O A RIGINAL RTICLES

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Journal of Applied Sciences Research, 9(6): 3543-3551, 2013
ISSN 1819-544X
This is a refereed journal and all articles are professionally screened and reviewed
ORIGINAL ARTICLES
The Efficacy of Some Fungicides Alternatives on the Antagonistic Ability of Some BioControl Agents in vitro (Review Article)
Nehal S. El-Mougy, M.M. Abdel-Kader and S.M. Lashin
Plant Patholology Dept., National Research Centre, Giza, 12622, Egypt
ABSTRACT
The effect of plant resistance inducers, i.e. Potassium mono hydrogen phosphate salt and Calcium chloride,
mixture of Humic & Folic acids (AF); some essential oils, Cinnamon, Clove and Thyme as well as plant extracts
Halfa Bar, Ginger and Bay laurel on the antagonistic ability of three isolates of Trichoderma spp. as well as one
isolate of each of Bacillus subtilis, Pseudomonas fluorescens and Saccaromyces serevisiae against the linear
growth of the root pathogenic fungi was evaluated In vitro. Obtained data revealed that concentrations used of
calcium chloride enhance significantly the antagonistic ability of T. harzianum, T. viride and T. hamatum,
respectively. Similar trend was also observed with the mixture of Humic and Folic acids. The antagonists T.
harzianum and T. viride resulted in reduction of pathogenic fungal growth to 100% at concentration of 0.2% and
at 0.4%, respectively. Also, the obtained results revealed that Potassium mono-hydrogen phosphate have
significant enhancement effect on the antagonistic ability of tested fungi followed by Sodium bicarbonate and
Potassium bicarbonate. As for essential oils, Cinnamon oil have superior enhancement for increasing the
antagonistic efficacy of T. harzianum, T. viride and T. hamatum followed by Clove and Thyme oils at all used
concentrations. Data also showed that the antagonistic efficacy was increased as the concentration increased of
tested essential oils. All plant extract at different concentrates could enhance the antagonistic ability of tested
fugal bio-agents in respective order when halfa bar, ginger and bay laurel added to growth media. As for
bacterial and yeast antagonists, the obtained results revealed that the antagonistic efficacy of B. subtilis, P.
fluorescns and S. serevisiae against pathogenic fungal growth increased as the concentration of either calcium
chloride, or the mixture of Humic and folic acids increased in growth media. Also, different concentrations of
Potassium, Sodium bicarbonates and Potassium mono-hydrogen phosphate have positive effect for enhancing
the efficacy of antagonistic ability of tested bio-agents. Moreover, in general Thyme oil had more enhancing
effect on the antagonistic ability than that of both Cinnamon and Clove oils at all tested concentrations. As for
plant extracts, all tested concentrations could enhance the efficacy of antagonistic ability of bacterial and yeast
bio-agents. The present review summarizes studies aimed to evaluate different control measures of fungicides
alternatives approaches, e.g. some plant resistance inducers, essential oils and plant extracts on the antagonistic
ability of some fungal, bacterial and yeast bio-agents in vitro. This work was carried out during a project
supported by the Science and Technology Development Fund (STDF), Egypt, grant No. 1059.
Key words: Antagonistic ability, antagonistic bacteria and yeast, Chemical plant resistance inducers, Essential
oils, fungal bio-agents, Plant extracts, Root pathogenic fungi, soil borne pathogenic fungi.
Introduction
Plant diseases caused by soil-borne pathogens play an important role in the destruction of natural resources
in agriculture. Root rot disease, caused by soil-borne pathogenic fungi including Pythium spp., Rhizoctonia spp.,
and Fusarium spp. Sclerotinia spp. and other pathogenic fungi cause widespread, serious economic loss both in
greenhouse and field production systems under conditions favorable for disease development. Chemical
pesticides have been extensively used for control fungal plant disease but their employment favored the
selection of fungicides resistant strains as well as negative effect on non-target organisms and environment
(Benitez et al., 2004).
