Combined mapping of AFLP and RFLP markers in barley

Genetic diversity, allelic variation and marker trait associations in gamma irradiated mutants of rice (Oryza sativa L.)

PURPOSE

Rice is a prime staple crop for more than half of the world population. Improved White Ponni (IWP) is a premium quality grain rice variety that is fetching a good price and is increasingly popular among the consumers of Tamil Nadu. Tall plant stature of IWP makes them susceptible to lodging and medium duration are two undesirable traits in the variety increases yield losses in the field and also productivity. In this context, we aimed to generate a large mutant population of IWP irradiated with various doses of gamma irradiation to recover putative mutants for semi-dwarfism and earliness.

MATERIALS AND METHODS

Totally, 34 putative mutants (22 early, 11 semi-dwarf and early and 1 Narrow-leaf dwarf mutant) were phenotyped for nine morphological traits and genotyped using 34 microsatellite markers linked to a trait of interest of earliness and semi-dwarfism. Trait variability, allelic variations, genetic structure and marker-trait associations in gamma-irradiated putative mutants of Improved White Ponni (IWP) rice were investigated in this study.

RESULTS

The hierarchical clustering of morphological data produced five clusters with a dissimilarity coefficient of 1.39. A minimum dissimilarity coefficient of 0.23 was observed between the mutants IWPM9 and IWPM20 and a maximum dissimilarity coefficient of 2.55 was observed between IWPM1 and IWPM25. In cluster analysis with molecular marker data, five clusters with a similarity coefficient of 0.67 were observed. The mutant IWPM29 exhibited the most divergence from the wild type at the genotype level. The first principal component explained 50.99% of the total variability and the majority of the traits were contributed positively. The single-marker analysis revealed the strong association of SSR marker RM3912 with the traits plant height, panicle length and number of grains per panicle with an R² value of 0.235, 0.235 and 0.250 respectively.

CONCLUSIONS

The study identified semi-dwarf and short-duration rice mutants of IWP that can be utilized as potential breeding stocks. The trait-linked SSR markers can improve selection cycles in advanced breeding programs.

Amplified Fragment Length Polymorphism: Applications and Recent Developments

AFLP or amplified fragment length polymorphism is a PCR-based molecular technique that uses selective amplification of a subset of digested DNA fragments from any source to generate and compare unique fingerprints of genomes. It is more efficient in terms of time, economy, reproducibility, informativeness, resolution, and sensitivity, compared to other popular DNA markers. Besides, it requires very small quantities of DNA and no prior genome information. This technique is widely used in plants for taxonomy, genetic diversity, phylogenetic analysis, construction of high-resolution genetic maps, and positional cloning of genes, to determine relatedness among cultivars and varietal identity, etc. The review encompasses in detail the various applications of AFLP in plants and the major advantages and disadvantages. The review also considers various modifications of this technique and novel developments in detection of polymorphism. A wet-lab protocol is also provided.

A Genetic Evaluation System for New Zealand White Rabbit Germplasm Resources Based on SSR Markers

Simple Summary

The New Zealand white rabbit (Oryctolagus cuniculus) is one of the most important breeds of commercial and experimental rabbits in the world, and also one of the most raised rabbit breeds in China. Our goal was to develop a suite of microsatellite markers to aid future conservation genetics research for the Oryctolagus cuniculus breeds. Based on the genetic diversity of 130 New Zealand white rabbits, we obtained a set combination of 22 markers. Then, we performed a genetic analysis of 200 New Zealand white rabbits corresponding to two generations with this combination. It can be used to evaluate the breed conservation of rabbit germplasm resources.

Abstract

At present, there is an abundance of quality domestic rabbit breeds in China. However, due to the lack of technical standards for the genetic evaluation of rabbit germplasm resources, there have been a number of problems, such as poor breed conservation. By studying the genetic diversity of 130 New Zealand white rabbits (regardless of generation), we obtained the best simple sequence repeat (SSR) marker combination. We found that, when using microsatellite markers for the effective genetic evaluation of domestic rabbits, the number of records should be greater than 60 and the marker number more than 22. Through the comparative analysis of 30 combinations of 22 markers, the optimal combination of 22 markers was determined, and the 22 SSR polymorphic loci were distributed on different chromosomes. We performed a genetic analysis of 200 New Zealand white rabbits corresponding to two generations, using the best SSR polymorphic loci combination. There were no significant differences in the genetic diversity parameters between the two generations of rabbits (p > 0.05), indicating that the characteristics of this excellent rabbit germplasm have been effectively preserved. At the same time, we verified that the established method can be used to evaluate the breed conservation of rabbit germplasm resources.

Construction of genetic linkage map and identification of QTLs related to agronomic traits in maize using DNA transposon-based markers

Transposable elements (TEs), are a rich source for molecular marker development as they constitute a significant fraction of the eukaryotic genome and impact the overall genome structure. Here, we utilize Mutator-based transposon display (Mu-TD), and CACTA-derived sequence-characterized amplified regions (SCAR) anchored by simple sequence repeats and single nucleotide polymorphisms to locate quantitative trait loci (QTLs) linked to agriculturally important traits on a genetic map. Specifically, we studied recombinant inbred line populations derived from a cross between dent corn and waxy corn. The resulting linkage map included 259 Mu-anchored fragments, 34 SCARs, and 614 SSR markers distributed throughout the ten maize chromosomes. Linkage analysis revealed three SNP loci associated with kernel starch synthesis genes (sh2, su1, wx1) linked to either Mu-TD loci or SSR markers, which may be useful for maize breeding programs. In addition, we used QTL analysis to determine the chromosomal location of traits related to grain yield and kernel quality. We identified 24 QTLs associated with nine traits located on nine out of ten maize chromosomes. Among these, 13 QTLs involved Mu loci and two involved SCARs. This study demonstrates the potential use of DNA transposon-based markers to construct linkage maps and identify QTLs linked to agronomic traits.

Mutation-based selection and analysis of Komagataeibacter hansenii HDM1-3 for improvement in bacterial cellulose production

AIMS

A low yield of bacterial cellulose (BC) always results from an excessive accumulation of organic acids. Screening and the selection of bacterial mutants with a low accumulation of organic acids is an efficient approach for improving BC production.

