John Maina Wagacha

Mycotoxin problem in Africa: Current status, implications to food safety and health and possible management strategies

Mycotoxins are toxic secondary metabolites of fungal origin and contaminate agricultural commodities before or under post-harvest conditions. They are mainly produced by fungi in the Aspergillus, Penicillium and Fusarium genera. When ingested, inhaled or absorbed through the skin, mycotoxins will cause lowered performance, sickness or death on humans and animals. Factors that contribute to mycotoxin contamination of food and feed in Africa include environmental, socio-economic and food production. Environmental conditions especially high humidity and temperatures favour fungal proliferation resulting in contamination of food and feed. The socio-economic status of majority of inhabitants of sub-Saharan Africa predisposes them to consumption of mycotoxin contaminated products either directly or at various points in the food chain. The resulting implications include immuno-suppression, impaired growth, various cancers and death depending on the type, period and amount of exposure. A synergistic effect between mycotoxin exposure and some important diseases in the continent such as malaria, kwashiorkor and HIV/AIDS have been suggested. Mycotoxin concerns have grown during the last few decades because of their implications to human and animal health, productivity, economics of their management and trade. This has led to development of maximum tolerated limits for mycotoxins in various countries. Even with the standards in place, the greatest recorded fatal mycotoxin-poisoning outbreak caused by contamination of maize with aflatoxins occurred in Africa in 2004. Pre-harvest practices; time of harvesting; handling of produce during harvesting; moisture levels at harvesting, transportation, marketing and processing; insect damage all contribute to mycotoxin contamination. Possible intervention strategies include good agricultural practices such as early harvesting, proper drying, sanitation, proper storage and insect management among others. Other possible interventions include biological control, chemical control, decontamination, breeding for resistance as well as surveillance and awareness creation. There is need for efficient, cost-effective sampling and analytical methods that can be used for detection analysis of mycotoxins in developing countries.

Interactions of Fusarium species during prepenetration development

Interspecies interactions between Fusarium avenaceum, Fusarium culmorum, Fusarium graminearum, Fusarium poae, and Fusarium tricinctum were studied during early growth stages of isolates on model surfaces. Additionally, germination and germ tube growth of the pathogens were studied on attached and detached wheat leaves at 10 °C and 22 °C. Two-species interactions between Fusarium isolates during germination and germ tube growth were assessed after 8 hours of incubation. All species except F. tricinctum germinated and grew faster at higher than lower temperature. All species were able to germinate with more than one germ tube per conidium cell; and germination and germ tube growth were faster on leaves than on glass surface. Interactions among Fusarium species during germination and germ tube growth were predominantly competitive with macroconidia-producing species being more competitive. It is concluded that the type of conidia as well as environmental factors influence the competitiveness of Fusarium species during early stages of growth.

Interactions among vegetable-infesting aphids, the fungal pathogen Metarhizium anisopliae (Ascomycota: Hypocreales) and the predatory coccinellid Cheilomenes lunata (Coleoptera: Coccinellidae)

Entomopathogenic fungi are among biocontrol agents being considered for the control of aphids on a variety of crops. Predatory coccinellids, although generalist, are also among important natural enemies that must be conserved for aphid management. Laboratory studies were carried out to investigate the interaction between three vegetable-infesting aphids, Metarhizium anisopliae isolate ICIPE 62 and the coccinellid predator Cheilomenes lunata. At a concentration of 1 × 108 conidial ml–1, the fungus was found to cause mortality of 7.5% to C. lunata, compared to 2.5% mortality in the control at 10 days post-treatment. Female adult C. lunata to which fungus-infected aphids were offered as prey never accepted them as food source in non-choice bioassays. However, live and dead non-infected aphids were fed upon. In choice bioassay, a total of 1–3 out of 24 infected non-sporulating aphids per species (average of 0.1–0.4 aphids per arena) were consumed by 48 h-starved C. lunata within a period of 60 min, but avoided sporulating cadavers. Foraging adult C. lunata enhanced the spread of conidia of M. anisopliae from infected cadavers to fourth instars Aphis gossypii feeding on okra (0.8–15.0% mortality), Brevicoryne brassicae (3.3–15.0% mortality) and Lipaphis pseudobrassicae (0.8–14.2% mortality) on kale plants. Results of this study demonstrate compatibility between M. anisopliae and C. lunata, and could provide a sustainable strategy for effective management of aphids on crucifers and okra cropping systems.

Antifungal Activity of Essential Oil of Eucalyptus camaldulensis Dehnh. against Selected Fusarium spp.

