Genetic characterization of cucumber genetic resources in the NARO Genebank indicates their multiple dispersal trajectories to the East.

KEY MESSAGE: Genotyping-by-sequencing of 723 worldwide cucumber genetic resources revealed that cucumbers were dispersed eastward via at least three distinct routes, one to Southeast Asia and two from different directions to East Asia. The cucumber (Cucumis sativus) is an economically important vegetable crop cultivated and consumed worldwide. Despite its popularity, the manner in which cucumbers were dispersed from their origin in South Asia to the rest of the world, particularly to the east, remains a mystery due to the lack of written records. In this study, we performed genotyping-by-sequencing (GBS) on 723 worldwide cucumber accessions, mainly deposited in the Japanese National Agriculture and Food Research Organization (NARO) Genebank, to characterize their genetic diversity, relationships, and population structure. Analyses based on over 60,000 genome-wide single-nucleotide polymorphisms identified by GBS revealed clear genetic differentiation between Southeast and East Asian populations, suggesting that they reached their respective region independently, not progressively. A deeper investigation of the East Asian population identified two subpopulations with different fruit characteristics, supporting the traditional classification of East Asian cucumbers into two types thought to have been introduced by independent routes. Finally, we developed a core collection of 100 accessions representing at least 93.2% of the genetic diversity present in the entire collection. The genetic relationships and population structure, their associations with geographic distribution and phenotypic traits, and the core collection presented in this study are valuable resources for elucidating the dispersal history and promoting the efficient use and management of genetic resources for research and breeding in cucumber.

Domestication of azuki bean and soybean in Japan: From the insight of archeological and molecular evidence.

Domestication of azuki bean and soybean has enabled them to acquire non-dormant seeds, non-shattering pods, and larger seed size. Seed remains of the Jomon period recently discovered at archeological sites in the Central Highlands of Japan (6,000-4,000 BP) suggest that the use of azuki bean and soybean and their increase in seed size began earlier in Japan than in China and Korea; molecular phylogenetic studies indicate that azuki bean and soybean originated in Japan. Recent identification of domestication genes indicate that the domestication traits of azuki bean and soybean were established by different mechanisms. Analyses of domestication related genes using DNA extracted from the seed remains would reveal further details about their domestication processes.

Elucidation of genetic variation and population structure of melon genetic resources in the NARO Genebank, and construction of the World Melon Core Collection.

Numerous genetic resources of major crops have been introduced from around the world and deposited in Japanese National Agriculture and Food Research Organization (NARO) Genebank. Understanding their genetic variation and selecting a representative subset ("core collection") are essential for optimal management and efficient use of genetic resources. In this study, we conducted genotyping-by-sequencing (GBS) to characterize the genetic relationships and population structure in 755 accessions of melon genetic resources. The GBS identified 39,324 single-nucleotide polymorphisms (SNPs) that are distributed throughout the melon genome with high density (one SNP/10.6 kb). The phylogenetic relationships and population structure inferred using this SNP dataset are highly associated with the cytoplasm type and geographical origin. Our results strongly support the recent hypothesis that cultivated melon was established in Africa and India through multiple independent domestication events. Finally, we constructed a World Melon Core Collection that covers at least 82% of the genetic diversity and has a wide range of geographical origins and fruit morphology. The genome-wide SNP dataset, phylogenetic relationships, population structure, and the core collection provided in this study should largely contribute to genetic research, breeding, and genetic resource preservation in melon.

Construction of genetic linkage map and genome dissection of domestication-related traits of moth bean (Vigna aconitifolia), a legume crop of arid areas.

