Biology Reference
In-Depth Information
11.2.3.2 Fungal and Oomycete Parasites and/or Pathogens
Considering the vast lack of knowledge and the importance to seaweed aquaculture,
the significance of oomycetes and fungi infecting marine algae was outlined in two
recent reviews (Gachon et al.
2010
; Li et al.
2010
) and in a topic chapter
(Strittmatter et al.
2009
). A comprehensive report (Li et al.
2010
) included 15
species of oomycetes, six species of chytrids, 31 Ascomycota species, and one
species of mitosporic fungi. In nature, both the oomycetes and chytrids frequently
occurred and induced prevalence of disease, which could destroy the populations of
host plants greatly. However, the Ascomycota growing on algae have never
occurred as epidemics so far. Further investigations are required in this field, such
as performing tests to satisfy Koch's postulates, investigations of host specificity,
interactions between host and parasite, and the potential effects of environmental
factors on occurrence of a disease.
Despite their small size and ephemeral life stages, filamentous brown algae are
plagued by various pathogens, including viruses (M
uller et al.
1998
), which are not
commented in this chapter, which focuses on eukaryotic parasites. In addition,
numerous historical records described ectocarpoids with abnormal sporangia or
vegetative cells suspected to contain unknown parasites (Rattray
1885
;M
€
uller et al.
1998
). The oomycete
Eurychasma dicksonii
has been described mainly in wild
populations of
Pylaiella littoralis
(K
€
uller
1999
), but it displays a broad
host range and infects various brown algae, including
Ectocarpus
(M
upper and M
€
€
uller et al
.
1999
), in which it was initially described by Wright (
1879
).
E. dicksonii
belongs to
the most early branching clade within the oomycete lineage (Sekimoto et al.
2008
;
K
€
upper et al.
2006
).
€
11.3 Cross-Talk Between Host and Colonizers and Defenses
Against Colonization
Resistance against epibionts can be generally mediated by either structural or
chemical means, with both mechanisms interfering with the settling and penetration
of spores or propagules. Algal basiphytes can exhibit a variety of defenses against
attachment and colonization (Ducker and Knox
1984
), including rapid growth by
having ephemeral life histories (den Hartog
1972
), changes in pH at the plant
surface, and sloughing of outer cell walls
(Ulva,
coralline algae) (Filion-Myklebust
and Norton
1981
; Johansen 1981; Moss
1982
; Steneck
1982
; Russell and Veltcamp
1984
).
Chondrus crispus
will shed outer layers of cell wall and cuticule
glycoproteins (Craigie et al.
1992
), whereas
Ascophyllum
produces slime and
may lose an entire epidermal layer.
Eucheuma,
a carrageenophyte, has a slimy
surface during growth and is free of epiphytes, but when it ceases growth, the plant
surface loses that slime and becomes epiphytized (Dawes et al.
2000
). Survivorship
of epiphyte recruits may also be related to the host, as epiphytes may be less
