CAAREA Activities & Key postharvest solutions for aflatoxin
control
Said M.S. Massomo
Open University of Tanzania
Morogoro Regional Centre
www.out.ac.tz
Email: said.massomo@out.ac.tz
smsmassomo@yahoo.com
Aflatoxin Stakeholders Workshop. Dar es Salaam December 3-4, 2012
Massomo, SMS 1
CAAREA Objectives
1.
Establish aflatoxin diagnostics platform at BecA-ILRI, and develop
novel aflatoxin diagnostics
2. Characterize maize fungi from around Kenya and Tanzania:
information, biobank and inoculum.
3. Identify maize germplasm resistant to aflatoxin accumulation (G x E).
4. Test modelling as a potential predictive tool and to contextualize
findings regionally (risk map).
5. National breeders will affect subsequent changes to maize breeding
programs in Kenya and Tanzania.
Introduction
• Aflatoxins are primarily
produced by the fungi
– Aspergillus flavus Link
– A. parasiticus Speare
• Optimal conditions for fungal
development are
– high temperatures 36 to 38 C
– high humidity >85%
A. flavus image from:
http://www.pfdb.net/photo/mirhendi_h/box020909/
Factors influencing Aflatoxin Production
Fungal growth and
aflatoxin contamination
are the consequence of
interactions among the
fungus, the host and the
environment
Pathogen
Aggressiveness
Other
factors
Favourable
Environment
Host Plant
Susceptibility
Interaction vary with
• Geographic location, agricultural and agronomic practices,
• The susceptibility of commodities to fungal invasion during preharvest, storage, and/or processing periods
CAAREA objective II
• To characterize the diversity,
distribution and toxigenicity of
Aspergillus flavus (and to a
limited extent, other relevant
fungi) in Kenya and Tanzania
• Determine relation to maize
contamination by aflatoxins
across AEZs/regions
• Mainly focused on pre harvest
with some post harvest
component
Country Wide Survey
• Work with and through the NARs
• Activity I: Field trials
– 20 sites of 10 varieties will be
planted across Agro Ecological
Zones
– Data/item to be collected
• Maize phenotypic characters
• Insect abundance, Weather …
• Collection of maize cob samples
• Activity II: Interviews of farmers
• Activity III: Collection of maize
samples from farmers
• Biophysical data
• Management data
• Maize Genotyping
(maize map)
• Area planted to maize
• Planting density
• Integrated index of
insect load
• Maize sample
aflatoxin concentration
Isolation & Characterization
of A. flavus
• Isolation of fungi from seeds at
ARI-Mikocheni & at BECA-ILRI
• Characterization work at BECAILRI lab
• Characterization of A. flavus
isolates:
– Morphology (S or L strain)
– Toxigenicity (extent & type(s) of
toxin produced)
– Microsatellite genotyping
– Other Molecular tools
• Grouping of A. flavus basing on
vegetative compatibility groups
Isolation & Identification
Characterization
Strain selection for
Inoculum production &Field
inoculation (screening for
resistance)
Biobank
for future studies
Fungi survey data from 11 sites in two zones
Activity
Aspergillus flavus
isolates
Mid and highland Tanzania
19
Lowland in Tanzania
57
Total Tanzania
76
16 genera identified
Fungal isolations/training,
ARI Mikocheni , Dar
Tanzania
AF KBK02
AF KBK12
AF KBK05
Distribution and diversity of toxigenic A. flavus strains in Kenya
AF KBK10
AF KBK11
AF KBK24
KAT05
KAT03
KAT06
AF KBK20
AF KBK19
KAT07
AF KBK18
KAT04
AF KBK17
KAT02
KAT11
KAT10
KBK13
KAT12
PK08
PK02
PK04
AF KBK08
AF KBK07
AF KBK13
AF KBK04
AF KBK16
AF KBK09
AF KBK06
PK07
PK03
PK06
PK05
PK01
PK09
AF KBK03
AF KBK01
AF KBK14
MTW 1A
KK1A
KAT01
AF KBK21
AF KBK26
AF KBK22
AF KBK23
MTW 4A
MTW 2A
MTW 3A
AF KBK25
AF KBK15
Fungal survey: postharvest component
•
PCR assay being used to
determine prevalence of
Aspergillus flavus and A.
parasiticus in post harvest
samples.
•
This will ensure that pre harvest
prevalence data does not “miss”
part of the problem in some
areas.
Major Drivers: Pre Harvest
Pathogen abundance
• Basal inoculum load & prevalence of toxigenic strains and
microbiological interactions
– Continuous cropping, double cropping & Soil etc.
Stressful Environment
• Untimely planting  Water stress or wetness at harvest
• High-temperature stress
• Low input farming practice  stressed plants
– high crop densities, low fertility and weed competition
Low host plant resistance
Other factors
• Insect damage of the host plant
• Growth of other molds or microbes
Major Drivers: Post Harvest
Environment
• High-temperature & High humidity
Host
• Resistance factors
– (i.e. Grain texture, resistance to Aspergillus & insect
infestation)
Pathogen
• Basal inoculum density in & around the store
Other factors
• Pest infestation & microbe interactions & endophytes
Interventions:
Post Harvest, Pre processing
• Public education and awareness to sensitize the
population on aflatoxin risk and its management
– Across all the relevant industry sectors
– Using effective communication strategies
• e.g Mobile phone sms & Community radios
• Timely harvesting
• Moisture control/Drying of crop
– Rapid and proper drying
– Avoid drying on bare ground (Use of drying platforms and
drying on mats)
Interventions:
Post Harvest, Pre processing cont..
• Sorting (infected and insect damaged cobs)
• Improved farm storage and drying methods
– e.g Hermetic storage (sealed/air tight containers)
• Proper transportation and packaging (dry &
aerated)
• Pest Management
– Cleaning of store before introduction of new produce
– Reduce pest infestation
Interventions:
Post Harvest, Pre processing
• Good food regulatory systems
– To regulate quality & safety of food
• Efficient monitoring and surveillance with
rapid, cost-effective sampling and analytical
methods
• Finding alternative uses for contaminated grain
• Behavioural changes on food supplementation
• Dietary change?
Interventions:
Post Harvest, Pre processing cont..
• Other strategies
– Mould inhibitors
– Detoxification of aflatoxins
• Physical (Sorting, Flotation & Physical segregation)
• Chemically (e.g. Ammonia & Calcium hydroxide)
• Microbiologically (e.g. Fermentation, pro-biotics or lactic
acid bacteria into the diet)
– Alteration of Bioavailability by Aflatoxin
• Enterosorbents in human diets
• Chemisorbents in livestock
Interventions:
Post Harvest, Processing period
• Practising food processing procedures that may
involve processes such as
• Grain cleaning, dehulling, washing, wet and dry milling,
roasting, baking, frying etc.
Integrated suite
of intervention measures
should be advocated
Challenges
• Existence of favourable climatic conditions for
fungal development & aflatoxin accumulation
• Difficult to accurately estimate aflatoxins
concentration
– When large quantity of material are involved
– Variability associated with testing procedures
• Cost-effectiveness of the control methods
• Food insecurity and drought
• Limited resources at Household level
Thank you!
Thank you!