Nucleotide diversity of a genomic sequence similar to SHATTERPROOF (PvSHP1) in domesticated and wild common bean (Phaseolus vulgaris L.)

Genetic Diversity and Population Structure of Common Bean (Phaseolus vulgaris L.) Landraces in the Lazio Region of Italy

Common bean cultivation has historically been a typical component of rural economies in Italy, particularly in mountainous and hilly zones along the Apennine ridge of the central and southern regions, where the production is focused on local landraces cultivated by small-scale farmers using low-input production systems. Such landraces are at risk of genetic erosion because of the recent socioeconomic changes in rural communities. One hundred fourteen accessions belonging to 66 landraces still being grown in the Lazio region were characterized using a multidisciplinary approach. This approach included morphological (seed traits), biochemical (phaseolin and phytohemagglutinin patterns), and molecular (microsatellite loci) analyses to investigate their genetic variation, structure, and distinctiveness, which will be essential for the implementation of adequate ex situ and in situ conservation strategies. Another objective of this study was to determine the original gene pool (Andean and Mesoamerican) of the investigated landraces and to evaluate the cross-hybridization events between the two ancestral gene pools in the P. vulgaris germplasm in the Lazio region. Molecular analyses on 456 samples (four for each of the 114 accessions) revealed that the P. vulgaris germplasm in the Lazio region exhibited a high level of genetic diversity (He = 0.622) and that the Mesoamerican and Andean gene pools were clearly differentiated, with the Andean gene pool prevailing (77%) and 12% of landraces representing putative hybrids between the two gene pools. A model-based cluster analysis based on the molecular markers highlighted three main groups in agreement with the phaseolin patterns and growth habit of landraces. The combined utilisation of morphological, biochemical, and molecular data allowed for the differentiation of all landraces and the resolution of certain instances of homonymy and synonymy. Furthermore, although a high level of homozygosity was found across all landraces, 32 of the 66 examined (49%) exhibited genetic variability, indicating that the analysis based on a single or few plants per landrace, as usually carried out, may provide incomplete information.

Molecular Hallmarks, Agronomic Performances and Seed Nutraceutical Properties to Exploit Neglected Genetic Resources of Common Beans Grown by Organic Farming in Two Contrasting Environments

Common bean (Phaseolus vulgaris L.) is an essential source of food proteins and an important component of sustainable agriculture systems around the world. Thus, conserving and exploiting the genetic materials of this crop species play an important role in achieving global food safety and security through the preservation of functional and serependic opportunities afforded by plant species diversity. Our research aimed to collect and perform agronomic, morpho-phenological, molecular-genetic, and nutraceutical characterizations of common bean accessions, including lowland and mountain Venetian niche landraces (ancient farmer populations) and Italian elite lineages (old breeder selections). Molecular characterization with SSR and SNP markers grouped these accessions into two well-separated clusters that were linked to the original Andean and Mesoamerican gene pools, which was consistent with the outputs of ancestral analysis. Genetic diversity in the two main clusters was not distributed equally the Andean gene pool was found to be much more uniform than the Mesoamerican pool. Additional subdivision resulted in subclusters, supporting the existence of six varietal groups. Accessions were selected according to preliminary investigations and historical records and cultivated in two contrasting Venetian environments: sea-level and mountain territories. We found that the environment significantly affected some nutraceutical properties of the seeds, mainly protein and starch contents. The antioxidant capacity was found significantly greater at sea level for climbing accessions and in the mountains for dwarf accessions. The seed yield at sea level was halved than mountain due to a seeds reduction in weight, volume, size and density. At sea level, bean landraces tended to have extended flowering periods and shorter fresh pod periods. The seed yield was positively correlated with the length of the period during which plants had fresh pods and negatively correlated with the length of the flowering period. Thus, the agronomic performance of these genetic resources showed their strong connection and adaptation to mountainous environments. On the whole, the genetic-molecular information put together for these univocal bean entries was combined with overall results from plant and seed analyses to select and transform the best accessions into commercial varieties (i.e., pure lines) suitable for wider cultivation.

