Potential Use of Extracts of Seaweeds Against Plant Pathogens 191
wightii, product (at 0.4%), in combination with mancozeb (0.3%), at 15 day intervals, reduced disease
incidence by up to 80%, as compared to the control (Raghavendra et al. 2008). An extract obtained from
the red alga S. robusta amended at 0.5 or 1% w/w, individually or in combination, with the plant growthpromoting bacterium Pseudomonas aeruginosa showed significant control of plant pathogenic fungi
such as M. phaseolina, R. solani, and F. solani in pepper roots (Sultana et al. 2005). In fact, a symbiotic
combination of P. aeruginosa and an extract of S. robusta showed better control of M. phaseolina infection
than when they were used individually. A similar observation was made with extracts of the brown seaweed
Padina pavonia, when used in combination with P. aeruginosa and against R. solani. Combined use of
compatible strains of P. aeruginosa with whole seaweeds, and or their extracts, holds tremendous promise
for symbiotic associations, of which we will see and hear more in future. A commercial seaweed product,
with oligosaccharides extracted from Ascophyllum nodosum (Basak 2008), was used in combination with
field (Bacillus amyloliquefaciens KPS46 and Paenibacillus pabuli SW01/4) and commercial biological
control agents (Trichoderma harzianum, and B. subtilis) on disease epidemics of soybean (Thowthampitak
and Prathuangwong 2007). The combined treatments significantly reduced diseases such as Sclerotium
root-rot (Sclerotinia sclerotiorum), damping-off (Rhizoctonia solani), anthracnose (Colletotrichum spp.),
bacterial pustule (Xanthomonas axonopodis pv. glycines), soybean mosaic virus SMV and soybean crinkle
leaf virus (SCLV) severity by 34–90%. This was suggested as good management strategy to be adopted
in sustainable agriculture systems.
Advances in nanotechnology have been emerging as potential eco-friendly methods of suppressing
pathogens that could incorporate seaweed components with anti-pathogenic properties. This has been
demonstrated with examples such as bio-nanoparticles prepared with a crude ethyl acetate extract of Ulva
fasciata that showed strong inhibition of Xanthomonas campestris pv. malvacearum with a minimum
inhibitory concentration of 40.00 ± 5.77 μg/mL (Rajesh et al. 2012). Such advances will help towards
integrated management of plant diseases and minimal application of synthetic pesticides.
Conclusions
There is compelling evidence that disease resistance in plants, imparted by various seaweed extracts
is associated with the priming and activation of plant defence pathways that are often associated with
resistance to plant pathogens. Since many diseases of agricultural crops are caused by such pathogens
as Alternaria, Fusarium, Phytophthora, Pythium, Botrytis, Verticillium, extracts of seaweeds, or their
fractionated components, may offer a valuable tool to improve the health and productivity of commercial
agriculture. There is a tremendous amount of work which remains to be completed on synergies of these
components and also their interactions with beneficial soil-living and endophytic plant bacteria. Moreover,
many marine algae, out of necessity, produce a large number of anti-bacterial and anti-fungal compounds,
which have no apparent ecotoxicity and many of these seaweeds, though not all, can be sustainably
harvested or grown in quantity using well-established techniques of mass culture. The acceptance of
seaweed components as disease management tools might be accelerated using new technologies with an
enhanced ability to control plant diseases. There is a need to carefully evaluate further algal products for
their potential and potent roles in future biocontrol of plant pathogens.
Acknowledgements
We thank Dr R. Loureiro for constructive comments on the manuscript.
References
Abouraïcha, E.F., E.Z. Alaoui-Talibi, A. Daoulas-Ouafi, R.E. Boutachfaiti, E. Petit, A. Douira, B. Courtois, J.Courtois and
C.E. Modafar. 2017. Glucuronan and oligoglucuronans isolated from green algae activate natural defence responses in
apple fruit and reduce postharvest blue and gray mold decay. J. Appl. Phycol. 29: 471–480.
