178 Marine Macro- and Microalgae: An Overview
Porcia et al. 2010). The major bioactive substances in seaweeds can be broadly identified as aromatics,
sterols, dibutanoids, proteins, peptides, and sulphated polysaccharides. Some of these are unique compounds,
only found in macroalgae, for example, carrageenans, fucoidans (Khan et al. 2009; Sangha et al. 2010;
Seth and Shanmugam 2016). Many of the secondary metabolites are abundant in marine seaweeds and are
probably synthesized as chemical defences to cope with extreme environments such as, salinity, extreme
temperature variations, high and low light intensities, and UV rays amongst others. In addition, these
compounds also protect and mitigate against damage which may be caused by colonization by epiphytes,
microbial organisms, or grazing herbivores (Kubanek et al. 2003). Taken together, these attributes may
be part of the reasons why certain seaweeds and their extracts have biological activity, especially against
a variety of microbes, including plant pathogens. Some of the algal-derived compounds within seaweed
extracts have direct or indirect effects on the suppression of pathogens infecting plants and humans and
thus have attracted scientific interest in the utilization of macroalgal extracts for plant disease management.
In fact, a growing body of literature suggests that the bioactive compounds present and as extracted from
certain seaweeds may be an economically viable resource of agricultural importance that can influence not
only the plant growth, but also plant-pathogen interactions, thereby assisting crop production through the
relief of stress from plant pathogens (Cox et al. 2010; Craigie 2010; de Freitas et al. 2015; Esserti et al.
2017). Identification of the active components in seaweeds will facilitate the commercialization of seaweed
products, further the success for their industrial uses, and lead to very specific and surgical applications
with recommended rates and timings (Patier et al. 1993; Jiao et al. 2011).
A large number of seaweed extracts have been tested against various microbes infecting humans,
animals and plants (Reichelt and Borowitzka 1984; Gonzalez del Val et al. 2001; Paulert et al. 2007;
Khan et al. 2009; Craigie 2010; Bahar et al. 2016; Shi et al. 2017). With information on the anti-microbial
activity of seaweed extracts against human pathogens and the benefits of seaweed extracts to the human
gut microbiome being of great interest and discussed elsewhere (Wang et al. 2009; Charoensiddhi et
al. 2017), the documentation of many marine algal extracts and their effects against plant pathogens
is also a fast emerging area of phycology (Jayaraj et al. 2008; Paulert et al. 2010; Sangha et al. 2010;
Subramanian et al. 2011; Stadnik and de Freitas 2014; Bhattacharyya et al. 2015; Abouraïcha et al.
2017; Esserti et al. 2017). Extracts of red, green, and brown seaweeds, including examples from
the Phaeophyceae such as: Ecklonia maxima, Saccharina (Laminaria) saccharina, Fucus serratus,
F. vesiculosus, Sargassum spp. and Ascophyllum nodosum, Chlorophyceae Ulva lactuca, Codium sp., and
Rhodophyceae such as Kappaphycus alvarezii are potential crop biostimulants and anti-microbial agents
in agriculture (Khan et al. 2009; Craigie 2010; Burketova et al. 2015; Esserti et al. 2017; Abouraïcha et al.
2017). Information on seaweed extracts against plant microbes generated by in vitro and in vivo bioassays,
in conjunction with greenhouse and field trials, reflect the potential for the application of seaweed extracts
in plant disease management. The widespread application of seaweed extracts for the suppression of
various diseases is possible for selective pathogen control (McLachlan 1985; Craigie 2010). Furthermore,
the natural origin and renewable, sustainable nature of the seaweed resources, from which many of the
extracts are responsibly and commercially extracted, so too along with cost effectiveness and safety to
the environment, make these seaweed extracts compatible with an integrated approach to biocontrol and
plant disease management, that may find multiple and widespread applications in agriculture (Aziz et al.
2003; Chandia and Matsuhiro 2008; Courtois 2009).
Herewith, we review the successful use of selected seaweed extracts to suppress plant diseases through
direct or indirect activity in agricultural systems. This information will help to identify certain bioactive
seaweeds and their extracts and encourage new ways for their applications in an integrated approach to
plant disease management.
