Control of Toxigenic Fungi and Aflatoxin with Botanicals
BY
ANJORIN, TOBA SAMUEL
University of Abuja, Abuja
At
AFLATOXIN STAKEHOLDERS WORKSHOP
Agricultural Research Council of Nigeria, Agricultural Research House, Plot
223D, Cadastral Zone B6, Mabushi District, Wuse Abuja, Nigeria
NOVEMBER 5-6, 2012
• INTRODUCTION
• Aflatoxins (Aspergillus flavus toxins - B1, B2, G1 and G2)
are biologically active secondary metabolites produced
by certain strains of Aspergillus parasiticus, Aspergillus
nominus and Aspergillus flavus (Cotty et al., 1994).
• More than 280 plant species have been investigated for
their inhibitory effect on toxigenic Aspergilli and nearly
100 of these plants had some activity on growth or
toxin production by fungi (Montes and Carvajal, 1998).
Plant leaves, stems, bark, bud, seeds or roots
offer potential for fungi control through the
production and release of toxic mixtures of
phytocompounds/allelochemicals in them
(Macias, 1998).
• Justification for the use of phytofungicides
• Vast fields in developing countries are blessed
with abundant plants with fungicidal potential
• Botanical fungicides are locally renewable,
user-friendly and environmentally safe.
(Rotimi and Moems, 2003)
Table 1. Plants containing antimicrobial activity (Cowan, 1999)
Common name
Scientific name
Compound
Class
Activityd
Betel pepper
Piper betel
Catechols,
eugenol
Essential oils
General
fungi
Ceylon
cinnamon
Cinnamomum
verum
Essential
others
oils, Terpenoids,
tannins
Garlic
Allium sativum
Allicin, ajoene
General
Sulfoxide
General
Grapefruit peel Citrus paradise
Terpenoid
Fungi
Green tea
Camellia sinensis Catechin
Flavonoid
General
Lantana
6,7Lantana camara dimethylesculeti alkaloid
n
General
Mesquite
Prosopis juliflora Phenethylamine alkaloid
General
Olive oil
Olea europaea
Hexanal
Aldehyde
General
Orange peel
Citrus sinensis
d-limonene
Terpenoid
Fungi
•
•
•
•
•
Anti fungal Activity of Some Botanicals
Karapynar (1989) reported the inhibitory effect of crude extracts from ground red
pepper on the growth of A. parasiticus NRRL 2999 and its aflatoxin production in
vitro.
Aflatoxin production in fungal mycelia grown for 96 h in culture media containing
50% neem leaf and seed extracts was inhibited by 90 and 65%, respectively
(Razzaghi-Abyaneh et al., 2005).
Recently, Srichana et al. (2009) studied the efficacy of betel leaf extract on growth
of A. flavus and it was found that the extract at 10,000 ppm completely inhibited
the growth of this fungus.
Similarly Pundir and Jain (2010) studied the efficacy of 22 plant extracts against
food associated fungi and found that ginger extract are more effective than other
plant extracts.
• Awuah and Ellis (2002) reported the effective use of powders of leaves of
O. grattisimum and cloves (Sizygium aromaticum) combination with some
packaging materials to protect groundnut kernels artificially inoculated
with A. parasiticus.
• Inhibitory effects of onion extracts on A. flavus growth, with an ether
extract of onions, thio-propanol-S-oxide, being demonstrated to inhibit
growth (Fan and Chen 1999)
Inhibition of Aflatoxin Production by Essential Oils
The antifungal activity of essential oils or their constituents such
as thymol, carvacrol and vanillin could be in different ways;
• The antiaflatoxigenic activity of EOs of different 32 plants are
indicated by many researcher (Table 2). For instance, the EOs
of Syzygium aromaticum and Lippia turbinate inhibited
aflatoxin production.
• They could also be added to grain in storage to protect it from
fungal infection. These oils could be used as a substitute for
chemical fungicides.
• They may also prove valuable as ‘lead structure’ for the
development of synthetic compounds as they are natural and
nontoxic to humans and animals alike (Soliman and Badeaa,
2002; Bluma et al., 2007).
Table 3: Plant leaves locally used by Abuja, Nigerian farmers for
their stored farm produce against fungi
Name
Family
1. Iron weed Asteraceae
(Blumea
perotitiana)
2. Bush tea Lamiaceae
(Hyptis
suaveolens)
3. Ground star Rubiaceae
weed
(Mitracarpus
villosus))
4.
