Showing papers by "International Institute of Tropical Agriculture published in 2013"

An equivalent soil mass procedure for monitoring soil organic carbon in multiple soil layers

Abstract: Summary Soil carbon stocks are commonly quantified at fixed depths as the product of soil bulk density, depth and organic carbon (OC) concentration. However, this method systematically overestimates OC stocks in treatments with greater bulk densities such as minimum tillage, exaggerating their benefits. Its use has compromised estimates of OC change where bulk densities differed between treatments or over time periods. We argue that its use should be discontinued and a considerable body of past research re-evaluated. Accurate OC estimations must be based on quantification in equivalent soil masses (ESMs). The objective of this publication is to encourage accurate quantification of changes in OC stocks and other soil properties using ESM procedures by developing a simple procedure to quantify OC in multiple soil layers. We explain errors inherent in fixed depth procedures and show how these errors are eliminated using ESM methods. We describe a new ESM procedure for calculating OC stocks in multiple soil layers and show that it can be implemented without bulk density sampling, which reduces sampling time and facilitates evaluations at greater depths, where bulk density sampling is difficult. A spreadsheet has been developed to facilitate calculations. A sample adjustment procedure is described to facilitate OC quantification in a single equivalent soil mass layer from the surface, when multiple-layer quantification is not necessary.

Identification of Drought, Heat, and Combined Drought and Heat Tolerant Donors in Maize

Abstract: Low maize (Zea mays L.) yields and the impacts of climate change on maize production highlight the need to improve yields in eastern and south - ern Africa. Climate projections suggest higher temperatures within drought-prone areas. research in model species suggests that tol - erance to combined drought and heat stress is genetically distinct from tolerance to either stress alone, but this has not been confirmed in maize. In this study we evaluated 300 maize inbred lines testcrossed to CML539. Experiments were conducted under optimal conditions, reproduc - tive stage drought stress, heat stress, and com - bined drought and heat stress. Lines with high levels of tolerance to drought and combined drought and heat stress were identified. Signifi - cant genotype × trial interaction and very large plot residuals were observed; consequently, the repeatability of individual managed stress trials was low. Tolerance to combined drought and heat stress in maize was genetically dis - tinct from tolerance to individual stresses, and tolerance to either stress alone did not confer tolerance to combined drought and heat stress. This finding has major implications for maize drought breeding. Many current drought donors and key inbreds used in widely grown African hybrids were susceptible to drought stress at elevated temperatures. Several donors toler - ant to drought and combined drought and heat stress, notably La p osta Sequia C7-F64-2-6-2-2 and DTpYC9-F46-1-2-1-2, need to be incorpo - rated into maize breeding pipelines.

Phenotypic approaches to drought in cassava: review.

Abstract: Cassava is an important crop in Africa, Asia, Latin America and the Caribbean. Cassava can be produced adequately in drought conditions making it the ideal food security crop in marginal environments. Although cassava can tolerate drought stress, it can be genetically improved to enhance productivity in such environments. Drought adaptation studies in over three decades in cassava have identified relevant mechanisms which have been explored in conventional breeding. Drought is a quantitative trait and its multigenic nature makes it very challenging to effectively manipulate and combine genes in breeding for rapid genetic gain and selection process. Cassava has a long growth cycle of 12 - 18 months which invariably contributes to a long breeding scheme for the crop. Modern breeding using advances in genomics and improved genotyping, is facilitating the dissection and genetic analysis of complex traits including drought tolerance, thus helping to better elucidate and understand the genetic basis of such traits. A beneficial goal of new innovative breeding strategies is to shorten the breeding cycle using minimized, efficient or fast phenotyping protocols. While high throughput genotyping have been achieved, this is rarely the case for phenotyping for drought adaptation. Some of the storage root phenotyping in cassava are often done very late in the evaluation cycle making selection process very slow. This paper highlights some modified traits suitable for early-growth phase phenotyping that may be used to reduce drought phenotyping cycle in cassava. Such modified traits can significantly complement the high throughput genotyping procedures to fast track breeding of improved drought tolerant varieties. The need for metabolite profiling, improved phenomics to take advantage of next generation sequencing technologies and high throughput phenotyping are basic steps for future direction to improve genetic gain and maximize speed for drought tolerance breedi

Smallholder farmers’ perceptions of and adaptations to climate change in the Nigerian savanna