Pod shattering in grain legumes: emerging genetic and environment-related patterns

A reduction in pod shattering is one of the main components of grain legume domestication. Despite this, many domesticated legumes suffer serious yield losses due to shattering, particularly under arid conditions. Mutations related to pod shattering modify the twisting force of pod walls or the structural strength of the dehiscence zone in pod sutures. At a molecular level, a growing body of evidence indicates that these changes are controlled by a relatively small number of key genes that have been selected in parallel across grain legume species, supporting partial molecular convergence. Legume homologs of Arabidopsis thaliana silique shattering genes play only minor roles in legume pod shattering. Most domesticated grain legume species contain multiple shattering-resistance genes, with mutants of each gene typically showing only partial shattering resistance. Hence, crosses between varieties with different genes lead to transgressive segregation of shattering alleles, producing plants with either enhanced shattering resistance or atavistic susceptibility to the trait. The frequency of these resistance pod-shattering alleles is often positively correlated with environmental aridity. The continued development of pod-shattering-related functional information will be vital for breeding crops that are suited to the increasingly arid conditions expected in the coming decades.

Pod indehiscence in common bean is associated with the fine regulation of PvMYB26

In legumes, pod shattering occurs when mature pods dehisce along the sutures, and detachment of the valves promotes seed dispersal. In Phaseolus vulgaris (L)., the major locus qPD5.1-Pv for pod indehiscence was identified recently. We developed a BC4/F4 introgression line population and narrowed the major locus down to a 22.5 kb region. Here, gene expression and a parallel histological analysis of dehiscent and indehiscent pods identified an AtMYB26 orthologue as the best candidate for loss of pod shattering, on a genomic region ~11 kb downstream of the highest associated peak. Based on mapping and expression data, we propose early and fine up-regulation of PvMYB26 in dehiscent pods. Detailed histological analysis establishes that pod indehiscence is associated with the lack of a functional abscission layer in the ventral sheath, and that the key anatomical modifications associated with pod shattering in common bean occur early during pod development. We finally propose that loss of pod shattering in legumes resulted from histological convergent evolution and that it is the result of selection at orthologous loci.

Genetic Diversity, Nitrogen Fixation, and Water Use Efficiency in a Panel of Honduran Common Bean (Phaseolus vulgaris L.) Landraces and Modern Genotypes

Common bean (Phaseolus vulgaris L.) provides critical nutrition and a livelihood for millions of smallholder farmers worldwide. Beans engage in symbiotic nitrogen fixation (SNF) with Rhizobia. Honduran hillside farmers farm marginal land and utilize few production inputs; therefore, bean varieties with high SNF capacity and environmental resiliency would be of benefit to them. We explored the diversity for SNF, agronomic traits, and water use efficiency (WUE) among 70 Honduran landrace, participatory bred (PPB), and conventionally bred bean varieties (HON panel) and 6 North American check varieties in 3 low-N field trials in Ontario, Canada and Honduras. Genetic diversity was measured with a 6K single nucleotide polymorphism (SNP) array, and phenotyping for agronomic, SNF, and WUE traits was carried out. STRUCTURE analysis revealed two subpopulations with admixture between the subpopulations. Nucleotide diversity was greater in the landraces than the PPB varieties across the genome, and multiple genomic regions were identified where population genetic differentiation between the landraces and PPB varieties was evident. Significant differences were found between varieties and breeding categories for agronomic traits, SNF, and WUE. Landraces had above average SNF capacity, conventional varieties showed higher yields, and PPB varieties performed well for WUE. Varieties with the best SNF capacity could be used in further participatory breeding efforts.

