186 Marine Macro- and Microalgae: An Overview
implicated the potential application of seaweed extract to manage other pathogens in other commercial
crops, particularly the mustard family.
A few studies have shown that direct application of selected seaweed extracts to the soil has resulted
in indirect protection of plants against pathogens, possibly through an improved soil environment. Soil
applications of liquid seaweed extract to cabbage (Brassica oleracea var. capitata) stimulated microbes
that were antagonistic to Pythium ultimum, resulting in the reduced incidence of damping-off disease
in seedlings (Dixon and Walsh 2002). Soil amendments using dry powder from brown, green, and red
seaweeds was shown to have broad spectrum activity to control root infecting fungal pathogens of different
crops (see Sultana et al. 2005, 2008, 2009, 2011a for details). Extracts of the seaweeds Stokeyia indica
(Cystoseira indica), Padina pavonia (brown), and Solieria robusta (red), at concentrations of 1% w/w,
effectively reduced infection by Macrophomina phaseolina, Rhizoctonia solani and Fusarium solani on
okra roots. In contrast, an extract of Codium iyengarii (Chlorophyta) was effective at the lower dose of 0.5%
w/w against F. solani (Sultana et al. 2005). The application of Solieria indica and S. robusta, used as soil
amendments, was able to suppress root-infecting fungi, that is, M. phaseolina, R. solani, and F. solani in chili
roots, thus suggesting a broad applicability of these treatments (Sultana et al. 2008). Similar results were
observed in tomato using the powdered brown seaweeds Spatoglossum asperum and Sargassum swartzii
as soil amendments on these root-rotting fungi (Sultana et al. 2009). Sultana et al. (2011a) compared the
efficacy of the extract of the red seaweed, S. robusta in combination with chemical fertilizers and pesticides
on soybeans. Soil amendments using S. robusta was more effective at suppressing the root-rot fungus
F. solani, than the commercial fungicide Topsin-M. Although the seaweed was less effective against
M. phaseolina and R. solani than Topsin-M, there seemed to be promising aspects of using seaweeds in
control management practices against soil pathogens and also a role in enhancement of the activity of
beneficial organisms (i.e., a “prebiotic” effect on beneficial soil microorgansims). Rekanović et al. (2010)
evaluated the activity of a commercial seaweed concentrate from the kelp Ecklonia maxima against
wilt in peppers caused by Verticillium dahliae and compared extract treatment with two conventional
fungicides, that is, thiophanate-methyl and carbendazim. Although pre-treatment of the pepper plants
with carbendazim was the most efficient fungicide (69.64%), the seaweed concentrates also proved to be
effective when applied at a 1.0% concentration (41.96%). In contrast, the activity of thiophanate-methyl
against Verticillium-induced wilt was 60.71%. The results showed that although the seaweed extract was less
effective than thiophanate-methyl and carbendazim, it showed activity against the pathogen, as compared
to the control. These observations are important when non-synthetic solutions to plant disease are sought.
Marine algae in general, are a rich source of bioactive compounds, such as cell wall polysaccharides,
ulvans, laminarins, etc., which are present in specific groups (e.g., green, red, and brown) of seaweeds.
Polysaccharides from seaweeds are extensively used to suppress plant pathogens. Ulvan, carrageenan,
laminarin, and fucans are some of the notable polysaccharide compounds with reported anti-microbial
activities, be it as direct suppressants or by induced plant responses. Ascochyta phaseolorum and
Peronosopora manshurica infections were reduced with pre-application of soybean seeds with extracts of
Laminaria (or Saccharina), or associated fucoidans (from Laminaria cichorioides) and polymannuronic
acid and fucoidan from Fucus evanescens (Zaostrovnykh et al. 2009). Pre-treatment of plants with an
oligosaccharide extract from the L. cichorioides, or the fucoidan fraction derived from L. cichorioides
and polymannuronic acid and fucoidan from F. evanescens, showed a reduced (5%) infection by
A. phaseolorum and P. manshurica, as compared to 15% in the controls. Trouvelot et al. (2008) showed
that sulphated laminarin (PS3) could elicit defense responses in grapevine (Vitis vinifera) against downy
mildew (Plasmopara viticola) through induction of H 2 O 2 production at the infection sites, up-regulation
of defence-related genes, callus and phenol depositions, and the hyper-sensitive response. PS3 was also
shown to induce defence responses in tobacco and Arabidopsis against tobacco mosaic virus. Aziz et al.
(2003) studied the ability of laminarin to elicit defense responses in grapevines against B. cinerea and
P. viticola; pre-treatment reduced infections by approximately 55 and 75%, respectively.
Extensive research has been published on the use of ulvan, a polysaccharide extracted from green
macroalgae, for the induction of plant defences to pathogens. Paulert et al. (2010) reported on the
priming activity of ulvan, against the fungal pathogen Blumeria graminis. Ulvan pre-treatment of whole
plants significantly reduced the severity of B. graminis infection, by 45% in wheat and 80% in barley.
implicated the potential application of seaweed extract to manage other pathogens in other commercial
crops, particularly the mustard family.