Abkhoo, J. and S.K. Sabbagh. 2016. Control of Phytophthora melonis damping-off, induction of defense responses, and gene
expression of cucumber treated with commercial extract from Ascophyllum nodosum. J. Appl. Phycol. 28: 1333–1342.
wightii, product (at 0.4%), in combination with mancozeb (0.3%), at 15 day intervals, reduced disease
incidence by up to 80%, as compared to the control (Raghavendra et al. 2008). An extract obtained from
the red alga S. robusta amended at 0.5 or 1% w/w, individually or in combination, with the plant growthpromoting bacterium Pseudomonas aeruginosa showed significant control of plant pathogenic fungi
such as M. phaseolina, R. solani, and F. solani in pepper roots (Sultana et al. 2005). In fact, a symbiotic
combination of P. aeruginosa and an extract of S. robusta showed better control of M. phaseolina infection
than when they were used individually. A similar observation was made with extracts of the brown seaweed
Padina pavonia, when used in combination with P. aeruginosa and against R. solani. Combined use of
compatible strains of P. aeruginosa with whole seaweeds, and or their extracts, holds tremendous promise
for symbiotic associations, of which we will see and hear more in future. A commercial seaweed product,
with oligosaccharides extracted from Ascophyllum nodosum (Basak 2008), was used in combination with
field (Bacillus amyloliquefaciens KPS46 and Paenibacillus pabuli SW01/4) and commercial biological
control agents (Trichoderma harzianum, and B. subtilis) on disease epidemics of soybean (Thowthampitak
and Prathuangwong 2007). The combined treatments significantly reduced diseases such as Sclerotium
root-rot (Sclerotinia sclerotiorum), damping-off (Rhizoctonia solani), anthracnose (Colletotrichum spp.),
bacterial pustule (Xanthomonas axonopodis pv. glycines), soybean mosaic virus SMV and soybean crinkle
leaf virus (SCLV) severity by 34–90%. This was suggested as good management strategy to be adopted
in sustainable agriculture systems.
Advances in nanotechnology have been emerging as potential eco-friendly methods of suppressing
pathogens that could incorporate seaweed components with anti-pathogenic properties. This has been
demonstrated with examples such as bio-nanoparticles prepared with a crude ethyl acetate extract of Ulva
fasciata that showed strong inhibition of Xanthomonas campestris pv. malvacearum with a minimum
inhibitory concentration of 40.00 ± 5.77 μg/mL (Rajesh et al. 2012). Such advances will help towards
integrated management of plant diseases and minimal application of synthetic pesticides.
Conclusions
There is compelling evidence that disease resistance in plants, imparted by various seaweed extracts
is associated with the priming and activation of plant defence pathways that are often associated with
resistance to plant pathogens. Since many diseases of agricultural crops are caused by such pathogens
as Alternaria, Fusarium, Phytophthora, Pythium, Botrytis, Verticillium, extracts of seaweeds, or their
fractionated components, may offer a valuable tool to improve the health and productivity of commercial
agriculture. There is a tremendous amount of work which remains to be completed on synergies of these
components and also their interactions with beneficial soil-living and endophytic plant bacteria. Moreover,
many marine algae, out of necessity, produce a large number of anti-bacterial and anti-fungal compounds,
which have no apparent ecotoxicity and many of these seaweeds, though not all, can be sustainably
harvested or grown in quantity using well-established techniques of mass culture. The acceptance of
seaweed components as disease management tools might be accelerated using new technologies with an
enhanced ability to control plant diseases. There is a need to carefully evaluate further algal products for
their potential and potent roles in future biocontrol of plant pathogens.
Acknowledgements
We thank Dr R. Loureiro for constructive comments on the manuscript.
References
Abouraïcha, E.F., E.Z. Alaoui-Talibi, A. Daoulas-Ouafi, R.E. Boutachfaiti, E. Petit, A. Douira, B. Courtois, J.Courtois and
C.E. Modafar. 2017. Glucuronan and oligoglucuronans isolated from green algae activate natural defence responses in
apple fruit and reduce postharvest blue and gray mold decay. J. Appl. Phycol. 29: 471–480.
Abkhoo, J. and S.K. Sabbagh. 2016. Control of Phytophthora melonis damping-off, induction of defense responses, and gene
expression of cucumber treated with commercial extract from Ascophyllum nodosum. J. Appl. Phycol. 28: 1333–1342.