Plant pathogenic fungi are ubiquitous in intensive agricultural areas and are extensively controlled by using
a large number of inorganic and organic chemical fungicides. No doubt these chemicals are effective in crop
protection; however, they exhibit negative environmental and economic aspects, such as pollution of the soil–
water system, a specificity and selection of resistant phytopathogenic populations, which lead to soil quality
deterioration, rather than high costs of production (Iacomi-Vasilescu et al., 2004). It therefore appears that an
urgent investigation of possible alternative, environmentally safe, bioactive natural organic molecules able to
Corresponding Author: N.S. El-Mougy, Plant Patholology Dept., National Research Centre, Giza, 12622, Egypt.
E-mail [email protected]
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control phytopathogenic fungi in soil is needed. Application of biological control using antagonistic
microorganisms has proved to be successful for controlling various plant diseases (Sivan, 1987).
In this respect, the development of alternative methods for plant pathogens is of great interest not only for
scientists but also for agriculture. Biological control agents are risk free both for environment and non-target
organisms, and could reduce the use of chemical products. Most bio-control agents (BAs) have varied
performance in different environmental conditions. Some of this variability has been attributed to differences in
physical and chemical properties found in natural environments where bio-control agents are applied
(Thomashow and Weller, 1996; Duffy et al., 1997). The growth medium used to produce these agents, has a
profound effect on them and their products. The accurate incorporation of nutrients has improved the biomass
production of BAs, but unexpectedly did not enhance (Slininger et al., 1996) or even decreased the bio-control
efficacy (Moënne-Loccoz et al., 1999). Recognition of the environmental factors that regulate the growth and
bio-control efficacy of antagonist bacteria is an essential step towards advancing the level and reliability of their
bio-control potential (Duffy and Defago, 1999). Commercial production of disease-suppressive strains of
bacteria such as P. fluorescens and B. subtilis as bio-control agents in postharvest diseases requires low cost and
high biomass production while maintaining their bio-control efficacy (Costa et al., 2001). A successful diseasecontrol program could involve just a single practice, but the long term reduction of disease losses generally
requires the application of several control measures. Biological control approach depends upon the
establishment and maintenance of a threshold population of introduced bio-agent into the soil, and a drop in
viability below that level may eliminate the possibility of biological control. Many soil edaphic factors,
including temperature, moisture, pH and nutrition influence the survival and establishment of the bio-agent and
their interaction with the pathogens.
The present review focuses on cited reports concerning recorded compounds that are safe to humans and the
environment as well as could enhance the antagonistic ability of introduced fungal bio-agents to the soil. Several
in vitro studies conducted with the efficacy of some chemical plant resistance inducers, essential oils and plant
extracts on the antagonistic ability of some bio-agents, i.e. Trichoderma harzianum, T. viride, T. hamatum,
Pseudomonas fluorescens, Bacillus subtilis and the yeast Saccaromyces serevisiae are included in present
review.
(A) Effect of some chemical plant resistance inducers on antagonistic ability:

Fungal bio-agents:
Many investigations concerned with the use of abiotic factors for induction of plant resistance against
several diseases. The effect of chemical plant resistance inducers on the antagonistic ability of the fungal
antagonistic agents against the linear growth of the root pathogenic fungi was evaluated in vitro (Abdel-Kader et
al., 2012a). They tested the antagonistic ability of Trichoderma harzianum, T. Viride and T. hamatum. These
antagonistic fungi were isolated from cucumber, cantaloupe, tomato and pepper grown in plastic houses under
protected cultivation systems and showing root rot disease symptoms (El-Mougy et al., 2011). The results
obtained by Abdel-Kader et al., (2012) revealed that concentrations used of calcium chloride enhance
significantly the antagonistic ability of T. harzianum, T. viride and T. hamatum, respectively. Only, T.
