Characterizing patterns of seasonal drought stress for use in common bean breeding in East Africa under present and future climates.

Common bean (Phaseolus vulgaris L.) is the second most important source of dietary protein and the third most important source of calories in Africa, especially for the poor. In East Africa, drought is an important constraint to bean production. Therefore, breeding programs in East Africa have been trying to develop drought resistant varieties of common bean. To do this, breeders need information about seasonal drought stress patterns including their onset, intensity, and duration in the target area of the breeding program, so that they can mimic this pattern during field trials. Using the Decision Support for Agrotechnology Transfer (DSSAT) v4.7 model together with historical and future (Coupled Model Inter-comparison Project 6, CMIP6) climate data, this study categorized Ethiopia, Tanzania, and Uganda into different target population of environments (TPEs) based on historical and future seasonal drought stress patterns. We find that stress-free conditions generally dominate across the three countries under historical conditions (50-80% frequency). These conditions are projected to increase in frequency in Ethiopia by 2-10% but the converse is true for Tanzania (2-8% reduction) and Uganda (17-20% reduction) by 2050 depending on the Shared Socioeconomic Pathway (SSP). Accordingly, by 2050, terminal drought stresses of various intensities (moderate, severe, extreme) are prevalent in 34% of Uganda, around a quarter of Ethiopia, and 40% of the bean growing environments in Tanzania. The TPEs identified in each country serve as a basis for prioritizing breeding activities in national programs. However, to optimize resource use in international breeding programs to develop genotypes that are resilient to future projected stress patterns, we argue that common bean breeding programs should focus primarily on identifying genotypes with tolerance to severe terminal drought, with co-benefits in relation to adaptation to moderate and extreme terminal drought. Little to no emphasis on heat stress is warranted by 2050s.

High Temperature Tolerance in a Novel, High-Quality Phaseolus vulgaris Breeding Line Is Due to Maintenance of Pollen Viability and Successful Germination on the Stigma.

The common bean (Phaseolus vulgaris L.) is an important nutritional source globally but is sensitive to high temperatures and thus particularly vulnerable to climate change. Derived from a breeding program at CIAT (Colombia), a heat-tolerant breeding line, named heat-tolerant Andean-type 4 (HTA4), was developed by a series of crosses of parents with a small-bean tepary genotype (Phaseolus acutifolius L.) in their pedigree, which might be the donor of heat stress (HS) tolerance. Importantly, in HTA4, the large, commercially desirable Andean-type beans was restored. To assess underlying tolerance mechanisms, HTA4, together with a heat-sensitive Colombian variety (Calima), was exposed to HS (31 °C/24 °C HS vs. 26 °C/19 °C day/night) under controlled environment conditions. Vegetative growth and photosynthetic performance were not negatively impacted by HS in either genotype, although senescence was delayed in Calima. HS during the reproductive stage caused an increase in pod number in Calima but with few fully developed seeds and many pods aborted and/or abscised. In contrast, HTA4 maintained a similar filled pod number under HS and a higher seed weight per plant. Pollen showed high sterility in Calima, with many non-viable pollen grains (24.9% viability compared to 98.4% in control) with a thicker exine and fewer starch granules under HS. Calima pollen failed to adhere to the stigma and germinate under HS. In HTA4, pollen viability was significantly higher than in Calima (71.1% viability compared to 95.4% under control), and pollen successfully germinated and formed pollen tubes in the style under HS. It is concluded that HTA4 is heat tolerant and maintains a high level of reproductive output due to its ability to produce healthy pollen that is able to adhere to the stigma.

Large genomic introgression blocks of Phaseolus parvifolius Freytag bean into the common bean enhance the crossability between tepary and common beans.