The moth bean (Vigna aconitifolia), possibly the most primitive crop of the genus Vigna, is a highly drought- and heat-resistant legume grown in arid areas. Moth bean domestication involved phenotypic changes, including reduction of seed dormancy and pod shattering, increased organ size, and earlier flowering and maturity. However, the genetics of the domestication process in moth bean is not known. In this study, we constructed a genetic linkage map for moth bean and used the map to identify quantitative trait loci (QTL) for domestication-related traits of an F2 population of 188 individuals produced from a cross of wild moth bean (TN67) and cultivated moth bean (ICPMO056). The genetic linkage map comprised 11 linkage groups (LG) of 172 simple sequence repeat markers and spanned a total length of 1016.8 centiMorgan (cM), with an average marker distance of 7.34 cM. A comparative genome analysis showed high genome synteny between moth bean and mungbean (Vigna radiata), adzuki bean (Vigna angularis), rice bean (Vigna umbellata), and yardlong bean (Vigna unguiculata). In total, 50 QTLs and 3 genes associated with 20 domestication-related traits were identified. Most of the QTLs belonged to five LGs (1, 2, 4, 7, and 10). Key traits related to domestication such as seed dormancy and pod shattering were controlled by large-effect QTLs (PVE > 20%) with one or two minor QTLs, whereas all other traits were controlled by one-seven minor QTLs, apart from seed weight, which was controlled by one major and seven minor QTLs. These results suggest that a small number of mutations with large phenotypic effects have contributed to the domestication of the moth bean. Comparative analysis of QTLs with related Vigna crops revealed that there are several domestication-related large-effect QTLs that had not been used in moth bean domestication. This study provides a basic genetic map and identified genome regions associated with domestication-related traits, which will be useful for the genetic improvement of the moth bean and related Vigna species.

Multiple organ gigantism caused by mutation in VmPPD gene in blackgram (Vigna mungo).

Seed size is one of the most important traits in leguminous crops. We obtained a recessive mutant of blackgram that had greatly enlarged leaves, stems and seeds. The mutant produced 100% bigger leaves, 50% more biomass and 70% larger seeds though it produced 40% less number of seeds. We designated the mutant as multiple-organ-gigantism (mog) and found the mog phenotype was due to increase in cell numbers but not in cell size. We also found the mog mutant showed a rippled leaf (rl) phenotype, which was probably caused by a pleiotropic effect of the mutation. We performed a map-based cloning and successfully identified an 8 bp deletion in the coding sequence of VmPPD gene, an orthologue of Arabidopsis PEAPOD (PPD) that regulates arrest of cell divisions in meristematic cells. We found no other mutations in the neighboring genes between the mutant and the wild type. We also knocked down GmPPD genes and reproduced both the mog and rl phenotypes in soybean. Controlling PPD genes to produce the mog phenotype is highly valuable for breeding since larger seed size could directly increase the commercial values of grain legumes.

The Vigna Genome Server, 'VigGS': A Genomic Knowledge Base of the Genus Vigna Based on High-Quality, Annotated Genome Sequence of the Azuki Bean, Vigna angularis (Willd.) Ohwi & Ohashi.

The genus Vigna includes legume crops such as cowpea, mungbean and azuki bean, as well as >100 wild species. A number of the wild species are highly tolerant to severe environmental conditions including high-salinity, acid or alkaline soil; drought; flooding; and pests and diseases. These features of the genus Vigna make it a good target for investigation of genetic diversity in adaptation to stressful environments; however, a lack of genomic information has hindered such research in this genus. Here, we present a genome database of the genus Vigna, Vigna Genome Server ('VigGS', http://viggs.dna.affrc.go.jp), based on the recently sequenced azuki bean genome, which incorporates annotated exon-intron structures, along with evidence for transcripts and proteins, visualized in GBrowse. VigGS also facilitates user construction of multiple alignments between azuki bean genes and those of six related dicot species. In addition, the database displays sequence polymorphisms between azuki bean and its wild relatives and enables users to design primer sequences targeting any variant site. VigGS offers a simple keyword search in addition to sequence similarity searches using BLAST and BLAT. To incorporate up to date genomic information, VigGS automatically receives newly deposited mRNA sequences of pre-set species from the public database once a week. Users can refer to not only gene structures mapped on the azuki bean genome on GBrowse but also relevant literature of the genes. VigGS will contribute to genomic research into plant biotic and abiotic stresses and to the future development of new stress-tolerant crops.

Reciprocal translocation identified in Vigna angularis 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.

QTL mapping for salt tolerance and domestication-related traits in Vigna marina subsp. oblonga, a halophytic species.

