Genetic diversity of the azuki bean (Vigna angularis (Willd.) Ohwi & Ohashi) gene pool as assessed by SSR markers

To facilitate the wider use of genetic resources including newly collected cultivated and wild azuki bean germplasm, the genetic diversity of the azuki bean complex, based on 13 simple sequence repeat (SSR) primers, was evaluated and a core collection was developed using 616 accessions originating from 8 Asian countries. Wild germplasm from Japan was highly diverse and represented much of the allelic variation found in cultivated germplasm. The SSR results together with recent archaeobotanical evidence support the view that Japan is one center of domestication of azuki bean, at least for the northeast Asian azuki bean. Cultivated azuki beans from China, Korea, and Japan were the most diverse and were genetically distinct from each other, suggesting a long and relatively isolated history of cultivation in each country. Cultivated azuki beans from eastern Nepal and Bhutan were similar to each other and quite distinct from others. For two primers, most eastern Nepalese and Bhutanese cultivated accessions had null alleles. In addition, wild accessions from the Yangtze River region of China and the Himalayan region had a null allele for one or the other of these primers. Whether the distinct diversity of azuki bean in the Himalayan region is due to introgression or separate domestication events requires further study. In contrast, western Nepalese azuki beans showed an SSR profile similar to that of Chinese azuki beans. The genetic distinctness of cultivated azuki beans from Vietnam has been revealed for the first time. The specific alleles indicate that Vietnamese azuki beans have been cultivated in isolation from Chinese azuki beans for a long time. Wild germplasm from the Himalayan region showed the highest level of variation. Based on the results, Himalayan germplasm could be considered a novel gene source for azuki bean breeding. A comparison with mungbean SSR analysis revealed that the mean gene diversity of cultivated azuki bean (0.74) was much higher than that of cultivated mungbean (0.41). The reduction in gene diversity due to domestication, the domestication bottleneck, in azuki bean is not strong compared with that in mungbean.     

Mitochondrial restriction fragment length polymorphisms in wild Phaseolus vulgaris L.: insights on the domestication of the common bean

Summary Previous examination of intraspecific mitochondrial DNA (mtDNA) diversity in common bean, Phaseolus vulgaris, showed that five restriction fragment length polymorphisms (RFLPs) distinguish the mitochondrial genomes of the two major gene pools of cultivated beans, the Mesoamerican and the Andean. In the study presented here, mtDNA was used to compare the amount of diversity in cultivated beans to that in collections of wild beans to gain an understanding of how and when the mitochondrial genomes of the gene pools became distinct. The mtDNA of six wild bean accessions from Central and South America were digested with nine restriction endonucleases and analyzed by Southern hybridization. A total of twenty RFLPs were detected demonstrating a significantly higher amount of mtDNA variability in wild beans than in cultivated ones. All of the wild beans had the same mtDNA pattern for four out of the five inter-gene pool RFLPs, indicating that the polymorphism arose soon after domestication: two in the gene pool of the cultivated Mesoamerican beans and two in the gene pool of the cultivated Andean beans. The fifth RFLP must have occurred before domestication since the locus was also polymorphic in the wild beans. Wild beans from the south Andes were distinct and less variable than wild accessions of the north Andes and Mesoamerica. The distribution of mtDNA RFLPs among the wild beans supports the concept of two distinct domestication events for P. vulgaris.     

Ancient and recent evolutionary history of the bruchid beetle, Acanthoscelides obtectus Say, a cosmopolitan pest of beans

