218
A. D. BONEY
Mowat (1963, 1964) commented on the auxin and gibberellin content of
plants utilized as dried seaweed meals.
Whilst in general the value of using the large brown seaweeds as
manures have long been realized in coastal areas, more recent work has
indicated the ways in which the eBciency of the soil dressing can be
markedly improved, and the methods of liquefaction offer a potential
source of exploitation which could be of very marked value in horticultural practices. The fact that not all seaweeds are of equivalent value
has been well underlined.
X. FACTORS INFLUENCING THE SEAWEED CROP
A. Diseases of economically important seaweeds
1. Fungal diseases
There have been some reports in recent years on the effects of
fungi on Porphyra. Thus Arasaki (1947) described a Pythium disease of
Porphyra tenera which destroyed significant quantities of the population and was a potential threat to its large-scale culture. Optimum
conditions for growth of the fungus were a sea temperature of 2Oo-24"C,
and salinities in the range of 4 to So/,,. Fungal infection in the early
fall could be followed by a second I' wave " of the disease. The disease
was not readily observed on immature thalli; Johnson and Sparrow
(1961) questioned whether the fungal growth was more in the nature
of an invasion of senescent Porphyra plants. Suto (1952) observed that
fungal infection of Porphyra tended to be more prominent during mild
winters when the sea temperature was higher than average. A more
recent report of Pythium infection has been made by Tsuruga and
Nitta (1960). Chytrid infection of the Porphyra thallus has also been
reported (Arasaki, 1960; Arasaki et al., 1960). This infection has been
frequently observed in the culture fields in the seas of central and
northern Japan during the main growing season, November to March.
An intracellular species of Olpidiopsis has been identified as the
causative agent, infecting the host plant at all stages in its life-history
except the Conchocelis-phase. Whilst damage to mature fronds is slight
it could have more severe effects on sporelings and young thalli.
Arasaki et al. (1960) have reported that gall-like growths can result from
chytrid infection. Suto (1962) reports that fungal disease of Porphyra
on " hibi " may be controlled by exposure of the plants to the air for
daily periods of 3 hours. Laver diseases are known to be more prevalent
when the plants are grown in deeper water (Kurogi, 1963b).
Other diseased conditions of uncertain cause have been reported.
A. D. BONEY
Mowat (1963, 1964) commented on the auxin and gibberellin content of
plants utilized as dried seaweed meals.
Whilst in general the value of using the large brown seaweeds as
manures have long been realized in coastal areas, more recent work has
indicated the ways in which the eBciency of the soil dressing can be
markedly improved, and the methods of liquefaction offer a potential
source of exploitation which could be of very marked value in horticultural practices. The fact that not all seaweeds are of equivalent value
has been well underlined.
X. FACTORS INFLUENCING THE SEAWEED CROP
A. Diseases of economically important seaweeds
1. Fungal diseases
There have been some reports in recent years on the effects of
fungi on Porphyra. Thus Arasaki (1947) described a Pythium disease of
Porphyra tenera which destroyed significant quantities of the population and was a potential threat to its large-scale culture. Optimum
conditions for growth of the fungus were a sea temperature of 2Oo-24"C,
and salinities in the range of 4 to So/,,. Fungal infection in the early
fall could be followed by a second I' wave " of the disease. The disease
was not readily observed on immature thalli; Johnson and Sparrow
(1961) questioned whether the fungal growth was more in the nature
of an invasion of senescent Porphyra plants. Suto (1952) observed that
fungal infection of Porphyra tended to be more prominent during mild
winters when the sea temperature was higher than average. A more
recent report of Pythium infection has been made by Tsuruga and
Nitta (1960). Chytrid infection of the Porphyra thallus has also been
reported (Arasaki, 1960; Arasaki et al., 1960). This infection has been
frequently observed in the culture fields in the seas of central and
northern Japan during the main growing season, November to March.
An intracellular species of Olpidiopsis has been identified as the
causative agent, infecting the host plant at all stages in its life-history
except the Conchocelis-phase. Whilst damage to mature fronds is slight
it could have more severe effects on sporelings and young thalli.
Arasaki et al. (1960) have reported that gall-like growths can result from
chytrid infection. Suto (1962) reports that fungal disease of Porphyra
on " hibi " may be controlled by exposure of the plants to the air for
daily periods of 3 hours. Laver diseases are known to be more prevalent
when the plants are grown in deeper water (Kurogi, 1963b).
Other diseased conditions of uncertain cause have been reported.