Diseases, pathogens and parasites of Undaria pinnatifida

3.2.2. Known pathogens in native range
Viruses
There are no virus diseases known from Undaria pinnatifida or other Undaria species.
Bacteria
Gram-negative bacteria such as Aeromonas, Flavobacterium, Moraxella, Pseudomonas, and
Vibrio are associated with the "spot-rotting" disease ("Anaaki sho"; Kimura et al. 1976) and
the so-called "shot hole disease" (Tsukidate 1991) in Japanese Undaria. Severe outbreaks of
infections with Vibrio especially affect young sporophytes ("sporelings") of U. pinnatifida
(Anon. 1991). The "shot hole disease" is characterised by brown spots appearing on the
thallus blade near the midrib which subsequently fuse together and spread onto the pinnate
part of the blade (Tsukidate 1991).
The "green spot disease/rot" caused by unspecified bacteria in Japan (Ishikawa & Saga 1989;
Vairappan et al. 2001) and South Korea (Kang 1982) manifests with similar symptoms, first
as green spots of rotting host tissue that result in small holes with green margins, and in the
distal parts of the frond these enlarge and finally coalesce, accelerating the decay of the frond
(Kang 1982). Japanese Undaria is furthermore infected by an unspecified bacterium causing
the "yellow hole disease" (Ishikawa & Saga 1989; Vairappan et al. 2001) and “spot-rotting”
disease (Kito et al. 1976).
Bacteria enter the thallus of U. pinnatifida through openings like dead mucilage channels, and
digest cells and cell walls in the medulla. Cells of the cortex and meristoderm show ultrastructural
damage (e.g. vacuolation of the dictyosome). When the host cells die, the disease
symptoms become macroscopically visible (Kito et al. 1976).
In China, the bacterium Halomonas venusta has been identified as a causative agent in “spot
decay” (Ma et al. 1997a, b, 1998), and Vibrio logei in “green decay diseases” (Jiang et al.
1997) of U. pinnatifida.
Animals
Some small crustacean species are associated with diseases in Undaria: The “pin hole
disease” is caused by frond-mining nauplii of harpacticoid copepoda in Undaria from Japan
(Anon. 1991) and South Korea (Tsukidate 1991), e.g. by species such as Amenophia
orientalis, Parathalestris infestus, Scutellidium sp. (Ho & Hong 1988; Park et al. 1990; Anon.
1991; Rho et al. 1993; Shimono et al. 2004) and Thalestris sp. (Kang 1982).
Ceinina japonica, a gammeride amphipod from South Korea, invades the midrib of U.
pinnatifida through the holdfast and bores a tunnel which may cause the longitudinal
separation of the entire frond through the midrib. In heavily damaged thalli the holdfast may
depart from the substrate (Kang 1982).
Fungi
A fungal infection occurs in Undaria from Japan, the so-called “chytrid blight” (Tsukidate
1991). The name implies that this disease is caused by a true fungus of the class
Chytridiomycetes, however, the culprit is an oomycete of the genus Olpidiopsis (Akiyama
1977a). The fungus affects sporophytes, where it grows inside host cells, killing them slowly.
Infected thalli gradually loose colour and disintegrate, juvenile thalli suffer severe damage or
eventually die.
12 • Diseases, pathogens and parasites of Undaria pinnatifida MAF Biosecurity New Zealand