Abstract: The savanna region of Africa is a potential breadbasket of the continent but is severely affected by climate change. Understanding farmers’ perceptions of climate change and the types of adjustments they have made in their farming practices in response to these changes will offer some insights into necessary interventions to ensure a successful adaptation in the region. This paper explores how smallholder farmers in the Nigerian savanna perceive and adapt to climate change. It is based on a field survey carried out among 200 smallholder farm households selected from two agro-ecological zones. The results show that most of the farmers have noticed changes in climate and have consequently adjusted their farming practices to adapt. There are no large differences in the adaptation practices across the region, but farmers in Sudan savanna agro-ecological zone are more likely to adapt to changes in temperature than those in northern Guinea savanna. The main adaptation methods include varying planting dates, use of drought tolerant and early maturing varieties and tree planting. Some of the farmers are facing limitations in adapting because of lack of information on climate change and the suitable adaptation measures and lack of credit. The study then concludes that to ensure successful adaptation to climate change in the region, concerted efforts are needed to design and promote planned adaptation measures that fit into the local context and also to educate farmers on climate change and appropriate adaptation measures.

Nutritional Evaluation of Five African Indigenous Vegetables

Abstract: The promotion and consumption of indigenous vegetables could help mitigate food insecurity and alleviate malnutrition in developing countries. In this respect, 17 accessions (candidate breeding lines that have not yet officially been released) of five African indigenous vegetables: amaranth (Amaranthus cruentus), nightshade (Solanum scabrum), African eggplant (Solanum aethiopicum), jute mallow (Corchorus olitorius) and okra (Abelmoschus callei), previously selected for their superior agronomic and horticultural traits, were evaluated in Cameroon for minerals (Ca, Mg, K, P, Zn and Fe), proteins, and carotenoids content. Nutrient content differed significantly (P<0.001) between cultivars. Amaranth (especially line AM-NKgn) had the highest Ca, Mg, and Zn content in comparison to other genera. Nightshade had the highest K and Fe content. The highest K and Fe levels were found in nightshades BG24 and SS52, respectively. Nightshade had the highest level of protein, especially line BFS1. The highest amount of carotenoids was identified in the eggplant variety Oforiwa. The study revealed that these vegetables are important sources of some vital nutrients. Increased production and consumption of these nutrient-rich vegetables will help reduce the nutrition-related disorders in Africa.

Marker-trait association analysis of functional gene markers for provitamin A levels across diverse tropical yellow maize inbred lines.

Abstract: Biofortification of staple crops is a cost effective and sustainable approach that can help combat vitamin A and other micronutrient deficiencies in developing countries. PCR -based DNA markers distinguishing alleles of three key genes of maize endosperm carotenoid biosynthesis (PSY1, lcyE and crtRB1) have been developed to facilitate maize provitamin A biofortification via marker assisted selection. Previous studies of these functional DNA markers revealed inconsistent effects. The germplasm previously employed for discovering and validating these functional markers was mainly of temperate origin containing low frequencies of the favourable allele of the most significant polymorphism, crtRB1-5′TE. Here, we investigate the vitamin A biofortification potential of these DNA markers in a germplasm panel of diverse tropical yellow maize inbred lines, with mixed genetic backgrounds of temperate and tropical germplasm to identify the most effective diagnostic markers for vitamin A biofortification. The functional DNA markers crtRB1-5′TE and crtRB1-3′TE were consistently and strongly associated with provitamin A content across the tropical maize inbred lines tested. The alleles detected by these two functional markers were in high linkage disequilibrium (R2 = 0.75) and occurred in relatively high frequency (18%). Genotypes combining the favourable alleles at the two loci (N = 20) displayed a 3.22 fold average increase in β-carotene content compared to those genotypes lacking the favourable alleles (N = 106). The PSY1 markers were monomorphic across all of the inbred lines. The functional DNA markers for lcyE were associated with lutein, and with the ratio of carotenoids in the alpha and beta branches, but not with provitamin A levels. However, the combined effects of the two genes were stronger than their individual effects on all carotenoids. Tropical maize inbred lines harbouring the favourable alleles of the crtRB1-5′TE and 3′TE functional markers produce higher levels of provitamin A. Such maize lines can be used as donor parents to speed up the development of provitamin A biofortified tropical maize varieties adapted to growing conditions and consumer preferences, providing a route towards mitigation of vitamin A malnutrition in Sub-Saharan Africa.

