Mesoamerican Bean Research Articles

Cell size differences affect photosynthetic capacity in a Mesoamerican and an Andean genotype of Phaseolus vulgaris L.

The efficiency of CO2 flux in the leaf is hindered by a several structural and biochemical barriers which affect the overall net photosynthesis. However, the dearth of information about the genetic control of these features is limiting our ability for genetic manipulation. We performed a comparative analysis between three-week-old plants of a Mesoamerican and an Andean cultivar of Phaseolus vulgaris at variable light and CO2 levels. The Mesoamerican bean had higher photosynthetic rate, maximum rate of rubisco carboxylase activity and maximum rate of photosynthetic electron transport at light saturation conditions than its Andean counterpart. Leaf anatomy comparison between genotypes showed that the Mesoamerican bean had smaller cell sizes than the Andean bean. Smaller epidermal cells in the Mesoamerican bean resulted in higher stomata density and consequently higher stomatal conductance for water vapor and CO2 than in the Andean bean. Likewise, smaller palisade and spongy mesophyll cells in the Mesoamerican than in the Andean bean increased the cell surface area per unit of volume and consequently increased mesophyll conductance. Finally, smaller cells in the Mesoamerican also increased chlorophyll and protein content per unit of leaf area. In summary, we show that different cell sizes controls the overall net photosynthesis and could be used as a target for genetic manipulation to improve photosynthesis.

Phenotype based clustering, and diversity of common bean genotypes in seed iron concentration and cooking time.

Common bean is the world's most important directly consumed legume food crop that is popular for calories, protein and micronutrients. It is a staple food in sub-Saharan Africa, and a significant source of iron for anemic people. However, several pests, soil and weather challenges still impede its production. Long cooking time, and high phytic acid and polyphenols that influence bioavailable iron also limit the health benefits. To inform population improvement strategies and selection decisions for resilient fast cooking and iron biofortified beans, the study determined diversity and population structure within 427 breeding lines, varieties, or landraces mostly from Alliance Uganda and Columbia. The genotypes were evaluated for days to flowering and physiological maturity, yield, seed iron (FESEED) and zinc (ZNSEED) and cooking time (COOKT). Data for all traits showed significant (P≤0.001) differences among the genotypes. Repeatability was moderate to high for most traits. Performance ranged from 52 to 87 ppm (FESEED), 23-38 ppm (ZNSEED), 36-361 minutes (COOKT), and 397-1299 kg/ha (yield). Minimal differences existed between the gene pools in the mean performance except in yield, where Mesoamerican beans were better by 117 kg/ha. The genotypes exhibited high genetic diversity and thus have a high potential for use in plant breeding. Improvement of FESEED and ZNSEED, COOKT and yield performance within some markets such as red and small white beans is possible. Hybridization across market classes especially for yellow beans is essential but this could be avoided by adding other elite lines to the population. Superior yielding and fast cooking, yellow and large white beans were specifically lacking. Adding Fe dense elite lines to the population is also recommended. The population was clustered into three groups that could be considered for specific breeding targets based on trait correlations.

Pathogenic variability of the fungus Colletotrichum lindemuthianum on dry bean in South Africa