The production of the common bean (Phaseolus vulgaris L.), one of the most important sources of protein and minerals and one of the most consumed grain legumes globally, is highly affected by heat and drought constraints. In contrast, the tepary bean (Phaseolus acutifolius A. Gray), a common bean-related species, is adapted to hot and dry climates. Hybridization to introduce complex traits from the tepary bean into the common bean has been challenging, as embryo rescue is required. In this study, we report three novel interspecific lines that were obtained by crossing lines from prior common bean × tepary bean hybridization with Phaseolus parvifolius Freytag in order to increase the male gametic diversity to facilitate interspecific crosses. These interspecific lines enhanced the crossability of the common bean and tepary bean species while avoiding the embryo rescue process. Crossing these three interspecific lines with tepary beans resulted in 12-fold more hybrid plants than crossing traditional common beans with tepary beans. Whole-genome sequencing analysis of these three interspecific lines shows large introgressions of genomic regions corresponding to P. parvifolius on chromosomes that presumably contribute to reproductive barriers between both species. The development of these lines opens up the possibility of increasing the introgression of desirable tepary bean traits into the common bean to address constraints driven by climate change.

Multivariate genomic analysis and optimal contributions selection predicts high genetic gains in cooking time, iron, zinc, and grain yield in common beans in East Africa.

Common bean (Phaseolus vulgaris L.) is important in African diets for protein, iron (Fe), and zinc (Zn), but traditional cultivars have long cooking time (CKT), which increases the time, energy, and health costs of cooking. Genomic selection was used to predict genomic estimated breeding values (GEBV) for grain yield (GY), CKT, Fe, and Zn in an African bean panel of 358 genotypes in a two-stage analysis. In Stage 1, best linear unbiased estimates (BLUE) for each trait were obtained from 898 genotypes across 33 field trials in East Africa. In Stage 2, BLUE in a training population of 141 genotypes were used in a multivariate genomic analysis with genome-wide single nucleotide polymorphism data from the African bean panel. Moderate to high genomic heritability was found for GY (0.45 ± 0.10), CKT (0.50 ± 0.15), Fe (0.57 ± 0.12), and Zn (0.61 ± 0.13). There were significant favorable genetic correlations between Fe and Zn (0.91 ± 0.06), GY and Fe (0.66 ± 0.17), GY and Zn (0.44 ± 0.19), CKT and Fe (-0.57 ± 0.21), and CKT and Zn (-0.67 ± 0.20). Optimal contributions selection (OCS), based on economic index of weighted GEBV for each trait, was used to design crossing within four market groups relevant to East Africa. Progeny were predicted by OCS to increase in mean GY by 12.4%, decrease in mean CKT by 9.3%, and increase in mean Fe and Zn content by 6.9 and 4.6%, respectively, with low achieved coancestry of 0.032. Genomic selection with OCS will accelerate breeding of high-yielding, biofortified, and rapid cooking African common bean cultivars.

Genomics, genetics and breeding of common bean in Africa: A review of tropical legume project.

Common bean (Phaseolus vulgaris L.) is an important legume crop worldwide. The International Centre for Tropical Agriculture (CIAT) and its national partners in Africa aim to overcome production constraints of common bean and address the food, nutrition needs and market demands through development of multitrait bean varieties. Breeding is guided by principles of market-driven approaches to develop client-demanded varieties. Germplasm accessions from especially two sister species, P. coccineus and P. acutifolius, have been utilized as sources of resistance to major production constraints and interspecific lines deployed. Elucidation of plant mechanisms governing pest and disease resistance, abiotic stress tolerance and grain nutritional quality guides the selection methods used by the breeders. Molecular markers are used to select for resistance to key diseases and insect pests. Efforts have been made to utilize modern genomic tools to increase scale, efficiency, accuracy and speed of breeding. Through gender-responsive participatory variety selection, market-demanded varieties have been released in several African countries. These new bean varieties are a key component of sustainable food systems in the tropics.

Single and Multi-trait GWAS Identify Genetic Factors Associated with Production Traits in Common Bean Under Abiotic Stress Environments.

