Marine Fungal Diversity and Bioprospecting 2.4 Habitat Characteristics and Their Effect on Fungal Diversity 17
Part A | 2.4
Of the 150 species, more than 30 species of marine
fungi are found in the mangroves in the New World.
Only a few seem to be host specific [2.4]. For example, Avicennia germinans specifically acts as a host
for the fungal species Rhabdosphora avicenniae and
Mycosphaerella pneumatophorae, whereas Rhizophora
mangle forms another host for Didymosphaeria rhizophora and Leptosphaeria australensis. They are quite
abundant in mangroves due to the easy availability of
wood as their bait. Large numbers of fungi are found
on Avicennia marina, A. officinalis, Rhizophora mucronata, R. apiculata, and Sonneratia alba. The fungal
biodiversity in mangroves may reflect the age of the
plants. A well-developed mangrove habitat provides
a larger number of fungal species than new mangrove
sites.
2.3.3 Fungi as Endophytes
Fungal endophytes are microfungi, mostly belonging
to the family Ascomycetes. They colonize the internal
tissues of vascular plants without producing any apparent disease symptoms. Fungal endophytes are now
considered an important component of biodiversity. The
distribution of endophytic mycoflora differs with the
host. The fungal endophytes can modify the host plants
at genetic, physiological, and ecological levels. It has
been suggested that the association of fungi as endophytes with mangrove roots would confer protection
from adverse environmental conditions and would allow the latter to successfully compete with saprophytic
fungi that decompose senescent roots.
Mangroves are a special kind of host plant and also
an abundant resource for endophytic fungi diversity.
More than 200 species of endophytic fungi have been
isolated and identified from mangroves, this being the
second largest community of marine fungi. Most endophytic fungi have wide range of hosts, and a few
only have a single host. Although several temperate
plants have been studied for their endophyte assemblages, very few tropical plants have been screened
for endophytes [2.32, 33]. Recently, endophytic fungi
were isolated from mature green leaves of A. officinalis along the southeast coast of India and it was
observed that the occurrences of dominant endophytic
fungi are Rhizopus sp. (51:7%), Penicillium lividum
(45%), and A. ochraceus (45%). Species richness and
diversity are high in the leaves of R. mucronata, and
the most dominant endophytes are P. lividum (45%)
and sterile mycelia (40%). F. moniliforme (45%), Alternaria sp. (46:7%) are the dominant endophytes in
leaves of R. annamalayana [2.34]. However, the composition and dominant species on each mangrove plant
are different and their colonization varies with different parts (leaves, twigs, and stems), the age of the host
plants, and with the seasons [2.35].
Scientists have been astonished at the adaptation of
mangrove fungi in extreme environments and have suggested that fungi, in particular endophytes, are promising sources for screening new products. Sampling and
characterization of endophytic fungal diversity is an
emerging challenge and promises to lead to the discovery of new species, novel compounds, and a better
understanding of their role in ecosystems.
2.4 Habitat Characteristics and Their Effect on Fungal Diversity
Despite of the insufficiency of data, generalizations
have been made on habitat characteristics [2.2]. Five littoral mycogeographic zones such as arctic, temperate,
subtropical, tropical, and Antarctic zones, have been
proposed based on the sea-surface temperature. Temperature holds the first position among environmental
and biological factors controlling the distribution of marine fungi, and then come the availability of substrates
or hosts, salinity, hydrostatic pressure, and the availability of oxygen.
2.4.1 Effects of the Substratum
Marine fungi are commonly colonized in different
substrata, which includes leaves and drift mangrove
woods, Avicennia alba, Bruguiera cylindrica, and
Rhizphora apiculata [2.35–37]. An abundance of the
Hyphomycetes group of fungi on marine and mangrove
substrates has been reported [2.20]. This might be due
to the adaptation of their spores to the marine ecosystem by way of production of appendages, which provide
buoyancy in water, entrapment, and adherence to the
substrates, as reported in mangrove wood driftwood
and animal substrates [2.38–40]. In addition to the
above, Hyphomycetes also possess an enzyme producing ability and hence, they could potentially colonize
lignocellulosic woody substrates. Maximum diversity
of fungi on the woody litter of Rhizophora (64 spp.) and
Avicennia (55 spp.) are reported from the Godavari and
Krishna deltas of the east coast of India [2.41, 42]. The
Part A | 2.4
Of the 150 species, more than 30 species of marine
fungi are found in the mangroves in the New World.
