Linkage analysis of rice bacterial blight resistance gene xa20 in XM6, a mutant line from IR24

Bacterial blight caused by Xanthomonas oryzae pv. oryzae (Xoo) is an important disease constraining rice (Oryza sativa L.) production worldwide. The XM6 line was induced by N-methyl-N-nitrosourea from IR24, an Indica cultivar that is susceptible to Philippine and Japanese Xoo races. XM6 was confirmed to carry a recessive gene named xa20, resistant to six Philippine and five Japanese Xoo races. The chromosomal gene location was found using 10 plants with the shortest lesion length in an F₂ population consisting of 298 plants from a susceptible Japonica variety Koshihikari × XM6. Analysis using PCR-based DNA markers covering the whole rice genome indicated the gene as located on the distal region of the long arm of chromosome 3. The IKC3 line carries IR24 genetic background with Koshihikari fragment on chromosome 3 where a resistance gene was thought to be located. The F₂ population from IKC3 × XM6 clearly showed a bimodal distribution separating resistant and susceptible plants. Further linkage analysis conducted using this F₂ population revealed that xa20 is located within the 0.8 cM region flanked by DNA markers KIC3-33.88 (33.0 Mb) and KIC3-34.06 (33.2 Mb). This study yields important findings for resistance breeding and for the genetic mechanism of Xoo resistance.     

A novel aphid resistance locus in cowpea identified by combining SSR and SNP markers

The utility of combining simple sequence repeat (SSR) and single nucleotide polymorphism (SNP) marker genotyping was determined for genetically mapping a novel aphid (Aphis craccivora) resistance locus in cowpea breeding line SARC 1‐57‐2 and for introgressing the resistance into elite cultivars by marker‐assisted backcrossing (MABC). The locus was tagged with codominant SSR marker CP 171F/172R with a recombination fraction of 5.91% in an F₂ population from ‘Apagbaala’ x SARC 1‐57‐2. A SNP‐genotyped biparental recombinant inbred line population was genotyped for CP 171F/172R, which was mapped to position 11.5 cM on linkage group (LG) 10 (physical position 30.514 Mb on chromosome Vu10). Using CP 171F/172R for foreground selection and a KASP‐SNP‐based marker panel for background selection in MABC, the resistance from SARC 1‐57‐2 was introduced into elite susceptible cultivar ‘Zaayura’. Five BC₄F₃ lines of improved ‘Zaayura’ that were isogenic except for the resistance locus region had phenotypes similar to SARC 1‐57‐2. This study identified a novel aphid resistance locus and demonstrated the effectiveness of integrating SSR and SNP markers for trait mapping and marker‐assisted breeding.     

Characterization of a mini core collection of Japanese wheat varieties using single-nucleotide polymorphisms generated by genotyping-by-sequencing

A core collection of Japanese wheat varieties (JWC) consisting of 96 accessions was established based on their passport data and breeding pedigrees. To clarify the molecular basis of the JWC collection, genome-wide single-nucleotide polymorphism (SNP) genotyping was performed using the genotyping-by-sequencing (GBS) approach. Phylogenetic tree and population structure analyses using these SNP data revealed the genetic diversity and relationships among the JWC accessions, classifying them into four groups; “varieties in the Hokkaido area”, “modern varieties in the northeast part of Japan”, “modern varieties in the southwest part of Japan” and “classical varieties including landraces”. This clustering closely reflected the history of wheat breeding in Japan. Furthermore, to demonstrate the utility of the JWC collection, we performed a genome-wide association study (GWAS) for three traits, namely, “days to heading in autumn sowing”, “days to heading in spring sowing” and “culm length”. We found significantly associated SNP markers with each trait, and some of these were closely linked to known major genes for heading date or culm length on the genetic map. Our study indicates that this JWC collection is a useful set of germplasm for basic and applied research aimed at understanding and utilizing the genetic diversity among Japanese wheat varieties.     