METHODS AND RESULTS

In combination with the proton suicide method (medium containing NaBr-NaBrO₃ ), diethyl sulphate chemical mutagenesis coupled with ⁶⁰ Co-γ irradiation treatment were performed for the screening and selection of desired mutant lines with a high yield of BC. Two high-yield strains, Br-3 and Co-5, as well as a low-yield strain, Br-12, were obtained. Amplified fragment length polymorphism (AFLP) was applied to explore the differences between the mutant lines and the wild type. For the Br-12 line, three specific fragments were verified, corresponding to TonB-dependent transport (TBDT), exopolysaccharides output protein (PePr) and an unknown gene. For Co-5, two specific fragments were matched, acsD and UDP-galactose-4-epimerase. In addition, metabolic analysis for the mutant lines indicated that BC production may be limited by excessive accumulation of organic acids in the fermentation. The limitation would be resolved by the cross-talk of genes involved in BC biosynthesis.

CONCLUSIONS

Reduced organic acid by-products from glucose in bypasses were found to be responsible for the high-yield BC synthesis in Komagataeibacter hansenii mutant strains.

SIGNIFICANCE AND IMPACT OF THE STUDY

The metabolic process was varied by mutagenesis-induced gene disruption of the metabolic products. A new idea was provided for the targeted screening and characterization of mutants in the future.

Discovery and mapping of genomic regions governing economically important traits of Basmati rice

BACKGROUND

Basmati rice, originated in the foothills of Himalayas, commands a premium price in the domestic and international markets on account of its unique quality traits. The complex genetic nature of unique traits of Basmati as well as tedious screening methodologies involved in quality testing have been serious constraints to breeding quality Basmati. In the present study, we made an attempt to identify the genomic regions governing unique traits of Basmati rice.

RESULTS

A total of 34 Quantitative Trait Loci (QTLs) for 16 economically important traits of Basmati rice were identified employing F(2), F(3) and Recombinant Inbred Line (RIL) mapping populations derived from a cross between Basmati370 (traditional Basmati) and Jaya (semi-dwarf rice). Out of which, 12 QTLs contributing to more than 15 % phenotypic variance were identified and considered as major effect QTLs. Four major effect QTLs coincide with the already known genes viz., sd1, GS3, alk1 and fgr governing plant height, grain size, alkali spreading value and aroma, respectively. For the remaining major QTLs, candidate genes were predicted as auxin response factor for filled grains, soluble starch synthase 3 for chalkiness and VQ domain containing protein for grain breadth and grain weight QTLs, based on the presence of non-synonymous single nucleotide polymorphism (SNPs) that were identified by comparing Basmati genome sequence with that of Nipponbare.

CONCLUSIONS

To the best of our knowledge, the current study is the first attempt ever made to carry out genome-wide mapping for the dissection of the genetic basis of economically important traits of Basmati rice. The promising QTLs controlling important traits in Basmati rice, identified in this study, can be used as candidates for future marker-assisted breeding.

Genotyping analysis using an RFLP assay

RFLP (Restriction Fragment Length Polymorphism) is a commonly used technique that can be used for genotyping for nearly all organisms, including plants, animals, and humans. RFLP is widely used in genetic and genomic research, such as genome mapping and gene identification. The technique involves DNA digestion, gel electrophoresis, capillary transfer of DNA, and southern hybridization. In this chapter, we aim to give a detailed introduction of how to perform RFLPs for identifying genotypes.

Development and use of molecular markers: past and present

Molecular markers, due to their stability, cost-effectiveness and ease of use provide an immensely popular tool for a variety of applications including genome mapping, gene tagging, genetic diversity diversity, phylogenetic analysis and forensic investigations. In the last three decades, a number of molecular marker techniques have been developed and exploited worldwide in different systems. However, only a handful of these techniques, namely RFLPs, RAPDs, AFLPs, ISSRs, SSRs and SNPs have received global acceptance. A recent revolution in DNA sequencing techniques has taken the discovery and application of molecular markers to high-throughput and ultrahigh-throughput levels. Although, the choice of marker will obviously depend on the targeted use, microsatellites, SNPs and genotyping by sequencing (GBS) largely fulfill most of the user requirements. Further, modern transcriptomic and functional markers will lead the ventures onto high-density genetic map construction, identification of QTLs, breeding and conservation strategies in times to come in combination with other high throughput techniques. This review presents an overview of different marker technologies and their variants with a comparative account of their characteristic features and applications.

Phylogeny of ten species of the genus Hordeum L. as revealed by AFLP markers and seed storage protein electrophoresis

The phylogenetic relationships of 60 accessions representing ten species of the genus Hordeum were investigated based on AFLP markers and seed storage protein SDS-PAGE electrophoresis. A total of 339 AFLP polymorphic markers were scored as a result of fingerprinting the studied taxa using seven AFLP primer combinations, whereas 46 polymorphic protein bands resulted from the water soluble and water non-soluble seed storage protein electrophoresis. The phylogenetic tree deduced from AFLP analysis is concordant in a large extent with that deduced from seed storage protein electrophoresis. The studied taxa were clustered according to their genome type into two main groups representing the Old and New World's species. Inside each group the species were clustered according to their genome type. Highly significant cophenetic correlation coefficient was obtained between both AFLP (0.96) and seed storage protein (0.89) indicating the reliability of the results.

Direct and reverse pollen-mediated gene flow between GM rice and red rice weed

Several studies have reported transgenic rice transferring transgenes to red rice weed. However, gene flow also occurs in the opposite direction resulting in transgenic seeds that have incorporated the traits of wild red rice. We quantified this reverse flow being higher than the direct gene flow, nevertheless transgenic seeds carrying wild genes would remain in the spike and therefore most of it would be removed at harvesting. This phenomenon must be considered in fields used for elite seed production and in developing countries where there is a higher risk of GM red rice weed infestation increasing from year to year.

Potential risks of genetically modified (GM) crops must be identified before their commercialization, as happens with all new technologies. One of the major concerns is the proper risk assessment of adventitious presence of transgenic material in rice fields due to cross-pollination. Several studies have been conducted in order to quantify pollen-mediated gene flow from transgenic rice (Oryza sativa) to both conventional rice and red rice weed (O. sativa f. spontanea) under field conditions. Some of these studies reported GM pollen-donor rice transferring GM traits to red rice. However, gene flow also occurs in the opposite direction, in a phenomenon that we have called reverse gene flow, resulting in transgenic seeds that have incorporated the traits of wild red rice. We quantified reverse gene flow using material from two field trials. A molecular analysis based on amplified fragment length polymorphisms was carried out, being complemented with a phenotypic identification of red rice traits. In both field trials, the reverse gene flow detected was greater than the direct gene flow. The rate of direct gene flow varied according to the relative proportions of the donor (GM rice) and receptor (red rice) plants and was influenced by wind direction. The ecological impact of reverse gene flow is limited in comparison with that of direct gene flow because non-shattered and non-dormant seeds would be obtained in the first generation. Hybrid seed would remain in the spike and therefore most of it would be removed during harvesting. Nevertheless, this phenomenon must be considered in fields used for elite seed production and in developing countries where farmers often keep some seed for planting the following year. In these cases, there is a higher risk of GM red rice weed infestation increasing from year to year and therefore a proper monitoring plan needs to be established.