harzianum, exhibit complete reduction (100%) in all pathogenic fungal growth at concentration of 2 and 4%
comparing with the range of 47.7-61.1% in medium free of calcium chloride. Similar observation was recorded
with T. viride at concentration of 4% comparing with the range of 37.7-46.6% in medium free of calcium
chloride. Meanwhile, T. hamatum showed less response to the calcium chloride concentrations as enhancement
factor to antagonistic ability. Similarly, calcium chloride at 2% (20 mg/ml) obviously inhibited spore
germination and germ tube growth of R. stolonifer PDA medium (Tian et al. 2002). This result further supports
the results of Wisniewski et al. (1995), who found that calcium chloride might reduce fungal infection through
direct inhibition of spore germination and growth. Maouni et al. (2007) reported that in vitro, calcium chloride
significantly reduced pear fruit decay caused by A. alternata and Penicillium expansum when used at 4 and 6%.
Furthermore, calcium chloride was reported to suppress growth of the citrus mould pathogen Penicillium
digitatum (Droby et al.1997). It is also known that addition of calcium chloride can also improve the activity of
biocontrol agents (Droby et al. 1997; McLaughlin et al. 1990).
The efficacy of Potassium, Sodium bicarbonates and Potassium mono-hydrogen phosphate on the
antagonistic ability of Trichoderma spp. were also studied (Abdel-Kader et al., (2012a). They reported that
Potassium mono-hydrogen phosphate have significant enhancement effect on the antagonistic ability of tested
fungi followed by Sodium bicarbonate and Potassium bicarbonate, respectively. Their data also revealed that
Potassium bicarbonate concentrations showed lesser effect on the antagonistic ability of tested fungal bioagents. In this concern it was observed that the reduction in linear growth of pathogenic fungi against
antagonists fluctuated referring to concentration used for each pathogenic fungus. Enhancement of antagonistic
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ability of tested fungal bio-agents could be arranged in descending order as T. harzianum, T. viride and T.
hamatum.
In this respect, many workers also reported that potassium and sodium bicarbonate showed inhibitory
effects against several pathogenic fungi. In addition, bicarbonate salts has been shown to have a considerable
inhibitory effect on several fungi and causes the collapse of hyphal walls and shrinkage of conidia (Punja and
Grogan, 1982 and Ziv & Zitter, 1992). Hypothesis have been proposed for the inhibitory mechanisms of
bicarbonate as hydrogen ion concentration of bicarbonate salts has been shown to have a profound inhibitory
effect on sclerotia and conidia germination of S. rolfsii and S. fuliginea, respectively (Punja and Grogan, 1982
and Homma et al., 1981).
As for the mixture of Humic and Folic acids similar trend was also recorded (Abdel-Kader et al., 2012a).
Their reported data revealed that concentrations of 0.4 and 0.6% increased the antagonistic ability of tested
fungi. They added that antagonists resulted in reduction of pathogenic fungal growth to 100% which was
observed at concentration of 0.2% for T. harzianum and at 0.4% for T. viride comparing to (47.7-61.1%) and
(37.7-46.6%) for T. harzianum and T. viride respectively in medium free of Humic and Folic acids mixture.
Also, T. hamatum showed lesser response to Humic and Folic acids mixture concentrations that its antagonistic
ability was able to reduce pathogenic fungal growth from the range of (44.4-56.6%) in control treatment up to
(71.1-82.2) in medium contains 0.6% Humic and Folic acids.
A number of studies have demonstrated that humic acids (HA) and fulvic acids (FA) are able to control
plant diseases caused by various soil-borne phytopathogenic fungi (EL-Masry et al., 2002; Loffredo et al.,
2007). In contrast, Loffredo et al., (2008) evaluated two concentrations of humic and fulvic (HS) acid on the
growth in vitro of one plant pathogenic, Sclerotinia sclerotiorum, and two antagonistic, Trichoderma viride and
T. harzianum. They found that the presence of HS in the growing medium caused a relevant inhibition of the
mycelial growth of S. sclerotiorum and a marked stimulation of sclerotial formation that was exhibited as early
appearance and numerical increase. On the contrary, the same HS treatments generally did not inhibit the
growth of the two Trichoderma species.