The genetic improvement of economically important production traits of dry bean (Phaseolus vulgaris L.), for geographic regions where production is threatened by drought and high temperature stress, is challenging because of the complex genetic nature of these traits. Large scale SNP data sets for the two major gene pools of bean, Andean and Middle American, were developed by mapping multiple pools of genotype-by-sequencing reads and identifying over 200k SNPs for each gene pool against the most recent assembly of the P. vulgaris genome sequence. Moderately sized B ean A biotic S tress E valuation (BASE) panels, consisting of genotypes appropriate for production in Central America and Africa, were assembled. Phylogenetic analyses demonstrated the BASE populations represented broad genetic diversity for the appropriate races within the two gene pools. Joint mixed linear model genome-wide association studies with data from multiple locations discovered genetic factors associated with four production traits in both heat and drought stress environments using the BASE panels. Pleiotropic genetic factors were discovered using a multi-trait mixed model analysis. SNPs within or near candidate genes associated with hormone signaling, epigenetic regulation, and ROS detoxification under stress conditions were identified and can be used as genetic markers in dry bean breeding programs.

Fine-mapping of angular leaf spot resistance gene Phg-2 in common bean and development of molecular breeding tools.

KEY MESSAGE: The Common Bean Angular Leaf Spot Resistance Gene Phg-2 was fine-mapped to a 409-Kbp region, and molecular markers for breeders were developed and validated in field experiments. Common bean (Phaseolus vulgaris L.) is an important food legume in Latin America, Asia and Africa. It is an important source of protein, carbohydrates and micro-minerals, particularly for smallholder farmers. Common bean productivity is affected by angular leaf spot (ALS) disease caused by the pathogenic fungus Pseudocercospora griseola, resulting in significant yield losses, particularly in low-input smallholder farming systems in the tropics. The ALS resistance gene Phg-2, which was found in several highly resistant common bean genotypes, was investigated in crosses between Mesoamerican pre-breeding lines and elite Andean breeding lines. Next-generation sequencing (NGS) data sets were used to design new SNP-based molecular markers. The Phg-2 locus was confirmed to be the major locus providing ALS resistance in these crosses. The locus was fine-mapped to a 409-Kbp region on chromosome 8. Two clusters of highly related LRR genes were identified in this region, which are the best candidate genes for Phg-2. Molecular markers were identified that are closely linked to the Phg-2 resistance gene and also highly specific to the donor germplasm. Marker-assisted selection (MAS) was used to introgress the Phg-2 resistance locus into Andean breeding germplasm using MAB lines. The usefulness of molecular markers in MAS was confirmed in several field evaluations in complex breeding crosses, under inoculation with different ALS pathotypes. This project demonstrates that NGS data are a powerful tool for the characterization of genetic loci and can be applied in the development of breeding tools.

Reduction in nutritional quality and growing area suitability of common bean under climate change induced drought stress in Africa.

Climate change impacts on food security will involve negative impacts on crop yields, and potentially on the nutritional quality of staple crops. Common bean is the most important grain legume staple crop for human diets and nutrition worldwide. We demonstrate by crop modeling that the majority of current common bean growing areas in southeastern Africa will become unsuitable for bean cultivation by the year 2050. We further demonstrate reductions in yields of available common bean varieties in a field trial that is a climate analogue site for future predicted drought conditions. Little is known regarding the impact of climate change induced abiotic stresses on the nutritional quality of common beans. Our analysis of nutritional and antinutritional compounds reveals that iron levels in common bean grains are reduced under future climate-scenario relevant drought stress conditions. In contrast, the levels of protein, zinc, lead and phytic acid increase in the beans under such drought stress conditions. This indicates that under climate-change induced drought scenarios, future bean servings by 2050 will likely have lower nutritional quality, posing challenges for ongoing climate-proofing of bean production for yields, nutritional quality, human health, and food security.

Resequencing of Common Bean Identifies Regions of Inter-Gene Pool Introgression and Provides Comprehensive Resources for Molecular Breeding.