Only a few seem to be host specific [2.4]. For example, Avicennia germinans specifically acts as a host
for the fungal species Rhabdosphora avicenniae and
Mycosphaerella pneumatophorae, whereas Rhizophora
mangle forms another host for Didymosphaeria rhizophora and Leptosphaeria australensis. They are quite
abundant in mangroves due to the easy availability of
wood as their bait. Large numbers of fungi are found
on Avicennia marina, A. officinalis, Rhizophora mucronata, R. apiculata, and Sonneratia alba. The fungal
biodiversity in mangroves may reflect the age of the
plants. A well-developed mangrove habitat provides
a larger number of fungal species than new mangrove
sites.
2.3.3 Fungi as Endophytes
Fungal endophytes are microfungi, mostly belonging
to the family Ascomycetes. They colonize the internal
tissues of vascular plants without producing any apparent disease symptoms. Fungal endophytes are now
considered an important component of biodiversity. The
distribution of endophytic mycoflora differs with the
host. The fungal endophytes can modify the host plants
at genetic, physiological, and ecological levels. It has
been suggested that the association of fungi as endophytes with mangrove roots would confer protection
from adverse environmental conditions and would allow the latter to successfully compete with saprophytic
fungi that decompose senescent roots.
Mangroves are a special kind of host plant and also
an abundant resource for endophytic fungi diversity.
More than 200 species of endophytic fungi have been
isolated and identified from mangroves, this being the
second largest community of marine fungi. Most endophytic fungi have wide range of hosts, and a few
only have a single host. Although several temperate
plants have been studied for their endophyte assemblages, very few tropical plants have been screened
for endophytes [2.32, 33]. Recently, endophytic fungi
were isolated from mature green leaves of A. officinalis along the southeast coast of India and it was
observed that the occurrences of dominant endophytic
fungi are Rhizopus sp. (51:7%), Penicillium lividum
(45%), and A. ochraceus (45%). Species richness and
diversity are high in the leaves of R. mucronata, and
the most dominant endophytes are P. lividum (45%)
and sterile mycelia (40%). F. moniliforme (45%), Alternaria sp. (46:7%) are the dominant endophytes in
leaves of R. annamalayana [2.34]. However, the composition and dominant species on each mangrove plant
are different and their colonization varies with different parts (leaves, twigs, and stems), the age of the host
plants, and with the seasons [2.35].
Scientists have been astonished at the adaptation of
mangrove fungi in extreme environments and have suggested that fungi, in particular endophytes, are promising sources for screening new products. Sampling and
characterization of endophytic fungal diversity is an
emerging challenge and promises to lead to the discovery of new species, novel compounds, and a better
understanding of their role in ecosystems.
2.4 Habitat Characteristics and Their Effect on Fungal Diversity
Despite of the insufficiency of data, generalizations
have been made on habitat characteristics [2.2]. Five littoral mycogeographic zones such as arctic, temperate,
subtropical, tropical, and Antarctic zones, have been
proposed based on the sea-surface temperature. Temperature holds the first position among environmental
and biological factors controlling the distribution of marine fungi, and then come the availability of substrates
or hosts, salinity, hydrostatic pressure, and the availability of oxygen.
2.4.1 Effects of the Substratum
Marine fungi are commonly colonized in different
substrata, which includes leaves and drift mangrove
woods, Avicennia alba, Bruguiera cylindrica, and
Rhizphora apiculata [2.35–37]. An abundance of the
Hyphomycetes group of fungi on marine and mangrove
substrates has been reported [2.20]. This might be due
to the adaptation of their spores to the marine ecosystem by way of production of appendages, which provide
buoyancy in water, entrapment, and adherence to the
substrates, as reported in mangrove wood driftwood
and animal substrates [2.38–40]. In addition to the
above, Hyphomycetes also possess an enzyme producing ability and hence, they could potentially colonize
lignocellulosic woody substrates. Maximum diversity
of fungi on the woody litter of Rhizophora (64 spp.) and
Avicennia (55 spp.) are reported from the Godavari and
Krishna deltas of the east coast of India [2.41, 42]. The