Acanthoscelides obtectus Say is a bruchid species of Neotropical origin, and is specialized on beans of the Phaseolus vulgaris L. group. Since the domestication and diffusion of beans, A. obtectus has become cosmopolitan through human-mediated migrations and is now a major pest in bean granaries. Using phylogeographic methods applied to mitochondrial DNA (mtDNA) and nuclear microsatellite molecular markers, we show that the origin of this species is probably further south than Mesoamerica, as commonly thought. Our results also indicate that A. obtectus and its Mesoamerican sister species Acanthoscelides obvelatus, two morphologically close species differing principally in voltinism, speciated in allopatry: A. obtectus (multivoltine) arising in Andean America and A. obvelatus (univoltine) in Mesoamerica. In contrast to Mesoamerica where beans fruit once yearly, wild beans in Andean America fruit year-round, especially in regions showing little or no seasonality. In such habitats where resources are continuously present, multivoltinism is adaptive. According to existing hypotheses, multivoltinism in A. obtectus is a new adaptation that evolved after bean domestication. Our data suggest the alternative hypothesis that multivoltinism is an older trait, adapted to exploit the year-round fruiting of wild beans in relatively aseasonal habitats, and allowed A. obtectus to become a pest in bean granaries. This trait also permitted this species to disperse through human-mediated migrations associated with diffusion of domesticated beans. We also show that diversity of Old World A. obtectus populations can be quite well explained by a single colonization event about 500 bp. Human-mediated migrations appear not to be rare, as our results indicate a second more recent migration event from Andean America to Mexico.     

Effects of water stress on the water relations of Phaseolus vulgaris and the drought resistant Phaseolus acutifolius

The tepary bean ( Phaseolus acutifolius Gray var. latifolius ), a drought resistant species, was compared under water stress conditions with the more drought susceptible P. vulgaris L. cvs Pinto and White Half Runner (WHR). In order to better understand the basis for the superior drought resistance of tepary, this study was designed to determine the relationships among leaf water potential, osmotic potential, turgor potential, and relative water content (RWC).
Plants were prestressed by withholding irrigation water. These stress pretreatments changed the relation between leaf water potential and relative water content of both species so that prestressed plants had lower water potentials than controls at the same leaf RWC. Tepary had lower water potentials at given RWC levels than Pinto or WHR; this can account for part of the superior resistance of tepary. In all genotypes, prestressed plants maintained osmotic potentials approximately 0.2 MPa lower than controls. Tepary reached osmotic potentials that were significantly lower (0.15 to 0.25 MPa) than Pinto or WHR. Both control and prestressed tepary plants had 0.05 to 0.25 MPa more turgor than Pinto or WHR at RWC values between 65 and 80%. Both prestressed and control tepary plants had greater elasticity (a lower elastic modulus) than Pinto or WHR. This greater turgor of tepary at low RWC values could be caused by several factors including greater tissue elasticity, active accumulation of solutes, or greater solute concentration.
Tepary had significantly lower osmotic potentials than the P. vulgaris cultivars, but there was little difference in osmotic potential between Pinto and WHR. Knowledge of differences in osmotic and turgor potentials among and within species could be useful in breeding for drought resistance in Phaseolus.     

Leaf epidermal characters related with plant's passive resistance to pathogens vary among accessions of wild beans Phaseolus vulgaris var. aborigineus (Leguminosae–Phaseoleae)

We report here whether accessions of Phaseolus vulgaris var. aborigineus, collected from the southernmost part of the Andean domestication center of common bean, presented differences among leaf epidermal characters. Epidermal microcharacters such as deposition of wax crystalloids, cuticle thickness, trichome types, size and density, stomata types and size, stomatal density and index were examined on the surface of 66 leaves of 11 accessions of P. vulgaris var. aborigineus by means of light and scanning electron microscopy. Unlike the leaves of cultivated beans, those of P. vulgaris var. aborigineus were hypostomatous. Among epidermal characters only the stomatal density, stomatal index, and the number of trichomes on the abaxial leaf epidermis were different between bean accessions. The stomatal density and index of the accessions were inversely related to the altitude of the area of the wild bean collection. This is the first report describing the presence of diversity among epidermal characters (e.g. hypostomatous leaves) in P. vulgaris var. aborigineus that might contribute to plant resistance to pathogens.     

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.     

New gene-derived simple sequence repeat markers for common bean (Phaseolus vulgaris L.)