QTL analysis of black rot resistance in cabbage using newly developed EST-SNP markers

One hundred sixty-one EST-SNP markers were newly developed for analysis of QTLs for resistance to black rot caused by Xanthomonas campestris pv. campestris by determining EST sequences of a resistant line obtained from cabbage ‘Early Fuji’ and a susceptible broccoli line. A linkage map consisting of nine linkage groups was constructed with a total of 209 markers, including these new SNP markers and previously reported DNA markers. F₂ plants grown in a field for 1 month were inoculated by spraying bacteria of race 1, and disease severity of each plant was recorded. Three QTLs, i.e., QTL-1, QTL-2, and QTL-3, were detected on linkage group C2, C4 and C5, respectively. QTL-1, which showed the highest LOD score and additive effect, was again detected in another F₂ population used the next year, suggesting QTL-1 to be a major QTL. QTL-2 and QTL-3 could be minor QTLs influenced by environmental factors. The genomic region harboring QTL-1 showed synteny with a region from 5.3 to 7.4 Mb from the short arm end of chromosome 5 of Arabidopsis thaliana, which is rich in TIR-NBS-LRR family genes. The identified SNP markers in QTL-1 are considered to be useful in marker-assisted selection for black rot resistance in Brassica oleracea lines.     

Screening and genetic analysis of resistance to peanut stunt virus in soybean: identification of the putative Rpsv1 resistance gene

The peanut stunt virus (PSV) causes yield losses in soybean and reduced seed quality due to seed mottling. The objectives of this study were to determine the phenotypic reactions of soybean germplasms to inoculation with two PSV isolates (PSV-K, PSV-T), the inheritance of PSV resistance in soybean cultivars, and the locus of the PSV resistance gene. We investigated the PSV resistance of 132 soybean cultivars to both PSV isolates; of these, 73 cultivars exhibited resistance to both PSV isolates. Three resistant cultivars (Harosoy, Tsurunotamago 1 and Hyuga) were crossed with the susceptible cultivar Enrei. The crosses were evaluated in the F₁, F₂ and F_2:3 generations for their reactions to inoculation with the two PSV isolates. In an allelism test, we crossed Harosoy and Tsurunotamago 1 with the resistant cultivar Hyuga. The results revealed that PSV resistance in these cultivars is controlled by a single dominant gene at the same locus. We have proposed Rpsv1, as the name of the resistance gene in Hyuga. We also constructed a linkage map using recombinant inbred lines between Hyuga × Enrei using 176 SSR markers. We mapped Rpsv1 near the Satt435 locus on soybean chromosome 7.     

Molecular mapping of quantitative trait loci for ascochyta blight and botrytis grey mould resistance in an inter-specific cross in chickpea (Cicer arietinum L.) using genotyping by sequencing

Ascochyta blight (AB) and botrytis grey mould (BGM) are the most devastating fungal diseases of chickpea worldwide. The wild relative of chickpea, C. reticulatum acc. ILWC 292 was found resistant to BGM whereas, GPF2 (Cicer arietinum L.) is resistant to AB. A total of 187 F₈ Recombinant Inbred Lines (RILs) developed from an inter-specific cross of GPF2 × C. reticulatum acc. ILWC 292 were used to identify quantitative trait loci (QTLs) responsible for resistance to AB and BGM. RILs along with parents were evaluated under artificial epiphytotic field/laboratory conditions for two years. Highly significant differences (P < 0.001) were observed for reaction to both pathogens in both years. Parents and RILs were genotyped-by-sequencing to identify genome wide single nucleotide polymorphism (SNPs). A total of 1365 filtered and parental polymorphic SNPs were used for linkage map construction, of which, 673 SNPs were arranged on eight linkage groups. Composite interval mapping revealed three QTLs for AB and four QTLs for BGM resistance. Out of which, two QTLs for AB and three QTLs for BGM were consistent in both years. These QTLs can be targeted for further fine mapping for deployment of resistance to AB and BGM in elite chickpea cultivars using marker-assisted-selection.     