Current State and Perspectives in Population Genomics of the Common Bean

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Diversification and genetic structure of the western-to-eastern progression of European Phaseolus vulgaris L. germplasm

BACKGROUND

Common bean (Phaseolus vulgaris L.) is the most important food legume for direct human consumption around the world, as it represents a valuable source of components with nutritional and health benefits.

RESULTS

We conducted a study to define and explain the genetic relatedness and diversification level of common bean (Phaseolus vulgaris L.) germplasm from Portugal to Ukraine, along a western-to-eastern line of southern European countries, including Poland. This was based on the P. vulgaris genetic structure, and was designed to better describe its distribution and domestication pathways in Europe. Using the multi-crop passport descriptors that include geographic origin and different phaseolin types (corresponding to the Mesoamerican and Andean gene pools), 782 accessions were obtained from nine gene banks and 12 geographic origins. We selected 33 genome/ gene-related/ gene-pool-related nuclear simple sequence repeat markers that covered the genetic diversity across the P. vulgaris genome. The overall polymorphic information content was 0.800. Without specifying geographic origin, global structure cluster analysis generated 10 genetic clusters. Among the PvSHP1 markers, the most informative for gene pool assignment of the European P. vulgaris germplasm was PvSHP1-B. Results of AMOVA show that 89% of the molecular variability is shared within the 782 accessions, with 4% molecular variability among the different geographic origins along this western-to-eastern line of southern Europe (including Poland).

CONCLUSIONS

This study shows that the diversification line of the European P. vulgaris germplasm followed from the western areas of southern Europe (Portugal, Spain, Italy, Slovenia) to the more eastern areas of southern Europe. This progression defines three geographically separated subgroups, as the northern (Poland, Ukraine, Romania), southern (Albania, Bulgaria), and central (Bosnia and Herzegovina, Serbia, Hungary) areas of eastern Europe.

Agronomic Performance and Nitrogen Fixation of Heirloom and Conventional Dry Bean Varieties Under Low-Nitrogen Field Conditions

Common beans (Phaseolus vulgaris) form a relationship with nitrogen-fixing rhizobia and through a process termed symbiotic nitrogen fixation (SNF) which provides them with a source of nitrogen. However, beans are considered poor nitrogen fixers, and modern production practices involve routine use of N fertilizer, which leads to the down-regulation of SNF. High-yielding, conventionally bred bean varieties are developed using conventional production practices and selection criteria, typically not including SNF efficiency, and may have lost this trait over decades of modern breeding. In contrast, heirloom bean genotypes were developed before the advent of modern production practices and may represent an underutilized pool of genetics which could be used to improve SNF. This study compared the SNF capacity under low-N field conditions, of collections of heirloom varieties with and conventionally bred dry bean varieties. The heirloom-conventional panel (HCP) consisted of 42 genotypes from various online seed retailers or from the University of Guelph Bean Breeding program seedbank. The HCP was genotyped using a single nucleotide polymorphism (SNP) array to investigate genetic relatedness within the panel. Field trials were conducted at three locations in ON, Canada from 2014 to 2015 and various agronomic and seed composition traits were measured, including capacity for nitrogen fixation (using the natural abundance method to measure seed N isotope ratios). Significant variation for SNF was found in the panel. However, on average, heirloom genotypes did not fix significantly more nitrogen than conventionally bred varieties. However, five heirloom genotypes fixed >60% of their nitrogen from the atmosphere. Yield (kg ha-1) was not significantly different between heirloom and conventional genotypes, suggesting that incorporating heirloom genotypes into a modern breeding program would not negatively impact yield. Nitrogen fixation was significantly higher among Middle American genotypes than among Andean genotypes, confirming previous findings. The best nitrogen fixing line was Coco Sophie, a European heirloom white bean whose genetic makeup is admixed between the Andean and Middle American genepools. Heirloom genotypes represent a useful source of genetics to improve SNF in modern bean breeding.

