A review of agricultural aflatoxin management strategies and emerging innovations in sub-saharan Africa

Aflatoxins are highly carcinogenic secondary metabolites produced by Aspergillus flavus, A. parasiticus and A. nomius. Aflatoxin contamination of food and animal feeds is, therefore, a major food security, food safety, trade, human and domestic animal health concern. Researchers worldwide have suggested various agriculture-based strategies to manage aflatoxigenic Aspergillus species and reduce contamination to safe levels. This paper reviews various agricultural strategies that could be employed to reduce contamination of aflatoxins in food crops and animal feeds, as well as the challenges faced by these reduction strategies. Among these strategies are innovations like AflasafeTM and solar grain driers. It is hoped that this critique will stimulate refinement of the existing aflatoxin control approaches and innovations to maximize their efficacy.Keywords: aflatoxins, plant resistance, atoxigenic strains, drying instruments, aflatoxin control, food safety, mycotoxins, post-harvest losse

Transformation and Regeneration Protocol for Two Farmer Preferred Open Pollinated Tropical Maize (Zea Mays) Varieties

Article PurchasedAbstract: In vitro regeneration of open pollinated varieties (OPVs) Kakamega Striga Tolerant Population 94 (KSTP’94) and ‘Namba Nane’ alongside a tropical inbred line (CML144) was evaluated using immature zygotic embryos as explants. Four callus induction media (CIM) regimes; Murashige and Skoog (MS), Linsmaier and Skoog (LS), Chu (N6) and N6*(N6 medium fortified with 0.35 gL-1 L-proline and 0.8 mgL-1 AgNO3) were evaluated for their potential to induce callus in the three genotypes. All the media were supplemented with sucrose and five levels of 2, 4-Dichlorophenoxyacetic acid (2, 4-D) (0.5, 1.0, 1.5, 2.0 and 2.5 mgL-1). Resulting calli were matured on MS and N6 basal media supplemented with 60 g/L sucrose and similar concentration levels (0.5, 1.0, 1.5, 2.0 and 2.5 mgL-1) of 2, 4-D while the subsequent embryogenic calli were regenerated on hormone-free media. Transformability of these varieties was assessed via histochemical analysis of β-glucuronidase (GUS) reporter gene following Agrobacterium-mediated transformation. Statistical analyses were done using Statistical Analysis Software (SAS) and Graphpad Prism softwares with mean separations achieved at 95% confidence intervals. Of the 2 OPVs, KSTP’94 recorded the highest callus induction frequency (84.4%) while Namba Nane (45.6%) had the lowest. Similarly, KSTP, 94 had the highest mean of mature somatic embryos (59.7%) while Namba Nane recorded the lowest (16.4%). Assessment of regeneration frequencies from embryogenic calli revealed no significant differences among the 3 lines although CML 144 had the highest mean number of juvenile plantlets (36.7%). Analysis of transformation frequency (upon selection of calli on media with basta) showed that Namba Nane recorded the lowest transformation frequency (average 13.5%) some words missing. Transformation frequency (based on GUS positive calli) of these varieties ranged from 0.8 to 2.1%. This work therefore provides an empirical platform for potential introduction of useful genes into these varieties

Efficacy of chemotherapy and thermotherapy in elimination of east African cassava mosaic virus from Tanzanian cassava landrace

Cassava mosaic disease is caused by cassava mosaic begomoviruses (CMBs) and can result in crop losses up to 100% in cassava (Manihot esculenta) in Tanzania. We investigated the efficacy of chemotherapy and thermotherapy for elimination of East African cassava mosaic virus (EACMV) of Tanzanian cassava. In vitro plantlets from EACMV‐infected plants obtained from coastal Tanzania were established in the greenhouse. Leaves were sampled from the plants and tested to confirm the presence of EACMV. Plantlets of plants positive for EACMV were initiated in Murashige and Skoog (MS) medium. On the second subculture, they were subjected into chemical treatment in the medium containing salicylic acid (0, 10, 20, 30 and 40 mg/L) and ribavirin (0, 5, 10, 15 and 20 mg/L). In the second experiment, EACMV‐infected plantlets were subjected to temperatures between 35 and 40°C with 28°C as the control. After 42 days of growth, DNA was extracted from plant leaves and PCR amplification was performed using EACMV specific primers. It was found that plant survival decreased with increasing levels of both salicylic acid and ribavirin concentrations. In general, plants treated with salicylic acid exhibited a lower plant survival % than those treated with ribavirin. However, the percentage of virus‐free plants increased with an increase in the concentration of both ribavirin and salicylic acid. The most effective concentrations were 20 mg/L of ribavirin and 30 mg/L of salicylic acid; these resulted in 85.0% and 88.9% virus‐free plantlets, respectively. With regard to thermotherapy, 35°C resulted in 79.5% virus‐free plantlets compared to 69.5% at 40°C. Based on virus elimination, ribavirin at 20 mg/L, salicylic acid 30 mg/L and thermotherapy at 35°C are recommended for production of EACMV free cassava plantlets from infected cassava landraces