Lophira Ochnaceae
(Lophira
lanceolata)
Local names
Gw*: Sinmisinmi
Parts used
Whole leaf
Ba: Gbagbaje
Leaf powder
Ha:Tabataba
Gw:Basamsin
Ba.:Adabwa
Ha:Dadoya
Gw: Jiji pampi
Ba: Olugodotondo
Ha:Gogamasu
Gw: Gbonrii
Ba: Zhimya
Nu:Gbetseti
Use
For
seed
dressing
Whole leaf
Fumigant in
the
farm
powder/
produce store
Leaf
slurry
Leaf
Seed/tuber
powder/extract dressing
at
low
concentration
Leaf
Yam
sett
powder/extract dressing
• 5.0 Mechanism of Action
• (1) The result could be in the form of damage to
the enzymatic cell system, including those
associated with energy production and synthesis
of structural compounds (Conner and Beuchat,
1984 a, b),
• (2) Denaturation of the enzymes responsible for
spore germination or interference.
• 3)Essential oils protect the cells from harmful
impact of aflatoxins as they reduce DNA binding
formation of aflatoxins.
• Utilization of botanicals in fungi management
• a.Direct spray applications of various extracts of biologically
effective plant products like leaves, stem, roots and whole plants
especially for the control of leaf-borne fungi on the field (Preharvest).
• B.Soil amendment of the effective plant materials for the control of
the soil inhabiting pathogenic fungi like Aspergillus, Fusarium and
root-knot nematodes. e.g. amendment of de-oiled cakes of neem
and castor (Pre-harvest)
• c. Intercropping/mixed cropping of the biologically active plant/
crop with the main crop
to minimize the toxigenic fungiinfection incidences (Pre-harvest).
• d. Use of botanical based commercial formulations for the pest
management in agriculture.
• e. Several such formulations based on neem has already been
registered in Nigeria and now available for commercial use and
export e.g. bionimbecidin Green gold®. (Preharvest such as for seed
dressing) and for post harvest in the store)
•
Formulation of biofungicide
•
Production of commercial phytofungicides is more sophisticated than the homeproduced crude form.
•
•
Digestion of plant materials
The use of variety of solvents such as hexane, ethanol, pentane, methanol or ether
singly or in a mixture for fractionating the components or extracting the active
compounds in the fungicidal plants.
•
Once the active ingredient has been extracted and purified, it has to be added to
inert compounds. During the process of isolating the active ingredients, it should
be bioassay guided (McGuffin, 2001).
•
A standard of active ingredient from fungicidal plant is required for the
registration of commercial botanical fungicide and their subsequent use on a
commercial scale.
It is a fact that phytochemicals are prone to photo-, microbial- and thermaldegradation if not properly packed or stored.
•
•
In the formulation of plant fungicide, biological activity and its efficacy should be
stabilized and further enhanced by the addition of stabilizers, antioxidants and
synergists. Certain additives could be added to increase the shelf-life and ease of
handling.
•
Sun screens such as para-amino benzoic acid (PABA) could be added to reduce the
photoxidation of most active ingredient by ultra-violet light (Zubkoff, 1999).
• CHALLENGES
• Collection and utilization of natural products seemed to be
expensive in terms of time and labour.
• Crude and inadequate processing tools and implements
and facilities such as grinding stone instead of a grinder or a
blender thus making their preparation full of drudgery.
• Scarcity of certain plant materials especially those that
people compete for because of its efficacy such as
Erythrophleum suaveolens
•
• Low efficacy of most botanicals due to their brief
persistence or short shelf-life as they are easily prone to
microbial, thermal or photo degradation.
• Bulkiness of some botanical materials during collection,
preparation and application, such as 10 kg of neem leaf
powder required for amending 100 m2 of tomato field per
time.
• CONCLUSION
• Protocols on production of fungitoxic compounds
for large scale production should be developed.
Communication between researchers and
extension organization should be intensified.
Through this, phytofungicide research can be
directed at farmers need and the knowledge
concerning their use will be provided.
• Plant fungicide production could be sequentially
integrated into a sustainable crop protection
system in the developing countries. Integrated
Disease Management strategy of prevention and
control of toxigenic fungi and aflatoxins should be
considered.
•
THANKS FOR LISTENING