Pythium porphyrae

P. porphyrae can destroy an entire crop of nori within 3 weeks.[9][10][7] It prefers low salinity and warm water (24-28 °C).[11][12][13][7] It will only grow in the 15-35 °C range.[14] Mild winters correlate with higher infestations and lower crop yields,[15] possibly due to decreased temperatures inducing the development of sex organs in the oomycete.[2] Losses can be combated by destroying diseased fronds and exposing thalli to the air for 3–4 hours daily.[7] The oospores can be spread in contaminated organic matter and the sporangia can spread through the water.[16]

P. porphyrae has a mycelial thallus that is eucarpic, meaning only part of the thallus turns into sporangia.[16] It is primarily a facultative parasite of algae, but can also be saprobic.[16]

Its hyphae can grow up to 4.5 µm wide,[14][16] and are not septate.[2] On algae, the hyphae will extend through the cell wall.[2] It does not have haustoria not chlamydospores.[16] The appressoria are club-shaped.[16] It has sporangia that are unbranched, filamentous,[2][4] and non-inflated,[4] typically forming 6-17 zoospores per vesicle.[2][14][16] Encysted zoospores are 8-12 µm in diameter.[16] Hyphal swellings are intercalary and globose, from 12-28 µm in diameter.[16] Oogonia average 17 µm in diameter and are also intercalary and globose, but rarely are terminal.[14][16] In each oogonium are 1-2 diclinous antheridia[4][16][2] coming out far away from the oogonial stalk.[14] The antheridia's cells are clavate (club shaped) or globose.[2][14][16] The antheridia will be apical to the oogonial wall.[16] Sometimes there will be two antheridial cells on one stalk.[14] The yellowish oospores average 15 µm in diameter, have thick (~2 µm) walls, and are plerotic (fill the whole oogonium).[14][16] Conidia are spherical at 8.8-30.8 μm diameter, but rarely produced.[2]

P. porphyrae shares many physical traits with P. marinum and P. monospermum,[14] and appears to be most closely related to P. adhaerens.[3][4] 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.[14] P. monospermum and P. marinum also have oogonia terminally on short branches, yet in P. porphyrae they tent to be intercalary.[14]

In a laboratory it will grow 5 mm per day[4] on seawater-cornmeal agar with low aerial mycelium[16] and colorless colonies,[2] but will not grow at all on potato-carrot agar.[14]

P. porphyrae has been found in Japan,[2] Netherlands, New Zealand,[3] and Korea, but this range is likely underreported.[16] 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.[3]

• Bangia atropurpurea[16]
• Callophyllis adhaerens[16]
• Chondrus crispus[3][4]
• Gelidium elegans[16]
• Gloiosiphonia capillaris[16]
• Gracilaria spp.[16]
• Grateloupia turuturu[16]
• Griffithsia subcylindrica[16]
• Lomentaria hakodatensis[16]
• Mastocarpus papillatus[17]
• Polyopes affinis (Carpopeltis affinis)[16]
• Polysiphonia morrowii[16]
• Pterocladiella capillacea[16]
• Pyropia cinnamomea[3]
• Pyropia plicata[3]
• Pyropia suborbiculata[3]
• Pyropia tenera[3][11][16][2]
• Pyropia virididentata[3]
• Pyropia yezoensis[14][4][16][2]
• Rhodymenia intricata[16]
• Stylonema alsidii[16]
• Wrangelia tanegana[16]

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.[18]

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[4] Clade A has two clusters, and P. porphyrae shares one with the species also originating on algae, P. adhaerens.[4]

A 2017 study of Pythium species in Clade A showed the following phylogenetic tree.[3] It further demonstrated that P. porphyrae and P. chondricola are the same species.[3][4] 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.[3]

• Pythium in turfgrass
• Pythiosis

• Data related to Pythium porphyrae at Wikispecies