Common bean ( L.) is the most important grain legume for human consumption and is a major nutrition source in the tropics. Because bean production is reduced by both abiotic and biotic constraints, current breeding efforts are focused on the development of improved varieties with tolerance to these stresses. We characterized materials from different breeding programs spanning three continents to understand their sequence diversity and advance the development of molecular breeding tools. For this, 37 varieties belonging to , (A. Gray), and L. were sequenced by whole-genome sequencing, identifying more than 40 million genomic variants. Evaluation of nuclear DNA content and analysis of copy number variation revealed important differences in genomic content not only between and the two other domesticated species, but also within , affecting hundreds of protein-coding genomic regions. A large number of inter-gene pool introgressions were identified. Furthermore, interspecific introgressions for disease resistance in breeding lines were mapped. Evaluation of newly developed single nucleotide polymorphism markers within previously discovered quantitative trait loci for common bacterial blight and angular leaf spot provides improved specificity to tag sources of resistance to these diseases. We expect that this dataset will provide a deeper molecular understanding of breeding germplasm and deliver molecular tools for germplasm development, aiming to increase the efficiency of bean breeding programs.

Iron Bioavailability Studies of the First Generation of Iron-Biofortified Beans Released in Rwanda.

This paper represents a series of in vitro iron (Fe) bioavailability experiments, Fe content analysis and polyphenolic profile of the first generation of Fe biofortified beans (Phaseolus vulgaris) selected for human trials in Rwanda and released to farmers of that region. The objective of the present study was to demonstrate how the Caco-2 cell bioassay for Fe bioavailability can be utilized to assess the nutritional quality of Fe in such varieties and how they may interact with diets and meal plans of experimental studies. Furthermore, experiments were also conducted to directly compare this in vitro approach with specific human absorption studies of these Fe biofortified beans. The results show that other foods consumed with beans, such as rice, can negatively affect Fe bioavailability whereas potato may enhance the Fe absorption when consumed with beans. The results also suggest that the extrinsic labelling approach to measuring human Fe absorption can be flawed and thus provide misleading information. Overall, the results provide evidence that the Caco-2 cell bioassay represents an effective approach to evaluate the nutritional quality of Fe-biofortified beans, both separate from and within a targeted diet or meal plan.

Priority regions for research on dryland cereals and legumes.

Dryland cereals and legumes  are important crops in farming systems across the world.  Yet they are frequently neglected among the priorities for international agricultural research and development, often due to lack of information on their magnitude and extent. Given what we know about the global distribution of dryland cereals and legumes, what regions should be high priority for research and development to improve livelihoods and food security? This research evaluated the geographic dimensions of these crops and the farming systems where they are found worldwide. The study employed geographic information science and data to assess the key farming systems and regions for these crops. Dryland cereal and legume crops should be given high priority in 18 farming systems worldwide, where their cultivated area comprises more than 160 million ha. These regions include the dryer areas of South Asia, West and East Africa, the Middle East and North Africa, Central America and other parts of Asia. These regions are prone to drought and heat stress, have limiting soil constraints, make up half of the global population and account for 60 percent of the global poor and malnourished. The dryland cereal and legume crops and farming systems merit more research and development attention to improve productivity and address development problems. This project developed an open access dataset and information resource that provides the basis for future analysis of the geographic dimensions of dryland cereals and legumes.

Studies of Cream Seeded Carioca Beans (Phaseolus vulgaris L.) from a Rwandan Efficacy Trial: In Vitro and In Vivo Screening Tools Reflect Human Studies and Predict Beneficial Results from Iron Biofortified Beans.