QTL mapping in F2 population [V. luteola × V. marina subsp. oblonga] revealed that the salt tolerance in V. marina subsp. oblonga is controlled by a single major QTL. The habitats of beach cowpea (Vigna marina) are sandy beaches in tropical and subtropical regions. As a species that grows closest to the sea, it has potential to be a gene source for breeding salt-tolerant crops. We reported here for the first time, quantitative trait loci (QTLs) mapping for salt tolerance in V. marina. A genetic linkage map was constructed from an F2 population of 120 plants derived from an interspecific cross between V. luteola and V. marina subsp. oblonga. The map comprised 150 SSR markers. The markers were clustered into 11 linkage groups spanning 777.6 cM in length with a mean distance between the adjacent markers of 5.59 cM. The F2:3 population was evaluated for salt tolerance under hydroponic conditions at the seedling and developmental stages. Segregation analysis indicated that salt tolerance in V. marina is controlled by a few genes. Multiple interval mapping consistently identified one major QTL which can explain about 50% of phenotypic variance. The flanking markers may facilitate transfer of the salt tolerance allele from V. marina subsp. oblonga into related Vigna crops. The QTL for domestication-related traits from V. marina are also discussed.

Molecular characterization of an isoamylase 1-type starch debranching enzyme (DBEI) in grain amaranth (Amaranthus cruentus L.).

The purpose of this study was to characterize the molecular profile of a starch debranching enzyme (DBE) in grain amaranth. A cDNA clone that encodes a putative DBE was isolated from amaranth perisperm and then sequenced. This amaranth DBE appears to be an ISA1-type DBE (DBEI), based on its substrate specificity and the sequence similarity between the 2,391-bp cDNA clone and ISA1 s from potato and Arabidopsis. The mature DBEI of amaranth consists of 796 amino acids (90.5 kDa). We analyzed the transcript levels of the DBEI gene in amaranth seeds during various developmental stages and in plant tissues by qRT-PCR and RT-PCR analyses. The transcript levels of the DBEI gene rapidly increased at the middle stage of seed maturation. This result indicates that the enzyme encoded by the amaranth DBEI gene plays an important role in starch accumulation throughout the seed during the middle stage of seed development. We detected DBEI transcripts in storage and non-storage tissues. At the six-leaf stage, there were high levels of the DBEI transcripts in leaves, petioles, and the stem, and low levels in the root. Therefore, we suggest that the DBEI expression is not specific to non-storage and/or storage tissues. This summary of the basic characteristics of the DBEI gene will contribute to further studies on starch biosynthesis in Amaranthus.

NIASGBdb: NIAS Genebank databases for genetic resources and plant disease information.

The National Institute of Agrobiological Sciences (NIAS) is implementing the NIAS Genebank Project for conservation and promotion of agrobiological genetic resources to contribute to the development and utilization of agriculture and agricultural products. The project's databases (NIASGBdb; http://www.gene.affrc.go.jp/databases_en.php) consist of a genetic resource database and a plant diseases database, linked by a web retrieval database. The genetic resources database has plant and microorganism search systems to provide information on research materials, including passport and evaluation data for genetic resources with the desired properties. To facilitate genetic diversity research, several NIAS Core Collections have been developed. The NIAS Rice (Oryza sativa) Core Collection of Japanese Landraces contains information on simple sequence repeat (SSR) polymorphisms. SSR marker information for azuki bean (Vigna angularis) and black gram (V. mungo) and DNA sequence data from some selected Japanese strains of the genus Fusarium are also available. A database of plant diseases in Japan has been developed based on the listing of common names of plant diseases compiled by the Phytopathological Society of Japan. Relevant plant and microorganism genetic resources are associated with the plant disease names by the web retrieval database and can be obtained from the NIAS Genebank for research or educational purposes.

De novo assembly of the complete organelle genome sequences of azuki bean (Vigna angularis) using next-generation sequencers.

Since chloroplasts and mitochondria are maternally inherited and have unique features in evolution, DNA sequences of those organelle genomes have been broadly used in phylogenetic studies. Thanks to recent progress in next-generation sequencer (NGS) technology, whole-genome sequencing can be easily performed. Here, using NGS data generated by Roche GS Titanium and Illumina Hiseq 2000, we performed a hybrid assembly of organelle genome sequences of Vigna angularis (azuki bean). Both the mitochondrial genome (mtDNA) and the chloroplast genome (cpDNA) of V. angularis have very similar size and gene content to those of V. radiata (mungbean). However, in structure, mtDNA sequences have undergone many recombination events after divergence from the common ancestor of V. angularis and V. radiata, whereas cpDNAs are almost identical between the two. The stability of cpDNAs and the variability of mtDNAs was further confirmed by comparative analysis of Vigna organelles with model plants Lotus japonicus and Arabidopsis thaliana.