Common bean is an important and diverse crop legume with several wild relatives that are all part of the Phaseoleae tribe of tropical crop legumes. Sequence databases have been a good source of sequences to mine for simple sequence repeats (SSRs). The objective of this research was to evaluate 14 sequence collections from common bean for SSRs and to evaluate the diversity of the polymorphic microsatellites derived from these collections. SSRs were found in 10 of the GenBank sequence collections with an average of 11.3% of sequences containing microsatellite motifs. The most common motifs were based on tri- and dinucleotides. In a marker development programme, primers were designed for 125 microsatellites which were tested on a panel of 18 common bean genotypes. The markers were named as part of the bean microsatellite-database (BMd) series, and the average polymorphism information content was 0.404 for polymorphic markers and predicted well the genepool structure of common beans and the status of the wild and cultivated accessions that were included in the study. Therefore, the BMd series of microsatellites is useful for multiple studies of genetic relatedness and as anchor markers in future mapping of wide crosses in the species.     

Phaseolin variability among wild and cultivated common beans (Phaseolus vulgaris) from Colombia

Phaseolin seed protein variability in a group of 8 wild and 77 cultivated common bean (Phaseolus vulgaris) accessions was determined using 1-dimensional SDS/ PAGE and 2-dimensional IEF-SDS/PAGE. Wild common bean accessions exhibited the 'CH' and 'B' patterns, previously undescribed among either wild or cultivated common beans. The cultivated genotypes showed (in decreasing frequency) the previously described 'S,' T,' and 'C phaseolin patterns as well as the new 'B' pattern similar to the pattern identified in a Colombian wild common bean accession. In the northeastern part of the Colombian bean-growing region, the cultivars exhibited almost exclusively an 'S' phaseolin type, while in the south-western part, the 'T' and 'C phaseolin cultivars were more frequent. Seed size analysis indicated that 'T' and 'C' phaseolin cultivars had larger seeds than 'S' and 'B' phaseolin cultivars. Our results suggest that Colombia is a meeting place for Andean and Middle American common bean germplasms, as well as a domestication center for the common bean.     

Structure of genetic diversity in the two major gene pools of common bean (Phaseolus vulgaris L., Fabaceae)

Domesticated materials with well-known wild relatives provide an experimental system to reveal how human selection during cultivation affects genetic composition and adaptation to novel environments. In this paper, our goal was to elucidate how two geographically distinct domestication events modified the structure and level of genetic diversity in common bean. Specifically, we analyzed the genome-wide genetic composition at 26, mostly unlinked microsatellite loci in 349 accessions of wild and domesticated common bean from the Andean and Mesoamerican gene pools. Using a model-based approach, implemented in the software STRUCTURE, we identified nine wild or domesticated populations in common bean, including four of Andean and four of Mesoamerican origins. The ninth population was the putative wild ancestor of the species, which was classified as a Mesoamerican population. A neighbor-joining analysis and a principal coordinate analysis confirmed genetic relationships among accessions and populations observed with the STRUCTURE analysis. Geographic and genetic distances in wild populations were congruent with the exception of a few putative hybrids identified in this study, suggesting a predominant effect of isolation by distance. Domesticated common bean populations possessed lower genetic diversity, higher F _ST, and generally higher linkage disequilibrium (LD) than wild populations in both gene pools; their geographic distributions were less correlated with genetic distance, probably reflecting seed-based gene flow after domestication. The LD was reduced when analyzed in separate Andean and Mesoamerican germplasm samples. The Andean domesticated race Nueva Granada had the highest F _ST value and widest geographic distribution compared to other domesticated races, suggesting a very recent origin or a selection event, presumably associated with a determinate growth habit, which predominates in this race. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Diversity in the rhizobia associated with Phaseolus vulgaris L. in Ecuador, and comparisons with Mexican bean rhizobia