Dry bean (Phaseolus vulgaris L) anthracnose is an economically important seed-borne fungal disease caused by the fungus Colletotrichum lindemuthianum. The pathogenic variability of C. lindemuthianum was evaluated in a glasshouse study. A total of 32 isolates were collected in three provinces, namely KwaZulu-Natal, Mpumalanga and North-West. The isolates were collected from different fields of dry bean at research stations and also from small-scale farmers’ fields. Inoculum developed from the different isolates was sprayed onto 12 CIAT differential dry bean cultivars that were used to identify pathogen races. The inoculation was carried out during the trifoliate developmental stage of the dry bean seedlings raised in pots 14 days post-sowing. Using the CIAT binomial system, eight pathogenic races of C. lindemuthianum were identified, namely, 3, 6, 7, 81, 83, 89, 263 and 323 out of the 32 isolates evaluated. Only pathogenic races 7, 81, 83 and 89 were found in the more humid locations of the province of KwaZulu-Natal. Races 7, 81 and 89 are internationally recognized and show characteristics reported of races in Brazil. Race 6 was identified in Mpumalanga and North west provinces and this was important as it has been reported in other Southern African countries. The races populations were distinct between locations as they infected both the Andean and the Meso-American bean landraces. The most important dry bean landraces were AB 136, G 2333, Kaboon, TU and PI 207262 as they showed complete resistance from the isolates. The study findings suggests that these six landraces can be successfully used to improve anthracnose resistance, especially G 2333 because of its horizontal resistance that can be used to improve the current cultivars used for the control of anthracnose in South Africa. Additionally, Cornell 49242 was one of the landraces of importance, as it showed glimpses of anthracnose that faded overtime under controlled suitable environmental conditions. Use of these landraces will ensure stability in the long-term control of dry bean anthracnose since the pathogen C. lindemuthianum is highly variable and widely distributed in South Africa. Key words: Anthracnose, Colletotrichum lindemuthianum, dry bean, disease, pathogenic races, seed, differential cultivars, resistance

Performance of Mesoamerican bean (Phaseolus vulgaris L.) lines in an unfertilized oxisol

Introduction. Common beans (Phaseolus vulgaris L.) in Central America and the Caribbean are often produced on low fertility soils which reduces crop yield. Bean breeding programs need to identify genotypes that have superior adaptation to these conditions. Objective. Identify Mesoamerican bean germplasm lines with superior adaptation to low soil fertility. Materials and methods. The performance of twenty-seven Mesoamerican bean (Phaseolus vulgaris L.) lines from the Bean Abiotic Stress Evaluation (BASE) 120 panel were evaluated in an unfertilized oxisol at Isabela, Puerto Rico over five growing seasons (four-year period from 2015-2018). The lines were inoculated with a mixture of Rhizobium etli and R. tropici to promote symbiotic nitrogen fixation (SNF). Results. Four lines produced mean seed yields >1,200 kg ha-1 and had estimates of nitrogen derived from the atmosphere (NDFA) >50 %. Greater nodule number was positively correlated with % NDFA, later maturity and seed yield. The heat and drought tolerant small red cultivar ‘Rojo Chortí’ and the heat tolerant white cultivar ‘Verano’ had among the smallest apparent C isotope discrimination values suggesting greater water use efficiency. Among the elite lines in the trial, root rot damage was minimal and the basal root growth angles were intermediate (40-60 %), which favored the uptake of water and soil nutrients. Conclusion. Mesoamerican bean lines with superior seed yield and enhanced symbiotic nitrogen fixation in a low fertility soil were identified. Many of these lines also possess resistance to other biotic and abiotic factors that limit bean seed yield in Central America and the Caribbean.

TECHNOLOGICAL-NUTRITIONAL QUALITY TRAITS AND RELATIONSHIP TO BIOACTIVE COMPOUNDS IN MESOAMERICAN AND ANDEAN BEANS

ABSTRACT The common bean exhibits wide genetic variability for technological quality traits, mineral concentrations, and bioactive compounds. For this reason, investigating the correlations between those traits in common bean lines of different gene pools contributes to the progress of biofortification programs. In the present study, two recombinant inbred line populations of Mesoamerican and Andean common bean were evaluated at the F5:7 generation. Technological quality was evaluated based on mass of 100 grains and seed coat color, which was determined using a colorimeter that analyzed the L* (white to black), a* (green to red) and b* (blue to yellow) values. The concentration of six minerals and bioactive compounds (phytates and phenolic compounds) was evaluated and used to characterize the nutritional composition of the lines. The evaluated common bean lines differed (p ≤ 0.05) for all technological quality traits, mineral concentrations, and bioactive compounds, except for the zinc concentration in Andean beans. Seed coat color (L*, a*, and b* values) was highly correlated with most of the evaluated minerals and with the phytates in Mesoamerican beans. In Andean beans, seed coat color (L*, a*, and b* values) was correlated with the concentrations of potassium, magnesium, iron, and phenolic compounds. The nutritional composition of common bean lines of different classes is variable: black beans have higher concentrations of potassium, phosphorus, calcium, zinc, and phytates; carioca beans stand out with high magnesium concentration; and cranberry beans have higher concentrations of potassium, magnesium, and iron.