Combining ability, heterotic patterns and genetic diversity of extra-early yellow inbreds under contrasting environments

Abstract: Information on the combining ability, heterotic patterns and genetic diversity of maize (Zea mays L.) inbreds is crucial for the success of a hybrid program targeting the stress environments of West Africa (WA). Studies were conducted in 2011 at four locations in Nigeria to (i) determine the combining ability of 20 extra-early yellow inbred lines, (ii) classify the inbred lines into heterotic groups, and (iii) determine the genetic diversity among the lines. General combining ability (GCA) effects were greater than specific combining ability (SCA) effects across test environments suggesting that additive gene action was more important than the nonadditive in the set of inbred lines. The lines were classified into four heterotic groups based on SCA effects, and three groups based on heterotic groups’ specific and GCA, the GCA effects of multiple traits of inbred lines and molecular markers. TZEEI 79, TZEEI 67, and TZEEI 81 were the best inbred testers while TZEEI 95 × TZEEI 79 was the best single-cross tester. TZEEI 88 × TZEEI 66 and TZEEI 96 × TZEEI 73 were identified as ideal hybrids for further testing, promotion for adoption and commercialization in WA.

Soil Heterogeneity and Soil Fertility Gradients in Smallholder Farms of the East African Highlands

Abstract: Heterogeneity in soil fertility in these smallholder systems is caused by both inherent soil-landscape and human-induced variability across farms differing in resources and practices. Interventions to address the problem of poor soil fertility in Africa must be designed to target such diversity and spatially heterogeneity. Data on soil management and soil fertility from six districts in Kenya and Uganda were gathered to understand the determinants of soil heterogeneity within farms. Analysis of the variance of soil fertility indicators across 250 randomly selected farms (i.e., 2607 fields), using a mixed model that considered site, sampling frame, farm type, and field as random terms, revealed that the variation in soil organic C (6.5–27.7 g kg-1), total N (0.6–3.0 g kg-1), and available P (0.9–27 mg kg-1) was mostly related to differences in the inherent properties of the soils across sites (50 to 60% of total variance). Exchangeable K+ (0.1–1.1 cmol(+) kg-1), Ca2+ (1.5–14.5 cmol(+) kg-1), Mg2+ (0.6–3.7 cmol(+) kg-1), and pH (5.1–6.9) exhibited larger residual variability associated with field-to-field differences within farms (30 to 50%). Soil fertility indicators decreased significantly with increasing distance from the homesteads. When this variable was included in the model, the unexplained residual variances—associated with soil heterogeneity within farms—were 38% for soil C; 32% for total N; 49% for available P; 56, 49, and 38% for exchangeable K+, Ca2+ and Mg2+, respectively; and 49% for the pH. In allocating nutrient resources, farmers prioritized fields they perceived as most fertile, reinforcing soil heterogeneity. Categorization of fields within a farm with respect to distance from the homestead, and soil fertility classes as perceived by farmers, were identified as entry points to target soil fertility recommendations to easily recognizable, distinct entities.

Genetic architecture of delayed senescence, biomass, and grain yield under drought stress in cowpea.

Abstract: The stay-green phenomenon is a key plant trait with wide usage in managing crop production under limited water conditions. This trait enhances delayed senescence, biomass, and grain yield under drought stress. In this study we sought to identify QTLs in cowpea (Vigna unguiculata) consistent across experiments conducted in Burkina Faso, Nigeria, Senegal, and the United States of America under limited water conditions. A panel of 383 diverse cowpea accessions and a recombinant inbred line population (RIL) were SNP genotyped using an Illumina 1536 GoldenGate assay. Phenotypic data from thirteen experiments conducted across the four countries were used to identify SNP-trait associations based on linkage disequilibrium association mapping, with bi-parental QTL mapping as a complementary strategy. We identified seven loci, five of which exhibited evidence suggesting pleiotropic effects (stay-green) between delayed senescence, biomass, and grain yield. Further, we provide evidence suggesting the existence of positive pleiotropy in cowpea based on positively correlated mean phenotypic values (0.34< r <0.87) and allele effects (0.07< r <0.86) for delayed senescence and grain yield across three African environments. Three of the five putative stay-green QTLs, Dro-1, 3, and 7 were identified in both RILs and diverse germplasm with resolutions of 3.2 cM or less for each of the three loci, suggesting that these may be valuable targets for marker-assisted breeding in cowpea. Also, the co-location of early vegetative delayed senescence with biomass and grain yield QTLs suggests the possibility of using delayed senescence at the seedling stage as a rapid screening tool for post-flowering drought tolerance in cowpea breeding. BLAST analysis using EST sequences harboring SNPs with the highest associations provided a genomic context for loci identified in this study in closely related common bean (Phaseolus vulgaris) and soybean (Glycine max) reference genomes.

Improving the productivity and income of Ghanaian cocoa farmers while maintaining environmental services: what role for certification?