Common beans (Phaseolus vulgaris L.) have centers of origin in both Mesoamerica and Andean South America, and have been domesticated in each region for perhaps 5000 years. A third major gene pool may exist in Ecuador and Northern Peru. The diversity of the rhizobia associated with beans has also been studied, but to date with an emphasis on the Mesoamerican center of origin. In this study we compared bean rhizobia from Mexico and Andean South America using both phenotypic and phylogenetic approaches. When differences between the rhizobia of these two regions were shown, we then examined the influence of bean cultivar on the most probable number (MPN) count and biodiversity of rhizobia recovered from different soils. Three clusters of bean rhizobia were distinguished using phenotypic analysis and principal-component analysis of Box AIR-PCR banding patterns. They corresponded principally to isolates from Mexico, and the northern and southern Andean regions, with isolates from southern Ecuador exhibiting significant genetic diversity. Rhizobia from Dalea spp., which are infective and effective on beans, may have contributed to the apparent diversity of rhizobia recovered from the Mesoamerican region, while the rhizobia of wild Phaseolus aborigineus from Argentina showed only limited similarity to the other bean rhizobia tested. Use of P. vulgaris cultivars from the Mesoamerican and Andean Phaseolus gene pools as trap hosts did not significantly affect MPN counts of bean rhizobia from the soils of each region, but did influence the diversity of the rhizobia recovered. Such differences in compatibility of host and Rhizobium could be a factor in the poor reputation for nodulation and N2 fixation in this crop.     

Resistance of Phaseolus species to ice crystallization at subzero temperature

Dry bean ( Phaseolus vulgaris L.) cultivars possess little or no freezing tolerance and are killed at the temperature of ice formation in their tissues. An increase in frost tolerance by 2–3°C would expand dry bean production in the short growing seasons of the Canadian prairies and possibly to higher altitudes in the tropics where episodic frosts occur during the growing season. The objective of this study was to determine the differences in frost resistance of Phaseolus species in both controlled and field environments. Leaflets of dry bean cv. CDC Nighthawk, and wild relatives from the primary gene pool ( P. vulgaris var. mexicanus Freytag and P. vulgaris var. aborigineus (Burkart) Baudet) and the tertiary gene pool ( P. acutifolius var. tenuifolius A. Gray, P. filiformis Bentham, P. angustissimus A. Gray and P. ritensis M.E. Jones) were subjected to subzero temperatures with and without ice nucleation to determine the levels of tolerance and avoidance, respectively. The lethal temperature at which 50% of the leaflets were killed (LT₅₀) was 0.5–1°C lower for species of the tertiary gene pool compared to those from the primary gene pool. Leaflets of species from the tertiary gene pool were also characterized by extensive supercooling compared to leaflets of species from the primary gene pool. Resistance of Phaseolus species to spring and autumn frosts were determined on seedlings transplanted to the field. Phaseolus angustissimus , a species of the tertiary gene pool had the highest seedling survival in response to both autumn and spring frosts, when the minimum air temperatures were −5 and −7°C, respectively. Frost resistance of Phaseolus angustissimus , if successfully introgressed into bean germplasm, may enable the development of frost resistant dry bean cultivars.     

Phaseolus (Fabaceae) in Archaeology: AMS

Beans of several species were domesticated in tropical America thousands of years ago, to be combined with maize and other crops in highly successful New World agricultural systems. Radiocarbon dates on charcoal associated with Phaseolus in archaeological sites, in Mexico and Peru indicated the presence of domesticated beans as early as 10 000 years ago. However, direct dates on the beans and pods themselves by accelerator mass spectrometry (AMS) do not provide evidence for the cultivation in Mexico of common beans, P. vulgaris, and teparies, P. acutifolius, before about 2500 B.P. in the Tehuacán Valley, and of common beans about 1300 years ago in Tamaulipas and 2100 years ago in the Valley of Oaxaca. AMS dates support the presence in the Peruvian Andes of domesticated common beans by about 4400 B.P. and lima beans by about 3500 B. P. and lima beans by about 5600 B.P. in the coastal valleys of Peru. The late appearance of common and lima beans in the Central Highlands of Mesoamerica supports the importance of missing evidence that may be obtained from prehistoric agricultural sites in western Mexico and in Central America which are located within the range of the wild populations of these species. Additionally, biochemical studies of subsamples of the dated specimens should be carried out in order to extend the molecular evidence for the independent domestication of North and South American common beans.     