Virulence and genetic diversity of Colletotrichum lindemuthianum and resistance of local common bean germplasm to anthracnose in Pernambuco State, Brazil

Anthracnose is a severe disease of common bean that, under favorable conditions, can cause a 100% yield loss. For effective resistance breeding, the virulence and genetic variability of the causal pathogen, Colletotrichum lindemuthianum, must be understood and the emergence of new races monitored to ensure the development of broad-spectrum, durable resistance. In the present study, 28 isolates of C. lindemuthianum collected in Pernambuco, Brazil, were characterized: i) for their pathogenicity on a differential common bean cultivar set, ii) for their genetic variability, based on the Internally Transcribed Spacer (ITS) region sequences, and iii) for their ability to cause anthracnose on a selection of 20 common bean accessions. The 12 differential cultivars were inoculated with the 28 isolates, identifying 16 races of C. lindemuthianum: 2, 3, 8, 9, 10, 64, 65, 72, 73, 75, 81, 85, 89, 117, 139, and 331. Except for race 81, all were reported for the first time in Pernambuco; this was the first report of race 139 in Brazil and of race 331 in the world. The ITS region sequence of 17 isolates revealed the presence of 27 SNPs, four SNPs in the ITS 1 region, and 23 SNPs in the ITS 2 region. Of the 20 common bean accessions screened for resistance with the 16 isolates of C. lindemuthianum, the Andean accessions ‘Praia’ and ‘Africano 4’ were the most resistant. The broad resistance detected in some common bean accessions indicates their utility as potential sources of resistance to C. lindemuthianum, particularly in areas where Mesoamerican beans and Mesoamerican races of the pathogen are predominant.

Physical quality and mineral composition of new Mesoamerican bean lines developed for cultivation in Brazil

The present study was undertaken to evaluate whether new common bean lines present differences in their physical quality and mineral composition traits; investigate correlations between those traits; and to select common bean lines for use in human nutrition and in breeding programs. Four experiments were carried out to examine 17 genotypes (cultivars and lines) of carioca beans (beige seed coat with brown streaks) and black beans, which represent the technological advances of six breeding programs in Brazil. A significant genotype × environment interaction was observed for all evaluated traits, except for potassium concentration. Most physical quality traits were correlated with each other (r ≥ 0.848), and almost all evaluated pairs of minerals exhibited a positive correlation with each other (r ≥ 0.609). Indirect selection based on the highest values for normal grains and uptake is efficient for identifying fast-cooking common bean lines, and it is possible to select mineral-biofortified common bean lines. The LP 09-33 and LEC 01-16 carioca bean lines and the TB 03-11 and CHP 01-182-48 black bean lines present high physical quality and better mineral composition, and their use in human nutrition and in breeding programs is therefore recommended.

Novel Alleles for Black and Gray Seed Color Genes in Common Bean

Seed coat color is one of the most important characteristics of common bean (Phaseolus vulgaris L.). To understand the genetic basis of this trait a cross was made of two small seeded Mesoamerican bean plants from China, the varieties Longyundou 4 (Long 4) with black seed and Longyundou 5 (Long 5) with white seed. Using phenotypic classification, the genetic analysis showed that the inheritance of black, gray, and white seed color could be explained primarily by two independent genes in an additive‐dominant, two gene epistasis model with a significant (χ2 = 1.65, p = 0.44) fit to the 12:3:1 segregation ratio. We also analyzed seed color as a quantitative trait to see whether significant loci aligned with any known seed color genes. To that end we developed 2357 new physically confirmed simple sequence repeat (SSR) markers (BMp series) based on the whole‐genome sequences of common bean and genetically mapped 105 into the F2 bean map. Combining the results of the phenotypic analysis and the new genetic map, two major additive quantitative trait loci (QTL) were found on chromosome Pv07; near the markers BMg87, BMp7s201, and BMp7s206 that explained more than 38% of the phenotypic variation. This region may contain the Asp gene but was distal to the P gene. Several other epistatic QTL for seed color were detected on chromosome Pv08 possibly related to the V locus and on chromosome Pv11. The new linked markers would accelerate the cloning of seed coat color genes of common bean and their selection.

