrae they tent to be intercalary.[13]
A 2017 study of Pythium species in Clade A showed the following phylogenetic tree.[2] It further demonstrated that P. porphyrae and P. chondricola are the same species.[2][3]P. adhaerens may also be conspecific based solely on genetic comparison, but showed a number of physical differences that show it may be a separate but very closely related species.[2]
^Griffith, Chuck (2005). "Dictionary of Botanical Epithets". Dictionary of Botanical Epithets. Retrieved 3 October 2017. purple-red porphyra porphyr noun/f πορφυρα the purple-fish or the dye that was made from it
^Arasaki, S. (1956). "The diseases of asakusanori and their control" [The diseases of asakusanori and their control]. 病蟲害雜誌 (Plant Protection) (in Japanese). 10: 243–6. OCLC41036343.
^ARASAKI, S. (1962). Studies on the artificial culture of Porphyra tenera Kjellm. 111. On the red wasting disease of Porphyra, especially on the physiology of the causal fungus Pythium sp.nov. [In Japanese, English summary.] Journal of the Agricultural Laboratory, Abiko, Japan. Central Research Institute of Electric Power Industry 3, 87-93
^ abArasaki, Satoshi (1947). "アサクサノリめ腐敗病に關する研究" [Studies on the Wasting Disease of the Cultured Lavers (Porphyra tenera)]. Nippon Suisan Gakkaishi (Bulletin of the Japanese Society of Scientific Fisheries) (in Japanese). 13 (3): 74–90. doi:10.2331/suisan.13.74. ISSN0021-5392.
^SUTO, S., SAITO, Y., AKIYAMA, K. & UMEBAYASHI, 0. (1972). Text Book of Diseases and their Symptoms in Porphyra. [In Japanese.] Contribution E, Number I 8 of Tokai Regional Fisheries Research Laboratory, Japan. 37 pp.
^SAKURAI, Y., AKIYAMA, K. & SATO, S. (1974). On the formation and the discharge of zoospores of Pythium porphyrae in experimental conditions. [In Japanese, English summary.] Bulletin of the Tohoku Regional Fisheries Research Laboratory (33), I 19-27.
^Suto, S (1953). "Seaweed production and phycological research in Japan". Proceedings of the 1st International Seaweed Symposium, Edinburgh, 14–17 July 1952: 96–99. OCLC22404162.
^ abcdefghijklmnopqrstuvwxyzaaabacadaeafSpencer, M. A. (2004). "Pythium porphyrae. (Descriptions of Fungi and Bacteria)". IMI Descriptions of Fungi and Bacteria. 162 (Sheet 1617). Retrieved 10 October 2017. A description is provided for Pythium porphyrae. Information is included on the disease caused by the organism, its transmission, geographical distribution, and hosts. DISEASES: Red-rot disease, red-wasting disease. HOSTS: Bangia atropurpurea, Callophyllis adhaerens, Polyopes affinis (syn
^"Turkish Washcloth or Black Tar Spot". Slater Museum of Natural History. Slater Museum of Natural History. Marine Panel. Tacoma, WA: University of Puget Sound. 2017. Retrieved 6 October 2017.
