BIO-CONTROL AGENTS IN MANAGEMENT OF POST-HARVEST DISEASES

Abstract

Plant diseases are among the main constraints affecting the production and productivity of crops
both in terms of quality and quantity. Use of chemicals continues to be the major tactic to mitigate the menace
of crop diseases. However, because of the environmental concerns, health conscious attitude of human beings
and other hazards associated with the use of chemicals, use of bio agents to suppress the disease-causing
activity of plant pathogens is gaining importance. Of various biological approaches, the use of antagonistic
microorganisms is becoming popular throughout the world. Several postharvest diseases can now be
controlled by microbial antagonists. Although the mechanism(s) by which microbial antagonists suppress the
postharvest diseases is still unknown, competition for nutrients and space is most widely accepted mechanism
of their action. In addition, production of antibiotics, direct parasitism, and possibly induced resistance in the
harvested commodity are other modes of their actions by which they suppress the activity of postharvest
pathogens in fruits and vegetables. Microbial antagonists are applied either before or after harvest, but
postharvest applications are more effective than preharvest applications. Efficacy of microbial antagonist(s)
can be enhanced if they are used with salt additives, nutrients and natural plant products and physical
treatments.

Full text

Life Sciences International Research Journal : Volume 4 Issue 1 (2017) ISSN 2347-8691
ISBN 978-93-84124-98-4
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BIO-CONTROL AGENTS IN MANAGEMENT OF POST-HARVEST DISEASES
MIDHUN BABYCHAN, ELIZABETH T JOJY, GOLDA MARIA SYRIAC
Abstract: Plant diseases are among the main constraints affecting the production and productivity of crops
both in terms of quality and quantity. Use of chemicals continues to be the major tactic to mitigate the menace
of crop diseases. However, because of the environmental concerns, health conscious attitude of human beings
and other hazards associated with the use of chemicals, use of bio agents to suppress the disease-causing
activity of plant pathogens is gaining importance. Of various biological approaches, the use of antagonistic
microorganisms is becoming popular throughout the world. Several postharvest diseases can now be
controlled by microbial antagonists. Although the mechanism(s) by which microbial antagonists suppress the
postharvest diseases is still unknown, competition for nutrients and space is most widely accepted mechanism
of their action. In addition, production of antibiotics, direct parasitism, and possibly induced resistance in the
harvested commodity are other modes of their actions by which they suppress the activity of postharvest
pathogens in fruits and vegetables. Microbial antagonists are applied either before or after harvest, but
postharvest applications are more effective than preharvest applications. Efficacy of microbial antagonist(s)
can be enhanced if they are used with salt additives, nutrients and natural plant products and physical
treatments.
Keywords: Antibiosis, Bio-Control, Parasitism, Post-Harvest.
1.Introduction: Post-harvest diseases need to be
controlled to maintain the quality and abundance of
fruits and vegetables produced by growers around the
world. Post-harvest decay of fruits and vegetables
accounts for significant level of post-harvest losses. It
is estimated that about 20-25 percent of the harvested
fruits and vegetables are decayed by pathogens even
in developed countries (Singh and Sharma,2007). In
developing countries, the percent loss is quite high
ranging up to 50 percent (Eceket and Ogawa,1985).
And these losses were managed by fungicides and it
has contributed significant increases in the quality
and quantity of the produce over the past years. The
excessive use of agrochemicals leads to the
environmental pollution and health issues, fear-
mongering by some opponents of pesticide, has led to
considerable change in people’s attitude towards the
use of agrochemicals. The purposeful utilization of
living organisms whether introduced or indigenous,
other than the disease resistant host plants, to
suppress the activities or populations of one or more
plant pathogens is referred to as biocontrol. Among
different biological approaches, use of the microbial
antagonists like yeasts, fungi, and bacteria is quite
promising and gaining popularity (Korsten, 2006).
2.Criteria for an ideal antagonist: A potential
microbial antagonist should have certain desirable
characteristics to make it an ideal bioagent (Barkai-
Golan, 2001): The antagonist should be: [1] genetically
stable; [2] effective at low concentrations; [3] not
fastidious in its nutritional requirements; [4] capable
of surviving under adverse environmental conditions;
[5] effective against a wide range of the pathogens
and different harvested commodities; [6] resistant to
pesticides; [7] a non-producer of metabolites harmful
to human; [8] non-pathogenic to the host; [9]
preparable in a form that can be effectively stored
and dispensed; and [10] compatible with other
chemical and physical treatments. In addition, a
microbial antagonist should have an adaptive
advantage over specific pathogen (Wilson and
Wisniewski, 1989).
3.Mode of Action: Biological control using
antagonists has proved to be one of the most
promising alternatives, either alone or part of an
integrated pest management policy to reduce
pesticide use (Wilson and Wisniewski, 1993).
However, it is important to understand the mode of
action of the microbial antagonists because, it will
help in developing some additional means and
procedures for better results from the known
antagonists, and it will also help in selecting more
effective and desirable antagonists or strains of
antagonists (Wilson and Wisniewski, 1989).
3.1. Competition for nutrients and space:
Competition for nutrition and space between the
microbial antagonists and the pathogen is considered
as the major mode of action by which microbial
antagonists suppress pathogens causing decay in
harvested fruits and vegetables (Droby et al., 1989).
Competition for nutrients was demonstrated for
Pichia guilliermondii against Penicillium digitatum co-
cultivated on synthetic media (Droby et al., 1989): the
addition of exogenous nutrients resulted in a reduced
efficacy because the antagonists offered better results
when nutrients were scarce. Rapid colonization of
fruit wound by the antagonist is critical for decay
control and manipulations leading to improved
colonization enhance biocontrol (Mercier and
Wilson, 1994). Thus, microbial antagonists should
have the ability to grow more rapidly than the
pathogen. Competition for rare but essential