Complete genome sequence of bean leaf crumple virus, a novel begomovirus infecting common bean in Colombia.

A copy of the complete genome of a novel bipartite begomovirus infecting common bean (Phaseolus vulgaris L.) in Colombia was obtained by rolling-circle amplification (RCA), cloned, and sequenced. The virus is associated with leaf crumple symptoms and significant yield losses in Andean and Mesoamerican beans. Such symptoms have been reported increasingly in Colombia since at least 2002, and we detected the virus in leaf material collected since 2008. Sequence analysis showed that the virus is a member of a distinct species, sharing 81% and 76% nucleotide (nt) sequence identity (in DNA-A and DNA-B, respectively) to other begomoviruses infecting common bean in the Americas.The data obtained support the taxonomic status of this virus (putatively named 'bean leaf crumple virus', BLCrV) as a member of a novel species in the genus Begomovirus.

English

Angular leafspot (ALS), caused by the fungus, Pseudocercospora griseola, is one of the most important disease of common bean in Tanzania. Breeding for resistance to this disease is complicated by the variable nature of the pathogen. In Tanzania, a thorough analysis of the variability of this pathogen is lacking which limits breeding for durable resistance. This work aimed at characterizing P. griseola in relation to its host in Tanzania. A sample collection of both P. griseola and common bean was conducted in the 2013 and 2014 growing seasons from nine regions. Single spore isolation was performed for P. griseola isolates and DNA was extracted from both P. griseola mycelium and bean leaves from which the pathogen was collected. For characterization of the gene pool origin of the host, Phaseolin DNA marker was evaluated and for the pathogen, the Internal Transcribed Spacer region (ITS) and the Actin gene sequences were evaluated. Phylogenetic analysis showed the presence of 69.7% Andean and 30.3% Mesoamerican strains of P. griseola in Tanzania. The common bean host genotypes showed a similar distribution with 84.2% Andean and 15.8% Mesoamerican. In both cases, Andean strains of the pathogen and Andean bean genotypes outnumbered Mesoamerican. In relation to the common bean genotypes, Andean genotypes were more susceptible to ALS as compared to Mesoamerican genotypes. There were few strains that were of Andean origin but were pathogenic on Mesoamerican common bean genotypes, a group that has previously been termed Afro-Andean. Geographically, most of the regions of Tanzania had only Andean strains except for Kagera where 60% were Mesoamerican strains, and in Arusha and Tanga, where 50 and 33% were Mesoamerican, respectively. Only three regions, Kagera, Mbeya and Rukwa, were found to grow Mesoamerican beans. The findings of this study are important in setting basic objectives for breeding for angular leaf spot disease in Tanzania. Key words: Actin gene, angular leaf spot (ALS), Internal Transcribed Spacer region (ITS), Phaseolin protein, Phaseolus vulgaris.

GGE Biplot Analysis of Yield Associations with Root Traits in a Mesoamerican Bean Diversity Panel

Common bean (Phaseolus vulgaris L.) production is subject to prolonged and crop‐failure‐threatening drought events worldwide. One of the best approaches in identifying parents and progeny with local adaptation to a target environment is the characterization of multiple environments. In this study, we used genotype plus genotype × environment (GGE) biplot analysis to examine the informativeness of the testing environments used by the bean breeding program at Michigan State University to select for drought tolerance. A group of 96 diverse Mesoamerican common bean genotypes assembled from breeding programs and germplasm collections across the United States were tested in two Michigan locations for 3 yr. Genotype plus genotype × environment biplots were used to rank genotypes according to environments and treatments (irrigated and rainfed) within environments. A genotype × trait analysis was also used to identify traits relevant to yield under rainfed and irrigated environments. Significant differentiation and nonredundancy were found among the environments, suggesting that resource use is efficient. Rainfed environments were better at discriminating high‐performing genotypes in Michigan. Genotype × trait analysis showed a significantly negative correlation between growth habit and seed yield. A common feature of the better adapted and higher yielding genotypes under Michigan conditions was the upright type II growth habit. A number of root architecture traits such as taproot diameter were independent or associated with yield in common bean under different environments. Genotypes with contrasting traits associated with yield under rainfed and irrigated conditions were identified and could be used in the development of future common bean cultivars with improved drought tolerance.