Genetic analysis and QTL mapping of seed coat color in sesame (Sesamum indicum L.)

Seed coat color is an important agronomic trait in sesame, as it is associated with seed biochemical properties, antioxidant content and activity and even disease resistance of sesame. Here, using a high-density linkage map, we analyzed genetic segregation and quantitative trait loci (QTL) for sesame seed coat color in six generations (P1, P2, F1, BC1, BC2 and F2). Results showed that two major genes with additive-dominant-epistatic effects and polygenes with additive-dominant-epistatic effects were responsible for controlling the seed coat color trait. Average heritability of the major genes in the BC1, BC2 and F2 populations was 89.30%, 24.00%, and 91.11% respectively, while the heritability of polygenes was low in the BC1 (5.43%), in BC2 (0.00%) and in F2 (0.89%) populations. A high-density map was constructed using 724 polymorphic markers. 653 SSR, AFLP and RSAMPL loci were anchored in 14 linkage groups (LG) spanning a total of 1,216.00 cM. The average length of each LG was 86.86 cM and the marker density was 1.86 cM per marker interval. Four QTLs for seed coat color, QTL1-1, QTL11-1, QTL11-2 and QTL13-1, whose heritability ranged from 59.33%-69.89%, were detected in F3 populations using CIM and MCIM methods. Alleles at all QTLs from the black-seeded parent tended to increase the seed coat color. Results from QTLs mapping and classical genetic analysis among the P1, P2, F1, BC1, BC2 and F2 populations were comparatively consistent. This first QTL analysis and high-density genetic linkage map for sesame provided a good foundation for further research on sesame genetics and molecular marker-assisted selection (MAS).

Comparative mapping in intraspecific populations uncovers a high degree of macrosynteny between A- and B-genome diploid species of peanut

BACKGROUND

Cultivated peanut or groundnut (Arachis hypogaea L.) is an important oilseed crop with an allotetraploid genome (AABB, 2n = 4x = 40). Both the low level of genetic variation within the cultivated gene pool and its polyploid nature limit the utilization of molecular markers to explore genome structure and facilitate genetic improvement. Nevertheless, a wealth of genetic diversity exists in diploid Arachis species (2n = 2x = 20), which represent a valuable gene pool for cultivated peanut improvement. Interspecific populations have been used widely for genetic mapping in diploid species of Arachis. However, an intraspecific mapping strategy was essential to detect chromosomal rearrangements among species that could be obscured by mapping in interspecific populations. To develop intraspecific reference linkage maps and gain insights into karyotypic evolution within the genus, we comparatively mapped the A- and B-genome diploid species using intraspecific F2 populations. Exploring genome organization among diploid peanut species by comparative mapping will enhance our understanding of the cultivated tetraploid peanut genome. Moreover, new sources of molecular markers that are highly transferable between species and developed from expressed genes will be required to construct saturated genetic maps for peanut.

RESULTS

A total of 2,138 EST-SSR (expressed sequence tag-simple sequence repeat) markers were developed by mining a tetraploid peanut EST assembly including 101,132 unigenes (37,916 contigs and 63,216 singletons) derived from 70,771 long-read (Sanger) and 270,957 short-read (454) sequences. A set of 97 SSR markers were also developed by mining 9,517 genomic survey sequences of Arachis. An SSR-based intraspecific linkage map was constructed using an F2 population derived from a cross between K 9484 (PI 298639) and GKBSPSc 30081 (PI 468327) in the B-genome species A. batizocoi. A high degree of macrosynteny was observed when comparing the homoeologous linkage groups between A (A. duranensis) and B (A. batizocoi) genomes. Comparison of the A- and B-genome genetic linkage maps also showed a total of five inversions and one major reciprocal translocation between two pairs of chromosomes under our current mapping resolution.

CONCLUSIONS

Our findings will contribute to understanding tetraploid peanut genome origin and evolution and eventually promote its genetic improvement. The newly developed EST-SSR markers will enrich current molecular marker resources in peanut.

AFLP Marking and Polymorphism among Progenies of Gymnema sylvestre: an Important Medicinal Plant of India

The level of polymorphism among twelve selected progenies of Gymnema sylvestre was investigated through AFLP markers by multiplexing PCR reactions using 64 (8×8) primer combinations. Fourteen primer combinations were selected as the most suitable combination for G. sylvestre. Analysis of the 12 progenies with these 14 primer pairs produced 1689 fragments of which 972 (57.5%) were polymorphic and 485 (28.7%) were unique to a particular genotype. The number of fragments produced by individual primer pairs was in the range of 55 to 225. Out of these, polymorphic fragments were in the range of 34 (E-ACC/M-CAC) to 157 (E-AGG/M-CAG) and unique bands observed were 8 (E-ACC / M-CAC) to 69 (E-AGG/M-CAC). Different primer combinations detected different levels of polymorphism, ranging from 33% (E-AGG/ M-CAC) to 69.8% (E-AGG/ M-CAC). From the observations, it appears that the primer combinations E-AGG/M-CAC, E-AGG/CTG, E-AGG/CAG and E-ACA / CAT were the most informative for the detection of polymorphism among the progenies compared with others, since they produced a high number of unique fragments. The similarity coefficient ranged from 0.212 to 0.731. High similarity was observed between progeny S8 and S9 (73%) and high divergence between progenies S3 and S11. Among the selected progeny, S9 was found to be the most similar to the parent (63%), while genotype S11 was the most distant (36.9%).

Genetic linkage map of a high yielding FELDA deli×yangambi oil palm cross

Enroute to mapping QTLs for yield components in oil palm, we constructed the linkage map of a FELDA high yielding oil palm (Elaeis guineensis), hybrid cross. The parents of the mapping population are a Deli dura and a pisifera of Yangambi origin. The cross out-yielded the average by 8–21% in four trials all of which yielded comparably to the best current commercial planting materials. The higher yield derived from a higher fruit oil content. SSR markers in the public domain - from CIRAD and MPOB, as well as some developed in FELDA - were used for the mapping, augmented by locally-designed AFLP markers. The female parent linkage map comprised 317 marker loci and the male parent map 331 loci, both in 16 linkage groups each. The number of markers per group ranged from 8–47 in the former and 12–40 in the latter. The integrated map was 2,247.5 cM long and included 479 markers and 168 anchor points. The number of markers per linkage group was 15–57, the average being 29, and the average map density 4.7 cM. The linkage groups ranged in length from 77.5 cM to 223.7 cM, with an average of 137 cM. The map is currently being validated against a closely related population and also being expanded to include yield related QTLs.