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micronutrients, such as iron, has also shown to be
important in biological disease control. Plants
actively respond to a variety of environmental
stimulating factors, including gravity, light,
temperature, physical stress, water and nutrient
availability and chemicals produced by soil and plant
associated microorganisms (Audenaert et al., 2002).
These stimuli will either induce or condition the host
plant defenses through biochemical changes that
enhance resistance against subsequent infection by a
variety of pathogens.
3.2. Antibiosis: Production of antibiotics is the
second important mechanism by which microbial
antagonists suppress the pathogens of harvested
fruits and vegetables. Many microbes secrete one or
compounds possessing antibiotic activity. It has been
shown that some antibiotics produced by
microorganisms are particularly effective against
plant pathogens and the diseases they cause. Bacterial
antagonists like Bacillus subtilis and Pseudomonas
cepacia Burkh are known to kill pathogens by
producing antibiotic iturin (Gueldner et al., 1988).
The antagonism so produced by Bacillus subtilis was
effective in controlling fungal rot in citrus (Singh and
Deverall, 1984). Although, antibiosis might be an
effective tool for controlling postharvest diseases in a
few fruits and vegetables, at present, emphasis is
being given for the development of non-antibiotic
producing microbial antagonists for the control of
postharvest diseases of fruits and vegetables (El-
Ghaouth et al., 2004). The use of antibiotics in food
products is a major concern today, due to the
development of human as well as plant pathogens
resistant to these compounds.
3.3. Parasitism: Direct parasitism is yet another
mode of action by which the antagonists interact
with the pathogens. According to Wisniewski et al.
(1991), a strong adhesion in vitro of Pichia
guilliermondii antagonist to Botrytis cinerea
mycelium is due to a lectin link. Similarly, El-
Ghaouth et al., 1998 observed that Candida saitona
attached strongly to the hyphae of Botrytis cinerea
and caused swellings.
Lytic enzymes are also produced by the microbial
antagonists to control the pathogenic
microorganisms. These enzymes act by degrading the
cell wall of the phytopathogenic fungi. Strong
attachment of microbial antagonist with enhanced
activity of cell wall degradation enzymes may be
responsible for enhancing the efficacy of microbial
agents in controlling the postharvest diseases of fruits
and vegetables (Wisniewski et al., 1991).
3.4. Induced Resistance: Induced resistance is
defined as the state of enhanced defensive capacity
developed by plants when appropriately stimulated.
Many antagonistic yeasts are effective when applied
before pathogen inoculation. This observation
suggested that application of yeast cell induce
resistance in the fruit skin. Microbial antagonists
induce disease resistance in the harvested
commodities by the production of antifungal
compounds, as in avocado (Persea americana Mill)
fruit (Prusky et al., 1994) and accumulation of
phytoalexins like scoparone and scopoletin in citrus
fruit (Rodov et al., 1994). These antifungal
compounds are produced by the microbial
antagonists, thereby, providing biocontrol on the
harvested commodities.
4.Application methods of microbial antagonist:
After a potential microbial antagonist is selected, and
its application method is to be found out. Usually,
there are two method of application: pre-harvest
application and post-harvest application.
4.1. Pre-harvest application: In several cases,
pathogen infect fruits and vegetables in the field and
their latent infection become major factor for decay
during transportation or storage of fruits and
vegetables. Therefore, pre-harvest application of
microbial antagonistic culture is often effective to
control post-harvest decay of fruits and
vegetables(Irtwange,2006). The many purpose of
preharvest application is to colonize the antagonist
on the surface of fruits so that wounds inflicted
during harvesting can be colonized by the antagonist
before colonization of the pathogen. Although it is
difficult to control post-harvest disease of strawberry
even with pre-harvest application of fungicides, some
success has been achieved with field application of
various microbial antagonist like Gliocladium roseum
Bainer, Trichoderma harzianum (Sutton et al,1997;
Kovach et al,2000). Preharvest application of
Aureobasidium pullulans reduced storage rots in
strawberry significantly grapes, cherries and apples
(Lima et al,1997; Schena et al,2003; Leibinger et
al,1997).
4.2. Post-Harvest Application: Post-harvest
application of microbial antagonistic is a better,
practical and useful methods for controlling post-
harvest diseases of fruits and vegetables. In this
method, microbial cultures are applied either as post-
harvest sprays or as dip in antagonistic solution
(Irtwange,2006). Post-harvest application of
Trichoderma harzianum, Trichoderma viride,
Gliocladium roseum and Paecilomyces variotii bainier
resulted in better control of botrytis rot in
strawberries and Alternaria rot in lemon. A
significant reduction in storage decay was achieved
by bringing several yeast species in direct contact
with wounds in the peel of the harvested fruits. For
instance, direct contact of microbial antagonist and
infected fruit peel has been quite useful for the
suppression of the pathogen Penicillium digitatum,
Penicillium italicum (Chalutz and Wilson,1990);
Botrytis cinerea in apples (Gullino et al,1992).

