Diseases, pathogens and parasites of Undaria pinnatifida

Taxa belonging to the Bigyra, including species of Olpidiopsis, Eurychasmidium, Petersenia,
Pontisma have been described from a number of hosts (e.g. Sparrow 1934, 1936; Aleem
1950b, c, 1952b; Feldmann & Feldmann 1967; Whittick & South 1972; van der Meer &
Pueschel 1985; Molina 1986; West et al. 2006).
The geographic coverage of studies on marine fungi in red algae is very incomplete and
currently reflects the regions where the key workers have been based. For example, the
studies reporting on Chytridium and Rhizophidium species are Sparrow (1936) in the northwest
Atlantic, Aleem (1952b) in Sweden and Raghukumar (1987a, b) in India. Similarly, the
only papers focusing on thraustochytrids are Quick (1974) in Florida, USA and Raghukumar
(1986b, 1987a, b) and Raghukumar et al. (1992) in India.
Other algae
Parasitic red algae
More research has been published on red algal parasites than on any other area of algal
diseases, pathogens and parasites considered in this study. Red algal parasites are quite
common, making up to 15% of all named red algal genera, although this figure needs revising
as the last comprehensive review of red algal parasites was by Goff (1982). Red algal
parasitism is the most specific symbiosis between two red algae: parasitic red algae are
symbionts that have a reduced size and are either completely colourless or have reduced
pigmentation and must rely on their nutrition from their host. In the past two decades a lot has
been learned about the origin of red algal parasites (Goff et al. 1996, 1997, Zuccarello et al.
2004), their development (Goff & Coleman 1984, 1985; Goff & Zuccarello 1994; Zuccarello
& West 1994a), and host specificity (Nonomura & West 1981b; Goff & Zuccarello 1994;
Goff et al. 1997, Zuccarello & West 1994b, c). However only a very small percentage of
these parasitic red algae have been studied in any detail beyond their first description.
The host specificity and evolutionary studies are especially revealing in the context of algal
pathogenicity and the effects of new interactions. Evolutionary studies have revealed that
many red algal parasites are derived directly from their hosts (Goff et al. 1996, 1997). This
was able to be understood once the development of parasites on their hosts was elucidated
(Goff & Coleman 1984, 1985; Goff & Zuccarello 1994), showing that their unusual
development was very similar to post-fertilisation processes in red algae. Early in their
development, either upon spore germination or soon after, red algal parasites transfer into a
host cell the cytoplasm of an entire cell, or the complete contents of a spore. This
“transforms” the host cell as it now develops as a parasite, presumably under the control of
the transferred parasite nucleus, producing more parasite nuclei and dividing to form new
parasite cells. Finally reproductive structures are formed which eventually will lead to new
infections. These developmental processes are similar to the nuclear transfer and subsequent
events that occur during post-fertilisation development in most red algae, and thus red algal
parasitism has been hypothesised to have been derived from these post-fertilisation processes
(Goff et al. 1996, 1997).
Nuclear transfer places constraints on the host range of red algal parasites. The majority of red
algal parasites appear to be host specific, although this could be an artifact of naming new
parasite species when parasites are found on new hosts. However, when host range has been
tested in culture it has been shown to be quite limited (e.g. Goff & Zuccarello 1994).
Occasionally parasites can grow on closely related host species (Nonomura & West 1981b;
Zuccarello & West 1994b, c), but often this alternate host development is reduced and
reproductive structures are not produced. Thus evidence to date supports a high level of host
specificity. However, on an evolutionary time scale this is shown not to be so, as “host
jumps” have been discovered using molecular markers. Parasites of the Gigartinales family
MAF Biosecurity New Zealand Diseases, pathogens and parasites of Undaria pinnatifida • 23