Improved AFLP protocol using dual-suppression PCR and its application to species with large genomes

To improve the amplified fragment length polymorphism assay, dual-suppression PCR was introduced into the preamplification step of the assay. The dual-suppression PCR blocked completely the amplification of fragments with the same sequence (Bsp1407I-Bsp1407I or NlaIII-NlaIII) at both ends and amplified selectively fragments with different adaptor sequences (Bsp1407I-NlaIII) at each end. Two protocols, referred to as A and B, were established for species with medium- and large-sized genomes, respectively. Both protocols incorporated the dual-suppression PCR. Protocol A resulted in high-quality electrophoretic profiles for black cottonwood and rice, which have medium-sized genomes. In protocol B, an intensely selective PCR step was added to protocol A. Protocol B yielded profiles for Japanese black pine and Japanese cedar that were improved significantly relative to protocol A: the number of strong peaks increased and that of low peaks decreased. Japanese black pine and Japanese cedar have large genomes. The optimal profiles were generated with a total of eight or nine selective nucleotides.

Linkage disequilibrium and population structure in wild and domesticated populations of Phaseolus vulgaris L

Together with the knowledge of the population structure, a critical aspect for the planning of association and/or population genomics studies is the level of linkage disequilibrium (LD) that characterizes the species and the population used for such an analysis. We have analyzed the population structure and LD in wild and domesticated populations of Phaseolus vulgaris L. using amplified fragment length polymorphism markers, most of which were genetically mapped in two recombinant inbred populations. Our results reflect the previous knowledge of the occurrence of two major wild gene pools of P. vulgaris, from which two independent domestication events originated, one in the Andes and one in Mesoamerica. The high level of LD in the whole sample was mostly due to the gene pool structure, with a much higher LD in domesticated compared to wild populations. In relation to association studies, our results also suggest that whole-genome-scan approaches are feasible in the common bean. Interestingly, an excess of inter-chromosomal LD was found in the domesticated populations, which suggests an important role for epistatic selection during domestication. Moreover, our results indicate the occurrence of a strong bottleneck in the Andean wild population before domestication, suggesting a Mesoamerican origin of P. vulgaris. Finally, our data support the occurrence of a single domestication event in Mesoamerica, and the same scenario in the Andes.

Analysis of the phylogenetic relationships among several species of Gramineae using ACGM markers

To study the transferability of rice (Oryza sativa L.) genome data, we used amplified consensus genetic markers to analyze the phylogenetic relationships among several species and genera in Gramineae. Ten accessions representing five grass genera (Oryza, Zea, Setaria, Triticum, and Phyllostachys) were used. According to the genetic distances, a cluster tree was constructed. The relationships among the five genera could be simply described as ((Oryza + (Zea +Setaria)) +Triticum) +Phyllostachys. The results suggest that the genetic distance between rice and maize (Z. mays L.) or rice and millet (Setaria italica L.) is closer than that between rice and wheat (Triticum aestivum L) or rice and bamboo.

Construction of a first genetic map of distylous Turnera and a fine-scale map of the S-locus region

As a prelude to discovery of genes involved in floral dimorphism and incompatibility, a genetic map of distylous Turnera was constructed along with a fine-scale map of the S-locus region. The genetic map consists of 79 PCR-based molecular markers (48 AFLP, 18 RAPD, 9 ISSR, 4 RAMP), 5 isozyme loci, one additional gene, and the S-locus, spanning a total distance of 683.3 cM. The 86 markers are distributed in 5 linkage groups, corresponding to the haploid chromosome number. Molecular markers tightly linked or co-segregating with the S-locus in an initial mapping population of 94 individuals were used to assay an additional 642 progeny to construct a map of the S-locus region. The fine-scale map consists of 2 markers (IS864a and RP45E9) flanking the S-locus at distances of 0.41 and 0.54 cM, respectively, and 3 additional markers (OPK14c, RP45G18, and RP81E18) co-segregating with the S-locus in the total mapping population of 736 individuals. The genetic map constructed will serve as a framework for localization of genes outside the S-locus affecting distyly, while molecular markers of the fine-scale map will be used to initiate chromosome walking to find the genes residing at the S-locus.

Genetic diversity of Actinobacillus pleuropneumoniae assessed by amplified fragment length polymorphism analysis

Amplified fragment length polymorphism (AFLP) was evaluated as a method for genotypic characterization and subtyping within the bacterial species Actinobacillus pleuropneumoniae. A total of 155 isolates of A. pleuropneumoniae, representing the serotypic variation described to occur within this species, were analyzed. In order to elucidate the species boundaries, six strains of the phylogenetically closely related species Actinobacillus lignieresii were also included. Furthermore, the ability of AFLP to subtype was studied using 42 isolates of serovar 2 and the performance compared to that obtained by pulsed-field gel electrophoresis (PFGE). AFLP analysis provided a clear separation of A. lignieresii and A. pleuropneumoniae and divided the isolates of A. pleuropneumoniae into 20 clusters. Most of the serovars of A. pleuropneumoniae were represented by single and quite homogeneous clusters. The exceptions were serovars 10, K2:O7, and K1:O7, which were represented by two clusters each. In the cases where the serovars were represented by more than one cluster, the existence of these clusters was supported by additional phenotypic or genotypic properties. Furthermore, AFLP typing was able to allocate serologically nontypeable isolates to appropriate genetic groups within the species. Further investigations are needed to determine whether some of the clusters revealed through AFLP analysis represent additional serovars. When evaluated as a method for subtyping within serovar 2 of A. pleuropneumoniae, AFLP was found to achieve a degree of separation among isolates superior to that obtained by PFGE. However, a higher degree of separation between serovar 2 isolates was obtained by a combination of the two methods.

The reference genetic linkage map for the multinational Brassica rapa genome sequencing project

We describe the construction of a reference genetic linkage map for the Brassica A genome, which will form the backbone for anchoring sequence contigs for the Multinational Brassica rapa Genome Sequencing Project. Seventy-eight doubled haploid lines derived from anther culture of the F(1) of a cross between two diverse Chinese cabbage (B. rapa ssp. pekinensis) inbred lines, 'Chiifu-401-42' (C) and 'Kenshin-402-43' (K) were used to construct the map. The map comprises a total of 556 markers, including 278 AFLP, 235 SSR, 25 RAPD and 18 ESTP, STS and CAPS markers. Ten linkage groups were identified and designated as R1-R10 through alignment and orientation using SSR markers in common with existing B. napus reference linkage maps. The total length of the linkage map was 1,182 cM with an average interval of 2.83 cM between adjacent loci. The length of linkage groups ranged from 81 to 161 cM for R04 and R06, respectively. The use of 235 SSR markers allowed us to align the A-genome chromosomes of B. napus with those of B. rapa ssp. pekinensis. The development of this map is vital to the integration of genome sequence and genetic information and will enable the international research community to share resources and data for the improvement of B. rapa and other cultivated Brassica species.