Abstract: Ghana, as the second largest global producer of cocoa, is strategically positioned on the world market. Consumer concerns over ethical and environmental issues associated with cocoa production are a potential threat to its position. These concerns have given rise to certification. Certification dictates the way cocoa can be produced and consequently affects producers’ incomes and environmental services. The expected profitability, yield, and environmental impact of Rainforest Alliance certified shade-grown cocoa production (RA-Cocoa) is estimated and compared to an extensive shaded production system (Ext-Cocoa) and an intensified full sun production system (High-Tech). Ext-Cocoa represents most cocoa production systems in Ghana, while High-Tech is promoted by the government as a tool for attaining its target output of 1 million tons. Under the baseline assumptions High-Tech was the most profitable; RA-Cocoa generated positive returns, while Ext-cocoa was a break even proposition. Simulation of different p...

Physiological and molecular characterization of drought responses and identification of candidate tolerance genes in cassava

Abstract: Cassava is an important root crop to resource-poor farmers in marginal areas, where its production faces drought stress constraints. Given the difficulties associated with cassava breeding, a molecular understanding of drought tolerance in cassava will help in the identification of markers for use in marker-assisted selection and genes for transgenic improvement of drought tolerance. This study was carried out to identify candidate drought-tolerance genes and expression-based markers of drought stress in cassava. One drought-tolerant (improved variety) and one drought-susceptible (farmer-preferred) cassava landrace were grown in the glasshouse under well-watered and water-stressed conditions. Their morphological, physiological and molecular responses to drought were characterized. Morphological and physiological measurements indicate that the tolerance of the improved variety is based on drought avoidance, through reduction of water loss via partial stomatal closure. Ten genes that have previously been biologically validated as conferring or being associated with drought tolerance in other plant species were confirmed as being drought responsive in cassava. Four genes (MeALDH, MeZFP, MeMSD and MeRD28) were identified as candidate cassava drought-tolerance genes, as they were exclusively up-regulated in the drought-tolerant genotype to comparable levels known to confer drought tolerance in other species. Based on these genes, we hypothesize that the basis of the tolerance at the cellular level is probably through mitigation of the oxidative burst and osmotic adjustment. This study provides an initial characterization of the molecular response of cassava to drought stress resembling field conditions. The drought-responsive genes can now be used as expression-based markers of drought stress tolerance in cassava, and the candidate tolerance genes tested in the context of breeding (as possible quantitative trait loci) and engineering drought tolerance in transgenics.

Root hairs explain P uptake efficiency of soybean genotypes grown in a P-deficient Ferralsol

Abstract: Background and aims Incorporating soybean (Glycine max) genotypes with a high nitrogen fixation potential into cropping systems can sustainably improve the livelihoods of smallholder farmers in Western Kenya. Nitrogen fixation is, however, often constrained by low phosphorus (P) availability. The selection of soybean genotypes for increased P efficiency could help to overcome this problem. This study investigated the contribution of different root traits to variation in P efficiency among soybean genotypes.

Sexuality Generates Diversity in the Aflatoxin Gene Cluster: Evidence on a Global Scale

Abstract: Aflatoxins are produced by Aspergillus flavus and A. parasiticus in oil-rich seed and grain crops and are a serious problem in agriculture, with aflatoxin B1 being the most carcinogenic natural compound known. Sexual reproduction in these species occurs between individuals belonging to different vegetative compatibility groups (VCGs). We examined natural genetic variation in 758 isolates of A. flavus, A. parasiticus and A. minisclerotigenes sampled from single peanut fields in the United States (Georgia), Africa (Benin), Argentina (Cordoba), Australia (Queensland) and India (Karnataka). Analysis of DNA sequence variation across multiple intergenic regions in the aflatoxin gene clusters of A. flavus, A. parasiticus and A. minisclerotigenes revealed significant linkage disequilibrium (LD) organized into distinct blocks that are conserved across different localities, suggesting that genetic recombination is nonrandom and a global occurrence. To assess the contributions of asexual and sexual reproduction to fixation and maintenance of toxin chemotype diversity in populations from each locality/species, we tested the null hypothesis of an equal number of MAT1-1 and MAT1-2 mating-type individuals, which is indicative of a sexually recombining population. All samples were clone-corrected using multi-locus sequence typing which associates closely with VCG. For both A. flavus and A. parasiticus, when the proportions of MAT1-1 and MAT1-2 were significantly different, there was more extensive LD in the aflatoxin cluster and populations were fixed for specific toxin chemotype classes, either the non-aflatoxigenic class in A. flavus or the B1-dominant and G1-dominant classes in A. parasiticus. A mating type ratio close to 1∶1 in A. flavus, A. parasiticus and A. minisclerotigenes was associated with higher recombination rates in the aflatoxin cluster and less pronounced chemotype differences in populations. This work shows that the reproductive nature of the population (more sexual versus more asexual) is predictive of aflatoxin chemotype diversity in these agriculturally important fungi.

