RESUMO
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.
RESUMO
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.
Assuntos
Resistência à Doença/genética , Phaseolus/genética , Melhoramento Vegetal , Doenças das Plantas/genética , Ascomicetos/patogenicidade , Mapeamento Cromossômico , Marcadores Genéticos , Genótipo , Técnicas de Genotipagem , Phaseolus/microbiologia , Fenótipo , Doenças das Plantas/microbiologia , Polimorfismo de Nucleotídeo Único , Análise de Sequência de DNARESUMO
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.
RESUMO
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.
Assuntos
Pool Gênico , Ferro/metabolismo , Phaseolus/genética , Locos de Características Quantitativas/genética , Sementes/genética , Sementes/metabolismo , Zinco/metabolismo , Biomassa , Mapeamento Cromossômico , Cruzamentos Genéticos , Genética Populacional , Endogamia , América Latina , Minerais/metabolismo , Repetições Minissatélites , Phaseolus/metabolismo , Técnica de Amplificação ao Acaso de DNA Polimórfico , Recombinação Genética/genéticaRESUMO
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.