An intervarietal genetic linkage map of Indian bread wheat (Triticum aestivum L.) and QTL maps for some metric traits

Bread wheat (Triticum aestivum L.) exhibits very narrow genetic diversity and hence there is high relatedness among cultivated varieties. However, a population generated from an intervarietal cross, with the parents differing in a large number of traits, could lead to the generation of QTL maps which will be useful in practice. In this report a genetic linkage map of wheat is constructed using a cross between two Indian bread wheat varieties: Sonalika and Kalyansona. The linkage map consisted of 236 markers and spanned a distance of 3639 cM, with 1211.2 cM for the A genome, 1669.2 cM for the B genome, 192.4 cM for the D genome and 566.2 cM for unassigned groups. Linkage analysis defined 37 linkage groups of which 24 were assigned to 17 chromosomes. The genetic map was used to identify QTLs by composite internal mapping (CIM) for three metric traits, viz. culm length (CL), flag leaf length (FLL) and flag leaf breadth (FLB). Of 25 QTLs identified in this study, 15 have not been reported previously. Multitrait CIM (MCIM) analysis was carried out for traits that were significantly correlated such as FLB-FLL and CL-FLB-FLL. Detection of a large number of QTLs for the three traits analysed suggests that in parent cultivars that are not too diverse, the differences at genetic level detected as polymorphisms may be mostly associated with QTLs for the observed differences.

A comparison of AFLPs and microsatellites to identify the population structure of brown trout (Salmo trutta L.) populations from Hardangervidda, Norway

A total of 495 fish from 11 Hardangervidda lakes were genotyped in order to compare amplified fragment length polymorphisms (AFLP) and microsatellites in terms of their capacity to infer population genetic structure. The 11 microsatellites used in this study gave a greater polymorphism information content and greater gene diversity, with an average of 14.8 alleles per locus, than the six AFLP primer combinations used. However, the AFLPs resulted in 178 polymorphic loci and a 3.1 times larger marker index (effective multiplex ratio multiplied with the gene diversity). Comparable population structuring, for example in terms of distinguishing fish from the different river systems, was obtained with both marker systems. An AFLP and microsatellite multilocus Bayesian assignment test with the structure program divided the fish into six groups largely concurrent with main branches on a population neighbour-joining tree. Yet, the admixture status of individuals is mostly contradictory in the AFLP and the microsatellite analyses. The results are discussed concerning migration between lake populations.

Genomic distribution of MITEs in barley determined by MITE-AFLP mapping

Miniature inverted-repeat transposable elements (MITEs) represent a large superfamily of transposons that are moderately to highly repetitive and frequently found near or within plant genes. To elucidate the organization of MITEs in the barley genome, MITEs were integrated into the genetic map of barley. In this report, we describe the use of MITEs in amplified fragment length polymorphism (AFLP) mapping, and demonstrate their superiority over conventional AFLP mapping. Barley MITEs include members of the Stowaway, Barfly, and Pangrangja families. By amplifying the flanking sequences of these MITEs, a total of 214 loci were mapped from a population of 93 doubled-haploid segregating individuals between Hordeum vulgare ssp. vulgare and H. vulgare ssp. spontaneum. The 214 MITE-AFLP and 40 anchor simple sequence repeat (SSR) loci were distributed on 7 linkage groups, covering a total map distance of 1 165 cM. The average marker density on each chromosome ranged between 3.4 and 9.6 cM per locus. Only 1 MITE-based locus was frequently found to be associated with MITE loci from the same family, resulting in clusters in chromosomal subregions. In barley, it will be possible to cover the entire genome with a limited set of MITE-based primers and to build highly dense maps of specific regions.

AFLP-based differentiation of tropical African Festuca species compared to the European Festuca complex

For the first time amplified fragment length polymorphism (AFLP) fingerprinting is applied to classify tropical African Festuca species. Five afro-alpine narrow- and two afro-montane broad-leaved species from Uganda and Ethiopia are compared to ten European grass species. A principal coordinate analysis (PCoA) accounts for 62.5% with its first three coordinates. The PCoA and the neighbor-joining (NJ) distinguish the five narrow-leaved African Festuca species from all other species. The broad-leaved African Festuca africana and Festuca simensis are linked to the broad-leaved European species through Festuca altissima and Festuca gigantea, respectively. The narrow- and broad-leaved European species are separated as expected in the NJ. One narrow-leaved African alpine species recently described appears merged (i.e. Festuca richardii with Festuca abyssinica). We provide chromosome numbers for all seven Ugandan species and compare taxonomy and AFLP classification. Our most striking result is that the narrow-leaved African Festuca species are unique and not clustering with the narrow-leaved European species.

Genetic Relationships Between Cercospora kikuchii Populations from South America and Japan

ABSTRACT A collection 160 isolates of Cercospora kikuchii was made from South America and 245 from Japan. DNA fingerprint patterns were analyzed based on amplified fragment length polymorphism among the sample isolates, dividing the isolates into seven lineages (I to VII). Partial nucleotide sequence analyses of the beta-tubulin gene supported this division into seven lineages. Lineages I and III commonly existed in South America and Japan. In all, 136 of the 160 isolates from South America and 223 of the 245 isolates from Japan belonged to lineage I, indicating that lineage I was the major lineage in each area; 5 isolates from South America and 8 isolates from Japan belonged to lineage III. Lineages II (12 isolates) and IV (2 isolates) were specific to Japan and lineages V (3 isolates), VI (1 isolate), and VII (15 isolates) specifically existed in South America. These results suggest that the population genetic structure of C. kikuchii was different between South America and Japan, but the dominance of lineage I was common between the two areas.