Genomic dissection of pod shattering in common bean: mutations at non-orthologous loci at the basis of convergent phenotypic evolution under domestication of leguminous species

The complete or partial loss of shattering ability occurred independently during the domestication of several crops. Therefore, the study of this trait can provide an understanding of the link between phenotypic and molecular convergent evolution. The genetic dissection of 'pod shattering' in Phaseolus vulgaris is achieved here using a population of introgression lines and next-generation sequencing techniques. The 'occurrence' of the indehiscent phenotype (indehiscent versus dehiscent) depends on a major locus on chromosome 5. Furthermore, at least two additional genes are associated with the 'level' of shattering (number of shattering pods per plant: low versus high) and the 'mode' of shattering (non-twisting versus twisting pods), with all of these loci contributing to the phenotype by epistatic interactions. Comparative mapping indicates that the major gene identified on common bean chromosome 5 corresponds to one of the four quantitative trait loci for pod shattering in Vigna unguiculata. None of the loci identified comprised genes that are homologs of the known shattering genes in Glycine max. Therefore, although convergent domestication can be determined by mutations at orthologous loci, this was only partially true for P. vulgaris and V. unguiculata, which are two phylogenetically closely related crop species, and this was not the case for the more distant P. vulgaris and G. max. Conversely, comparative mapping suggests that the convergent evolution of the indehiscent phenotype arose through mutations in different genes from the same underlying gene networks that are involved in secondary cell-wall biosynthesis and lignin deposition patterning at the pod level.

Convergent Evolution of the Seed Shattering Trait

Loss of seed shattering is a key trait in crop domestication, particularly for grain crops. For wild plants, seed shattering is a crucial mechanism to achieve greater fitness, although in the agricultural context, this mechanism reduces harvesting efficiency, especially under dry conditions. Loss of seed shattering was acquired independently in different monocotyledon and dicotyledon crop species by ‘convergent phenotypic evolution’, leading to similar low dehiscent and indehiscent phenotypes. Here, the main aim is to review the current knowledge about seed shattering in crops, in order to highlight the tissue modifications that underlie the convergent phenotypic evolution of reduced shattering in different types of fruit, from the silique of Brassicaceae species, to the pods of legumes and spikes of cereals. Emphasis is given to legumes, with consideration of recent data obtained for the common bean. The current review also discusses to what extent convergent phenotypes arose from parallel changes at the histological and/or molecular levels. For this reason, an overview is included of the main findings relating to the genetic control of seed shattering in the model species Arabidopsis thaliana and in other important crops.

Pod Shattering: A Homologous Series of Variation Underlying Domestication and an Avenue for Crop Improvement

In wild habitats, fruit dehiscence is a critical strategy for seed dispersal; however, in cultivated crops it is one of the major sources of yield loss. Therefore, indehiscence of fruits, pods, etc., was likely to be one of the first traits strongly selected in crop domestication. Even with the historical selection against dehiscence in early domesticates, it is a trait still targeted in many breeding programs, particularly in minor or underutilized crops. Here, we review dehiscence in pulse (grain legume) crops, which are of growing importance as a source of protein in human and livestock diets, and which have received less attention than cereal crops and the model plant Arabidopsis thaliana. We specifically focus on the (i) history of indehiscence in domestication across legumes, (ii) structures and the mechanisms involved in shattering, (iii) the molecular pathways underlying this important trait, (iv) an overview of the extent of crop losses due to shattering, and the effects of environmental factors on shattering, and, (v) efforts to reduce shattering in crops. While our focus is mainly pulse crops, we also included comparisons to crucifers and cereals because there is extensive research on shattering in these taxa.