Combining Ability and Genetic Diversity of Extra-Early White Maize Inbreds under Stress and Nonstress Environments

Abstract: Maize (Zea mays L.) has the greatest yield potential in savannas of West and Central Africa (WCA). However, production in this agroecol - ogy is constrained by low levels of N, drought, and parasitism by striga ( Striga hermonthica

Breeding aflatoxin-resistant maize lines using recent advances in technologies - a review.

Abstract: Aflatoxin contamination caused by Aspergillus flavus infection of corn is a significant and chronic threat to corn being used as food or feed. Contamination of crops at levels of 20 ng g(-1) or higher (as regulated by the USFDA) by this toxin and potent carcinogen makes the crop unsalable, resulting in a significant economic burden on the producer. This review focuses on elimination of this contamination in corn which is a major US crop and the basis of many products. Corn is also "nature's example" of a crop containing heritable resistance to aflatoxin contamination, thereby serving as a model for achieving resistance to aflatoxin contamination in other crops as well. This crop is the largest production grain crop worldwide, providing food for billions of people and livestock and critical feedstock for production of biofuels. In 2011, the economic value of the US corn crop was US$76 billion, with US growers producing an estimated 12 billion bushels, more than one-third of the world's supply. Thus, the economics and significance of corn as a food crop and the threat to food safety due to aflatoxin contamination of this major food crop have prompted the many research efforts in many parts of the world to identify resistance in corn to aflatoxin contamination. Plant breeding and varietal selection has been used as a tool to develop varieties resistance to disease. This methodology has been employed in defining a few corn lines that show resistance to A. flavus invasion; however, no commercial lines have been marketed. With the new tools of proteomics and genomics, identification of resistance mechanisms, and rapid resistance marker selection methodologies, there is an increasing possibility of finding significant resistance in corn, and in understanding the mechanism of this resistance.

Unlocking the potential of tropical root crop biotechnology in east Africa by establishing a genetic transformation platform for local farmer-preferred cassava cultivars.

Abstract: Cassava genetic transformation capacity is still mostly restricted to advanced laboratories in the USA, Europe and China; and its implementation and maintainance in African laboratories has remained scarce. The impact of transgenic technologies for genetic improvement of cassava will depend largely on the transfer of such capabilities to researchers in Africa, where cassava has an important socioeconomic niche. A major constraint to the development of genetic transformation technologies for cassava improvement has been the lack of an efficient and robust transformation and regeneration system. Despite the success achieved in genetic modification of few cassava cultivars, including the model cultivar 60444, transgenic cassava production remains difficult for farmer-preferred cultivars. In this study, a protocol for cultivar 60444 developed at ETH Zurich was successfully implemented and optimized to establish transformation of farmer-preferred cassava cultivars popular in east Africa. The conditions for production and proliferation of friable embryogenic calli (FEC) and Agrobacterium-mediated transformation were optimized for three east African farmer-preferred cultivars (Ebwanatereka, Kibandameno and Serere). Our results demonstrated transformation efficiencies of about 14-22 independent transgenic lines per 100 mg of FEC for farmer-preferred cultivars in comparison to 28 lines per 100 mg of the model cultivar 60444. The presence, integration and expression of the transgenes were confirmed by PCR, Southern blot analysis and histochemical GUS assay. This study reports the establishment of a cassava transformation platform at International Institute of Tropical Agriculture (IITA) hosted by Biosciences eastern and central Africa (BecA) hub in Kenya and provides the basis for transferring important traits such as virus resistance and prolonged shelf-life to farmer-preferred cultivars in east Africa. We anticipate that such platform will also be instrumental to transfer t

Assessing farmers’ interest in agroforestry in two contrasting agro-ecological zones of Rwanda