A high-resolution map of Arabidopsis recombinant inbred lines by whole-genome exon array hybridization

Recombinant populations were the basis for Mendel's first genetic experiments and continue to be key to the study of genes, heredity, and genetic variation today. Genotyping several hundred thousand loci in a single assay by hybridizing genomic DNA to oligonucleotide arrays provides a powerful technique to improve precision linkage mapping. The genotypes of two accessions of Arabidopsis were compared by using a 400,000 feature exon-specific oligonucleotide array. Around 16,000 single feature polymorphisms (SFPs) were detected in ~8,000 of the ~26,000 genes represented on the array. Allelic variation at these loci was measured in a recombinant inbred line population, which defined the location of 815 recombination breakpoints. The genetic linkage map had a total length of 422.5 cM, with 676 informative SFP markers representing intervals of ~0.6 cM. One hundred fifteen single gene intervals were identified. Recombination rate, SFP distribution, and segregation in this population are not uniform. Many genomic regions show a clustering of recombination events including significant hot spots. The precise haplotype structure of the recombinant population was defined with unprecedented accuracy and resolution. The resulting linkage map allows further refinement of the hundreds of quantitative trait loci identified in this well-studied population. Highly variable recombination rates along each chromosome and extensive segregation distortion were observed in the population.

A goal of many genetic studies is to discover the underlying genetic condition (the genotype) of a specific physical manifestation in an organism (the phenotype), such as diabetes in humans or leaf rust in cultivated wheat. A limitation to making such discoveries is the ability to resolve genotype. Gene arrays carry representations of the genome, called features, at high-density on a surface the size of a thumbnail. In this study, microarrays designed to measure gene expression were used to detect DNA sequence polymorphisms. DNA from two different Arabidopsis strains was hybridized to arrays representing nearly the entire coding region of the genome. Differences in hybridization intensity indicated differences in DNA sequence. The sequence differences, termed single feature polymorphisms, were then assayed in a population of 100 plants derived through inbreeding the progeny from the two parental strains. The precise location of the genetic recombination breakpoints was defined for each line. As a result, Singer et al. were able to generate one of the first very high-resolution genotyping data sets in a multicellular organism that allowed the construction of a high-resolution genetic map of Arabidopsis. This map will greatly facilitate attempts to make definitive associations between genotypes and phenotypes.

Characterization of chromosome-specific S-SAP markers and their use in studying genetic diversity in Aegilops species

The short interspersed nuclear element (SINE), Au, was used to develop sequence-specific amplified polymorphism (S-SAP) markers for U- and M-genome chromosomes. The markers were localized using Triticum aestivum (wheat)-- Aegilops geniculata and wheat-- Aegilops biuncialis disomic chromosome addition lines. Thirty-seven markers distributed over 6 U and 6 M chromosomes were produced. A genetic diversity study carried out on 37 accessions from Ae. biuncialis, Ae. comosa, Ae. geniculata, and Ae. umbellulata suggested that Ae. biuncialis have arisen from its diploid ancestors more recently than Ae. geniculata. Several earlier studies indicated that the M genomes in polyploid Aegilops species had accumulated substantial rearrangements, whereas the U genomes remained essentially unmodified. However, this cannot be attributed to the preferential insertion of retroelements into the M genome chromosomes. Fourteen markers from a total of 8 chromosomes were sequenced; 3 markers were similar to known plant genes, 1 was derived from a long terminal repeat (LTR) retrotransposon, and 10 markers did not match to any known DNA sequences, suggesting that they were located in the highly variable intergenic regions.

Characterization and genetic distance analysis of isolates of Peronosclerospora sorghi using AFLP fingerprinting

Sorghum downy mildew, caused by the obligate oomycete Peronosclerospora sorghi, has been controlled through the use of resistant cultivars and seed treatment with metalaxyl. A recent outbreak in fields planted with treated seed revealed the presence of a metalaxyl-resistant variant. Here, PCR-based methods including amplification from RAPD primers and two systems of automated AFLP analysis have been used to detect DNA-level genetic variation among 14 isolates including metalaxyl-resistant and susceptible isolates, as well as representatives of common pathotypes 1 and 3 and a new pathotype. In total, 1708 bands were detected after amplification of EcoRI/MseI fragments with 16 primer combinations. Nearly as many amplified products were observed using eight primer pairs with three-base extensions (LI-COR) as with two-base extensions (ABI-Prism genetic capillary system). Approximately 25% of the bands were polymorphic across the 14 isolates, with the majority of differences specific to the pathotype P1 isolate. The AFLP banding patterns are consistent with metalaxyl resistance and the new pathotype having evolved from pathotype 3.

Physical and genetic mapping of amplified fragment length polymorphisms and the leaf rust resistance Lr3 gene on chromosome 6BL of wheat

The Argentinian wheat cultivar Sinvalocho MA carries the Lr3 gene for leaf rust resistance on distal chromosome 6BL. In this cultivar, 33 spontaneous susceptible lines were isolated and cytogenetically characterized by C-banding. The analysis revealed deletions on chromosome 6BL in most lines. One line was nulli-6B, two lines were ditelo 6BS, two, three, and ten lines had long terminal deletions of 40, 30, and 20%, respectively, three lines showed very small terminal deletions, and one line had an intercalary deletion of 11%. Physical mapping of 55 amplified fragment length polymorphism (AFLP) markers detected differences between deletions and led to the division of 6BL into seven bins delimited by deletion breakpoints. The most distal bin, with a length smaller than 5% of 6BL, contained 22 AFLP markers and the Lr3 gene. Polymorphism for nine AFLPs between Sinvalocho MA and the rust leaf susceptible cultivar Gamma 6 was used to construct a linkage map of Lr3. This gene is at a genetic distance of 0.9 cM from a group of seven closely linked AFLPs. The location of the gene in a high recombinogenic region indicated a physical distance of approximately 1 Mb to the markers.

Genotyping of recombinant Pichia pastoris strains

A simplified amplified-fragment length polymorphism (AFLP) method was used to genotype Pichia pastoris strains obtained by transformation of P. pastoris strain GS115 with a single integration vector. A total of 14 transformants and 3 control strains were analyzed, which generated 16 different band patterns. A clonal variation was obtained after the transformation process due to genetic differences generated during the transformation event of the host strain. Furthermore, the cluster analysis showed that the transformants with lesser genetic differences with respect to the P. pastoris host strain are the recombinant strains with the highest level of recombinant protein production.

Genetic variation in Echinacea angustifolia along a climatic gradient

BACKGROUNDS AND AIMS

Echinacea angustifolia is a widespread species distributed throughout the Great Plains region of North America. Genetic differentiation among populations was investigated along a 1500 km north-south climatic gradient in North America, a region with no major geographical barriers. The objective of the study was to determine if genetic differentiation of populations could be explained by an isolation-by-distance model or by associations with climatic parameters known to affect plant growth and survival.

METHODS

Historical climatic data were used to define the nature of the climatic gradient and AFLP markers were used to establish patterns of population genetic differentiation among ten Echinacea populations collected from North Dakota to Oklahoma. A total of 1290 fragments were scored using six EcoRI/MseI and three PstI/MseI primer combinations. Assessment of the correlation between climatic, genetic and geographic distances was assessed by Mantel and partial Mantel tests.