Domesticating Vigna stipulacea: Chromosome-Level genome assembly reveals VsPSAT1 as a candidate gene decreasing hard-seededness.

To increase food production under the challenges presented by global climate change, the concept of de novo domestication-utilizing stress-tolerant wild species as new crops-has recently gained considerable attention. We had previously identified mutants with desired domestication traits in a mutagenized population of the legume Vigna stipulacea Kuntze (minni payaru) as a pilot for de novo domestication. Given that there are multiple stress-tolerant wild legume species, it is important to establish efficient domestication processes using reverse genetics and identify the genes responsible for domestication traits. In this study, we identified VsPSAT1 as the candidate gene responsible for decreased hard-seededness, using a Vigna stipulacea isi2 mutant that takes up water from the lens groove. Scanning electron microscopy and computed tomography revealed that the isi2 mutant has lesser honeycomb-like wax sealing the lens groove than the wild-type, and takes up water from the lens groove. We also identified the pleiotropic effects of the isi2 mutant: accelerating leaf senescence, increasing seed size, and decreasing numbers of seeds per pod. While doing so, we produced a V. stipulacea whole-genome assembly of 441 Mbp in 11 chromosomes and 30,963 annotated protein-coding sequences. This study highlights the importance of wild legumes, especially those of the genus Vigna with pre-existing tolerance to biotic and abiotic stresses, for global food security during climate change.

Unique Salt-Tolerance-Related QTLs, Evolved in Vigna riukiuensis (Na+ Includer) and V. nakashimae (Na+ Excluder), Shed Light on the Development of Super-Salt-Tolerant Azuki Bean (V. angularis) Cultivars.

Wild relatives of crops have the potential to improve food crops, especially in terms of improving abiotic stress tolerance. Two closely related wild species of the traditional East Asian legume crops, Azuki bean (Vigna angularis), V. riukiuensis "Tojinbaka" and V. nakashimae "Ukushima" were shown to have much higher levels of salt tolerance than azuki beans. To identify the genomic regions responsible for salt tolerance in "Tojinbaka" and "Ukushima", three interspecific hybrids were developed: (A) azuki bean cultivar "Kyoto Dainagon" × "Tojinbaka", (B) "Kyoto Dainagon" × "Ukushima" and (C) "Ukushima" × "Tojinbaka". Linkage maps were developed using SSR or restriction-site-associated DNA markers. There were three QTLs for "percentage of wilt leaves" in populations A, B and C, while populations A and B had three QTLs and population C had two QTLs for "days to wilt". In population C, four QTLs were detected for Na+ concentration in the primary leaf. Among the F2 individuals in population C, 24% showed higher salt tolerance than both wild parents, suggesting that the salt tolerance of azuki beans can be further improved by combining the QTL alleles of the two wild relatives. The marker information would facilitate the transfer of salt tolerance alleles from "Tojinbaka" and "Ukushima" to azuki beans.

The genetics of domestication of yardlong bean, Vigna unguiculata (L.) Walp. ssp. unguiculata cv.-gr. sesquipedalis.