Bacterial and yeast bio-agents:
The effect of Calcium chloride on the antagonistic ability of bacteria and yeast against some soil-borne
pathogenic fungi was evaluated in vitro (Abdel-Kader et al., 2012b). They recorded that the antagonistic
efficacy of Bacillus subtilis, Pseudomonas fluorescens and Saccaromyces serevisiae against pathogenic fungal
growth increased as the concentration of calcium chloride increased in growth media. In this regard, all tested
pathogenic fungi showed high sensitivity against the antagonist B. subtilis where their growth reduced by 100%
in the presence of calcium choride at 4% in growth media. Another feature at a lesser extent was observed with
P. flourescencse and S. serevisiae that they could reduced the pathogenic fungal growth to (46.6-77.7%) and
(65.5-87.7%), respectively at the same concentration of 4%. Many researchers have shown that calcium plays an
important role in the inhibition of postharvest decay of fruits (Conway and Sams, 1985; Conway et al., 1992)
and in enhancing the efficacy of postharvest bio-control agents (Conway et al., 1991; Wisniewski et al., 1995).
Postharvest calcium treatment of apples provided broad-spectrum protection against the postharvest pathogens
of Penicillium expansum and Botrytis cinerea (Saftner et al., 1997). The addition of CaCl2 (2% w/v) to the
formulation of the yeast bio-control agent, Candida oleophila, enhanced the ability of this yeast to protect
apples against postharvest decay (Wisniewski et al., 1995). The efficacy of controlling grey mould and blue
mould rots in apples was enhanced when Trichosporon sp., even at a low concentration of 105 CFU mL−1, was
applied in the presence of CaCl2 (2% w/v) in an aqueous suspension (Tian et al., 2001). Moreover, Tian et al.,
(2002) reported that combining CaCl2 with the yeast suspensions significantly enhanced the biocontrol activity
of Colletotricum guilliermondii in peaches and Pichia membranefaciens in nectarines to Rhizopus rot. The same
effects on bio-control activity, achieved by the addition of calcium, were also observed by using the yeasts of
Pichia guilliermondii (Droby et al., 1993) and Candida spp. (Wisniewski et al., 1995) as postharvest bio-control
agents. The addition of calcium directly inhibited the number of pathogens and indirectly increased the ability of
the yeast to inhibit the growth of pathogens and the resistance of fruit to pathogens (Tian et al., 2001).
Pathogen–antagonist interactions inside the wound, such as competition for space and nutrients and the
production of lytic enzymes on attachment of the antagonist to the mycelium, are believed to be the main
mechanisms of inhibiting diseases by fungal pathogens (Chalutz et al., 1988; Arras, 1996). Competition for
nutrients has been frequently cited as a mechanism of bio-control by antagonistic yeasts such as Pichia, Candida
and Cryptococcus spp. (Arras, 1996; Elad, 1996).
Regarding the effect of some plant resistance inducers on the antagonistic ability of bacteria and yeast
against pathogenic fungi with different concentrations of Potassium, Sodium bicarbonates and Potassium monohydrogen phosphate was evaluated in vitro. Abdel-Kader et al., (2012b) reported that Potassium mono-hydrogen
phosphate showed superior effect in this regard followed by Potassium bicarbonates and Sodium bicarbonate,
respectively. They added that Pythium sp. was more sensitive to B. subtilis, P. fluorescns and S. serevisiae, than
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that observed with S. sclerotiorum and M. phaseolina to the same antagonistic bacteria and yeast tested isolates.