Abstract: Uptake and management of agroforestry technologies differs among farms in Rwanda and needs to be documented as a basis for shaping future research and development programs. The objective of this study was to investigate current agroforestry practices, farmers’ preferences, tree management and perspectives for agroforestry technologies. The study consisted of a combination of a formal survey, a participatory tree testing, farmer evaluation and focus group discussions in the Central Plateau (moderate altitude) and the Buberuka (high altitude) agro-ecological zones. A survey and a tree testing exercise with a range of species: (timber species—Eucalyptus urophyla, Grevillea robusta; legume shrubs - Calliandra calothyrsus, Tephrosia vogelii; and fruit species—Persea americana and Citrus sinensis) were carried out in Simbi (Central Plateau) and Kageyo (Buberuka) with farmers from different wealth status who received tree seedlings for planting, managing, and evaluating. Simbi had more tree species farm−1 (4.5) than Kageyo (2.9). Fruit trees occurred most frequently in Simbi. Grevillea robusta, Calliandra calothyrsus and Tephrosia vogelii were mostly established along contours, fruit trees in homefields and Eucalyptus urophyla trees in woodlots. Survival was better on contours for Grevillea robusta (58–100 %) and Calliandra calothyrsus (50–72 %). Tree growth was strongly correlated with the total tree lop biomass in Eucalyptus urophyla (R 2 = 0.69). Grevillea robusta was most preferred in Simbi and Eucalyptus urophyla and Calliandra calothyrsus in Kageyo. The study provided information useful for revising the national agroforestry research and extension agenda and has important implications for other countries in the highlands of Africa.

Perceptions and outlook on intercropping coffee with banana as an opportunity for smallholder coffee farmers in Uganda

Abstract: Coffee and banana are important cash and food crops in Uganda and the surrounding East African highland region. Production is dominated by smallholders that have limited arable land and often coffee and banana are intercropped. No significant research and development efforts have been undertaken over the last few decades on this coffee/banana intercropping system. Because recent studies suggest that this system could be a practice with high benefits to the farmers, we decided to study the perceptions of stakeholders along the coffee value chain starting with farmers. Perception analysis based on open-ended interviews following interview guides revealed that a major limitation for the sustainability of this system was poor soil fertility conditions. Perceptions on the benefits of intercropping differed little among coffee actors; that is, banana intercropping provides additional food and income from smallholders’ limited land and helps farmers reduce risks related to drought, pest/disease attacks and coffee price volatility. However, farmers’ desire to minimize risks does not match the objective of stakeholders higher up the coffee value chain to maximize coffee production. Furthermore, research by public institutes, both national and international, is primarily organized for single crops and not systems. We conclude that the institutional setting of the coffee sector hampers the promotion of intercropping, despite the benefits for the farmer.

Genomic and Proteomic Analysis of Schizaphis graminum Reveals Cyclophilin Proteins Are Involved in the Transmission of Cereal Yellow Dwarf Virus

Abstract: Yellow dwarf viruses cause the most economically important virus diseases of cereal crops worldwide and are transmitted by aphid vectors. The identification of aphid genes and proteins mediating virus transmission is critical to develop agriculturally sustainable virus management practices and to understand viral strategies for circulative movement in all insect vectors. Two cyclophilin B proteins, S28 and S29, were identified previously in populations of Schizaphisgraminum that differed in their ability to transmit the RPV strain of Cereal yellow dwarf virus (CYDV-RPV). The presence of S29 was correlated with F2 genotypes that were efficient virus transmitters. The present study revealed the two proteins were isoforms, and a single amino acid change distinguished S28 and S29. The distribution of the two alleles was determined in 12 F2 genotypes segregating for CYDV-RPV transmission capacity and in 11 genetically independent, field-collected S. graminum biotypes. Transmission efficiency for CYDV-RPV was determined in all genotypes and biotypes. The S29 isoform was present in all genotypes or biotypes that efficiently transmit CYDV-RPV and more specifically in genotypes that efficiently transport virus across the hindgut. We confirmed a direct interaction between CYDV-RPV and both S28 and S29 using purified virus and bacterially expressed, his-tagged S28 and S29 proteins. Importantly, S29 failed to interact with a closely related virus that is transported across the aphid midgut. We tested for in vivo interactions using an aphid-virus co-immunoprecipitation strategy coupled with a bottom-up LC-MS/MS analysis using a Q Exactive mass spectrometer. This analysis enabled us to identify a third cyclophilin protein, cyclophilin A, interacting directly or in complex with purified CYDV-RPV. Taken together, these data provide evidence that both cyclophilin A and B interact with CYDV-RPV, and these interactions may be important but not sufficient to mediate virus transport from the hindgut lumen into the hemocoel.