Domestication patterns in common bean (Phaseolus vulgaris L.) and the origin of the Mesoamerican and Andean cultivated races

Chloroplast DNA polymorphisms were studied by PCR sequencing and PCR-restriction fragment length polymorphism in 165 accessions of domesticated landraces of common bean from Latin America and the USA, 23 accessions of weedy beans, and 134 accessions of wild beans covering the entire geographic range of wild Phaseolus vulgaris. Fourteen chloroplast haplotypes were identified in wild beans, only five of which occur also in domesticated beans. The chloroplast data agree with those obtained from analyses based on morphology and isozymes and with other DNA polymorphisms in supporting independent domestications of common bean in Mesoamerica and the Andean region and in demonstrating a founder effect associated with domestication in each region. Andean landraces have been classified into three different racial groups, but all share the same chloroplast haplotype. This suggests that common bean was domesticated once only in South America and that the races diverged post-domestication. The haplotype found in Andean domesticated beans is confined to the southern part of the range of wild beans, so Andean beans were probably domesticated somewhere within this area. Mesoamerican landraces have been classified into four racial groups. Our limited samples of Races Jalisco and Guatemala differ from the more widespread and commercially important Races Mesoamerica and Durango in types and/or frequencies of haplotypes. All four Mesoamerican races share their haplotypes with local wild beans in parts of their ranges. Independent domestications of at least some of the races in Mesoamerica and/or conversion of some locally adapted wild beans to cultigens by hybridization with introduced domesticated beans, followed by introgression of the domestication syndrome seem the most plausible explanations of the chloroplast and other molecular data.     

Genetic structure of a Lima bean base collection using allozyme markers

 Genetic diversity and structure within a Lima bean (Phaseolus lunatus L.) base collection have been evaluated using allozyme markers. The results obtained from the analysis of wild and cultivated accessions confirm the existence of Andean and Mesoamerican gene pools characterised by specific alleles. Wild and cultivated accessions of the same gene pool are grouped. The Andean natural populations have a very limited geographic distribution between Ecuador and northern Peru. The Mesoamerican wild form extends from Mexico up to Argentina through the eastern side of the Andes. Andean and Mesoamerican cultivated accessions of pantropical distribution contribute substantially to the genetic diversity of the Lima bean base collection. Population genetic parameters, estimated from allozymes, confirmed the predominant selfing mating system of the Lima bean. The selfing mating system, the occurrence of small populations, and low gene flow lead to an interpopulation gene diversity (D_ST=0.235) higher than the intrapopulation gene diversity (H_S=0.032). On the basis of the results, guidelines are given to preserve and exploit the genetic diversity of this threatened species. The results also confirm the independent domestication of the Lima bean in at least two centres, one of which is located at medium elevation in the western valleys of Ecuador and northern Peru. Received: 3 June 1997 / Accepted: 17 June 1997     

Multiple origins of the determinate growth habit in domesticated common bean (Phaseolus vulgaris)

Background and Aims

The actual number of domestications of a crop is one of the key questions in domestication studies. Answers to this question have generally been based on relationships between wild progenitors and domesticated descendants determined with anonymous molecular markers. In this study, this question was investigated by determining the number of instances a domestication phenotype had been selected in a crop species. One of the traits that appeared during domestication of common bean (Phaseolus vulgaris) is determinacy, in which stems end with a terminal inflorescence. It has been shown earlier that a homologue of the arabidopsis TFL1 gene – PvTFL1y – controls determinacy in a naturally occurring variation of common bean.

Methods

Sequence variation was analysed for PvTFL1y in a sample of 46 wild and domesticated accessions that included determinate and indeterminate accessions.