Many investigators reported the use of some safely chemicals in combination with bio-agents for enhancing the
biological activity. Sodium bicarbonate has been successfully used in combination with bacterial and yeasts biocontrol agents to enhance control of postharvest decays on citrus, pome, and stone fruits (Smilanick et al., 1999;
Wisniewski et al., 2001). Previous research has indicated that ammonium molybdate and sodium bicarbonate
could enhance the efficacy of biological control (Droby et al. 2003; Obagwu and Korsten 2003; Gamagae et al.
2004; Yao et al. 2004). Also, Janisiewicz et al., (2005) recorded that the addition of sodium bicarbonate reduced
apple decay caused by Penicillium expansum when combined with the yeast Metschnikowia pulcherrima more
than each treatment alone. The inhibitory effect of sodium bicarbonate on microorganisms may be due to a
reduction of cell turgor pressure that causes a collapse and shrinkage of hyphae and spores, resulting in
fungistasis (Fallik et al., 1997). Droby et al. (2003) observed that bio-control activity by Candida oleophila
against P. expansum and B. cinerea in apples and Monilinia fructicola and Rhizopus stolonifer in peaches was
enhanced by the addition of sodium bicarbonate. Furthermore, application of additives improved bio-control of
brown rot on sweet cherry fruit under various storage conditions. It is postulated that the enhancement of disease
control is directly because of the inhibitory effects of additives on pathogen growth, and indirectly because of
the relatively little influence of additives on the growth of antagonistic yeasts (Qin et al., 2006).
The effect of Humic and folic acids as a mixture on the antagonistic ability of bacteria and yeast against
some soil-borne pathogenic fungi was evaluated in vitro by several investigators. Abdel-Kader et al., (2012b)
reported that the efficacy of the antagonistic ability of tested bio-agents increased in parallel with increasing the
concentrations of Humic and folic acids mixture reaching its maximum at the highest concentration. In this
regards, complete inhibition in pathogenic fungal growth of A. solani, F. solani, F. oxysporum, R. solani, S.
rolfsii, M. phaseolina and Pythium sp., when grown against the antagonistic bacteria B. subtilis in the presence
of 0.6% of Humic and folic acids mixture in the growth media. This observation was also recorded for S.
serevisiae that its antagonistic ability was increased at concentration of 0.6% of Humic and folic acids mixture
to be able to cause complete inhibition in the growth of F. solani, F. oxysporum, R. solani and S. rolfsii. Also,
minimum fungal growth of the pathogen S. sclerotiorum and S. minor was recorded at the highest concentration
0.6% of Humic and folic acids mixture when grown against B. subtilis and S. serevisiae. Pseudomonas
fluorescns showed a lower response to all concentrations of Humic and folic acids mixture for increasing their
antagonistic ability. In this regards, Charest et al., (2005) investigated the in vitro influence of humic substances
(HS) on the inhibition of Pythium ultimum by two compost bacteria, Rhizobium radiobacter (Agrobacterium
radiobacter) and Pseudomonas aeruginosa. They found that HS enhanced the microbial antagonism when
added to a culture medium. Also, Prakash et al., (2010) reported that that bio-solubilization of humic acid
enhances plant growth and bio-control efficacy against phyto-pathogenic organism.
(B) Effect of some essential oils on antagonistic ability:

Fungal bio-agents:
It is well established that some plants contain compounds able to inhibit the microbial growth (Naqui et al.
1994). These plant compounds can be of different structures and different mode of action when compared with
antimicrobials conventionally used to control the microbial growth and survival (Nascimento et al. 2000).