Two microsatellite markers flanking a dominant gene for resistance to soybean cust nematode race 3

The purpose of this work was to identifymicrosatellite markers linked to a gene forresistance to Heterodera glycinesIchinohe (Soybean Cyst Nematode – SCN) insoybean cultivar Hartwig. ABC₁F₂ mapping population derivedfrom a cross between Hartwig (resistant)and the Brazilian soybean line Y23(susceptible) was used. About 200microsatellite or simple sequence repeat(SSR) primer pairs were tested in a bulkedsegregant analysis (BSA). Those thatshowed clear polymorphisms were amplifiedin the BC₁F₂ population, whichhad been previously inoculated andevaluated for resistance/susceptibility toSCN Race 3. Three SSR markers linked toSCN resistance were detected in thepopulation. Two of them, Satt 038 and Satt163, flanking a dominant resistant gene(d/a = –0.90), explained 37% of thephenotypic variance. This gene was mappedat the edge of molecular linkage group G. Broad and narrow sense heritabilities wereestimated to be 50.54% and 37.73%,respectively. A selection efficiency of91.18% was obtained with the simultaneoususe of the two markers. The identified SSRmarkers will be useful tools for assistingthe selection of homozygous genotypes andfor expediting the introgression of the SCNresistance locus from cv. Hartwig tosoybean elite cultivars.     

Genetic analysis and identification of DNA markers linked to a novel Phytophthora sojae resistance gene in the Japanese soybean cultivar Waseshiroge

The Glycine max (L.) Merr. cultivar Waseshiroge is highly resistant to several races of Phytophthora sojae in Japan. In order to determine which Rps gene might be present in Waseshiroge, 15 differential cultivars were challenged with 12 P. sojae isolates. None had a reaction pattern identical to that of Waseshiroge, indicating that Waseshiroge may contain a novel Rps gene. In order to characterize the inheritance of Waseshiroge resistance to P. sojae isolates, 98 F₂ progeny and 94 F_7:8 lines were produced from crosses between the susceptible cultivar Tanbakuro and Waseshiroge. Chi-square tests indicated that segregation fit a 3:1 ratio for resistance and susceptibility in two F₂ sub-populations of 42 and 56 seedlings. This and a 46.27:1.46:46.27 (or 63:2:63) ratio for resistance: segregation: susceptibility among the 94 F_7:8 lines indicated that resistance was controlled by a single dominant gene. DNA analyses were carried out on Tanbakuro, Waseshiroge and the 94 F_7:8 lines, and a linkage map was constructed with 17 SSR markers and nine new primer pairs that amplify marker loci linked to Rps1 on soybean chromosome 3 (linkage group N). The closest markers, Satt009 and T000304487l, map to locations 0.9 and 1.6 cM on each side of the estimated position of the Rps gene, respectively. The results showed that the Rps gene in Waseshiroge is either allelic to Rps1, or resides at a tightly linked locus in a gene cluster. A three-way-contingency table analysis indicated that marker-assisted selection with the two flanking markers could be used in the development of new resistant cultivars.     

QTL analysis of resistance to powdery mildew in hop (<Emphasis Type="Italic">Humulus lupulus</Emphasis> L.)

Hop with powdery mildew [HPM: caused by Podosphaera macularis (Wallr.) U. Braun & S. Takam.] results in significant losses in hop production by reducing yield and quality. One means of increasing yield and quality is the production of resistant hop lines. Breeding for resistance can be significantly improved and accelerated by use of marker-assisted selection. The objective of this preliminary study was to identify QTLs and markers for genetic resistance to HPM. A bi-parental mapping population between the resistant line “Newport” and susceptible line ‘21110M’. Phenotypic data was scored under controlled greenhouse conditions. Significant differences among offspring were observed and disease resistance did not follow a distinct binomial distribution, suggesting quantitative genetic control. Genotyping-by-sequencing resulted in approximately 375 K SNP markers, which were filtered down to 2263 markers mapped to 10 linkage groups. Interval Mapping identified four QTLs with one on linkage group 1 and three located on linkage group 6. Composite interval mapping identified three QTLs, all located on linkage group 6. Mixed linear models identified 15 markers associated with expression of resistance to HPM. Three of these 15 SNPs were also identified in QTL-CIM analysis. Evaluation of the scaffolds containing the significant SNP markers identified seven putative genes—several of which appear involved in disease resistance in other plant species. The SNP markers identified in this study still require validation in unrelated populations prior to implementation in breeding programs.     