A few studies have shown that direct application of selected seaweed extracts to the soil has resulted
in indirect protection of plants against pathogens, possibly through an improved soil environment. Soil
applications of liquid seaweed extract to cabbage (Brassica oleracea var. capitata) stimulated microbes
that were antagonistic to Pythium ultimum, resulting in the reduced incidence of damping-off disease
in seedlings (Dixon and Walsh 2002). Soil amendments using dry powder from brown, green, and red
seaweeds was shown to have broad spectrum activity to control root infecting fungal pathogens of different
crops (see Sultana et al. 2005, 2008, 2009, 2011a for details). Extracts of the seaweeds Stokeyia indica
(Cystoseira indica), Padina pavonia (brown), and Solieria robusta (red), at concentrations of 1% w/w,
effectively reduced infection by Macrophomina phaseolina, Rhizoctonia solani and Fusarium solani on
okra roots. In contrast, an extract of Codium iyengarii (Chlorophyta) was effective at the lower dose of 0.5%
w/w against F. solani (Sultana et al. 2005). The application of Solieria indica and S. robusta, used as soil
amendments, was able to suppress root-infecting fungi, that is, M. phaseolina, R. solani, and F. solani in chili
roots, thus suggesting a broad applicability of these treatments (Sultana et al. 2008). Similar results were
observed in tomato using the powdered brown seaweeds Spatoglossum asperum and Sargassum swartzii
as soil amendments on these root-rotting fungi (Sultana et al. 2009). Sultana et al. (2011a) compared the
efficacy of the extract of the red seaweed, S. robusta in combination with chemical fertilizers and pesticides
on soybeans. Soil amendments using S. robusta was more effective at suppressing the root-rot fungus
F. solani, than the commercial fungicide Topsin-M. Although the seaweed was less effective against
M. phaseolina and R. solani than Topsin-M, there seemed to be promising aspects of using seaweeds in
control management practices against soil pathogens and also a role in enhancement of the activity of
beneficial organisms (i.e., a “prebiotic” effect on beneficial soil microorgansims). Rekanović et al. (2010)
evaluated the activity of a commercial seaweed concentrate from the kelp Ecklonia maxima against
wilt in peppers caused by Verticillium dahliae and compared extract treatment with two conventional
fungicides, that is, thiophanate-methyl and carbendazim. Although pre-treatment of the pepper plants
with carbendazim was the most efficient fungicide (69.64%), the seaweed concentrates also proved to be
effective when applied at a 1.0% concentration (41.96%). In contrast, the activity of thiophanate-methyl
against Verticillium-induced wilt was 60.71%. The results showed that although the seaweed extract was less
effective than thiophanate-methyl and carbendazim, it showed activity against the pathogen, as compared
to the control. These observations are important when non-synthetic solutions to plant disease are sought.
Marine algae in general, are a rich source of bioactive compounds, such as cell wall polysaccharides,
ulvans, laminarins, etc., which are present in specific groups (e.g., green, red, and brown) of seaweeds.
Polysaccharides from seaweeds are extensively used to suppress plant pathogens. Ulvan, carrageenan,
laminarin, and fucans are some of the notable polysaccharide compounds with reported anti-microbial
activities, be it as direct suppressants or by induced plant responses. Ascochyta phaseolorum and
Peronosopora manshurica infections were reduced with pre-application of soybean seeds with extracts of
Laminaria (or Saccharina), or associated fucoidans (from Laminaria cichorioides) and polymannuronic
acid and fucoidan from Fucus evanescens (Zaostrovnykh et al. 2009). Pre-treatment of plants with an
oligosaccharide extract from the L. cichorioides, or the fucoidan fraction derived from L. cichorioides
and polymannuronic acid and fucoidan from F. evanescens, showed a reduced (5%) infection by
A. phaseolorum and P. manshurica, as compared to 15% in the controls. Trouvelot et al. (2008) showed
that sulphated laminarin (PS3) could elicit defense responses in grapevine (Vitis vinifera) against downy
mildew (Plasmopara viticola) through induction of H 2 O 2 production at the infection sites, up-regulation
of defence-related genes, callus and phenol depositions, and the hyper-sensitive response. PS3 was also
shown to induce defence responses in tobacco and Arabidopsis against tobacco mosaic virus. Aziz et al.
(2003) studied the ability of laminarin to elicit defense responses in grapevines against B. cinerea and
P. viticola; pre-treatment reduced infections by approximately 55 and 75%, respectively.
Extensive research has been published on the use of ulvan, a polysaccharide extracted from green
macroalgae, for the induction of plant defences to pathogens. Paulert et al. (2010) reported on the
priming activity of ulvan, against the fungal pathogen Blumeria graminis. Ulvan pre-treatment of whole
plants significantly reduced the severity of B. graminis infection, by 45% in wheat and 80% in barley.