Potential antimicrobial properties of plants had been related to their ability to synthesize, by the secondary
metabolism, several chemical compounds of relatively complex structures with antimicrobial activity, including
alkaloids, flavonoids, isoflavonoids, tannins, cumarins, glycosides, terpens, phenylpropannes, organic acids
(Nychas 1996). The aesthetic, medicinal and antimicrobial properties of plant essential oils have been known
since ancient times. Essential oils, i.e. Cinnamon, Clove and Thyme at different concentrations were evaluated
for their effect on the antagonistic ability of fungal antagonists against soil-borne pathogenic fungi, in vitro
conditions. In this concern (Abdel-Kader et al., 2012a) reported, in general, that all tested essential oils
enhanced the antagonistic ability of fungal bio-agents. They added that, Cinnamon oil have superior
enhancement for increasing the antagonistic efficacy of T. harzianum, T. viride and T. hamatum followed by
Clove and Thyme oils at all used concentrations. In addition, the antagonistic efficacy was increased as the
concentration increased of tested essential oils. Their data also showed that the antagonistic ability of T.
harzianum against tested pathogenic fungi in control treatment recorded between (48.8-61.1%) and enhanced up
to (77.7-88.8%); (68.8-88.8) and (66.6-88.8) at concentration of 1% of Cinnamon, clove and Thyme oils ,
respectively. Similarly, the antagonistic ability increased from (50.0-61.1%) up to (82.2-88.8%), (75.5-88.8) and
(77.7-83.3%) for T. viride at 1% of Cinnamon, clove and Thyme oils, respectively. Also, in respective order the
antagonistic ability of T. hamatum enhanced from (50.0-61.1%) in control up to (54.4-88.8), (73.3-86.6) and
(74.4-84.4) at 1% of tested oils.
Numerous studies on the fungicidal and fungistatic activities of essential oils have indicated that many of
them have the power to inhibit fungal growth. Thyme oil proved to be extremely effective as a fumigant as well
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as a contact fungicide against a range of the economically significant fungi Alternaria spp., Aspergillus spp.,
Botrytis cinerea, Erysiphe graminis (Alefyah and Avice 1997). The information was found in the literature
concerning mode of action of essential oils on/in the fungal cell in order to promote fungistatic or fungicide
effect. In general, inhibitory action of natural products on moulds involves cytoplasm granulation, cytoplasmic
membrane rupture and inactivation and/or inhibition of intercellular and extracellular enzymes. These biological
events could take place separately or concomitantly culminating with mycelium germination inhibition (Campo
et al. 2003).
Also, it is reported that plant lytic enzymes act in the fungal cell wall causing breakage of b-1,3 glycan, b1,6 glycan and chitin polymers (Brull and Coote 1999). The mode by which microorganisms are inhibited by
essential oils and their chemical compounds seem to involve different mechanisms. It has been hypothesized
that the inhibition involves phenolic compounds, because these compounds sensitize the phospholipid bilayer of
the microbial cytoplasmic membrane causing increased permeability and unavailability of vital intracellular
constituents (Juven et al. 1994). Reports indicated that essential oils containing carvacrol, eugenol and thymol
(phenolic compounds) had the highest antibacterial performances (Kim et al. 1995).
•
Bacterial and yeast bio-agents:
Great interest has been shown in combining microbial bio-control agents with other chemical components
to increase their activity against post-harvest pathogens (Droby et al., 1998). Essential oils are considered a
promising alternative with many having antimicrobial properties. However, very high concentration is needed
when applied to real food systems (Hammer et al., 2003; Ahmet et al., 2005). Also, application of essential oil is
a very attractive method for controlling postharvest diseases. Reported data of Abdel-Kader et al., (2012b)
showed the effect of some essential oils on the antagonistic ability of bacteria and yeast against pathogenic fungi
in vitro. Their obtained results revealed that, in general, Thyme oil had more enhancing effect on the
antagonistic ability than that of both Cinnamon and Clove oils at all tested concentrations. They added, it was
observed that the pathogenic fungal growth fluctuated at the same used concentration depending on the
antagonist. In their work, it was observed that the pathogenic fungal growth reduced between 66.6-88.8%, 66.683.3% and 61.1-68.8% when grown in dual culture against B. subtilis, P. fluorescens and S. serevisiae,
respectively in growth media supplemented with Thyme oil at concentration of 1%. It was reported that
essential oils and their components are gaining increasing interest because of their relatively safe status, their
wide acceptance by consumers, and their exploitation for potential multi-purpose functional use (Ormancey et
al., 2001). Essential oils have been used successfully in combination with a variety of treatments, such as
antibacterial agents, mild heat and salt compounds (Karatzas et al., 2000). Abd-Alla et al., (2009) reported that
the yeast, Saccharomyces cerevisiae, Candida tenuis and the commercial backing yeast of Saccharomyces
cerevisiae mixture (CBY) and/or peppermint, melon and rose essential oils were evaluated for their in vitro
activity against the fungal growth of Botrytis cinerea, Rhizopus stolonifer and Alternaria alternate the causal
agents of tomato fruit decay. Saccharomyces cerevisiae mixture (CBY) proved itself to have the highest
inhibitory effect on the growth of the pathogenic tested fungi followed by the two other yeast isolates S.