Identification of soybean mosaic virus resistance alleles in Jindou 1 soybean

Jindou 1 is a soybean cultivar from China, which is resistant to all seven Soybean mosaic virus (SMV) strains identified in the U.S. An F₂ population consisted of 91 plants derived from the cross Jindou 1× Essex were used for genetic analysis of SMV resistance. The segregation analysis of the F₂ population indicated that Jindou 1 contained a dominant gene for SMV G1 resistance. Co-segregating analyses showed that the gene was tightly linked to a SNP marker, 3gG2-snp2, which was derived from the SMV Rsv1 candidate gene 3gG2, with a genetic distance 1.1 cM and the gene was independent to the single nucleotide polymorphism (SNP) marker, Barc-040713-07825, which is linked to Rsv4 on chromosome 2 (linkage group D1b). The gene in Jindou 1 was assumed to be Rsv1-y based on an Rsv1-specific PCR-based marker 3gG2-f1/r1 and the SNP maker 3gG2-snp1. Beside Rsv1-y, Jindou 1 was postulated to have Rsv3 based on the reaction pattern to 7 SMV strains G1–G7 in comparisons with the patterns in SMV differential lines.     

The transformation of the photo-thermo sensitive genic male-sterile line 261S of rice via an expression vector containing the anti-Waxy gene

Transgenic photo-thermo sensitive genic male sterility Oryza sativa L. cv. “261S” plants with the anti-Waxy gene were successfully obtained using an Agrobacterium tumefaciens-mediated co-transformation method. Marker-free homozygous transgenic lines with the anti-Waxy gene were obtained. The setting seed rates of the transgenic plants via self-pollination or via crossing with the restorer line WX99075 rice and the 1000-grain weight of the transgenic plants and the F₂ hybrid seeds obtained by crossing the transgenic or non-transgenic plants with the restorer line WX99075 rice, and the number of panicles of the transgenic plants and yields of the F₂ hybrid rice, were analysed. Quality indexes of the transgenic plants and of the F₂ hybrid seeds were analysed. Our researches results indicate that hybrid female and hybrid descendant edibility could be improved via the introduction of the anti-Waxy gene, but the grain yields of the reserve seeds via self-pollination of the transgenic photo-thermo sensitive genic sterile lines and of the hybrid rice were not affected.     

Pathogenic diversity of Phytophthora sojae and breeding strategies to develop Phytophthora-resistant soybeans

Phytophthora stem and root rot, caused by Phytophthora sojae, is one of the most destructive diseases of soybean [Glycine max (L.) Merr.], and the incidence of this disease has been increasing in several soybean-producing areas around the world. This presents serious limitations for soybean production, with yield losses from 4 to 100%. The most effective method to reduce damage would be to grow Phytophthora-resistant soybean cultivars, and two types of host resistance have been described. Race-specific resistance conditioned by single dominant Rps (“resistance to Phytophthora sojae”) genes and quantitatively inherited partial resistance conferred by multiple genes could both provide protection from the pathogen. Molecular markers linked to Rps genes or quantitative trait loci (QTLs) underlying partial resistance have been identified on several molecular linkage groups corresponding to chromosomes. These markers can be used to screen for Phytophthora-resistant plants rapidly and efficiently, and to combine multiple resistance genes in the same background. This paper reviews what is currently known about pathogenic races of P. sojae in the USA and Japan, selection of sources of Rps genes or minor genes providing partial resistance, and the current state and future scope of breeding Phytophthora-resistant soybean cultivars.     

Development of novel clubroot resistant rapeseed lines (Brassica napus L.) effective against Japanese field isolates by marker assisted selection

Clubroot is an important disease infectible to cruciferous plants and a major threat to rapeseed production in Japan. However, no clubroot resistant rapeseed cultivars have been released. We surveyed pathotype variation of six isolates collected from rapeseed fields and found they were classified as pathotype groups 2 and 4 using Japanese F₁ Chinese cabbage cultivars. We produced the resynthesized clubroot resistant Brassica napus harboring two resistant loci, Crr1 and Crr2, by interspecific crossing and developed resistant rapeseed lines for southern and northern regions by marker-assisted selection and backcrossing. We improved the DNA marker for erucic acid content to remove linkage drag between Crr1 and high erucic acid content and successfully selected lines with clubroot resistance and zero erucic acid for northern regions. A novel line, ‘Tohoku No. 106’, suitable for southern regions showed stable resistance against all six isolates and high performance in infested fields. We conclude that Crr1 and Crr2 are important genes for CR rapeseed breeding and marker-assisted selection is effective in improving clubroot resistance.     