Key Results

Indeterminate types – wild and domesticated – showed only synonymous nucleotide substitutions. Determinate types – observed only among domesticated accessions – showed, in addition to synonymous substitutions, non-synonymous substitutions, indels, a putative intron-splicing failure, a retrotransposon insertion and a deletion of the entire locus. The retrotransposon insertion was observed in 70 % of determinate cultivars, in the Americas and elsewhere. Other determinate mutants had a more restricted distribution in the Americas only, either in the Andean or in the Mesoamerican gene pool of common bean.

Conclusions

Although each of the determinacy haplotypes probably does not represent distinct domestication events, they are consistent with the multiple (seven) domestication pattern in the genus Phaseolus. The predominance of determinacy in the Andean gene pool may reflect domestication of common bean prior to maize introduction in the Andes.     

Discrimination of American Cranberry Cultivars and Assessment of Clonal Heterogeneity Using Microsatellite Markers

Cranberries (Vaccinium macrocarpon Ait.) are an economically important fruit crop derived from a North American native species. We report the application of 12 simple sequence repeats (SSR) or microsatellite markers to assess the genetic diversity of cranberry cultivars. We studied 164 samples of 21 different cranberry cultivars, 11 experimental hybrids, and 6 representative accessions of wild species. Genetic cluster analysis, based on 117 SSR alleles, differentiated the major cranberry cultivars. However, some cranberry cultivar subclone variants and mislabeled samples were observed. Consensus genetic profiles identified the most likely clonal representatives of several important cranberry cultivars (e.g., “Ben Lear,” “Howes,” and “Stevens”). The markers were further used to confirm putative parents of several hybrid progenies. The long-term goal of our studies is to identify, preserve, and utilize unique genetic materials to breed improved cranberries. Attaining this goal will help growers maintain sustainability under changing economic and environmental conditions.     

Reciprocal translocation identified in <Emphasis Type="Italic">Vigna angularis</Emphasis> dominates the wild population in East Japan

Using an F₂ population derived from cultivated and wild azuki bean, we previously detected a reciprocal translocation and a seed size QTL near the translocation site. To test the hypothesis that the translocation in the cultivated variety contributed to the larger seed size, we performed further linkage analyses with several cross combinations between cultivated and wild azuki beans. In addition, we visually confirmed the translocation by cytogenetic approach using 25 wild and cultivated accessions. As a result, we found the translocation-type chromosomes in none of the cultivated accessions, but in a number of the wild accessions. Interestingly, all the wild accessions with the translocation were originally collected from East Japan, while all the accessions with normal chromosomes were from West Japan or the Sea of Japan-side region. Such biased geographical distribution could be explained by the glacial refugium hypothesis, and supported narrowing down the domestication origin of cultivated azuki bean.     

Protective mechanism of the Mexican bean weevil against high levels of alpha-amylase inhibitor in the common bean.

Alpha-amylase inhibitor (alpha AI) protects seeds of the common bean (Phaseolus vulgaris) against predation by certain species of bruchids such as the cowpea weevil (Callosobruchus maculatus) and the azuki bean weevil (Callosobruchus chinensis), but not against predation by the bean weevil (Acanthoscelides obtectus) or the Mexican bean weevil (Zabrotes subfasciatus), insects that are common in the Americas. We characterized the interaction of alpha AI-1 present in seeds of the common bean, of a different isoform, alpha AI-2, present in seeds of wild common bean accessions, and of two homologs, alpha AI-Pa present in seeds of the tepary bean (Phaseolus acutifolius) and alpha AI-Pc in seeds of the scarlet runner bean (Phaseolus coccineus), with the midgut extracts of several bruchids. The extract of the Z. subfasciatus larvae rapidly digests and inactivates alpha AI-1 and alpha AI-Pc, but not alpha AI-2 or alpha AI-Pa. The digestion is caused by a serine protease. A single proteolytic cleavage in the beta subunit of alpha AI-1 occurs at the active site of the protein. When degradation is prevented, alpha AI-1 and alpha AI-Pc do not inhibit the alpha-amylase of Z. subfasciatus, although they are effective against the alpha-amylase of C. chinensis. Alpha AI-2 and alpha AI-Pa, on the other hand, do inhibit the alpha-amylase of Z. subfasciatus, suggesting that they are good candidates for genetic engineering to achieve resistance to Z. subfasciatus.     