BACKGROUND AND AIMS: The genetics of domestication of yardlong bean [Vigna unguiculata (L.) Walp. ssp. unguiculata cv.-gr. sesquipedalis] is of particular interest because the genome of this legume has experienced divergent domestication. Initially, cowpea was domesticated from wild cowpea in Africa; in Asia a vegetable form of cowpea, yardlong bean, subsequently evolved from cowpea. Information on the genetics of domestication-related traits would be useful for yardlong bean and cowpea breeding programmes, as well as comparative genome study among members of the genus Vigna. The objectives of this study were to identify quantitative trait loci (QTLs) for domestication-related traits in yardlong bean and compare them with previously reported QTLs in closely related Vigna. METHODS: Two linkage maps were developed from BC(1)F(1) and F(2) populations from the cross between yardlong bean (V. unguiculata ssp. unguiculata cv.-gr. sesquipedalis) accession JP81610 and wild cowpea (V. unguiculata ssp. unguiculata var. spontanea) accession TVnu457. Using these linkage maps, QTLs for 24 domestication-related traits were analysed and mapped. QTLs were detected for traits related to seed, pod, stem and leaf. KEY RESULTS: Most traits were controlled by between one and 11 QTLs. QTLs for domestication-related traits show co-location on several narrow genomic regions on almost all linkage groups (LGs), but especially on LGs 3, 7, 8 and 11. Major QTLs for sizes of seed, pod, stem and leaf were principally located on LG7. Pleiotropy or close linkage of genes for the traits is suggested in these chromosome regions. CONCLUSIONS: This is the first report of QTLs for domestication-related traits in yardlong bean. The results provide a foundation for marker-assisted selection of domestication-related QTLs in yardlong bean and enhance understanding of domestication in the genus Vigna.

An SSR-based linkage map of yardlong bean (Vigna unguiculata (L.) Walp. subsp. unguiculata Sesquipedalis Group) and QTL analysis of pod length.

Yardlong bean (Vigna unguiculata (L.) Walp. subsp. unguiculata Sesquipedalis Group) (2n = 2x = 22) is one of the most important vegetable legumes of Asia. The objectives of this study were to develop a genetic linkage map of yardlong bean using SSR makers from related Vigna species and to identify QTLs for pod length. The map was constructed from 226 simple sequence repeat (SSR) markers from cowpea (Vigna unguiculata (L.) Walp. subsp. unguiculata Unguiculata Group), azuki bean (Vigna angularis (Willd.) Ohwi & Ohashi), and mungbean (Vigna radiata (L.) Wilczek) in a BC(1)F(1) ((JP81610 × TVnu457) × JP81610) population derived from the cross between yardlong bean accession JP81610 and wild cowpea (Vigna unguiculata subsp. unguiculata var. spontanea) accession TVnu457. The markers were clustered into 11 linkage groups (LGs) spanning 852.4 cM in total length with a mean distance between adjacent markers of 3.96 cM. All markers on LG11 showed segregation distortion towards the homozygous yardlong bean JP81610 genotype. The markers on LG11 were also distorted in the rice bean (Vigna umbellata (Thunb.) Ohwi & Ohashi) map, suggesting the presence of common segregation distortion factors in Vigna species on this LG. One major and six minor QTLs were identified for pod length variation between yardlong bean and wild cowpea. Using flanking markers, six of the seven QTLs were confirmed in an F(2) population of JP81610 × TVnu457. The molecular linkage map developed and markers linked to pod length QTLs would be potentially useful for yardlong bean and cowpea breeding.

Evaluation of soybean germplasm conserved in NIAS genebank and development of mini core collections.

Genetic variation and population structure among 1603 soybean accessions, consisted of 832 Japanese landraces, 109 old and 57 recent Japanese varieties, 341 landrace from 16 Asian countries and 264 wild soybean accessions, were characterized using 191 SNP markers. Although gene diversity of Japanese soybean germplasm was slight lower than that of exotic soybean germplasm, population differentiation and clustering analyses indicated clear genetic differentiation among Japanese cultivated soybeans, exotic cultivated soybeans and wild soybeans. Nine hundred ninety eight Japanese accessions were separated to a certain extent into groups corresponding to their agro-morphologic characteristics such as photosensitivity and seed characteristics rather than their geographical origin. Based on the assessment of the SNP markers and several agro-morphologic traits, accessions that retain gene diversity of the whole collection were selected to develop several soybean sets of different sizes using an heuristic approach; a minimum of 12 accessions can represent the observed gene diversity; a mini-core collection of 96 accession can represent a major proportion of both geographic origin and agro-morphologic trait variation. These selected sets of germplasm will provide an effective platform for enhancing soybean diversity studies and assist in finding novel traits for crop improvement.

New Sources of Resistance to Cadophora gregata f. sp. adzukicola and Fusarium oxysporum f. sp. adzukicola in Vigna spp.