The objective of this study was to evaluate the antifungal activity of essential oil (EO) of Eucalyptus camaldulensis Dehnh. against five Fusarium spp. commonly associated with maize. The essential oil had been extracted by steam distillation in a modified Clevenger-type apparatus from leaves of E. camaldulensis and their chemical composition characterized by gas chromatography mass spectrometry. Poisoned food technique was used to determine the percentage inhibition of mycelial growth, minimum inhibitory concentration, and minimum fungicidal concentration of the EO on the test pathogens. Antifungal activity of different concentrations of the EO was evaluated using disc diffusion method. The most abundant compounds identified in the EO were 1,8-cineole (16.2%), α-pinene (15.6%), α-phellandrene (10.0%), and p-cymene (8.1%). The EO produced complete mycelial growth inhibition in all the test pathogens at a concentration of 7-8 μL/mL after five days of incubation. The minimum inhibitory concentration and minimum fungicidal concentration of the EO on the test fungi were in the range of 7-8 μL/mL and 8–10 μL/mL, respectively. These findings confirm the fungicidal properties of E. camaldulensis essential oils and their potential use in the management of economically important Fusarium spp. and as possible alternatives to synthetic fungicides.

Chemical Composition and Antibacterial Activity of Essential Oils of Tagetes minuta (Asteraceae) against Selected Plant Pathogenic Bacteria

The objective of this study was to determine the chemical composition and antibacterial activity of essential oils (EOs) of Tagetes minuta against three phytopathogenic bacteria Pseudomonas savastanoi pv. phaseolicola, Xanthomonas axonopodis pv. phaseoli, and Xanthomonas axonopodis pv. manihotis. The essential oils were extracted using steam distillation method in a modified Clevenger-type apparatus while antibacterial activity of the EOs was evaluated by disc diffusion method. Gas chromatography coupled to mass spectrometry (GC/MS) was used for analysis of the chemical profile of the EOs. Twenty compounds corresponding to 96% of the total essential oils were identified with 70% and 30% of the identified components being monoterpenes and sesquiterpenes, respectively. The essential oils of T. minuta revealed promising antibacterial activities against the test pathogens with Pseudomonas savastanoi pv. phaseolicola being the most susceptible with mean inhibition zone diameters of 41.83 and 44.83 mm after 24 and 48 hours, respectively. The minimum inhibitory concentrations and minimum bactericidal concentrations of the EOs on the test bacteria were in the ranges of 24–48 mg/mL and 95–190 mg/mL, respectively. These findings provide a scientific basis for the use of T. minuta essential oils as a botanical pesticide for management of phytopathogenic bacteria.

Brine shrimp cytotoxicity and antimalarial activity of plants traditionally used in treatment of malaria in Msambweni district

Abstract Context: In Kenya, most people use traditional medicine and medicinal plants to treat many diseases including malaria. To manage malaria, new knowledge and products are needed. Traditional herbal medicine has constituted a good basis for antimalarial lead discovery and drug development. Objectives: To determine in vivo antimalarial activity and brine shrimp toxicity of five medicinal plants traditionally used to treat malaria in Msambweni district, Kenya. Materials and methods: A 0.2 ml saline solution of 100 mg/kg aqueous crude extracts from five different plant parts were administered orally once a day and evaluated for their in vivo chemosuppressive effect using Plasmodium berghei berghei-infected Swiss mice for four consecutive days. Their safety was also determined using Brine shrimp lethality test: Grewia trichocarpa Hochst ex A. Rich (Tiliaceae) root, Dicrostachys cinerea (L) Wight et Am (Mimosaceae) root, Tamarindus indica L. (Caesalpiniaceae) stem bark, Azadirachta indica (L) Burn. (Meliaceae) root bark, and Acacia seyal Del. (Mimosaceae) root. Results: Parasitaemia was as follows: A. indica, 3.1%; D. cinerea, 6.3%; T. indica, 25.1%; A. seyal, 27.8%; and G. trichocarpa, 35.8%. In terms of toxicity, A. indica root bark extract had an LC50 of 285.8 µg/ml and was considered moderately toxic. T. indica stem bark extract and G. trichocarpa root extract had an LC50 of 516.4 and 545.8 µg/ml, respectively, and were considered to be weakly toxic while A. seyal and D. cinerea root extracts had a LC50 >1000 µg/ml and were, therefore, considered to be non-toxic. Discussion and conclusion: All extracts had antimalarial activity that was not significant compared to chloroquine (p ≥ 0.05). No extract was toxic to the arthropod invertebrate, Artemia salina L. (Artemiidae) larvae, justifying the continued use of the plant parts to treat malaria.

Changes in the Fungal Microbiome of Maize During Hermetic Storage in the United States and Kenya

Prior to harvest, maize kernels are invaded by a diverse population of fungal organisms that comprise the microbiome of the grain mass. Poor post-harvest practices and improper drying can lead to the growth of mycotoxigenic storage fungi and deterioration of grain quality. Hermetic storage bags are a low-cost technology for the preservation of grain during storage, which has seen significant adoption in many regions of Sub-Saharan Africa. This study explored the use of high-throughput DNA sequencing of the fungal Internal Transcribed Spacer 2 (ITS2) region for characterization of the fungal microbiome before and after 3 months of storage in hermetic and non-hermetic (woven) bags in the United States and Kenya. Analysis of 1,377,221 and 3,633,944 ITS2 sequences from the United States and Kenya, respectively, resulted in 251 and 164 operational taxonomic units (OTUs). Taxonomic assignment of these OTUs revealed 63 and 34 fungal genera in the US and Kenya samples, respectively, many of which were not detected by traditional plating methods. The most abundant genus was Fusarium, which was identified in all samples. Storage fungi were detected in the grain mass prior to the storage experiments and increased in relative abundance within the woven bags. The results also indicate that storage location had no effect on the fungal microbiome of grain stored in the United States, while storage bag type led to significant changes in fungal composition. The fungal microbiome of the Kenya grain also underwent significant changes in composition during storage and fungal diversity increased during storage regardless of bag type. Our results indicated that extraction of DNA from ground kernels is sufficient for identifying the fungi associated with the maize. The results also indicated that bag type was the most important factor influencing changes in fungal microbiome during storage. The results also support the recommended use of hermetic storage for reducing food safety risks, especially from mycotoxigenic fungi.