cerevisiae and C. tenuis. All the tested concentrations of peppermint oil had not negative effect against the
viability of tested yeasts, while significant reduction in the populations of all yeast isolates was observed at
melon and rose oils treatments even at the lowest concentration tested. Peppermint oil showed superior
inhibitory effect against the growth of tested pathogenic fungi followed by rose and melon oils, respectively.
Mixtures of peppermint oil with any of yeast isolate showed high inhibitor effect against the pathogenic fungal
growth compared with rose and melon oils mixtures.
They added that, under storage conditions, application of carnauba wax formula containing either S.
cerevisiae or S. cerevisiae (CBY) combined with peppermint oil (1%) enhanced the efficacy of decay incidence
of tomato fruits (gray mould, soft rot and black rot) caused by all the tested pathogenic fungi, i.e. Botrytis
cinerea, Rhizopus stolonifer and Alternaria alternate during storage reaching up to 100% under artificial
inoculation better than each individual component. On the light of their study, it could be concluded that the
application of carnauba wax containing 1% peppermint oil combined with S. cerevisiae or S. cerevisiae (CBY),
could control several post-harvest diseases of tomato fruit without affecting tomato fruit quality under storage
conditions.
The mode by which microorganisms are inhibited by essential oils and their chemical compounds seem to
involve different mechanisms. It has been hypothesized that the inhibition involves phenolic compounds,
because these compounds sensitize the phospholipid bilayer of the microbial cytoplasmic membrane causing
increased permeability and unavailability of vital intracellular constituents (Juven et al., 1994). Reports
indicated that essential oils containing carvacrol, eugenol and thymol (phenolic compounds) had the highest
antibacterial performances (Kim et al., 1995).
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(C) Effect of some plant extracts on antagonistic ability:

Fungal bio-agents:
The use of plants or plant materials as fungicides is of a great importance and needs more attention (Bodde
1982) and various plant products like gum, oil, resins etc. are used as fungicidal compounds (Daoud et al. 1990;
Dwivedi et al. 1990). Several reports indicated that plant spices containing carvacrol, eugenol and thymol
(phenolic compounds) had the highest antibacterial performances (Kim et al. 1995). Alkaloids, flavonoids,
isoflavonoids, tanins, cumarins, glycosides, terpens and phenolic compounds were synthesized by plants as
secondary metabolites (Simões et al. 1999). However, there is little information on spices and their derivatives`
action on/in a fungal cell. In general, inhibitory action of natural products on moulds involves cytoplasm
granulation, cytoplasmic membrane rupture and inactivation and/or inhibition of intercellular and extracellular
enzymes. Moreover, the mode by which microorganisms are inhibited by spices and their chemical compounds
seem to involve different mechanisms. It was hypothesized that the inhibition involves phenolic compounds,
because these compounds sensitize the phospholipid bilayer of the microbial cytoplasmic membrane causing
increased permeability and unavailability of vital intracellular constituents (Juven et al. 1994).
The effect of some plant extracts, i.e. Halfa Bar, Ginger and Bay laurel on the antagonistic ability of
Trichoderma spp. against some soil-borne pathogenic fungi was estimated in vitro (Abdel-Kader et al., 2012a).