CUBAN BEAN DIVERSITY: Study could lead to new germplam sources, markets

CUBAN BEAN DIVERSITY: Study could lead to new germplam sources, markets

Pathogenic Variability of Angular Leaf Spot Disease of Common Bean in Western Kenya

Common bean (Phaseolus vulgaris L.) is the most important legume and is second only to maize as a food crop in Kenya. Despite its importance, bean productivity is declining in western Kenya due to several biotic and abiotic constraints including several fungal diseases. Among these diseases, angular leaf spot (Phaeoisariopsis griseola (Sacc.) is one of the most damaging and widely distributed diseases of common bean, causing yield losses as high as 80%. Furthermore, the problem is compounded by limited information on pathogen distribution and variability in western Kenya hindering breeding for angular leaf spot (ALS) resistance. Therefore, this study was carried out to characterise the ALS pathogen (Phaeoisariopsis griseola) (Sacc.) into different pathotypes. Forty-two isolates of P. griseola were collected from different bean growing areas of western Kenya and characterized into six pathotypes (63:11, 30:26, 33:23, 63:7, 31:10 and 63:63) by use of 12 differential cultivars. Advanced lines and commercial varieties obtained from KALRO-Kakamega were separately inoculated with six pathotypes of P. griseola and evaluated for disease reaction in the screenhouse. A screening trial of Mesoamerican and Andean bean genotypes showed that two varieties were tolerant (disease scores 1 to 3), fourteen varieties were moderately resistant (scores 4 to 6) and four varieties were susceptible (7 to 9). The tolerant varieties were small-seeded, while the susceptible varieties were mostly large-seeded.

A Phaseolus vulgaris Diversity Panel for Andean Bean Improvement

ABSTRACTDry beans (Phaseolus vulgaris L.) of the Andean gene pool, including red mottled, kidney, cranberry, and yellow seed types are important in Africa and the Americas. Andean dry bean breeding gains have lagged behind those of Mesoamerican beans. This difference may result from a narrower genetic base in the Andean gene pool and reduced breeding efforts. The objective of this research was to establish, genotype, and phenotype a panel of bean germplasm to be used for Andean dry bean breeding. An Andean diversity panel (ADP) was assembled, consisting of 396 accessions and including important cultivars, breeding lines, and landraces that originate mostly from Africa, the Caribbean, and North and South America. The panel was genotyped using the Illumina BARCBean6K_3 SNP BeadChip. The population contained two subgroups: Andean and Mesoamerican bean germplasm. The ADP was comprised of 349 Andean, 21 Mesoamerican, and 26 Andean–Mesoamerican admixed accessions. Most admixed lines came from Africa (12 accessions) and the Caribbean (five accessions). Association mapping was conducted for determinacy. Significant single‐nucleotide polymorphism (SNP) trait associations were found on chromosome Pv01, with the most significant SNP marker being 3.1 kb from the Terminal Flower 1 PvTFL1y gene. The ADP was evaluated for numerous traits in field trials in the United States and Africa. Variability was found for resistance to rust, angular leaf spot and common bacterial blight diseases; tolerance to low soil fertility; cooking time; and other traits that can be used to improve Andean bean germplasm for Africa and the Americas.