Iron (Fe) deficiency is a highly prevalent micronutrient insufficiency predominantly caused by a lack of bioavailable Fe from the diet. The consumption of beans as a major food crop in some populations suffering from Fe deficiency is relatively high. Therefore, our objective was to determine whether a biofortified variety of cream seeded carioca bean (Phaseolus vulgaris L.) could provide more bioavailable-Fe than a standard variety using in-vivo (broiler chicken, Gallus gallus) and in-vitro (Caco-2 cell) models. Studies were conducted under conditions designed to mimic the actual human feeding protocol. Two carioca-beans, a standard (G4825; 58 µg Fe/g) and a biofortified (SMC; 106 µg Fe/g), were utilized. Diets were formulated to meet the nutrient requirements of Gallus gallus except for Fe (33.7 and 48.7 µg Fe/g, standard and biofortified diets, respectively). In-vitro observations indicated that more bioavailable-Fe was present in the biofortified beans and diet (P<0.05). In-vivo, improvements in Fe-status were observed in the biofortified bean treatment, as indicated by the increased total-body-Hemoglobin-Fe, and hepatic Fe-concentration (P<0.05). Also, DMT-1 mRNA-expression was increased in the standard bean treatment (P<0.05), indicating an upregulation of absorption to compensate for less bioavailable-Fe. These results demonstrate that the biofortified beans provided more bioavailable Fe; however, the in vitro results revealed that ferritin formation values were relatively low. Such observations are indicative of the presence of high levels of polyphenols and phytate that inhibit Fe absorption. Indeed, we identified higher levels of phytate and quercetin 3-glucoside in the Fe biofortified bean variety. Our results indicate that the biofortified bean line was able to moderately improve Fe-status, and that concurrent increase in the concentration of phytate and polyphenols in beans may limit the benefit of increased Fe-concentration. Therefore, specific targeting of such compounds during the breeding process may yield improved dietary Fe-bioavailability. Our findings are in agreement with the human efficacy trial that demonstrated that the biofortified carioca beans improved the Fe-status of Rwandan women. We suggest the utilization of these in vitro and in vivo screening tools to guide studies aimed to develop and evaluate biofortified staple food crops. This approach has the potential to more effectively utilize research funds and provides a means to monitor the nutritional quality of the Fe-biofortified crops once released to farmers.

Polyphenolic compounds appear to limit the nutritional benefit of biofortified higher iron black bean (Phaseolus vulgaris L.).

BACKGROUND: Our objective was to determine if a biofortified variety of black bean can provide more bioavailable-iron (Fe) than a standard variety. Two lines of black beans (Phaseolus-vulgaris L.), a standard (DOR500; 59µg Fe/g) and biofortified (MIB465; 88µg Fe/g) were used. The DOR500 is a common commercial variety, and the MIB465 is a line developed for higher-Fe content. Given the high prevalence of Fe-deficiency anemia worldwide, it is important to determine if Fe-biofortified black beans can provide more absorbable-Fe. METHODS: Black bean based diets were formulated to meet the nutrient requirements for the broiler (Gallus-gallus) except for Fe (dietary Fe-concentrations were 39.4±0.2 and 52.9±0.9 mg/kg diet, standard vs. biofortified, respectively). Birds (n=14) were fed the diets for 6-weeks. Hemoglobin-(Hb), liver-ferritin and Fe-related transporter/enzyme gene-expression were measured. Hemoglobin-maintenance-efficiency and total-body-Hb-Fe values were used to estimate Fe-bioavailability. RESULTS: Hemoglobin-maintenance-efficiency values were higher (P<0.05) in the group consuming the standard-Fe beans on days 14, 21 and 28; indicating a compensatory response to lower dietary-Fe. Final total-Hb-Fe body content was higher in the biofortified vs. the standard group (26.6±0.9 and 24.4±0.8 mg, respectively; P<0.05). There were no differences in liver-ferritin or in expression of DMT-1, Dcyt-B, and ferroportin. In-vitro Fe-bioavailability assessment indicated very low Fe-bioavailability from both diets and between the two bean varieties (P>0.05). Such extremely-low in-vitro Fe-bioavailability measurement is indicative of the presence of high levels of polyphenolic-compounds that may inhibit Fe-absorption. High levels of these compounds would be expected in the black bean seed-coats. CONCLUSIONS: The parameters of Fe-status measured in this study indicate that only a minor increase in absorbable-Fe was achieved with the higher-Fe beans. The results also raise the possibility that breeding for increased Fe-concentration elevated the levels of polyphenolic-compounds that can reduce bean Fe-bioavailability, although the higher levels of polyphenolics in the higher-Fe beans may simply be coincidental or an environmental effect. Regardless, Fe-biofortified beans remain a promising vehicle for increasing intakes of bioavailable-Fe in human populations that consume high levels of these beans as a dietary staple, and the bean polyphenol profile must be further evaluated and modified if possible in order to improve the nutritional quality of higher-Fe beans.