Integrated Soil Fertility Management: Aggregate carbon and nitrogen stabilization in differently textured tropical soils

Abstract: Soil organic matter is important to improve and sustain soil fertility in tropical agroecosystems. The combined use of organic residue and fertilizer inputs is advocated for its positive effects on short-term nutrient supply, but the effect of the integrated use on long-term stabilization of soil organic C and N is still unclear. We conducted a 1.5-y soil incubation experiment with maize ( Zea mays ) residue and urea fertilizer to examine the stabilization of C and N in four Sub-Saharan African soils differing in texture (sand, sandy loam, clay loam, and clay). The inputs were enriched with 13 C and 15 N in a mirror-labelling design to trace the fate of residue-C and N, and fertilizer-N in combination. We hypothesized that combining inputs would enhance the stabilization of C and N relative to either input alone across a range of soil textures. The treatments were destructively sampled after 0.25, 0.5, and 1.5 y to assess input-derived C and N stabilization in soil macro- and microaggregate fractions. The combination treatment had a significant but small (2% of residue-applied C) increase in residue-C stabilized in the total soil after 0.25 y, but this increase did not persist after 0.5 and 1.5 y. While combining residue and fertilizer decreased the amount of residue-N stabilized within 53- to 2000-μm sized soil aggregates (e.g., 7% less at 1.5 y), it increased the stabilization of fertilizer-N at all sampling times (e.g., 20% more at 1.5 y). The increased amount of fertilizer-N stabilized was significantly greater than the amount of residue-N lost in the combined input treatments in the three finer textured soils at 1.5 y, indicating an interactive increase in the stabilization of new N. Our results indicate that combining residue with fertilizer inputs can increase the short-term stabilization of N, which has the potential to improve soil fertility. However, benefits to N stabilization from combining organic residues and fertilizer seem to be less in coarser-textured soils.

Genetic diversity assessment of extra­early maturing yellow maize inbreds and hybrid performance in Striga­infested and Striga­free environments

Abstract: Maize (Zea mays L.), a major staple food crop in West and Central Africa (WCA), is adapted to all agro-ecologies in the sub-region. Its production in the sub-region is greatly constrained by infestation of Striga hermonthica (Del.) Benth. The performance and stability of the extra-early maturing hybrids, which are particularly adapted to areas with short growing seasons, were assessed under Striga-infested and Striga-free conditions. A total of 120 extra-early hybrids and an open-pollinated variety (OPV) 2008 Syn EE-Y DT STR used as a control were evaluated at two locations each under Striga-infested (Mokwa and Abuja) and Striga-free (Ikenne and Mokwa) conditions in 2010/11. The Striga-resistant hybrids were characterized by higher grain yield, shorter anthesis–silking interval (ASI), better ear aspect, higher numbers of ears per plant (EPP), lower Striga damage rating, and lower number of emerged Striga plants at 8 and 10 weeks after planting (WAP) compared with the susceptible inbreds. Under Striga infestation, mean grain yield ranged from 0·71 to 3·18 t/ha and 1·19 to 3·94 t/ha under Striga-free conditions. The highest yielding hybrid, TZEEI 83×TZEEI 79, out-yielded the OPV control by 157% under Striga infestation. The hybrids TZEEI 83×TZEEI 79 and TZEEI 67×TZEEI 63 were the highest yielding under both Striga-infested and Striga-free conditions. The genotype main effect plus genotype×environment interaction (GGE) biplot analysis identified TZEEI 88×TZEEI 79 and TZEEI 81×TZEEI 95 as the ideal hybrids across research environments. Twenty-three pairs of simple sequence repeat (SSR) markers were used to assess the genetic diversity among the inbred lines. The correlations between the SSR-based genetic distance (GD) estimates of parental lines and the means observed in F1 hybrid under Striga infestation and optimum growing conditions were not significant for grain yield and other traits except ASI under optimum conditions. Grain yield of inbreds was not significantly correlated with that of F1 hybrids. However, a significant correlation existed between F1 hybrid grain yield and heterosis under Striga infestation (r=0·72, P<0·01). These hybrids have the potential for increasing maize production in Striga endemic areas in WCA.

Genetic diversity of cassava (Manihot esculenta Crantz) landraces and cultivars from southern, eastern and central Africa

Abstract: Studies to quantify genetic variation in cassava germplasm, available within the national breeding programmes in Africa, have been limited. Here, we report on the nature and extent of genetic variation that exists within 1401 cassava varieties from seven countries: Tanzania (270 genotypes); Uganda (268); Kenya (234); Rwanda (184); Democratic Republic of Congo (DRC; 177); Madagascar (186); Mozambique (82). The vast majority of these genotypes do not exist within a formal germplasm conservation initiative and were derived from farmers' fields and National Agricultural Research Systems breeding programmes. Genotypes were assayed using 26 simple sequence repeat markers. Moderate genetic variation was observed with evidence of a genetic bottleneck in the region. Some differentiation was observed among countries in both cultivars and landraces. Euclidean distance revealed the pivotal position of Tanzanian landraces in the region, and STRUCTURE analysis revealed subtle and fairly complex relationships among cultivars and among landraces and cultivars analysed together. This is likely to reflect original germplasm introductions, gene flow including farmer exchanges, disease pandemics, past breeding programmes and the introduction of cultivars from the International Institute of Tropical Agriculture – Nigeria. Information generated from this study will be useful to justify and guide a regional cassava genetic resource conservation strategy, to identify gaps in cassava diversity in the region and to guide breeding strategies.