Their reported data revealed that all plant extract at different concentrates could enhance the antagonistic ability
of tested fugal bio-agents. In this concern, the antagonistic efficacy of T. harzianum against pathogenic fungi
increased from the range of (48.8-61.1%) in media free of plant extracts up to (57.7-73.3%), (60.0-73.3%) and
(58.8-73.3%) at the highest concentration (4%) of Halfa Bar, Ginger and Bay laurel, respectively. Meanwhile,
the antagonistic efficacy of T. viride against pathogenic fungi also increased from the range of (50.0-61.1%), in
media free of plant extracts up to (61.1-68.8%), (58.8-71.1%) and (57.7-71.1%) at the highest concentration.
The recorded increase in antagonistic ability of T. hamatum was from (52.2-61.1) up to (61.1-71.1%), (60.075.5%) and (62.2-74.4%) in respective order with concentration (4%) of Halfa Bar, Ginger and Bay laurel
extracts. Also, Haikal (2007) reported that the efficacy of biological control of cucumber root-rot caused by the
pathogenic fungus F. solani was improved by using aqueous extract of aerial parts of A. indica; Z. spina-christi
and Z. coccineum in combination with the bio-control agent T. harzianum.

Bacterial and yeast bio-agents:
Many reports conducted with study the effect of some plant extracts on the antagonistic ability of bacteria
and yeast against pathogenic fungi was also evaluated in vitro. Recorded data of Abdel-Kader et al., (2012b)
revealed that all tested concentrations of tested plant extracts could enhance the efficacy of antagonistic ability
of bacterial and yeast bio-agents. Their data also, showed that no announced increase in the antagonistic ability
was observed. Significant increase in antagonistic ability was observed only with the highest concentration of
tested plant extracts. Moreover, no significant differences were observed between the tested Halfa Bar, Ginger
and Bay laurel extracts at all used concentrations. In this regard, also many researchers stated that several higher
plants and their constituents have been successfully used in plant disease control. The use of antifungal plant
extracts as a component of integrated disease management can be prove useful. The present review
demonstrated potential efficacy for enhancing the antagonistic ability of tested bacterial and yeast bio-agents
against various soil borne pathogenic fungi. Similar reports are cited in literature, Sarovenan and Marimuthu
(2003) reported that A. indica has improved the biological control of F. oxysporum f. sp. cubense, the causal
agent of wilt disease in banana seedlings, when mixed with the biocontrol agents such as Pseudomenas
fluerescens or T. harzianum and T. viride. Also, Radha and Padma (2011) reported that it was clear that the
methanolic extract of Majorana hortensis (majoram) leaves significantly increases the cell viability of the yeast
Saccharomyces cerevisiae.
Conclusion:
Hence, the objective of this review was to determine if plant resistance inducers, essential oils and plant
extracts could provide enhancement effect to antagonistic ability against soil-borne pathogenic fungi.
Considering their attribute and broad-spectrum activities, successful development of such compounds as
antifungal would not only provide a potent tool for control of root rot pathogenic fungi, but also could promise
success in multipurpose bio-rational alternatives to conventional fungicides for the management of other plant
diseases.
The present results may lead to the conclusion that since application of plant resistance inducers, essential
oils and plant extracts is proved to be applicable, safe and cost-effective method for controlling plant diseases.
Also, the use of them in agriculture could be a suitable alternative for inclusion in disease control systems and
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J. Appl. Sci. Res., 9(6): 3543-3551, 2013
could act sometimes as main or adjuvant antimicrobial compounds and do not leave a toxic residue in the
product. Therefore, this strategy have had favorable results, where the addition of a biological control agent in
combination with plant resistance inducers, essential oils and plant extracts could be resulted in increased
symptomless plant stand over the biological agent.
Acknowledgment
This work was supported financially by the Science and Technology Development Fund (STDF), Egypt,
Grant No. 1059.
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