Pythium porphyrae

Pythium porphyrae can destroy an entire crop of nori within 3 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]

Pythium porphyrae has a mycelial thallus that is eucarpic, meaning only part of the thallus turns into sporangia.[15] It is primarily a facultative parasite of algae, but can also be saprobic.[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 diclinous antheridia[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 yellowish oospores 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]

In a laboratory it will grow 5 mm per day[3] on seawater-cornmeal agar with low aerial mycelium[15] and colorless colonies,[1] but will not grow at all on potato-carrot agar.[13]

Pythium porphyrae has been found in Japan,[1] Netherlands, New Zealand,[2] and Korea, but this range is likely underreported.[15] It has a parasitic relationship with the following hosts. Though some species of Pyropia and Porphyra are susceptible to infection in their gametophytic phase, they are resistant in their Conchocelis (sporophytic) phase.[2]

• Bangia atropurpurea[15]
• Callophyllis adhaerens[15]
• Chondrus crispus[2][3]
• Gelidium elegans[15]
• Gloiosiphonia capillaris[15]
• Gracilaria spp.[15]
• Grateloupia turuturu[15]
• Griffithsia subcylindrica[15]
• Lomentaria hakodatensis[15]
• Mastocarpus papillatus[16]
• Polyopes affinis (Carpopeltis affinis)[15]
• Polysiphonia morrowii[15]
• Pterocladiella capillacea[15]
• Pyropia cinnamomea[2]
• Pyropia plicata[2]
• Pyropia suborbiculata[2]
• Pyropia tenera[2][10][15][1]
• Pyropia virididentata[2]
• Pyropia yezoensis[13][3][15][1]
• Rhodymenia intricata[15]
• Stylonema alsidii[15]
• Wrangelia tanegana[15]

A 2005 study concerning a case of Pythiosis from a related species (P. insidiosum) indicated that P. porphyrae is related to P. dissotocum, P. myriotylum, P. volutum, and P. vanterpoolii.[17]

In 2004, molecular analysis of Pythium determined that P. porphyrae is in "Clade A" along with P. adhaerens, P. deliense, P. aphanidermatum, and P. monospermum[3] Clade A has two clusters, and P. porphyrae shares one with the species also originating on algae, P. adhaerens.[3]

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]

• Pythium in turfgrass
• Pythiosis

• Data related to Pythium porphyrae at Wikispecies