Development of a Mesoamerican intra-genepool genetic map for quantitative trait loci detection in a drought tolerant × susceptible common bean (Phaseolus vulgaris L.) cross.

Drought is a major constraint to common bean (Phaseolus vulgaris L.) production, especially in developing countries where irrigation for the crop is infrequent. The Mesoamerican genepool is the most widely grown subdivision of common beans that include small red, small cream and black seeded varieties. The objective of this study was to develop a reliable genetic map for a Mesoamerican × Mesoamerican drought tolerant × susceptible cross and to use this map to analyze the inheritance of yield traits under drought and fully irrigated conditions over 3 years of experiments. The source of drought tolerance used in the cross was the cream-seeded advanced line BAT477 crossed with the small red variety DOR364 and the population was made up of recombinant inbred lines in the F5 generation. Quantitative trait loci were detected by composite interval mapping for the traits of overall seed yield, yield per day, 100 seed weight, days to flowering and days to maturity for each field environment consisting of two treatments (irrigated and rainfed) and lattice design experiments with three repetitions for a total of six environments. The genetic map based on amplified fragment length polymorphism and random amplified polymorphic DNA markers was anchored with 60 simple sequence repeat (SSR) markers and had a total map length of 1,087.5 cM across 11 linkage groups covering the whole common bean genome with saturation of one marker every 5.9 cM. Gaps for the genetic map existed on linkage groups b03, b09 and b11 but overall there were only nine gaps larger than 15 cM. All traits were inherited quantitatively, with the greatest number for seed weight followed by yield per day, yield per se, days to flowering and days to maturity. The relevance of these results for breeding common beans is discussed in particular in the light of crop improvement for drought tolerance in the Mesoamerican genepool.

QTL analyses for seed iron and zinc concentrations in an intra-genepool population of Andean common beans (Phaseolus vulgaris L.).

Legumes provide essential micronutrients that are found only in low amounts in the cereals or root crops. An ongoing project at CIAT has shown that the legume common bean is variable in the amount of seed minerals (iron, zinc, and other elements), vitamins, and sulfur amino acids that they contain and that these traits are likely to be inherited quantitatively. In this study we analyzed iron and zinc concentrations in an Andean recombinant inbred line (RIL) population of 100 lines derived from a cross between G21242, a Colombian cream-mottled climbing bean with high seed iron/zinc and G21078, an Argentinean cream seeded climbing bean with low seed iron/zinc. The population was planted across three environments; seed from each genotype was analyzed with two analytical methods, and quantitative trait loci (QTL) were detected using composite interval mapping and single-point analyses. A complete genetic map was created for the cross using a total of 74 microsatellite markers to anchor the map to previously published reference maps and 42 RAPD markers. In total, nine seed mineral QTL were identified on five linkage groups (LGs) with the most important being new loci on b02 and other QTL on b06, b08, and b07 near phaseolin. Seed weight QTL were associated with these on b02 and b08. These Andean-derived QTL are candidates for marker-assisted selection either in combination with QTL from the Mesoamerican genepool or with other QTL found in inter and intra-genepool crosses, and the genetic map can be used to anchor other intra-genepool studies.

