Potential Use of Extracts of Seaweeds Against Plant Pathogens 187
Montealegre et al. (2010) used ulvan to control the grey rot of apple fruits and found that post-harvest
applications reduced B. cinerea infections on apple by 56%. Yet another study, showed the potential of
ulvan to protect apples from pathogenic infections (Araújo et al. 2008). Two consecutive treatments of
extracted, sulphated polysaccharide from U. armoricana protected alfalfa (Medicago truncatula) against
anthracnose (Colletotrichum trifolii); the mechanisms were related to induced expression of several
pathogenesis-related genes such as PR-10 (Cluzet et al. 2004). Similarly, Paulert et al. (2007), using
2 mg ml
–1
of ulvan, demonstrated induced plant resistance to these pathogens. Paulert et al. (2011) evaluated
the potential of crude extracts and fractionated ulvan from U. fasciata to control bean (Phaseolus vulgaris)
anthracnose caused by C. lindemuthianum, under greenhouse conditions. The soluble, methanolic extract
did not reduce disease severity, however ulvan, sprayed at 10 mg ml
–1
, reduced disease severity by 38%.
These results indicated that ulvan itself can be a strong elicitor of plant resistance to Colletotrichum sp.
attacks. Borsato et al. (2010) showed that an ulvan spray treatment (10 mg mL
–1
) to bean plants, 3–6 days
before infection, induced resistance to rust caused by Uromyces appendiculatus. The diameter of the
pustules on the bean cultivars was reduced, and the activity of glucanases within the treated plants was
increased in moderately susceptible cultivars two days, post-inoculation. However, treatments were not
effective against fungal germination on leaf discs and the activity of plant peroxidases was unaffected.
Jaulneau et al. (2011) studied the effect of an aqueous extract of Ulva armoricana, rich in ulvan,
against three powdery mildew pathogens, for example, Erysiphe polygoni, E. necator, and Sphareotheca
fuliginea on the common bean, grapevine, and cucumber; they reported a noticeable difference in efficacy
based on the concentrations used. Weekly spraying at 3 g/l dry matter provided 50% protection, whereas
the severity of the symptoms was reduced by up to 90% at double the concentration (i.e., 6 g/l dry matter).
A reporter gene, tagged to a defence-gene promoter, in a transgenic tobacco line, was elicited by treatment
with extracts of U. armoricana that probably contributed to induced plant defence mechanisms against
the powdery mildew pathogen. U. armoricana is a reproducible source of active compounds which can
be used to efficiently protect crop plants against powdery mildew diseases. Similar results were observed
with ethanolic fractions of Ulva spp. which activated plant defence enzymes in Arabidopsis (Jaulneau et
al. 2010). Paulert et al. (2010) showed that ulvan could prime the chitin- and chitosan-elicited oxidative
burst in wheat and rice cells. The pre-treatment of wheat cells with the ulvan increased the chitin-elicited
oxidative burst by about five- to six-fold, as compared to chitosan (two-fold). Similarly, in rice cells, the
elicitation of H 2 O 2 production by chitin or chitosan was increased by 150 and 80 times, respectively after
ulvan pre-treatment. Furthermore, ulvan-treated plants showed reduced symptoms of Blumeria graminis
infection, by 45% in wheat and by 80% in barley.
Freitas et al. (2011) evaluated the effectiveness of ulvan, to induce resistance of Phaseolus vulgaris
to Colletotrichum lindemuthianum, in combination with kaolinite, amorphous silica, or attapulgite clay.
The formulations were applied twice to the bean plants (cv. Uirapuru), one at six days and again three
days before the foliage was inoculated with C. lindemuthianum. The application of ulvan (control) or its
formulations with amorphous silica or kaolinite reduced anthracnose severity by 45%. The efficiency of
ulvan in controlling anthracnose was maintained throughout 12 months of storage when it was formulated
with amorphous silica or kaolinite, but not with attapulgite. Araújo et al. (2008) revealed that resistance
to ‘Gala’ leaf spot in apples was induced with ulvan.
Virii and viroids: Caccamese et al. (1981) reported on the effectiveness of lipid extracts of more than
twenty algae against tobacco mosaic virus (TMV). Menard et al. (2005) studied the effect of PS3 on
tobacco, challenged with TMV. Pre-treatment of plants with PS3 decreased both the lesion number
and the lesion size, eight days after application, whereas the laminarin reduced only the lesion number.
