Pythium porphyrae
Scientific classification
Domain:	Eukaryota
Clade:	Diaphoretickes
Clade:	SAR
Clade:	Stramenopiles
Phylum:	Oomycota
Order:	Peronosporales
Family:	Pythiaceae
Genus:	Pythium
Species:	P. porphyrae
Binomial name
Pythium porphyrae M. Takah. & M. Sasaki, 1977 [1]
Synonyms [2] [3] [4]
Pythium chondricola De Cock, 1986

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 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. ^[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]

Description

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]

Ecology

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]

Taxonomy

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]

See also

• Pythium in turfgrass
• Pythiosis

References

External links

• Data related to Pythium porphyrae at Wikispecies