QTL for seed iron and zinc concentration and content in a Mesoamerican common bean (Phaseolus vulgaris L.) population.

Iron and zinc deficiencies are human health problems found throughout the world and biofortification is a plant breeding-based strategy to improve the staple crops that could address these dietary constraints. Common bean is an important legume crop with two major genepools that has been the focus of genetic improvement for seed micronutrient levels. The objective of this study was to evaluate the inheritance of seed iron and zinc concentrations and contents in an intra-genepool Mesoamerican × Mesoamerican recombinant inbred line population grown over three sites in Colombia and to identify quantitative trait loci (QTL) for each mineral. The population had 110 lines and was derived from a high-seed iron and zinc climbing bean genotype (G14519) crossed with a low-mineral Carioca-type, prostrate bush bean genotype (G4825). The genetic map for QTL analysis was created from SSR and RAPD markers covering all 11 chromosomes of the common bean genome. A set of across-site, overlapping iron and zinc QTL was discovered on linkage group b06 suggesting a possibly pleiotropic locus and common physiology for mineral uptake or loading. Other QTL for mineral concentration or content were found on linkage groups b02, b03, b04, b07, b08 and b11 and together with the b06 cluster were mostly novel compared to loci found in previous studies of the Andean genepool or inter-genepool crosses. The discovery of an important new locus for seed iron and zinc concentrations may facilitate crop improvement and biofortification using the high-mineral genotype especially within the Mesoamerican genepool.

Biofortified black beans in a maize and bean diet provide more bioavailable iron to piglets than standard black beans.

Our objective was to compare the capacities of biofortified and standard black beans (Phaseolus vulgaris L.) to deliver iron (Fe) for hemoglobin (Hb) synthesis. Two lines of black beans, one standard and the other biofortified (high) in Fe (71 and 106 microg Fe/g, respectively), were used. Maize-based diets containing the beans were formulated to meet the nutrient requirements for swine except for Fe (Fe concentrations in the 2 diets were 42.9 +/- 1.2 and 54.6 +/- 0.9 mg/kg). At birth, pigs were injected with 50 mg of Fe as Fe dextran. At age 28 d, pigs were allocated to the experimental diets (n = 10). They were fed 2 times per day for 5 wk and given free access to water at all times. Body weights and Hb concentrations were measured weekly. Hb repletion efficiencies (means +/- SEM) did not differ between groups and, after 5 wk, were 20.8 +/- 2.1% for the standard Fe group and 20.9 +/- 2.1% for the high Fe group. Final total body Hb Fe contents did not differ between the standard [539 +/- 39 mg (9.7 +/- 0.7 micromol)] and high Fe [592 +/- 28 mg (10.6 +/- 0.5 micromol)] bean groups (P = 0.15). The increase in total body Hb Fe over the 5-wk feeding period was greater in the high Fe bean group [429 +/- 24 mg (7.7 +/- 0.4 micromol)] than in the standard Fe bean group [361 +/- 23 mg (6.4 +/- 0.4 micromol)] (P = 0.034). We conclude that the biofortified beans are a promising vehicle for increasing intakes of bioavailable Fe in human populations that consume beans as a dietary staple.

Corrigendum to: Genetic mapping of basal root gravitropism and phosphorus acquisition efficiency in common bean.