Ecogeographic distribution ofPhaseolus spp. (Fabaceae) in Bolivia

WildPhaseolus vulgaris is distributed between northern Mexico and northern Argentina. Analysis of phaseolin and molecular markers (isozymes, Restriction Fragment Length Polymorphisms or RFLPs) indicate that this gene pool consists of two major groups, Mesoamerican and Andean, and a third intermediate group found in northwestern South America. Previous to this study, only four accessions of wildP. vulgaris beans from Bolivia had been collected and their genetic relationship with other wild beans from Latin America was not known. Due to the problem of intense erosion in some areas of Bolivia, it was our objective to survey and documentPhaseolus spp. in this area before their extinction. We conducted a collection expedition in May 1994 in the departments of Cochabamba, Chuquisaca and Tarija. This resulted in collections of four populations ofP. augusti, two of cultivatedP. lunatus and two mixtures of cultivatedP. vulgaris. The first mixture was made of “k’opurus” or beans consumed after toasting, and represented an addition of 17 accessions to the Bolivian collection. The second mixture was made of “porotos” and resulted in the addition of 10 new accessions. Seven germplasm collections of wildP. vulgaris were found, which allowed us to increase the number of known populations of wild common bean for Bolivia. Another accession was found as a wild-weed-crop complex. Seven of these wildP. vulgaris accessions along with another accession from Bolivia collected previously, and a number of P. vulgaris accessions from Mexico (17), Guatemala (3), Colombia (10), Ecuador (6), Peru (17) and Argentina (16) were analyzed with RAPDs. The use of 14 random primers and one SCAR (Sequence Characterized Amplified Region) resulted in 90 bands, of which 83 were polymorphic. This data was used to construct a dendrogram which shows clear separation into three clusters, corresponding to each of the gene pools and an intermediate group. The Bolivian wild P. vulgaris beans grouped with the accessions of southern Peru and Argentina into the Andean gene pool. RAPD analysis of genetic diversity correlated well with genetic diversity obtained with other markers. Moreover, the ease of analysis allowed us to obtain a large number of bands which was conducive to greater sensitivity and identification of geographic subgroups and accessions of hybrid origin.     

Wild to crop introgression and genetic diversity in Lima bean (Phaseolus lunatus L.) in traditional Mayan milpas from Mexico

Despite the evolutionary, ecological and economic importance of introgression between a domesticated species and its wild relatives in centers of diversity and domestication, the role of traditional farmers in this process has received limited attention. In the Yucatan Peninsula, the region of Mexico that has the greatest amount of domesticated varieties of Lima bean, wild populations grow sympatrically with conspecific varieties, allowing the Mayan farmer to act directly on introgressed seed. We used 11 microsatellite loci to assess levels of introgression in three wild-domesticated complexes of Lima bean from the Yucatan Peninsula and analyze its impact on the genetic diversity of this crop. structure and InStruct analyses showed similar results. The Instruct analysis indicated that the complex with the lowest level of introgression was one where the farmer actively selected against wild plants and introgressed seed. In contrast, the complex with the highest level of introgression was one where the farmer has been consciously selecting a weedy morphotype for 15 years and has already incorporated it into his diet. Genetic diversity of the domesticated pool was higher in the complex with the higher level of introgression. This study showed that farmers have an important role in limiting or favoring the wild to crop introgression and influencing the levels of genetic diversity in their domesticated pool. Only when traditional farmers’ knowledge is taken into account can we correctly understand the dynamics, generation and maintenance of genetic diversity of the landraces in the centers of diversity and domestication.