| dc.description.abstract | Mycotoxin poisoning resulting from contaminated cereal grains has become rampant in
Kenya. Understanding the fungal causes and management is important both to the farmers and
the consumers of the cereal grains and their products.
A survey was carried out during the 2004 wheat growing season in Nakuru and Nyandarua
districts. A total of 9 agroecological zones were selected, within which 10 farms in each
agroecological zone were randomly selected. A total of 89 farmers were interviewed on wheat
agronomic practices and they gave 94 samples for mycological and toxicological analysis. The
wheat kernels were plated on Potato Dextrose Agar and Spezieller Nahrastofarmer Agar media
that were amended with inorganic salts and the fungi that grew were identified based on colony
and other morphological characteristics to genus level and some to species level. Fourteen
Fusarium species were tested for pathogenicity on variety 'Mbuni' wheat ears in two greenhouse
growing cycles where Fusarium head blight disease severity was assessed as the percentage of
the spikelets bleached and the area under disease progress curve. Re-isolation of the Fusarium
species was done. Contamination of wheat with mycotoxins zearalenone, T-2, deoxynivalenol
and aflatoxin Bl was determined by competitive ELISA method. Eight wheat varieties grown in
Kenya were also tested for susceptibility to Fusarium head blight. Pathogenic strains of F.
graminearum were used to inoculate varieties under greenhouse conditions. The head blight was
assessed as percentage of spikelets bleached and area under the disease progress curve and kernel
weight reduction compared to un-inoculated control.
Results of the survey showed that, a total of 18 wheat varieties were grown in the area and
most farmers (77.9%) were found to use their own seeds for planting which were neither clean
nor certified. Wet conditions during flowering, ripening and harvesting of wheat, that favoured
diseasedevelopment prevailed in both districts. Farmers were found not taking any precautionary
measuresto avoid the build up of the disease. Prevalence of Fusarium head blight was found to
be 80.9%. Kernel contamination with fungi was high; Alternaria (100.0%), Epicoccum (100.0%),
Fusarium (85.0%), Aspergillus (72.0%), Penicillium (18.0%) and other fungi (2.0%). Fourteen
Fusarium species were isolated, with F. poae, F. graminearum, F. avenaceum, F.
chlamydosporum, F. moniliforme, F. equiseti and F. oxysporum being the most prevalent. F.
graminearum, F. avenaceum and F. moniliforme were found to be highly pathogenic, with a high
proportion of ears bleached. The area under disease progress curve was negatively correlated (P
:s 0.05) to 10 ear weight (r = -0.511) while disease severity was positively correlated (P:S 0.01) (r
= 0.973) to area under disease progress curve. Grain yield measured as 10 ear weight and 100
seed weight differed significantly (P :s 0.01) depending on Fusarium species used to inoculate
wheat ears. The re-isolation rate of the Fusarium species ranged from 30.0-90.0%.
Most samples (93.0%) were found to be contaminated with at least a toxin, with the most
toxic T-2 toxin having the highest prevalence. All the toxins were found to be at low levels with
the mean content being: 128.2Jlg/kg for deoxynivalenol, 5.5Jlg/kg for zearalenone, 25.9Jlg/kg for
T-2 and l.Sug/kg for aflatoxin B1. The wheat varieties were found to be susceptible to head
blight but they differed in the level of disease severity and kernel weight reduction. Most
susceptible varieties ('Mbuni' and 'Chiriku') had a high mean disease severity rating (59.3%, and
55.5%, respectively) and high area under disease progress curve (994.0, and 932.0, respectively).
The least susceptible variety ('Njoro Bw2') had a mean disease rating of 13.0% and area under
disease progress curve of 188.0. Mean reduction in kernel weight varied in the varieties and
ranged from 13.5% to 74.0% and was not correlated to mean disease rating and area under
disease progress curve.
The results indicated that Fusarium head blight and mycotoxin contamination in wheat
kernels is prevalent in the wheat growing areas of Nakuru and Nyandarua districts and there is
need to sensitize wheat growers on the disease management. Most Kenyan wheat varieties are
susceptible to Fusarium head blight. | en |