Effect of extrusion variables on extrudates properties of water yam flour – a response surface analysis

Abstract: Water yam (Dioscorea alata) flour was processed using standard wet milling procedure prior to the extrusion process, which led to the determination of extrudate properties of the flours. A single-screw extruder (DCE 330, NJ) was used in evaluating the extrudate properties, which included torque, mass flow rate, residence time, specific mechanical energy and expansion ratio of the flours from the water yam samples. The effect of extrusion and process variables: feed moisture content, screw speed and barrel temperature on the extruder torque, residence time, mass flow rate, specific mechanical energy and expansion ratio for the variety were determined and predictive models were also developed using response surface methodology. It was observed that changing the feed moisture content, barrel temperature and screw speed significantly (P < 0.05) affected expansion ratio, torque, mass flow rate, residence time and specific mechanical energy of all the extrudates. Increasing the feed moisture content (18–28% db) and screw speed (80–180 rpm) resulted in a substantial decrease in expansion ratio (46.6%), residence time (27.5%) and specific mechanical energy (83.6%); whereas, increasing the screw speed significantly increased the mass flow rate (64.5%) of extrudates. Regression analysis indicated that screw speed and feed moisture content were the major process variables showing significant (P < 0.05) linear, quadratic and interaction influences on mass flow rate, expansion ratio and specific mechanical energy. PRACTICAL APPLICATIONS This investigation was conducted with a broad intention of enhancing the value of water yam flours and its suitability for incorporation in the production of noodle-like products. This was accomplished by varying the feed moisture content, screw speed and barrel temperature, and determining their effects on resulting extrudate properties.

Estimating the Actual and Potential Adoption Rates and Determinants of NERICA Rice Varieties in Nigeria

Abstract: The paper uses the average treatment effect (ATE) to estimate the population potential adoption rates of the New Rice for Africa (NERICA) varieties in Nigeria when awareness and access to their seed are not constrained to farmers. It thus extends previous works in the literature that have focused on estimating potential adoption rates when only awareness of technology is not a constraint to farmers. The adoption gaps because of lack of awareness and access to seed, and the determinants of adoption are estimated as well. Results show that the potential NERICA adoption rate in Nigeria will be 54% if the entire population is aware and up to 62% if they have access to NERICA seed. The actually observed 19% adoption rate implies a population adoption gap of 35% and 43% because of lack of awareness and access to NERICA seed, respectively. It is also inferred from these results that, when awareness is not a constraint, about 8% of the population will fail to adopt NERICA because of lack of access to its seed. Al...

Optimization of regeneration and Agrobacterium-mediated transformation of immature cotyledons of chickpea (Cicer arietinum L.)

Abstract: Immature cotyledons collected at different time intervals from four genotypes of chickpea (C 235, BG 256, P 362 and P 372) were cultured adaxially on Murashige and Skoog (MS) medium supplemented with 6-benzyladenine, thidiazuron, kinetin, zeatin and dimethylallylaminopurine (2-iP), either alone or in combination with indole-3-acetic acid (IAA) or α-napthoxyacetic acid (α-NOA) for dedifferentiation and regeneration of adventitious shoots. Morphogenesis was achieved with explants cultured adaxially on MS medium with 13.68 μM zeatin, 24.6 μM 2-iP, 0.29 μM IAA and 0.27 μM α-NOA. Explants prepared from pods of 21 days after pollination, responded favourably to plant growth regulator treatment in shoot differentiation. Histological studies of the regenerating explants, revealed the initiation of meristematic activity in the sub-epidermal region during the onset of morphogenesis, which can be correlated with elevated activity of cytokinin oxidase-dehydrogenase, for cytokinin metabolism. The regenerated shoots were efficiently rooted in MS medium supplemented with 2.46 μM indole-3-butyric acid and acclimatized under culture room and glasshouse conditions for normal plant development leading to 76–80 % survival of the rooted plantlets. The immature cotyledon explants were used for Agrobacterium-mediated transformation with critical manipulation of cultural conditions like age of explant, O.D. of Agrobacterium suspension, concentration of acetosyringone, duration of sonication and co-cultivation for successful genetic transformation and expression of the reporter gene uidA (GUS). Integration of transgene was confirmed by molecular analysis. Transformation frequency up to 2.08 % was achieved in chickpea, suggesting the feasibility of using immature cotyledon explants for Agrobacterium-mediated transformation.