KEY RESULTS

PstI/MseI combinations produced significantly fewer fragments, but a larger percentage was unique compared with EcoRI/MseI markers. Using estimates of F(ST), populations in Oklahoma and southern Kansas were identified as the most divergent from the other populations. Both the neighbour-joining tree and principal co-ordinate analysis clustered the populations in a north-south spatial orientation. About 60% of the genetic variation was found within populations, 20% among populations and the remaining 20% was partitioned among groups that were defined by the topology of the neighbour-joining tree. Significant support was found for the isolation-by-distance model independent of the effects of annual mean precipitation, but not from annual mean temperature and freeze-free days.

CONCLUSIONS

Echinacea angustifolia populations exhibit genetic divergence along a north-south climatic gradient. The data support an isolation-by-distance restriction in gene flow that is independent of annual mean precipitation.

AFLP targeting of the 1-cM region conferring the vrs1 gene for six-rowed spike in barley, Hordeum vulgare L

Spike morphology is a key characteristic in the study of barley domestication, yield, and use. Multiple alleles at the vrs1 locus control the development and fertility of the lateral spikelets of barley. We developed five amplified fragment length polymorphism (AFLP) markers tightly linked to the vrs1 locus using well-characterized near-isogenic lines as plant materials. The AFLP markers were integrated into three different maps, in which 'Azumamugi' was used as the maternal parent. Of the three maps, Hordeum vulgare L. 'Azumamugi' x H. vulgare 'Golden Promise' showed recombination of the AFLP markers and the vrs1 locus (closest, 0.05 cM), providing the best mapping population for positional cloning of alleles at the vrs1 locus. Conversion of AFLP bands into polymorphic sequence-tagged sites (STSs) is necessary for further high-throughput genotype scoring and for bacterial artificial chromosome (BAC) library screening. We cloned and sequenced the five AFLP bands and synthesized primer pairs. PCR amplification generated DNAs of the same size from all four parental lines for each marker. Restriction endonuclease treatment of e40m36-1110/AccIII, e34m13-260/Psp1406I, e52m32-270/FokI, and e31m26-520/MnlI revealed fragment length polymorphisms between 'Azumamugi' and all the two-rowed parents. Allelism between the AFLPs and corresponding STS markers was confirmed genetically, indicating the usefulness of the STSs as genetic markers.

Linkage disequilibrium mapping of yield and yield stability in modern spring barley cultivars

Associations between markers and complex quantitative traits were investigated in a collection of 146 modern two-row spring barley cultivars, representing the current commercial germ plasm in Europe. Using 236 AFLP markers, associations between markers were found for markers as far apart as 10 cM. Subsequently, for the 146 cultivars the complex traits mean yield, adaptability (Finlay-Wilkinson slope), and stability (deviations from regression) were estimated from the analysis of variety trial data. Regression of those traits on individual marker data disclosed marker-trait associations for mean yield and yield stability. Support for identified associations was obtained from association profiles, i.e., from plots of P-values against chromosome positions. In addition, many of the associated markers were located in regions where earlier QTL were found for yield and yield components. To study the oligogenic genetic base of the traits in more detail, multiple linear regression of the traits on markers was carried out, using stepwise selection. By this procedure, 18-20 markers that accounted for 40-58% of the variation were selected. Our results indicate that association mapping approaches can be a viable alternative to classical QTL approaches based on crosses between inbred lines, especially for complex traits with costly measurements.

Barley Rom1 reveals a potential link between race-specific and nonhost resistance responses to powdery mildew fungi

The Rar1 gene, identified in the context of race-specific powdery mildew resistance mediated by the Hordeum vulgare (barley) resistance (R) gene Mla12, is required for the function of many R-mediated defense responses in mono- and dicotyledonous plant species. Mla resistance is associated with an oxidative burst and a subsequent cell death reaction of attacked cells. Rar1 mutants are impaired in these responses and, to identify genetic elements which negatively regulate the Mla12-triggered response, we have screened mutagenized Mla12 rar1 mutant populations for restoration of the resistance response. Here we describe the restoration of Mla12-specified resistance (rom1) mutant that restores features of disease resistance to a Blumeria graminis f. sp. hordei isolate expressing the avirulence gene AvrMla12 and retains susceptibility to an isolate lacking AvrMla12. Histochemical analyses show that, in rom1 mutant plants, a whole-cell oxidative burst and cell death response in attacked epidermal cells is restored in the incompatible interaction. Defense responses against tested inappropriate powdery mildews, B. graminis f. sp. tritici and Golovinomyces orontii, were diminished in rar1 mutant plants and enhanced in rom1 mutant plants relative to the wild type. These findings indicate antagonistic activities of Rar1 and Rom1 and reveal their contribution to nonhost and race-specific resistance responses.

Amplified fragment length polymorphism linkage analysis of common buckwheat (Fagopyrum esculentum) and its wild self-pollinated relative Fagopyrum homotropicum

Common buckwheat (Fagopyrum esculentum) (2n = 2x = 16) and Fagopyrum homotropicum (2n = 2x = 16) were mated in an interspecific cross and amplified fragment length polymorphism (AFLP) linkage maps were constructed by analyzing segregation in the F2 population. Six hundred and sixty-nine bands were identified using 20 AFLP primer combinations, of which 462 (69%) segregated in the F2 population. The map of F. esculentum has eight linkage groups with 223 markers covering a total of 508.3 cM. The map of F. homotropicum has eight linkage groups with 211 markers covering 548.9 cM. There was one to one correspondence of the esculentum and homotropicum linkage groups. Three morphological markers, distylous self-incompatibility, shattering habit, and winged seed, were located on the AFLP map. Distylous self-incompatibility and shattering habit are tightly linked to each other (1.3 cM) and are located near the center of linkage group 1. Winged seed is located on linkage group 4.

Comment on "AFLP data and the origins of domesticated crops"

We review some concepts and methods of handling and using DNA fingerprinting in phylogenetic analyses related to crop domestication. Particular reference is made to AFLP markers and mode and place of einkorn, barley, and tetraploid wheat domestication in the Neolithic by human communities in the Fertile Crescent. The reconsideration of AFLP databases of domesticated and wild lines demonstrates that phylogenetic tree topologies, originally described for the three species, match closely the new results obtained by principle coordinate analyse.