Beans (Phaseolus ssp.) as a Model for Understanding Crop Evolution

Here, we aim to provide a comprehensive and up-to-date overview of the most significant outcomes in the literature regarding the origin of Phaseolus genus, the geographical distribution of the wild species, the domestication process, and the wide spread out of the centers of origin. Phaseolus can be considered as a unique model for the study of crop evolution, and in particular, for an understanding of the convergent phenotypic evolution that occurred under domestication. The almost unique situation that characterizes the Phaseolus genus is that five of its ∼70 species have been domesticated (i.e., Phaseolus vulgaris, P. coccineus, P. dumosus, P. acutifolius, and P. lunatus), and in addition, for P. vulgaris and P. lunatus, the wild forms are distributed in both Mesoamerica and South America, where at least two independent and isolated episodes of domestication occurred. Thus, at least seven independent domestication events occurred, which provides the possibility to unravel the genetic basis of the domestication process not only among species of the same genus, but also between gene pools within the same species. Along with this, other interesting features makes Phaseolus crops very useful in the study of evolution, including: (i) their recent divergence, and the high level of collinearity and synteny among their genomes; (ii) their different breeding systems and life history traits, from annual and autogamous, to perennial and allogamous; and (iii) their adaptation to different environments, not only in their centers of origin, but also out of the Americas, following their introduction and wide spread through different countries. In particular for P. vulgaris this resulted in the breaking of the spatial isolation of the Mesoamerican and Andean gene pools, which allowed spontaneous hybridization, thus increasing of the possibility of novel genotypes and phenotypes. This knowledge that is associated to the genetic resources that have been conserved ex situ and in situ represents a crucial tool in the hands of researchers, to preserve and evaluate this diversity, and at the same time, to identify the genetic basis of adaptation and to develop new improved varieties to tackle the challenges of climate change, and food security and sustainability.

High Level of Nonsynonymous Changes in Common Bean Suggests That Selection under Domestication Increased Functional Diversity at Target Traits

Crop species have been deeply affected by the domestication process, and there have been many efforts to identify selection signatures at the genome level. This knowledge will help geneticists to better understand the evolution of organisms, and at the same time, help breeders to implement successful breeding strategies. Here, we focused on domestication in the Mesoamerican gene pool of Phaseolus vulgaris by sequencing 49 gene fragments from a sample of 45 P. vulgaris wild and domesticated accessions, and as controls, two accessions each of the closely related species Phaseolus coccineus and Phaseolus dumosus. An excess of nonsynonymous mutations within the domesticated germplasm was found. Our data suggest that the cost of domestication alone cannot explain fully this finding. Indeed, the significantly higher frequency of polymorphisms in the coding regions observed only in the domesticated plants (compared to noncoding regions), the fact that these mutations were mostly nonsynonymous and appear to be recently derived mutations, and the investigations into the functions of their relative genes (responses to biotic and abiotic stresses), support a scenario that involves new functional mutations selected for adaptation during domestication. Moreover, consistent with this hypothesis, selection analysis and the possibility to compare data obtained for the same genes in different studies of varying sizes, data types, and methodologies allowed us to identify four genes that were strongly selected during domestication. Each selection candidate is involved in plant resistance/tolerance to abiotic stresses, such as heat, drought, and salinity. Overall, our study suggests that domestication acted to increase functional diversity at target loci, which probably controlled traits related to expansion and adaptation to new agro-ecological growing conditions.

A Comprehensive Phenotypic Investigation of the "Pod-Shattering Syndrome" in Common Bean