Life Sciences International Research Journal : Volume 4 Issue 1 (2017) ISSN 2347-8691
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However, all the pathogens do not react in similar
fashion to a given antagonist.
5. Enhancing the bio efficacy of microbial
antagonist: Salt additives also improve the bio
efficacy of some microbial antagonists in controlling
postharvest decay on fruits and vegetable (El-
Ghaouth et al., 2004). Among different salt additives,
calcium chloride, calcium propionate, sodium
carbonate, sodium bicarbonate, potassium
metabisulphite, ethanol and ammonium molybdate
etc., have been found very successful when used with
microbial antagonists for controlling postharvest
diseases of fruits and vegetables more efficiently
(Janisiewicz et al., 2008). However, the effectiveness
of microbial antagonists depends upon the
concentration of the antagonist, concentration of salt
additive(s), their mutual compatibility and duration
and time at which they are applied. Usually, the
cultures should be applied well before the initiation
of infection process (Barkai-Golan, 2001). The efficacy
of the microbial antagonists can also be enhanced
considerably by the addition of some nutritious
compounds or natural plant products. For example,
additions of nitrogenous compounds like L-aspargine
and L-proline, and 2-deoxy-D-glucose, a sugar analog
helped in enhancing the bio efficacy of microbial
antagonists in controlling the postharvest decay rots
in some fruits and vegetables. When applied in fruit
wounds, the combination of Candida saitona and 2-
deoxy-D-glucose (0.2%) controlled fruit decay on
apples, oranges and lemons caused by Botrytis
cinerea, Penicillium expansum, and Penicillium
digitatum (El-Ghaouth et al., 2000). Some other
useful recommendations have emerged out of the
research conducted by the scientists for improving
the bio efficacy of microbial antagonists. For example,
a bioactive coating consisting of Cryptococcus saitona
+ glycochitosan has been developed to control fruit
decay in apple (El-Ghaouth et al., 2000). The bio
efficacy of microbial antagonists like Debaryomyces
hansenii, Cryptococcus laurentii, Rhodotorula glutinis,
Trichoderma harzianum etc., can be enhanced for
effective control of postharvest rots on different fruits
and vegetables by using additives like silicon, methyl
jasmonate, salicylic acid, gibberellic acid or dipping
fruit in beeswax or lac based formulations.
Integration of microbial antagonists with physical
methods such as curing or heat treatments could
enhance the bio efficacy of microbial antagonists. For
example, Singh and Mandal (2006) and Mandal et al.
(2007) reported that hot water treated peaches
inoculated with Debaryomyces hansenii could be
stored for longer time than those inoculated alone
with Debaryomyces hansenii, primarily by reducing
the decay loss caused by Rhizopus rot. In apple,
integration of yeasts microbial antagonists with hot
water dipping or bruising has been applied to check
postharvest rots caused by Penicillium expansum and
Botrytis cinerea (Conway et al., 2007).
6. Future Prospects: In the present crop production
scenario, the biocontrol is of utmost importance, but
its potential is yet to be exploited fully mainly
because the research in this area is still confined to
the laboratory and very little attention has been paid
to produce the commercial formulations of bio
agents. Moreover, whatever has been commercially
produced has not been used efficiently by the farmers
owing to the lack of information regarding its use. So,
it is need to popularize the concept of biocontrol
agent by the extension agencies and universities.
Most of the biocontrol agents perform well in the
laboratory but it fails to give its fullest potential in
the field. This is because of the physiological and
ecological constrains that limit the efficacy of the
biocontrol agent. To overcome such problems in the
field, genetic engineering can be effectively used.
Such as mutation or protoplasm using PEG thereby
increase the efficacy.
7. Conclusion: With people turning more health
conscious, Biological control seem to the best
alternative to disease suppression. Bio agents bring
the disease suppression with no environmental
hazards. Research has proved that the bio agents
trigger the growth of plants. Bio agents themselves
being nonpathogenic to plants need to be formulated
in a way that favors the activity and survival of
microbe it contains. Moreover, the novel concept of
bio control needs a space outside the laboratory to
see its fruits in present production systems.
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