Quantitative trait loci affecting growth-related traits in wild barley (Hordeum spontaneum) grown under different levels of nutrient supply

The genetic basis of phenotypic plasticity of relative growth rate (RGR), its components and associated morphological traits was studied in relation to nutrient limitation. In all, 140 F(3) lines from a cross, made between two Hordeum spontaneum (wild barley) accessions sampled in Israel, were subjected to growth analysis under two nutrient levels. Quantitative trait loci (QTLs) were detected for RGR and three of its components, leaf area ratio (LAR), specific leaf area and leaf mass fraction (LMF). Indications for close linkage (potential pleiotropy) were found, for example, for LAR and LMF. An interesting case is on chromosome 6, at which QTLs for RGR and seed mass were detected in the same region. These QTLs had opposite additive effects, supporting earlier results that plants growing from lighter seeds had a higher RGR. Only two QTLs were significant under both nutrient conditions, suggesting large QTL x environment interactions for most traits. For 21 out of 26 QTLs, however, the additive genetic effect was of identical sign in both nutrient environments, but reached the significance threshold in only one of them. Nevertheless, some QTLs detected in one of the two environments had virtually no effect in the other, and QTLs for plasticity were detected for RGR, LAR and LMF, as well as for some morphological traits. QTLs with opposite effects under high and low nutrients were not found. Thus, at the genetic level, there was no evidence for a trade-off between faster growth at high versus low nutrient levels.

A genetic analysis of relative growth rate and underlying components in Hordeum spontaneum

Species from productive and unproductive habitats differ inherently in their relative growth rate (RGR) and a wide range of correlated quantitative traits. We investigated the genetic basis of this trait complex, and specifically assessed whether it is under the control of just one or a few genes that can act as 'master switches' by simultaneously affecting a range of traits in the complex. To address this problem, we crossed two Hordeum spontaneum lines originating from two habitats that differ in productivity. The F3 offspring, in which parental alleles are present in different combinations due to recombination and segregation, was analysed for RGR and its underlying components (leaf area ratio, unit leaf rate, photosynthesis, respiration), as well as a number of other physiological and morphological parameters. For this intra-specific comparison, we found a complex of positively and negatively correlated traits, which was quite similar to what is generally observed across species. A quantitative trait loci (QTL) analysis showed three major and one minor QTL for RGR. Most other variables of the growth-trait complex showed fewer QTLs that were typically scattered over various locations on the genome. Thus, at least in H. spontaneum, we found no evidence for regulation of the trait complex by one or two master switches.

Development and validation of CAPS and AFLP markers for white rust resistance gene in Brassica juncea

White rust, caused by Albugo candida, is a very serious disease in crucifers. In Indian mustard (Brassica juncea), it can cause a yield loss to the extent of 89.9%. The locus Ac2(t) controlling resistance to white rust in BEC-144, an exotic accession of mustard, was mapped using RAPD markers. In the present study, we developed: (1) a more tightly linked marker for the white rust resistance gene, using AFLP in conjunction with bulk segregant analysis, and (2) a PCR-based cleaved amplified polymorphic sequence (CAPS) marker for the closely linked RAPD marker, OPB06(1000). The data obtained on 94 RILs revealed that the CAPS marker for OPB06(1000) and the AFLP marker E-ACC/M-CAA(350) flank the Ac2(t) gene at 3.8 cM and 6.7 cM, respectively. Validation of the CAPS marker in two different F(2) populations of crosses Varuna x BEC-144 and Varuna x BEC-286 was also undertaken, which established its utility in marker-assisted selection (MAS) for white rust resistance. The use of both flanking markers in MAS would allow only 0.25% misclassification and thus provide greater efficiency to selection.

Molecular and cytological examination of Calopogon (Orchidaceae, Epidendroideae): circumscription, phylogeny, polyploidy, and possible hybrid speciation

The orchid genus Calopogon R.Br. (Orchidaceae), native to eastern North America and the northern Caribbean, currently contains five species and up to three varieties. Using nuclear internal transcribed spacer (ITS) ribosomal DNA sequences, amplified fragment length polymorphisms (AFLPs), chloroplast DNA restriction fragments, and chromosome counts, we present a phylogenetic and taxonomic study of the genus. Calopogon multiflorus and C. pallidus are consistently sister species, but the relationships of C. barbatus, C. oklahomensis, and C. tuberosus are not as clear. In the ITS analysis C. oklahomensis is sister to C. barbatus, whereas it is sister to C. tuberosus in the plastid restriction fragment analysis. Furthermore, all species were found to have chromosome numbers of 2n = 38 and 40, with the exception of the putatively hybrid-derived C. oklahomensis with 2n = 114 and 120. The hexaploidy of the latter, plus the discrepancy in its position between the ITS and plastid restriction fragment trees, could suggest that it is of hybrid origin. However, the presence of unique morphological and molecular characters might indicate that it is either an ancient hybrid or not of hybrid derivation at all. Finally, using these molecular methods all taxa appear to generally be discrete groups, with the exception of C. tuberosus vars. latifolius and tuberosus, the former of which is best combined with the latter.

An intraspecific genetic map of velvetbean (Mucuna sp.) based on AFLP markers

Velvetbean ( Mucuna sp., n=11), a self-pollinated species, is an important legume used in tropical agricultural systems in rotation with other crops for nematode management and/or soil improvement. A genetic map of velvetbean was constructed in order to identify potential molecular markers linked to important morphological and agronomic traits that would be particularly useful for developing and improving the species. Traits such as seed coat color, pod color, and pod pubescence were among the main parameters observed in a process of genetic diversity estimation. Two slightly divergent velvetbean accessions, PI364362 and 'Edgar Farm White', a land race from Alabama, were used to make an intraspecific F(1) hybrid. Amplified fragment length polymorphism analysis (AFLP) detected an average of six polymorphic fragments per primer pair between the two parents. As expected for dominant markers, the sum of all AFLP bands from both parents was generally observed to be present in the AFLP profiles of the F(1) progeny, indicating full penetrance and the dominant nature of AFLP markers. An F(2) population was generated by self-pollinating a single F(1) plant. Using 37 AFLP primer pairs, we detected 233 polymorphic markers of which 164 (70.4%) segregated in 3:1 Mendelian ratios, while the remaining 69 (29.6%) both segregated and were scorable. The genetic linkage map constructed from this population comprised 166 markers, including two morphological traits (pod color and pod pubescence). Twenty linkage groups were found with an average distance between markers of 34.4 cM, covering a total of 687.9 cM. The linkage groups contained from 2 to 12 loci each and the distance between two consecutive loci ranged from 0 to 21.8 cM. The newly designated morphological traits pod color ( pdc) and pod pubescence ( pdp) co-segregated with each other at a distance of 4.2 cM. Two DNA markers designated ACGCAG2 and ACTCTG1 were located in the same group as pdc and pdp. The AFLP linkage map provides opportunities for use in marker-assisted selection and in the detection of loci controlling morphologically important traits.