Seed shattering in crops is a key domestication trait due to its relevance for seed dispersal, yield, and fundamental questions in evolution (e.g., convergent evolution). Here, we focused on pod shattering in common bean (Phaseolus vulgaris L.), the most important legume crop for human consuption in the world. With this main aim, we developed a methodological pipeline that comprises a thorough characterization under field conditions, including also the chemical composition and histological analysis of the pod valves. The pipeline was developed based on the assumption that the shattering trait itself can be treated in principle as a "syndrome" (i.e., a set of correlated different traits) at the pod level. We characterized a population of 267 introgression lines that were developed ad-hoc to study shattering in common bean. Three main objectives were sought: (1) to dissect the shattering trait into its "components," of level (percentage of shattering pods per plant) and mode (percentage of pods with twisting or non-twisting valves); (2) to test whether shattering is associated to the chemical composition and/or the histological characteristics of the pod valves; and (3) to test the associations between shattering and other plant traits. We can conclude the following: Very high shattering levels can be achieved in different modes; shattering resistance is mainly a qualitative trait; and high shattering levels is correlated with high carbon and lignin contents of the pod valves and with specific histological charaterstics of the ventral sheath and the inner fibrous layer of the pod wall. Our data also suggest that shattering comes with a "cost," as it is associated with low pod size, low seed weight per pod, high pod weight, and low seed to pod-valves ratio; indeed, it can be more exaustively described as a syndrome at the pod level. Our work suggests that the valve chemical composition (i.e., carbon and lignin content) can be used for a high troughput phenotyping procedures for shattering phenotyping. Finally, we believe that the application of our pipeline will greatly facilitate comparative studies among legume crops, and gene tagging.

To Have and to Hold: Selection for Seed and Fruit Retention During Crop Domestication

Crop domestication provides a useful model system to characterize the molecular and developmental bases of morphological variation in plants. Among the most universal changes resulting from selection during crop domestication is the loss of seed and fruit dispersal mechanisms, which greatly facilitates harvesting efficiency. In this review, we consider the molecular genetic and developmental bases of the loss of seed shattering and fruit dispersal in six major crop plant families, three of which are primarily associated with seed crops (Poaceae, Brassicaceae, Fabaceae) and three of which are associated with fleshy-fruited crops (Solanaceae, Rosaceae, Rutaceae). We find that the developmental basis of the loss of seed/fruit dispersal is conserved in a number of independently domesticated crops, indicating the widespread occurrence of developmentally convergent evolution in response to human selection. With regard to the molecular genetic approaches used to characterize the basis of this trait, traditional biparental quantitative trait loci mapping remains the most commonly used strategy; however, recent advances in next-generation sequencing technologies are now providing new avenues to map and characterize loss of shattering/dispersal alleles. We anticipate that continued application of these approaches, together with candidate gene analyses informed by known shattering candidate genes from other crops, will lead to a rapid expansion of our understanding of this critical domestication trait.

Landscape genetics, adaptive diversity and population structure in Phaseolus vulgaris

Here we studied the organization of genetic variation of the common bean (Phaseolus vulgaris) in its centres of domestication. We used 131 single nucleotide polymorphisms to investigate 417 wild common bean accessions and a representative sample of 160 domesticated genotypes, including Mesoamerican and Andean genotypes, for a total of 577 accessions. By analysing the genetic spatial patterns of the wild common bean, we documented the existence of several genetic groups and the occurrence of variable degrees of diversity in Mesoamerica and the Andes. Moreover, using a landscape genetics approach, we demonstrated that both demographic processes and selection for adaptation were responsible for the observed genetic structure. We showed that the study of correlations between markers and ecological variables at a continental scale can help in identifying local adaptation genes. We also located putative areas of common bean domestication in Mesoamerica, in the Oaxaca Valley, and the Andes, in southern Bolivia-northern Argentina. These observations are of paramount importance for the conservation and exploitation of the genetic diversity preserved within this species and other plant genetic resources.

Nucleotide diversity based on phaseolin and iron reductase genes in common bean accessions of different geographical origins

Discriminating genotypes within plant collections is imperative, and DNA sequence approaches for detecting single nucleotide polymorphisms (SNPs) have proved essential in any modern analysis of germplasm. By sequencing the α-Phs and PvFRO1 genes that, respectively, encode phaseolin and an iron reductase, we prospected for SNPs in exonic and intronic regions of both genes in a sample of 31 accessions of Phaseolus vulgaris from Mesoamerican and Andean gene pools, and one accession of Phaseolus lunatus, chosen as an outgroup. Sequence alignment showed 95 SNPs in α-Phs and 83 in PvFRO1, but diversity along the nucleotide sequences was not evenly distributed in both genes. Accessions from the same gene pool showed greater similarity than those from different gene pools, and the cluster patterns obtained in this study were consistent with the hierarchical organization into two P. vulgaris gene pools. The polymorphisms detected in the α-Phs gene allowed better discrimination among the accessions within each cluster than the PvFRO1 polymorphisms. Furthermore, some variations within exons changes amino acids in both predicted protein sequences. In an unprecedented result, the phaseolin-predicted amino acid variation allowed most of the accessions to be typified.