Meiotic behavior and pollinic viability in bean cultivars

The aims of this study were to determine the meiotic behavior and to estimate pollen grains via- bility in bean ( Phaseolus vulgaris L.) cultivars. Flower buds were collected during different developmental stages of the Mesoamerican bean cultivars IAPAR 44, Guapo Brilhante, BRS Expedito, BRS Valente, Guateian 6662 and Perola, and the Andean bean cultivar Irai, grown in a greenhouse. The meiotic index was determined by anther squashing of material fixed in absolute ethanol-glacial acetic acid (3:1) and stained with acetic orcein. No meiotic abnormalities were observed and the meiotic indices were high for all cultivars, indicating that the mismatch generated during crosses is not related to any meiotic changes. Estimation of pollen viability was made by comparing acetic orcein staining vs. Alexander's reactive: pollen viability was high in all cultivars with either stain, but was significantly higher when using the acetic orcein stain (>99%). Though some cultivar showed a significantly smaller pollen size, the range of variation among cultivars was low (means' range 51-66 μm).

Patterns of genetic diversity in the Andean gene pool of common bean reveal a candidate domestication gene

Most studies on the genetic diversity of common bean (Phaseolus vulgaris L.) have focussed on accessions from the Mesoamerican gene pool compared to the Andean gene pool. A deeper knowledge of the genetic structure of Argentinian germplasm would enable researchers to determine how the Andean domestication event affected patterns of genetic diversity in domesticated beans and to identify candidates for genes targeted by selection during the evolution of the cultivated common bean. A collection of 116 wild and domesticated accessions representing the diversity of the Andean bean in Argentina was genotyped by means of 114 simple sequence repeat (SSR) markers. Forty-seven Mesoamerican bean accessions and 16 Andean bean accessions representing the diversity of Andean landraces and wild accessions were also included. Using the Bayesian algorithm implemented in the software STRUCTURE we identified five major groups that correspond to Mesoamerican and Argentinian wild accessions and landraces and a group that corresponds to accessions from different Andean and Mesoamerican countries. The neighbour-joining algorithm and principal coordinate clustering analysis confirmed the genetic relationships among accessions observed with the STRUCTURE analysis. Argentinian accessions showed a substantial genetic variation with a considerable number of unique haplotypes and private alleles, suggesting that they may have played an important role in the evolution of the species. The results of statistical analyses aimed at identifying genomic regions with consistent patterns of variation were significant for 35 loci (~20 % of the SSRs used in the Argentinian accessions). One of these loci mapped in or near the genomic region of the glutamate decarboxylase gene. Our data characterize the population structure of the Argentinian germplasm. This information on its diversity will be very valuable for use in introgressing Argentinian genes into commercial varieties because the majority of present-day common bean varieties are of Andean origin.

Transcriptional and functional variation of NF‐YC1 in genetically diverse accessions of Phaseolus vulgaris during the symbiotic association with Rhizobium etli

Phaseolus vulgaris (common bean) is an agronomic important legume crop native to America, where two centres of genetic diversification (GD) are recognised, one in Mesoamerica and the other in the south Andes. Mesoamerican bean accessions have preferential and more efficient nodulation with Rhizobium etli strains carrying the allele nodC type-α, which is predominant in soils of Mesoamerica. It was previously demonstrated that the host nuclear factor NF-YC1, which is involved in nodule formation and rhizobial infection, contributes to this preferential selection and enhances nodulation in the domesticated accession NAG12 from Mesoamerica. Here, we show that both domesticated and wild Mesoamerican beans exhibit higher nodulation performance with a nodC type-α than with a nodC type-δ strain. Transcripts of NF-YC1 significantly increased in roots of these accessions 24 h post-inoculation (hpi) with the nodC type-α strain. On the other hand, accessions from the Andean GD centre formed a higher number of nodules with a strain carrying the nodC type-δ, which is predominant in Andean soils. However, NF-YC1 transcript levels did not exhibit significant changes in Andean accessions upon inoculation with the nodC type-δ strain, at least at 24 hpi. RNA interference (RNAi)-mediated gene silencing of NF-YC1 in the domesticated Andean accession Alubia showed that NF-YC1 or a closely related member of this family is required for nodule formation and bacterial infection, in agreement with observations in Mesoamerican common beans. Isolation and sequencing of the full-length ORF of NF-YC1 from Alubia revealed that it was identical to the sequence previously identified in the Mesoamerican accession NAG12. Interestingly, overexpression of NF-YC1 had a negative impact on nodule formation in the Alubia accession, independently of the R. etli lineage. Our findings suggest that transcriptional and functional variation of NF-YC1 occurs among genetically diverse bean accessions, which might positively or negatively contribute to the fine-tuning mechanisms that regulate nodule formation in the common bean-R. etli symbiosis.