Adzuki bean brown stem rot (BSR), caused by Cadophora gregata f. sp. adzukicola, and adzuki bean Fusarium wilt (AFW), caused by Fusarium oxysporum f. sp. adzukicola, are serious problems in Hokkaido, Japan, and have been managed using cultivars with multiple resistance. However, a limited number of adzuki bean varieties are resistant to these pathogens because of the frequent appearance of new races; thus, new sources of resistance have been sought in related Vigna spp., particularly in the section Angulares to which adzuki bean belongs. An analysis of selected Vigna accessions (JP81231 to JP235420) conserved in the Genebank of the National Institute of Agrobiological Sciences, Tsukuba, Japan, revealed wide variation in resistance spectra and resistance combinations, and eight disease response groups (A to H) were identified. Four of eight were newly detected response groups, suggesting the existence of novel resistance genes. Of 252 accessions from 26 species, 28 accessions in Vigna angularis var. nipponensis, V. hirtella, V. minima, and V. tenuicaulis (section Angulares) from group D, which were cross-compatible with adzuki bean, are expected to be potential sources of multiple resistance genes. They were resistant to all races of BSR and AFW pathogens examined.

Molecular Analysis of Genetic Diversity and Structure of the Lablab (Lablab purpureus (L.) Sweet) Gene Pool Reveals Two Independent Routes of Domestication.

In this study, genetic diversity and structure of 474 cultivated and 19 wild lablab (Lablab purpureus) accessions. were determined using 15 nuclear and 6 chloroplast SSR markers. The overall gene diversity was relatively low (0.3441). Gene diversity in the wild accessions (0.6059) was about two-folds greater than that in the cultivated accessions. In the wild accessions, gene diversity was greatest in the southern Africa, followed by East Africa. In the cultivated accessions, gene diversity was highest in the eastern Africa. The results suggested that South Africa is the center of origin and East Africa is the center of domestication of lablab. Different cluster analyses showed that 2-seeded-pod cultivated accessions (ssp. uncinatus) were clustered with wild accessions and that 4-(6)-seeded-pod cultivated accessions (ssp. purpureus and bengalensis) were intermingled. UPGMA tree suggested that ssp. purpureus and bengalensis were domesticated from 4-seeded-pod wild accessions of southern Africa. Haplotype network analysis based on nuclear SSRs revealed two domestication routes; the ssp. uncinatus is domesticated from 2-seeded-pod wild lablab (wild spp. uncinatus) from East Africa (Ethiopia), while the ssp. purpureus and bengalensis are domesticated from 4-seeded-pod wild lablab from Central Africa (Rwanda). These results are useful for understanding domestication and revising classification of lablab.

The genetics of domestication of rice bean, Vigna umbellata.

BACKGROUND AND AIMS: The Asian genus Vigna, to which four cultivated species (rice bean, azuki bean, mung bean and black gram) belong, is suitable for comparative genomics. The aims were to construct a genetic linkage map of rice bean, to identify the genomic regions associated with domestication in rice bean, and to compare these regions with those in azuki bean. METHODS: A genetic linkage map was constructed by using simple sequence repeat and amplified fragment length polymorphism markers in the BC(1)F(1) population derived from a cross between cultivated and wild rice bean. Using this map, 31 domestication-related traits were dissected into quantitative trait loci (QTLs). The genetic linkage map and QTLs of rice bean were compared with those of azuki bean. KEY RESULTS: A total of 326 markers converged into 11 linkage groups (LGs), corresponding to the haploid number of rice bean chromosomes. The domestication-related traits in rice bean associated with a few major QTLs distributed as clusters on LGs 2, 4 and 7. A high level of co-linearity in marker order between the rice bean and azuki bean linkage maps was observed. Major QTLs in rice bean were found on LG4, whereas major QTLs in azuki bean were found on LG9. CONCLUSIONS: This is the first report of a genetic linkage map and QTLs for domestication-related traits in rice bean. The inheritance of domestication-related traits was so simple that a few major QTLs explained the phenotypic variation between cultivated and wild rice bean. The high level of genomic synteny between rice bean and azuki bean facilitates QTL comparison between species. These results provide a genetic foundation for improvement of rice bean; interchange of major QTLs between rice bean and azuki bean might be useful for broadening the genetic variation of both species.