Molecular analysis of the parallel domestication of the common bean (Phaseolus vulgaris) in Mesoamerica and the Andes

We have studied the nucleotide diversity of common bean, Phaseolus vulgaris, which is characterized by two independent domestications in two geographically distinct areas: Mesoamerica and the Andes. This provides an important model, as domestication can be studied as a replicate experiment. We used nucleotide data from five gene fragments characterized by large introns to analyse 214 accessions (102 wild and 112 domesticated). The wild accessions represent a cross-section of the entire geographical distribution of P. vulgaris. A reduction in genetic diversity in both of these gene pools was found, which was three-fold greater in Mesoamerica compared with the Andes. This appears to be a result of a bottleneck that occurred before domestication in the Andes, which strongly impoverished this wild germplasm, leading to the minor effect of the subsequent domestication bottleneck (i.e. sequential bottleneck). These findings show the importance of considering the evolutionary history of crop species as a major factor that influences their current level and structure of genetic diversity. Furthermore, these data highlight a single domestication event within each gene pool. Although the findings should be interpreted with caution, this evidence indicates the Oaxaca valley in Mesoamerica, and southern Bolivia and northern Argentina in South America, as the origins of common bean domestication.

Identification and characterization of a homologue to the Arabidopsis INDEHISCENT gene in common Bean

Reduction in pod shattering represents a key component of the domestication syndrome in common bean (Phaseolus vulgaris) and makes this domesticate dependent upon the farmer for seed dispersal. Attempts to elucidate the genetic control of this process have led to the identification of a major gene (St) linked to the presence/absence of pod suture fibers affecting pod shattering. Although St has been placed on the common bean genetic map, the sequence and the specific functions of this gene remain unknown. The purpose of this study was to identify a candidate gene for St. In Arabidopsis thaliana, INDEHISCENT gene (IND) is the primary factory required for silique shattering. A sequence homologous to IND was successfully amplified in P. vulgaris and placed on the common bean map using two recombinant inbred populations (BAT93 × Jalo EEP558; Midas × G12873). Although PvIND maps near the St locus, the lack of complete cosegregation between PvIND and St and the lack of polymorphisms at the PvIND locus correlated with the dehiscent/indehiscent phenotype suggests that PvIND may not be directly involved in pod shattering and may not be the gene underlying the St locus. However, PvIND may be closely linked to an as yet unidentified regulatory element at the St locus. Alternatively, a more precise phenotyping method taking into account quantitative trait variation needs to be developed to more accurately map the St locus.

Mesoamerican origin of the common bean (Phaseolus vulgaris L.) is revealed by sequence data

Knowledge about the origins and evolution of crop species represents an important prerequisite for efficient conservation and use of existing plant materials. This study was designed to solve the ongoing debate on the origins of the common bean by investigating the nucleotide diversity at five gene loci of a large sample that represents the entire geographical distribution of the wild forms of this species. Our data clearly indicate a Mesoamerican origin of the common bean. They also strongly support the occurrence of a bottleneck during the formation of the Andean gene pool that predates the domestication, which was suggested by recent studies based on multilocus molecular markers. Furthermore, a remarkable result was the genetic structure that was seen for the Mesoamerican accessions, with the identification of four different genetic groups that have different relationships with the sets of wild accessions from the Andes and northern Peru-Ecuador. This finding implies that both of the gene pools from South America originated through different migration events from the Mesoamerican populations that were characteristic of central Mexico.