Epistasis in an Andean × Mesoamerican cross of common bean

The objective of this investigation was to check if epistasis is present in Andean × Mesoamerican beans crosses using triple test cross (TTC) method. The parents of the segregating population were Carioca–MG (Mesoamerican) and BRS Radiante (Andean). In July 2005, F2 progenies (backcrossed with the parents and F1 generation) were evaluated at two locations for three characters: number of pods plant−1, number of grains plant−1 and grain weight plant−1. The presence of epistasis was detected for all yield components. In the partitioning of epistasis in additive x additive (i) and dominant x dominant (j) and dominant × additive (l) it was observed that, for the traits number of pods/plant and number of grains/plant, only epistasis of the type (j) + (l) were significant. For the trait grain mass/plant, all types of epistasis were significant.

QTL Analysis of Root Architecture Traits and Low Phosphorus Tolerance in an Andean Bean Population

ABSTRACTTolerance to low P soils is a desirable trait in common bean (Phaseolus vulgaris L.) cultivars grown in acid‐weathered soils. Genetic variability in response to P‐deficient soils exists in the Andean gene pool. G19833, a low P–tolerant indeterminate Andean landrace, has been evaluated for quantitative trait loci (QTL) and tolerance to low P in combination with Mesoamerican parents. Our goal was to expand our understanding of phenotypic traits and QTL from G19833 expressed in an Andean background. An F5:7 recombinant inbred line (RIL) population developed from two Andean bean genotypes, G19833 and AND696, a determinate line susceptible to low P soils, was examined under low and high soil P levels in replicated field trials. Phosphorus uptake was reduced by 70% and yield by 60% in low P compared to high P treatments. A linkage map was developed with 11 linkage groups and a total length of 1105 cM. Quantitative trait loci for root growth, seed yield, seed P content, and P use efficiency colocalized near the fin gene on linkage group B1. Quantitative trait loci for root growth traits, seed yield, and P uptake colocalized on B11. Quantitative trait loci for root length density (cm cm−3) and root surface area (cm2) did not colocalize with QTL for P uptake. This study indicates that root traits did not play an important role in tolerance to low P soil in an Andean × Andean cross, contrary to previous results with the same P‐efficient Andean parent (G19833) crossed to a Mesoamerican bean genotype.

BAC end sequences corresponding to the B4 resistance gene cluster in common bean: a resource for markers and synteny analyses

In common bean, a complex disease resistance (R) gene cluster, harboring many specific R genes against various pathogens, is located at the end of the linkage group B4. A BAC library of the Meso-american bean genotype BAT93 was screened with PRLJ1, a probe previously shown to be specific to the B4 R gene cluster, leading to the identification of 73 positive BAC clones. BAC-end sequencing (BES) of the 73 positive BACs generated 75 kb of sequence. These BACs were organized into 6 contigs, all mapped at the B4 R gene cluster. To evaluate the potential of BES for marker development, BES-derived specific primers were used to check for linkage with two allelic anthracnose R specificities Co-3 and Co-3 ( 2 ), through the analysis of pairs of Near Isogenic Lines (NILs). Out of 32 primer pairs tested, two revealed polymorphisms between the NILs, confirming the suspected location of Co-3 and Co-3 ( 2 ) at the B4 cluster. In order to identify the orthologous region of the B4 R gene cluster in the two model legume genomes, bean BESs were used as queries in TBLASTX searches of Medicago truncatula and Lotus japonicus BAC clones. Putative orthologous regions were identified on chromosome Mt6 and Lj2, in agreement with the colinearity observed between Mt and Lj for these regions.