182 Marine Macro- and Microalgae: An Overview
Paulert et al. (2007) investigated cell-wall polysaccharides and crude extracts from the green alga
Ulva fasciata against Xanthomonas campestris, Erwinia carotovora, and the fungus Colletotrichum
lindemuthianum. Both methanol soluble and -insoluble (i.e., the remaining fraction) extracts were active
against X. campestris and E. carotovora. Using an agar diffusion assay and broth dilution method, the
minimal inhibitory concentration (MIC) was identified as being greatest against E. carotovora (e.g., the
MIC was 1 mg/ml). Interestingly, no in vitro activity of the ulvans (a water soluble polysaccharide in green
seaweeds), was observed against the test organisms. Tobacco plants injected with laminarin, purified from
the brown alga Laminaria digitata, when inoculated with Erwinia carotovora subsp. Carotovora, five days
after treatment, strongly reduced the infection, as compared to the control (Klarzynski et al. 2000). Yi et al.
(2001) used extracts from 23 species of seaweeds belonging to the divisions Chlorophyta, Phaeophyta, and
Rhodophyta and demonstrated that ethanolic extracts of selected rhodophytes (i.e., Laurencia okamurai,
Dasya scoparia, Grateloupia filicina, and Plocamium telfairiae) showed a wide spectrum of anti-bacterial
activity; Pseudomonas solancearum was more sensitive to the algal extracts, as compared to the other
microbes tested.
Fungi: One of the earliest reports of the effects of seaweed extracts against fungal pathogens was on the antifungal substances extracted from the brown alga, Dictyopteris zonarioides (Fenical et al. 1973). Barreto et
al. (1997) investigated the in vitro activity of several seaweeds against two phytopathogenic fungi, that is,
Verticillium sp. and Rhizoctonia solani. Extracts of six seaweeds, including the greens Caulerpa filiformis
and Ulva rigida, the brown Zonaria tornefortii and the reds Hypnea spicifera, Gelidium abottiorium
and Osmundaria serrata, inhibited fungal growth by more than 50%. In contrast, the extracts of the red
alga Spyridia cupressans and Beckerella pinnatifida demonstrated minimal anti-fungal activity, under
the conditions tested. Anti-fungal activity of extracts of the brown seaweed Cystoseira tamariscifolia
was reported against the plant pathogens Botrytis cinerea, Fusarium oxysporum, and Verticillium alboatrum (Abourriche et al. 1999) and also against the food spoiling pathogen Aspergillus spp. (Bhosale et
al. 1999). Martinez-Lozano et al. (2000) examined the anti-fungal properties of an extract of Sargassum
filipendula on Aspergillus niger, A. flavus, A. parasiticus, Penicillium sp., Fusarium oxysporum, Candida
albicans, and C. rugosa. An extract produced from the phaeophyte S. filipendula inhibited the growth
of all fungi tested, even at different concentrations. Aqueous and ethanolic extracts from Gracilaria
chilensis reduced the growth of Phytophthora cinnamonni under in vitro conditions (Jiménez et al. 2011).
Modulations of anti-microbial activity by the various seaweed extracts were dependent on the type of
seaweed, the extraction procedure, the solvents used for preparation of bioactive fractions and also the target
species tested. Chloroform and methanolic fractions of an ethanol extract of the phaeophyte Spatoglossum
asperum demonstrated antifungal activity against the plant pathogen, Macrophomina phaseolina, whereas
an n-hexane fraction suppressed Rhizoctonia solani and Fusarium solani (Ara et al. 2005). Using different
solvents, Yi et al. (2001) identified differential activity from of the extracts of 23 species of marine algae
belonging to the divisions Chlorophyta, Phaeophyta, and Rhodophyta against selected fungi. In this case,
the ethanol extract was highly effective against the fungus tested, for example, Penicilium citrinum, a
common filamentous fungus present in soil, cereals, spices, and other environments, was reported to be
the most sensitive to the extracts. Manilal et al. (2009) compared the crude extracts of fresh and dried
seaweeds prepared using different polar and non-polar solvents against pathogenic fungi and found that
methanol was the best solvent, in those experiments and conditions, for extraction of anti-microbial
metabolites from the dried seaweed samples. However, it is not surprising that contrasting results were
presented by Khanzada et al. (2007) who investigated the anti-fungal activity of various fractions of Solieria
robusta (Rhodophyta) against five fruit-spoiling fungi; that is, Aspergillus flavus, A. niger, A. ochraceus
K, Penicillium funiculosum, and Phytophthora infestans, all of which had been isolated from fruits. In
this case, the aqueous fraction was demonstrated to have the largest inhibition ratio, this was followed by
methanol, ethyl acetate, chloroform, and ethanolic solvents. Nevertheless, bioactivity of the extracts also
depended on the target species; some microbes are more resistant, even though seaweed extracts have been
shown to be effective against resistant strains of pathogens (Shanmughapriya et al. 2008).