Root gravitropism determines the relative distribution of plant roots in different soil layers, and therefore, may influence the acquisition of shallow soil resources such as phosphorus (P). Growth pouch and field studies were conducted to evaluate root gravitropism of common bean (Phaseolus vulgaris L.) in response to P deficiency and to detect quantitative trait loci (QTL) associated with this trait. A deep-rooted genotype, DOR364, was crossed with a shallow-rooted genotype, G19833, to obtain 86 F5.7 recombinant inbred lines (RILs). Root gravitropic traits were measured as basal root growth angle (BRGA), shallow basal root length (SBRL, basal root length in the top 0-3 cm of soil) and relative shallow basal root length (RSBRL, percentage of basal root length in the top 0-3 cm of soil relative to total basal root length). Large genetic variability for these traits was found in the parents and RILs, with BRGA ranging from -18.73 to 56.69º and SBRL ranging from 0.42 to 2.63 m per plant. The parents and six RILs with contrasting root gravitropism were further evaluated in the field, where root shallowness was significantly correlated with plant growth and P uptake. QTL were detected by single point analysis (SPA), interval mapping (IM) and composite interval mapping (CIM) techniques with a genetic map for the DOR364 × G19833 population consisting of 236 molecular markers. The IM/CIM QTL were detected among the 11 linkage groups of common bean, with 16 QTL controlling the above root traits and six QTL controlling P acquisition efficiency (PAE) in the field study. At least three of the root trait QTL were associated with QTL for PAE, suggesting that root gravitropic traits are associated with PAE and that QTL for these traits can be used to facilitate selection and breeding for higher P efficiency in common bean and other crops.

The usefulness of in vitro models to predict the bioavailability of iron and zinc: a consensus statement from the HarvestPlus expert consultation.

A combination of dietary and host-related factors determines iron and zinc absorption, and several in vitro methods have been developed as preliminary screening tools for assessing bioavailability. An expert committee has reviewed evidence for their usefulness and reached a consensus. Dialyzability (with and without simulated digestion) gives some useful information but cannot predict the correct magnitude of response and may sometimes predict the wrong direction of response. Caco-2 cell systems (with and without simulated digestion) have been developed for iron availability, but the magnitude of different effects does not always agree with results obtained in human volunteers, and the data for zinc are too limited to draw conclusions about the validity of the method. Caco-2 methodologies vary significantly between laboratories and require experienced technicians and good quality cell culture facilities to obtain reproducible results. Algorithms can provide semi-quantitative information enabling diets to be classified as high, moderate, or low bioavailability. While in vitro methods can be used to generate ideas and develop hypotheses, they cannot be used alone for important decisions concerning food fortification policy, selection of varieties for plant breeding programs, or for new product development in the food industry. Ultimately human studies are required for such determinations.

Genetic mapping of basal root gravitropism and phosphorus acquisition efficiency in common bean.

Root gravitropism determines the relative distribution of plant roots in different soil layers, and therefore, may influence the acquisition of shallow soil resources such as phosphorus (P). Growth pouch and field studies were conducted to evaluate root gravitropism of common bean (Phaseolus vulgaris L.) in response to P deficiency and to detect quantitative trait loci (QTL) associated with this trait. A deep-rooted genotype, DOR364, was crossed with a shallow-rooted genotype, G19833, to obtain 86 F5.7 recombinant inbred lines (RILs). Root gravitropic traits were measured as basal root growth angle (BRGA), shallow basal root length (SBRL, basal root length in the top 0-3 cm of soil) and relative shallow basal root length (RSBRL, percentage of basal root length in the top 0-3 cm of soil relative to total basal root length). Large genetic variability for these traits was found in the parents and RILs, with BRGA ranging from -18.73 to 56.69º and SBRL ranging from 0.42 to 2.63 m per plant. The parents and six RILs with contrasting root gravitropism were further evaluated in the field, where root shallowness was significantly correlated with plant growth and P uptake. QTL were detected by single point analysis (SPA), interval mapping (IM) and composite interval mapping (CIM) techniques with a genetic map for the DOR364 × G19833 population consisting of 236 molecular markers. The IM / CIM QTL were detected among the 11 linkage groups of common bean, with 16 QTL controlling the above root traits and six QTL controlling P acquisition efficiency (PAE) in the field study. At least three of the root trait QTL were associated with QTL for PAE, suggesting that root gravitropic traits are associated with PAE and that QTL for these traits can be used to facilitate selection and breeding for higher P efficiency in common bean and other crops.