Potential Use of Extracts of Seaweeds Against Plant Pathogens 185
(P. infestans) severity, as compared to plants given chemical fertilizer alone (Sharma et al. 2012).
Al-Mughrabi (2007) reported that seaweed extract, in combination with compost tea, reduced the incidence
and severity of late blight by 36% in comparison to the control. Extracts of A. nodosum when used alone,
or in combination, with other amendments showed some limited potential to reduce the total incidence
of grey mold (Botrytis cinerea), but not leather rot (Phytophthora cactorum), nor anthracnose caused
by Colletotrichum acutatum (Washington et al. 1999). Jeandet et al. (1996) reported that a commercial
product, containing a mixture of a seaweed extract plus AlCl2 hexahydrate, increased the efficacy of
iprodione for the control of grey mold on grapes. Abreu et al. (2008) studied extracts from 17 marine
seaweeds against bean anthracnose and observed that an extract of Bryothamnion seaforthii reduced the
disease severity in beans by up to 35%. In this study, a residual effect of Ulva fasciata extract was also
reported, as the application of seaweed extracts was able to reduce the anthracnose severity by 22%, 12 d
post-inoculation. Interestingly, extracts of the water plant (duckweed) Lemna sp. and U. fasciata caused
the reduction in disease severity at 7 d, post-inoculation by 55 and 44%, respectively.
Goicoechea et al. (2004) used a combination of an A. nodosum extract, along with other organic
amendments of natural origin, to investigate their ability to suppress diseases in greenhouse peppers;
seedlings, cv. “Piquillo”, were grown for three months in an organic medium (‘COA H’), that contained
salicylic acid (SA), soluble ammonium salts, and A. nodosum extract, and were then inoculated with
Verticillium dahliae Kleb. The pre-treated seedlings showed delayed appearance of disease symptoms and
the disease index, on day 33, was almost 40% lower than that measured in the control plants. Jayaraj et
al. (2008) used a commercial A. nodosum extract to suppress Alternaria radicana and Botrytis cinerea on
carrots in greenhouse trials. Pre-treatment of the plants with a commercial A. nodosum extract suppressed
foliar symptoms caused by A. radicana on carrots at 10 and 25 d post-inoculation. The authors also observed
a similar trend with B. cinerea infection after using the A. nodosum extract. In another trial, the same
A. nodosum extract treatment was used on cucumbers to compare soil drench against foliar applications.
It was reported that foliar, or drench and a combination of foliar and drench applications (at 0.5% or 1%
concentrations) of the A. nodosum extract, suppressed infection with three different, potential cucumber
pathogens (e.g., B. cinerea, F. oxysporum, and Didymella applanata). In growth room trials, treatments
with seaweed extract (A. nodosum) significantly reduced Verticillium wilt incidence and severity (i.e.,
70–80% reduction) in potatoes. The same treatment also reduced the severity of Verticillium wilt under field
conditions (Uppal et al. 2008). Meszka and Bielenin (2009) tested a commercial product (“Remedier WP”
containing mycelium and spores of two antagonistic fungi, e.g., Trichoderma harzianum and T. viride),
and plant extracts (from pine and spruce needles, horsetail, herbs and a seaweed, probably A. nodosum)
under field conditions, to test the protection of strawberry cultivars against V. dahliae. Amongst the tested
extracts, seaweed and herbs were the most effective at reducing the wilt disease (i.e., 43–76% reduction,
depending on the severity of the disease).
Application of seaweed extract reduced the incidence of gray mold (B. cinerea) on strawberries,
powdery mildew (Erysiphe polygoni) on turnips, and damping-off of tomato seedlings (Kulik 1995).
Spray treatment of ethanolic extracts of the phaeophyte, Lessonia trabeculata, on tomato leaves, reduced
the severity of the disease caused by B. cinerea (Jiminez et al. 2011). This effect was evident in a doseand seasonal dependent manner. Foliar applications of K. alvarezii reduced bacterial wilt and leaf curl
disease in tomato (Zodape et al. 2011). Various seaweed extracts have also been reported to be effective
in suppressing plant pathogens in some graminaceous crops, for example, the incidence of disease in
rice caused by Alternaria padwickii and Bipolaris oryzae was significantly reduced after seed treatment
with a commercial seaweed product (Dravya), prepared from Sargassum wightii (Sathyanarayana et
al. 2006). Reduction in diseases of greenhouse grown plants treated with seaweed based products has
also been observed. Flora and Rani (2012) reported the use of aqueous concentrates of Padina pavonia,
Acanthophora spicifera and Ulva lactuca as foliar sprays to suppress rice blast caused by Pyricularia
oryzae and observed a reduction in disease severity with all of the seaweed extracts tested, although a
higher activity was evident with the A. spicifera extract. A commercial A. nodosum extract, showed antifungal activity on the bentgrass (Agrostis stolonifera) against dollar spot disease, caused by the fungus,
Sclerotinia homoeocarpa (Zhang et al. 2003). An extract from the same brown seaweed was also shown
to suppress infection of the model plant Arabidopsis by S. sclerotiorum (Subramanian et al. 2011) which
(P. infestans) severity, as compared to plants given chemical fertilizer alone (Sharma et al. 2012).