Anti-microbial bioactive compounds in seaweeds
Seaweeds possess several metabolites, some of which exhibit antimicrobial activities. For example, the
brown seaweed A. nodosum is a major source of polyphenols, sulphated galactans and fucans, and volatile
halogenated compounds, for example, brominated vanadium peroxides that have been shown to have
bioactivity against microorganisms (Cardozo et al. 2007). Similarly, compounds such as aromatic esters,
Porcia et al. 2010). The major bioactive substances in seaweeds can be broadly identified as aromatics,
sterols, dibutanoids, proteins, peptides, and sulphated polysaccharides. Some of these are unique compounds,
only found in macroalgae, for example, carrageenans, fucoidans (Khan et al. 2009; Sangha et al. 2010;
Seth and Shanmugam 2016). Many of the secondary metabolites are abundant in marine seaweeds and are
probably synthesized as chemical defences to cope with extreme environments such as, salinity, extreme
temperature variations, high and low light intensities, and UV rays amongst others. In addition, these
compounds also protect and mitigate against damage which may be caused by colonization by epiphytes,
microbial organisms, or grazing herbivores (Kubanek et al. 2003). Taken together, these attributes may
be part of the reasons why certain seaweeds and their extracts have biological activity, especially against
a variety of microbes, including plant pathogens. Some of the algal-derived compounds within seaweed
extracts have direct or indirect effects on the suppression of pathogens infecting plants and humans and
thus have attracted scientific interest in the utilization of macroalgal extracts for plant disease management.
In fact, a growing body of literature suggests that the bioactive compounds present and as extracted from
certain seaweeds may be an economically viable resource of agricultural importance that can influence not
only the plant growth, but also plant-pathogen interactions, thereby assisting crop production through the
relief of stress from plant pathogens (Cox et al. 2010; Craigie 2010; de Freitas et al. 2015; Esserti et al.
2017). Identification of the active components in seaweeds will facilitate the commercialization of seaweed
products, further the success for their industrial uses, and lead to very specific and surgical applications
with recommended rates and timings (Patier et al. 1993; Jiao et al. 2011).
A large number of seaweed extracts have been tested against various microbes infecting humans,
animals and plants (Reichelt and Borowitzka 1984; Gonzalez del Val et al. 2001; Paulert et al. 2007;
Khan et al. 2009; Craigie 2010; Bahar et al. 2016; Shi et al. 2017). With information on the anti-microbial
activity of seaweed extracts against human pathogens and the benefits of seaweed extracts to the human
gut microbiome being of great interest and discussed elsewhere (Wang et al. 2009; Charoensiddhi et
al. 2017), the documentation of many marine algal extracts and their effects against plant pathogens
is also a fast emerging area of phycology (Jayaraj et al. 2008; Paulert et al. 2010; Sangha et al. 2010;
Subramanian et al. 2011; Stadnik and de Freitas 2014; Bhattacharyya et al. 2015; Abouraïcha et al.
2017; Esserti et al. 2017). Extracts of red, green, and brown seaweeds, including examples from
the Phaeophyceae such as: Ecklonia maxima, Saccharina (Laminaria) saccharina, Fucus serratus,
F. vesiculosus, Sargassum spp. and Ascophyllum nodosum, Chlorophyceae Ulva lactuca, Codium sp., and
Rhodophyceae such as Kappaphycus alvarezii are potential crop biostimulants and anti-microbial agents
in agriculture (Khan et al. 2009; Craigie 2010; Burketova et al. 2015; Esserti et al. 2017; Abouraïcha et al.
2017). Information on seaweed extracts against plant microbes generated by in vitro and in vivo bioassays,
in conjunction with greenhouse and field trials, reflect the potential for the application of seaweed extracts
in plant disease management. The widespread application of seaweed extracts for the suppression of
various diseases is possible for selective pathogen control (McLachlan 1985; Craigie 2010). Furthermore,
the natural origin and renewable, sustainable nature of the seaweed resources, from which many of the
extracts are responsibly and commercially extracted, so too along with cost effectiveness and safety to
the environment, make these seaweed extracts compatible with an integrated approach to biocontrol and
plant disease management, that may find multiple and widespread applications in agriculture (Aziz et al.
2003; Chandia and Matsuhiro 2008; Courtois 2009).
Herewith, we review the successful use of selected seaweed extracts to suppress plant diseases through
direct or indirect activity in agricultural systems. This information will help to identify certain bioactive
seaweeds and their extracts and encourage new ways for their applications in an integrated approach to
plant disease management.
Anti-microbial bioactive compounds in seaweeds
Seaweeds possess several metabolites, some of which exhibit antimicrobial activities. For example, the
brown seaweed A. nodosum is a major source of polyphenols, sulphated galactans and fucans, and volatile
halogenated compounds, for example, brominated vanadium peroxides that have been shown to have
bioactivity against microorganisms (Cardozo et al. 2007). Similarly, compounds such as aromatic esters,