Effect of Soil Fertility and Intercropping on the Incidence and Severity of Root Rot Diseases of Common Bean ( Phaseolus vulgaris L.)

High occurrence of root rots is attributed to continuous and inappropriate cropping systems, low soil fertility levels, low moisture in soil, use of farm saved seeds and use of root rot susceptible bean (Phaseolus vulgaris L.) varieties. This study evaluated the effect of soil fertility and intercropping on the incidence and severity of root rot diseases of common bean. Soil samples were collected at the start of the 2016 short rain cropping season to determine the soil nutrients status, and the incidence and population of soil borne fungal pathogens. The soil samples were analyzed for total nutrient status and pH levels. Soil borne fungal pathogens were isolated from the soil and stem bases by pour plate technique. Farm saved seeds of bean varieties KK8 and GLP2 were planted in field experiments at three sites in pure stand, intercropped with maize, applied with and without fertilizer. Data collected included seedling emergence, stand count, bean fly incidence, root rot distribution, incidence and severity, and yield. The pathogens isolated from soil and stem bases included F. oxysporum, F. solani, Pythium spp, Macrophomina and Rhizoctonia spp, with Fusarium spp. being the most predominant at 40% incidence and mean population of 3000 CFU/g of soil. Bean intercropped with maize had 22% lower intensity of root rot compared to the sole crop. The findings of this study demonstrate that low soil fertility, use of farm saved seeds and high inoculum levels of soil borne pathogens in the soil contributed to the high incidence of root rots in the study sites. In addition bean varieties intercropped with maize had a 17% lower incidence of root rot pathogens compared to bean varieties from sole crop. It was observed that intercropping system reduces pests and diseases. However, root rot pathogens isolated from bean intercropped with maize had a significantly lower incidence than the sole crops.

Silicon Induces Resistance to Bacterial Blight by Altering the Physiology and Antioxidant Enzyme Activities in Cassava

Cassava bacterial blight (CBB), caused by Xanthomonas axonopodis pv. manihotis (Xam) is a devastating disease limiting cassava production. The potential effect of Si application on the physiological and biochemical mechanisms attributed to Si-mediated resistance of cassava to Xam was evaluated. The optimal concentration of Si in enhancing resistance to CBB without detrimental effects on plant growth was determined using cultivars TME14 and TMS60444 known for their susceptibility to Xam. Varied concentrations of Si (0.7 to 2.1 mM) were administered by watering the plants three times per week before and after Xam inoculation. The optimized Si concentration was used to evaluate the effect of Si supplementation on resistance to CBB disease using eight farmer-preferred cassava cultivars. The population of Xam, cultivar resistance, chlorophyll content, lipid peroxidation, H2O2 content, activity of antioxidant enzymes and total Si content in cassava cultivars were quantified 21 days post inoculation. Silicon concentration of 1.4 mM was optimal in enhancing cassava resistance to Xam. Silicon-treated plants of all cassava cultivars showed significantly (P ≤ 0.05) lower Xam population ranging from 5% to 26.7% compared to non-Si treated control plants. Activities of antioxidant enzymes, malondialdehyde, H2O2 and chlorophyll contents were significantly (P ≤ 0.05) higher in Si treated plants than non-Si treated plants. Silicon accumulation in leaves of Si treated plants was higher compared to non-Si treated control plants.

Isolation of Actinomycetes from the Soils of Menengai Crater in Kenya

This study was carried out to isolate actinomycetes from the soils of Menengai crater. The study area was divided into regions A, B, C and D. Soil samples were collected from 8 sampling points from each region. The samples were separately mixed to form composite samples. Starch casein, Luria Bertani and starch nitrate agar were used in isolating actinomycetes using spread plate technique. Prior to isolation, the soil samples were heat for 1h at 121C followed by serial dilution upto 10. The isolates were characterized using cultural, morphological and biochemical means. Region B and C produced many actinomycetes than A and D. Luria Bertani agar was better in recovering actinomycetes than starch casein and starch nitrate agar. There was significant difference in the number of actinomycetes isolated using the three media (F=3.315 P=0.04218). The number of actinomycetes isolated from region A, B C, and D also varied significantly (F= 27.50 P=0.000). A total of 152 actinomycetes were isolated. There is need to test the actinomycetes isolates for production of antimicrobials.