Al-Mughrabi (2007) reported that seaweed extract, in combination with compost tea, reduced the incidence
and severity of late blight by 36% in comparison to the control. Extracts of A. nodosum when used alone,
or in combination, with other amendments showed some limited potential to reduce the total incidence
of grey mold (Botrytis cinerea), but not leather rot (Phytophthora cactorum), nor anthracnose caused
by Colletotrichum acutatum (Washington et al. 1999). Jeandet et al. (1996) reported that a commercial
product, containing a mixture of a seaweed extract plus AlCl2 hexahydrate, increased the efficacy of
iprodione for the control of grey mold on grapes. Abreu et al. (2008) studied extracts from 17 marine
seaweeds against bean anthracnose and observed that an extract of Bryothamnion seaforthii reduced the
disease severity in beans by up to 35%. In this study, a residual effect of Ulva fasciata extract was also
reported, as the application of seaweed extracts was able to reduce the anthracnose severity by 22%, 12 d
post-inoculation. Interestingly, extracts of the water plant (duckweed) Lemna sp. and U. fasciata caused
the reduction in disease severity at 7 d, post-inoculation by 55 and 44%, respectively.
Goicoechea et al. (2004) used a combination of an A. nodosum extract, along with other organic
amendments of natural origin, to investigate their ability to suppress diseases in greenhouse peppers;
seedlings, cv. “Piquillo”, were grown for three months in an organic medium (‘COA H’), that contained
salicylic acid (SA), soluble ammonium salts, and A. nodosum extract, and were then inoculated with
Verticillium dahliae Kleb. The pre-treated seedlings showed delayed appearance of disease symptoms and
the disease index, on day 33, was almost 40% lower than that measured in the control plants. Jayaraj et
al. (2008) used a commercial A. nodosum extract to suppress Alternaria radicana and Botrytis cinerea on
carrots in greenhouse trials. Pre-treatment of the plants with a commercial A. nodosum extract suppressed
foliar symptoms caused by A. radicana on carrots at 10 and 25 d post-inoculation. The authors also observed
a similar trend with B. cinerea infection after using the A. nodosum extract. In another trial, the same
A. nodosum extract treatment was used on cucumbers to compare soil drench against foliar applications.
It was reported that foliar, or drench and a combination of foliar and drench applications (at 0.5% or 1%
concentrations) of the A. nodosum extract, suppressed infection with three different, potential cucumber
pathogens (e.g., B. cinerea, F. oxysporum, and Didymella applanata). In growth room trials, treatments
with seaweed extract (A. nodosum) significantly reduced Verticillium wilt incidence and severity (i.e.,
70–80% reduction) in potatoes. The same treatment also reduced the severity of Verticillium wilt under field
conditions (Uppal et al. 2008). Meszka and Bielenin (2009) tested a commercial product (“Remedier WP”
containing mycelium and spores of two antagonistic fungi, e.g., Trichoderma harzianum and T. viride),
and plant extracts (from pine and spruce needles, horsetail, herbs and a seaweed, probably A. nodosum)
under field conditions, to test the protection of strawberry cultivars against V. dahliae. Amongst the tested
extracts, seaweed and herbs were the most effective at reducing the wilt disease (i.e., 43–76% reduction,
depending on the severity of the disease).
Application of seaweed extract reduced the incidence of gray mold (B. cinerea) on strawberries,
powdery mildew (Erysiphe polygoni) on turnips, and damping-off of tomato seedlings (Kulik 1995).
Spray treatment of ethanolic extracts of the phaeophyte, Lessonia trabeculata, on tomato leaves, reduced
the severity of the disease caused by B. cinerea (Jiminez et al. 2011). This effect was evident in a doseand seasonal dependent manner. Foliar applications of K. alvarezii reduced bacterial wilt and leaf curl
disease in tomato (Zodape et al. 2011). Various seaweed extracts have also been reported to be effective
in suppressing plant pathogens in some graminaceous crops, for example, the incidence of disease in
rice caused by Alternaria padwickii and Bipolaris oryzae was significantly reduced after seed treatment
with a commercial seaweed product (Dravya), prepared from Sargassum wightii (Sathyanarayana et
al. 2006). Reduction in diseases of greenhouse grown plants treated with seaweed based products has
also been observed. Flora and Rani (2012) reported the use of aqueous concentrates of Padina pavonia,
Acanthophora spicifera and Ulva lactuca as foliar sprays to suppress rice blast caused by Pyricularia
oryzae and observed a reduction in disease severity with all of the seaweed extracts tested, although a
higher activity was evident with the A. spicifera extract. A commercial A. nodosum extract, showed antifungal activity on the bentgrass (Agrostis stolonifera) against dollar spot disease, caused by the fungus,
Sclerotinia homoeocarpa (Zhang et al. 2003). An extract from the same brown seaweed was also shown
to suppress infection of the model plant Arabidopsis by S. sclerotiorum (Subramanian et al. 2011) which