Interestingly this study did not show induction of systemic acquired resistance to TMV, although previous
studies reported that PS3 could activate the salicylic acid (SA) signaling pathway in infiltrated tobacco
and Arabidopsis thaliana leaves (Menard et al. 2004). Laminarin used at 200–500 ug/mL was able to
inhibit TMV infection on tobacco by 66.48% and 66.66%, respectively (Fu et al. 2011). Lapshina et
al. (2007) showed that fucoidan from the brown alga Fucus evanescens inhibited infection of tobacco
plants with TMV by inhibiting the formation of intra-cellular, tubular inclusions, presumably formed
from the granular ones on the last stages of the infection process. Reunov et al. (2011) reported that
pre-treatment of Datura stramonium plants with fucoidan, extracted from Fucus evanescens, suppressed
Montealegre et al. (2010) used ulvan to control the grey rot of apple fruits and found that post-harvest
applications reduced B. cinerea infections on apple by 56%. Yet another study, showed the potential of
ulvan to protect apples from pathogenic infections (Araújo et al. 2008). Two consecutive treatments of
extracted, sulphated polysaccharide from U. armoricana protected alfalfa (Medicago truncatula) against
anthracnose (Colletotrichum trifolii); the mechanisms were related to induced expression of several
pathogenesis-related genes such as PR-10 (Cluzet et al. 2004). Similarly, Paulert et al. (2007), using
2 mg ml
–1
of ulvan, demonstrated induced plant resistance to these pathogens. Paulert et al. (2011) evaluated
the potential of crude extracts and fractionated ulvan from U. fasciata to control bean (Phaseolus vulgaris)
anthracnose caused by C. lindemuthianum, under greenhouse conditions. The soluble, methanolic extract
did not reduce disease severity, however ulvan, sprayed at 10 mg ml
–1
, reduced disease severity by 38%.
These results indicated that ulvan itself can be a strong elicitor of plant resistance to Colletotrichum sp.
attacks. Borsato et al. (2010) showed that an ulvan spray treatment (10 mg mL
–1
) to bean plants, 3–6 days
before infection, induced resistance to rust caused by Uromyces appendiculatus. The diameter of the
pustules on the bean cultivars was reduced, and the activity of glucanases within the treated plants was
increased in moderately susceptible cultivars two days, post-inoculation. However, treatments were not
effective against fungal germination on leaf discs and the activity of plant peroxidases was unaffected.
Jaulneau et al. (2011) studied the effect of an aqueous extract of Ulva armoricana, rich in ulvan,
against three powdery mildew pathogens, for example, Erysiphe polygoni, E. necator, and Sphareotheca
fuliginea on the common bean, grapevine, and cucumber; they reported a noticeable difference in efficacy
based on the concentrations used. Weekly spraying at 3 g/l dry matter provided 50% protection, whereas
the severity of the symptoms was reduced by up to 90% at double the concentration (i.e., 6 g/l dry matter).
A reporter gene, tagged to a defence-gene promoter, in a transgenic tobacco line, was elicited by treatment
with extracts of U. armoricana that probably contributed to induced plant defence mechanisms against
the powdery mildew pathogen. U. armoricana is a reproducible source of active compounds which can
be used to efficiently protect crop plants against powdery mildew diseases. Similar results were observed
with ethanolic fractions of Ulva spp. which activated plant defence enzymes in Arabidopsis (Jaulneau et
al. 2010). Paulert et al. (2010) showed that ulvan could prime the chitin- and chitosan-elicited oxidative
burst in wheat and rice cells. The pre-treatment of wheat cells with the ulvan increased the chitin-elicited
oxidative burst by about five- to six-fold, as compared to chitosan (two-fold). Similarly, in rice cells, the
elicitation of H 2 O 2 production by chitin or chitosan was increased by 150 and 80 times, respectively after
ulvan pre-treatment. Furthermore, ulvan-treated plants showed reduced symptoms of Blumeria graminis
infection, by 45% in wheat and by 80% in barley.
Freitas et al. (2011) evaluated the effectiveness of ulvan, to induce resistance of Phaseolus vulgaris
to Colletotrichum lindemuthianum, in combination with kaolinite, amorphous silica, or attapulgite clay.
The formulations were applied twice to the bean plants (cv. Uirapuru), one at six days and again three
days before the foliage was inoculated with C. lindemuthianum. The application of ulvan (control) or its
formulations with amorphous silica or kaolinite reduced anthracnose severity by 45%. The efficiency of
ulvan in controlling anthracnose was maintained throughout 12 months of storage when it was formulated
with amorphous silica or kaolinite, but not with attapulgite. Araújo et al. (2008) revealed that resistance
to ‘Gala’ leaf spot in apples was induced with ulvan.
Virii and viroids: Caccamese et al. (1981) reported on the effectiveness of lipid extracts of more than
twenty algae against tobacco mosaic virus (TMV). Menard et al. (2005) studied the effect of PS3 on
tobacco, challenged with TMV. Pre-treatment of plants with PS3 decreased both the lesion number
and the lesion size, eight days after application, whereas the laminarin reduced only the lesion number.
Interestingly this study did not show induction of systemic acquired resistance to TMV, although previous
studies reported that PS3 could activate the salicylic acid (SA) signaling pathway in infiltrated tobacco
and Arabidopsis thaliana leaves (Menard et al. 2004). Laminarin used at 200–500 ug/mL was able to
inhibit TMV infection on tobacco by 66.48% and 66.66%, respectively (Fu et al. 2011). Lapshina et
al. (2007) showed that fucoidan from the brown alga Fucus evanescens inhibited infection of tobacco
plants with TMV by inhibiting the formation of intra-cellular, tubular inclusions, presumably formed
from the granular ones on the last stages of the infection process. Reunov et al. (2011) reported that
pre-treatment of Datura stramonium plants with fucoidan, extracted from Fucus evanescens, suppressed