Jayaraj et al. (2011) provided economically important evidence on the positive applications of an
Ascophyllum extract against fungal diseases of greenhouse cucumbers. Abkhoo and Sabbagh (2016)
published evidence for the effects of a similar product (an Ascophyllum extract) against damping-off, also
Paulert et al. (2007) investigated cell-wall polysaccharides and crude extracts from the green alga
Ulva fasciata against Xanthomonas campestris, Erwinia carotovora, and the fungus Colletotrichum
lindemuthianum. Both methanol soluble and -insoluble (i.e., the remaining fraction) extracts were active
against X. campestris and E. carotovora. Using an agar diffusion assay and broth dilution method, the
minimal inhibitory concentration (MIC) was identified as being greatest against E. carotovora (e.g., the
MIC was 1 mg/ml). Interestingly, no in vitro activity of the ulvans (a water soluble polysaccharide in green
seaweeds), was observed against the test organisms. Tobacco plants injected with laminarin, purified from
the brown alga Laminaria digitata, when inoculated with Erwinia carotovora subsp. Carotovora, five days
after treatment, strongly reduced the infection, as compared to the control (Klarzynski et al. 2000). Yi et al.
(2001) used extracts from 23 species of seaweeds belonging to the divisions Chlorophyta, Phaeophyta, and
Rhodophyta and demonstrated that ethanolic extracts of selected rhodophytes (i.e., Laurencia okamurai,
Dasya scoparia, Grateloupia filicina, and Plocamium telfairiae) showed a wide spectrum of anti-bacterial
activity; Pseudomonas solancearum was more sensitive to the algal extracts, as compared to the other
microbes tested.
Fungi: One of the earliest reports of the effects of seaweed extracts against fungal pathogens was on the antifungal substances extracted from the brown alga, Dictyopteris zonarioides (Fenical et al. 1973). Barreto et
al. (1997) investigated the in vitro activity of several seaweeds against two phytopathogenic fungi, that is,
Verticillium sp. and Rhizoctonia solani. Extracts of six seaweeds, including the greens Caulerpa filiformis
and Ulva rigida, the brown Zonaria tornefortii and the reds Hypnea spicifera, Gelidium abottiorium
and Osmundaria serrata, inhibited fungal growth by more than 50%. In contrast, the extracts of the red
alga Spyridia cupressans and Beckerella pinnatifida demonstrated minimal anti-fungal activity, under
the conditions tested. Anti-fungal activity of extracts of the brown seaweed Cystoseira tamariscifolia
was reported against the plant pathogens Botrytis cinerea, Fusarium oxysporum, and Verticillium alboatrum (Abourriche et al. 1999) and also against the food spoiling pathogen Aspergillus spp. (Bhosale et
al. 1999). Martinez-Lozano et al. (2000) examined the anti-fungal properties of an extract of Sargassum
filipendula on Aspergillus niger, A. flavus, A. parasiticus, Penicillium sp., Fusarium oxysporum, Candida
albicans, and C. rugosa. An extract produced from the phaeophyte S. filipendula inhibited the growth
of all fungi tested, even at different concentrations. Aqueous and ethanolic extracts from Gracilaria
chilensis reduced the growth of Phytophthora cinnamonni under in vitro conditions (Jiménez et al. 2011).
Modulations of anti-microbial activity by the various seaweed extracts were dependent on the type of
seaweed, the extraction procedure, the solvents used for preparation of bioactive fractions and also the target
species tested. Chloroform and methanolic fractions of an ethanol extract of the phaeophyte Spatoglossum
asperum demonstrated antifungal activity against the plant pathogen, Macrophomina phaseolina, whereas
an n-hexane fraction suppressed Rhizoctonia solani and Fusarium solani (Ara et al. 2005). Using different
solvents, Yi et al. (2001) identified differential activity from of the extracts of 23 species of marine algae
belonging to the divisions Chlorophyta, Phaeophyta, and Rhodophyta against selected fungi. In this case,
the ethanol extract was highly effective against the fungus tested, for example, Penicilium citrinum, a
common filamentous fungus present in soil, cereals, spices, and other environments, was reported to be
the most sensitive to the extracts. Manilal et al. (2009) compared the crude extracts of fresh and dried
seaweeds prepared using different polar and non-polar solvents against pathogenic fungi and found that
methanol was the best solvent, in those experiments and conditions, for extraction of anti-microbial
metabolites from the dried seaweed samples. However, it is not surprising that contrasting results were
presented by Khanzada et al. (2007) who investigated the anti-fungal activity of various fractions of Solieria
robusta (Rhodophyta) against five fruit-spoiling fungi; that is, Aspergillus flavus, A. niger, A. ochraceus
K, Penicillium funiculosum, and Phytophthora infestans, all of which had been isolated from fruits. In
this case, the aqueous fraction was demonstrated to have the largest inhibition ratio, this was followed by
methanol, ethyl acetate, chloroform, and ethanolic solvents. Nevertheless, bioactivity of the extracts also
depended on the target species; some microbes are more resistant, even though seaweed extracts have been
shown to be effective against resistant strains of pathogens (Shanmughapriya et al. 2008).
Jayaraj et al. (2011) provided economically important evidence on the positive applications of an
Ascophyllum extract against fungal diseases of greenhouse cucumbers. Abkhoo and Sabbagh (2016)
published evidence for the effects of a similar product (an Ascophyllum extract) against damping-off, also