Midgut bacterial diversity analysis of laboratory reared and wild Anopheles gambiae and Culex quinquefasciatus mosquitoes in Kenya

Open Access JournalMidgut symbiotic bacteria are known to play fundamental roles in the biology of mosquitoes, however knowledge of midgut bacterial communities associated with mosquitoes is scanty due to limitation of the isolation techniques based on culturing. In this study, the composition and diversity of midgut bacteria in field collected and lab reared adult female Anopheles gambiae and Culex quinquefasciatus mosquitoes was explored using the Illumina sequencing. Deoxyribonucleic acid was isolated from the pooled midgut extracts and their 16S rRNA gene sequenced using Illumina sequencing platform. Operational taxonomic units (OTUs) were analyzed using QIIME 1.8.0; taxonomy was assigned using BLASTn against SILVA 119 and hierarchical clustering was done using R program software. Out of the total number of sequence reads obtained, 145 OTUs were realized at 3% genetic distance. The 145 OTUs spanned 12 phyla; Proteobacteria, Firmicutes, Cyanobacteria, Euryarchaeota, Gemmatimonadetes, Spirochaetae, Archeabacteria Verrucomicrobia, Chloroflexi, Bacteriodetes, Acidobacteria and Actinobacteria. Microbial community composition based on OTUs showed significant difference between field collected and lab reared mosquitoes (ᵪ2 = 45.0799, p = 3.2 × 10-5). Similarly, there was a significant difference in community composition at OTU level between Anopheles gambiae and Culex quinquefasciatus (ᵪ2 = 31.2257, p = 7.7 × 10-4). The bacterial composition and diversity appeared to be influenced by the environment and the species of the mosquitoes

Optimisation of a somatic embryogenesis and transformation protocol for farmer-preferred cassava cultivars in Kenya

Cassava ( Manihot esculenta Crantz ) is a major food crop in developing countries, and holds potential for industrial use. It is, however, affected by various biotic and abiotic stresses that greatly affect its production. The existing regeneration and transformation protocols are not compatible with all cassava cultivars, thus efficient and robust transformation and regeneration protocols for farmer-preferred cultivars need to be optimised for ease of transfer of novel genes. The objective of this study was to develop an efficient transformation and regeneration protocol for a farmer-preferred Kenyan cassava cultivar. We cultured immature leaf lobe and stem explants on Murashige and Skoog (MS) medium, supplemented with varying concentrations of 2,4-dichlorophenoxyacetic acid (2,4-D), Picloram and \ue1-naphthalene acetic acid (NAA). Plants were recovered on media with 6-Benzylaminopurine (BAP) and GA3 under a 16 hour light/8 hour darkness photoperiod regime. Results showed high regeneration and transformation frequencies for both cultivars. High frequencies of callus induction (>98%) for both cultivars, were obtained when 2,4-D and Picloram were used. Similarly, both auxins initiated somatic embryogenesis, with Picloram producing the highest frequency of somatic embryos (>92%) in TMS 60444, using stem explants. Gus assays revealed high frequencies of transformation of >77% (TMS 60444) and 60% (Kibanda meno mkubwa). This protocol offers promising perspectives for rapid improvement of these cultivars and, therefore, provides a platform for cleaning planting materials, as well as cassava genetic improvement programmes such as control of viral diseases.Le manioc ( Manihot esculenta Crantz ) est une culture vivri\ue8re de grande importance pour les pays en d\ue9veloppement, avec un potentiel pour l\u2019usage industriel. N\ue9anmoins, le manioc est sujet \ue0 des stress d\u2019origines biotique et abiotique, affectant sa production. Les protocoles de r\ue9g\ue9n\ue9ration et de transformation existante ne sont pas compatibles avec toutes les accessions de manioc. Ainsi, il est n\ue9cessaire de d\ue9velopper des protocoles de r\ue9g\ue9n\ue9ration et de transformation efficaces pour les accessions adopt\ue9es par les paysans, afin de faciliter les transferts de g\ue8nes d\u2019int\ue9r\ueat. L\u2019objectif de cet etude \ue9tait de d\ue9velopper un protocole de r\ue9g\ue9n\ue9ration et de transformation adapte a la vari\ue9t\ue9 de manioc. Des feuilles et tiges immatures ont \ue9t\ue9 cultiv\ue9es sur des media Murashige et Skoog (MS), auxquels diff\ue9rentes concentrations de 2,4-dichlorophenoxyacetic acide (2,4-D), Picloram et \ue1-naphtal\ue8ne ac\ue9tique acide (NAA). Les plantes ont \ue9t\ue9 recouvertes de 6-Benzylaminopurine (BAP) et GA3 sous une photop\ue9riode de 16h jour/8h nuit. Les r\ue9sultats ont montr\ue9 des fr\ue9quences \ue9lev\ue9es de r\ue9g\ue9n\ue9ration et de transformation pour les deux cultivars Kibanda meno mkubwa et TMS 60444. Des fr\ue9quences \ue9lev\ue9es d\u2019induction de callosit\ue9s (>98%) ont \ue9t\ue9 obtenues pour les deux cultivars, lorsque 2,4-D et Picloram ont \ue9t\ue9 utilis\ue9s. De la m\ueame fa\ue7on, les deux embryogen\ue8ses somatiques initi\ue9es a l\u2019auxine, avec des explants de tiges et du Picloram ont exhibe la fr\ue9quence la plus \ue9lev\ue9e d\u2019embryon somatique (>92%) en TMS 60444. Des essais de Gus ont r\ue9v\ue9l\ue9s des fr\ue9quences \ue9lev\ue9es de transformation >77% (TMS 60444) et 60% (Kibanda meno mkubwa). Ce protocole offre des perspectives pour l\u2019am\ue9lioration rapide de ces cultivars, et par cons\ue9quent, fournit une plateforme pour la production de mat\ue9riels de culture propres, mais aussi servira d\u2019outil dans les programmes d\u2019am\ue9lioration g\ue9n\ue9tique visant la lutte contre les maladies virales

