Perennial and seasonal contamination of maize by aflatoxins in eastern Kenya

Abstract Background Aflatoxin contamination of grain is a major constraint to sustained quality cereal production. The causative fungi, Aspergillus species infect crops in the field and continue to do so post-harvest where they produce toxins in store. The current study aimed at establishing seasonal variation in levels and types of aflatoxins in maize from the Eastern region of Kenya- the hot-spot for aflatoxicosis. Maize kernels were collected from farmers’ households in May and December 2013 -2 months after long rain and short rain season respectively. The total aflatoxins were quantified using Enzyme-Linked Immunosorbent Assay (ELISA), while the toxin composition was determined using Thin-Layer Chromatography (TLC) and confirmed using High-Performance Liquid Chromatography (HPLC). Results Generally, grain harvested after the long rains (May) had significantly (p = 0.019) lower aflatoxin levels and variation (5.68 ± 6.31 ppb, 100% Aflatoxin B1) than that of short rains (10.77 ± 10.14 ppb, 72% AFB1). Additionally, from the long and short rain seasons, the samples exceeding regulatory allowed limit (10 ppb) were 16 and 44% respectively. Conclusion In Eastern Kenya, consumption of maize harvested in the long rain season presents a recurrent risk of exposure to low levels of AFB1; while consumption of maize harvested after the short rain season presents a risk of seasonal exposure to high levels and mixed type of toxins However, this long term risk of exposure to aflatoxins is poorly documented hence these findings necessitate mitigation measures because AFB1– is a potent class 1 mutagenic toxin likely to cause liver cancer

Peanut (Arachis hypogea) accessions differentially accumulate aflatoxins upon challenge by Aspergillus flavus: Implications for aflatoxin mitigation

Peanut is among the most important oil crops grown in sub-Saharan Africa for its nutritive value and economic benefit. In this region, Aspergillus flavus infects peanuts and contaminates produce with aflatoxins leading to food insecurity through lowered quality. The impact of aflatoxins transcends the food chain causing harm to human and animal health. The selection and production of aflatoxin-tolerant varieties of peanut is a promising strategy to mitigate their potential harm. We studied the resistance of peanut kernels to aflatoxin accumulation in 25 peanut accessions collected from different growing locations in Kenya, Uganda, and Rwanda based on their unique phenotypic characteristics. To obtain sufficient planting material, the peanut accessions were multiplied separately under standard conditions and harvested at their respective maturity dates then dried and stored at 4 °C before further analysis. At the start of the experiment, the kernels were challenged with a laboratory-characterized toxigenic strain (Aspergillus flavus 1EM1901) and incubated at 28 °C for 7 days. Afterward, the accessions were analysed (ELISA) for aflatoxins. Of the 25 accessions tested, 60 % (n = 15) exhibited kernel resistance to aflatoxin accumulation while 40 % (n = 10) were susceptible (with aflatoxin levels ranging from 0.54 ppb to 1692.92 ppb). Two of the resistant accessions recorded a decrease in aflatoxin accumulation when challenged with toxigenic A. flavus. This differential accumulation of aflatoxins suggests the existence of an inherent trait that can be exploited in breeding programs of peanut varieties with low aflatoxin accumulation when grown in contaminated soils. These findings are further discussed

Importance of contact chemical cues in host recognition and acceptance by the braconid larval endoparasitoids Cotesia sesamiae and Cotesia flavipes

http://dx.doi.org/10.1016/j.biocontrol.2010.05.01

Sensilla on antennae, ovipositor and tarsi of the larval parasitoids, Cotesia sesamiae (Cameron 1906) and Cotesia flavipes Cameron 1891 (Hymenoptera: Braconidae): a comparative scanning electron microscopy study

Two braconid parasitoids of cereal stemborers in eastern Africa, Cotesia sesamiae and Cotesia flavipes, have been shown to display a similar hierarchy of behavioural events during host recognition and acceptance. In order to understand the mechanisms underlying host recognition and acceptance, the morphology of antennal sensilla on the last antennomeres, on the ovipositor, and on the fifth tarsomere and pretarsus of the prothoracic legs tarsi were studied using scanning electron microscopy followed by selective silver nitrate staining. It appeared that female C. sesamiae and C. flavipes shared the same types and distribution of sensory receptors, which enable them to detect volatiles and contact chemical stimuli from their hosts. In both parasitoids, four types of sensilla were identified on the three terminal antennomeres: (i) non-porous sensilla trichodea likely to be involved in mechanoreception, (ii) uniporous sensilla chaetica with porous tips that have gustatory functions, (iii) multiporous sensilla placodea, which are likely to have olfactory function, and (iv) sensilla coeloconica known to have thermo-hygroreceptive function. The tarsi of both parasitoids possessed a few uniporous sensilla chaetica with porous tips, which may have gustatory functions. The distal end of the ovipositor bore numerous dome-shaped sensilla. However, there were no sensilla coeloconica or styloconica, known to have gustatory function in other parasitoid species, on the ovipositors of the two braconid wasps.http://ann.sef.free.fr