Screening for potential Striga hermonthica fungal and bacterial biocontrol agents from suppressive soils in Western Kenya

Published online: 18 July 2017Striga hermonthica is a hemiparasitic weed that causes huge grain yield losses to small-scale farmers in Africa. Effective biocontrol agents against S. hermonthica can sustainably mitigate these losses. This study characterized the biocontrol potential of culturable fungal and bacterial isolates from S. hermonthica suppressive soils of western Kenya. These isolates were screened for their ability to produce antibiotic compounds and extra cellular enzymes and also their ability to cause S. hermonthica seed decay. Genomic DNA of the selected bacterial and fungal isolates was extracted and partial characterization of 16S rRNA and 18S rRNA genes performed respectively. Analysis show that antibiosis and enzymatic properties of potential biocontrol isolates correlated positively. Isolate KY041696 recorded high antibiosis, enzymatic and seed decay values. This study also revealed that bioactive bacterial isolates belonged to Bacillus, Streptomyces and Rhizobium genera. In this study, no fungal isolate caused S. hermonthica seed decay. This study therefore provides baseline information on the potential biocontrol microbes against S. hermonthica in Western Kenya that could be exploited further in the management of the weed

Distribution of parasitic nematodes in Kenyan rice fields and their relation to edaphic factors, rainfall and temperature

Published online: 09 Nov 2017Rice is the third most important crop in Kenya after maize and wheat. Plant parasitic nematodes (PPN) are a major rice production constraint. The objective of this study was to determine the distribution and abundance of rice PPN in Kenya and their association with environmental variables. Soil and plant samples were collected from rainfed upland and irrigated lowland rice fields in Kirogo, Thiba, Nyangati, Ombeyi, Kombura, Kakola and Mwambe Sub-locations. Twenty-two PPN genera were identified across all Sub-locations with the highest (20) number of nematode genera recorded in rainfed upland rice fields. The nematode genera Scutellonema, Hoplolaimus, Ditylenchus, Hemicycliophora, Heterodera, Paralongidorus and Tylenchus were not recorded in the irrigated lowland rice fields while Criconemella and Tylenchorhynchus were not observed in rainfed upland fields. Canonical correspondence analysis of the relationship between soil properties and nematode abundance revealed a significant (P < 0.05) relationship between PPN abundance and potassium, sodium, sand and clay. The relationship between rainfall, minimum temperature and nematode genera was significant (P < 0.05) while maximum temperature was not significant (P = 0.928). Our results provide critical information for designing nematode management strategies in Kenyan rice fields

KSTP 94, an open-pollinated maize variety has postattachment resistance to purple witchweed (Striga hermonthica)

Striga spp. are obligate root hemiparasites that constrain cereal production in sub-Saharan Africa. Although purple witchweed [ Striga hermonthica (Delile) Benth.] and Asiatic witchweed [ Striga asiatica (L.) Kuntze] infect all cereal crops, maize ( Zea mays L.) is particularly vulnerable to their infestations. A sustainable control strategy for Striga would be to breed crops with host-based resistance as part of an integrated management plan. In maize, the open-pollinated variety Kakamega Striga -tolerant population of the year 1994 (‘KSTP 94’) has been popularized as a Striga -tolerant/resistant variety. This resistance was earlier reported to result from production of low amounts of sorgomol, a less potent strigolactone. To determine whether KSTP 94 harbors postattachment resistance, we used a soil-free assay based on observation chambers called rhizotrons. We found that the size of Striga seedlings attached to ‘CML 144’ (a susceptible maize inbred line) were 2.5-fold longer than those on KSTP 94. In addition, KSTP 94 had significantly fewer Striga attachments, which corresponded to significantly lower biomass (2.6-fold) compared with CML 144. Histological analysis revealed that the low Striga growth and development while infecting KSTP 94 was due the parasite’s inability to penetrate the host’s endodermis and make effective xylem–xylem connections. We therefore conclude that in addition to preattachment resistance, KSTP 94 exhibits postattachment resistance to S. hermonthica and could therefore be a good genetic source for postattachment resistance breeding

First report of Lasiodiplodia theobromae causing dieback symptoms on plantain (Musa AAB subgroup) in Nigeria

Published online: 15 Aug 202