Molecular mapping and identification of QTL's associated to oat crown rust partial resistance

Summary Molecular mapping is a promising strategy for studying and understanding traits with complex genetic control, such as partial resistance to oat crown rust. The objectives of this research were to develop molecular maps from the progenies of the cross UFRGS7 (susceptible) × UFRGS910906 (partially resistant) and to identify QTLs (quantitative trait loci) associated to partial resistance to oat crown rust in two generations of that population.DNA of 86 genotypes of the F₂ and 90 genotypes of the F₆ UFRGS7 × UFRGS910906 population were used to generate AFLP markers. Molecular maps were constructed using Mapmaker Exp. 3.0 and QTLs for partial resistance to oat crown rust were identified with Mapmaker/QTL software. Five hundred and fifty seven markers in the F₂ and 243 markers in the F₆ generations were identified. The F₂ map integrated 250 markers in 37 linkage groups. The F₆ map integrated 86 markers in 17 linkage groups.Five QTLs were identified for partial resistance to oat crown rust in the F₂ generation and three QTLs in the F₆. The QTL identified on F₆ through the PaaaMctt340 AFLP marker showed consistency across two environments and two generations (F₄ and F₆), and appear to have potential for marker-assisted selection in oat.     

Development of EST-SSR markers and construction of a linkage map in faba bean (Vicia faba)

To develop a high density linkage map in faba bean, a total of 1,363 FBES (Faba bean expressed sequence tag [EST]-derived simple sequence repeat [SSR]) markers were designed based on 5,090 non-redundant ESTs developed in this study. A total of 109 plants of a ‘Nubaria 2’ × ‘Misr 3’ F₂ mapping population were used for map construction. Because the parents were not pure homozygous lines, the 109 F₂ plants were divided into three subpopulations according to the original F₁ plants. Linkage groups (LGs) generated in each subpopulation were integrated by commonly mapped markers. The integrated ‘Nubaria 2’ × ‘Misr 3’ map consisted of six LGs, representing a total length of 684.7 cM, with 552 loci. Of the mapped loci, 47% were generated from multi-loci diagnostic (MLD) markers. Alignment of homologous sequence pairs along each linkage group revealed obvious syntenic relationships between LGs in faba bean and the genomes of two model legumes, Lotus japonicus and Medicago truncatula. In a polymorphic analysis with ten Egyptian faba bean varieties, 78.9% (384/487) of the FBES markers showed polymorphisms. Along with the EST-SSR markers, the dense map developed in this study is expected to accelerate marker assisted breeding in faba bean.     

Gametophytic selection for wilt resistance and its impact on the segregation of wilt resistance alleles in chickpea (Cicer arietinum L.)

In the present study, the effect of gametophytic selection on the segregation of molecular markers linked and unlinked to wilt resistance loci was investigated. A homozygous resistant genotype WR315 (h₁h₁ h₂h₂) was crossed to two susceptible lines, Karikadle (H₁H₁ H₂H₂) and BG256 (h₁h₁ H₂H₂), to generate two different F₁ populations. Three F₁ plants from each cross were subjected to gametophytic selection by spraying a pathotoxin at flower bud initiation stage, while the remaining F₁ plants in each cross were treated as control by spraying them with water. Both control and treated F₁ plants were selfed to generate respective F₂ populations. The seeds of control and selected F₂ populations of both crosses were sown to raise the plants. The DNA from 60 to 70 plants in each treatment group were isolated and tested for presence of the markers linked and unlinked to wilt resistance loci. Both the linked and unlinked markers showed expected monogenic ratio of 3:1 individually in control population. In the selected F₂ population the markers CS 27₇₀₀ linked to H₁ locus, A07C₄₁₇ and H₄G₁₁ linked to H₂ locus of wilt resistance exhibited significant deviations for monogenic and digenic ratios. The unlinked markers NCPGR93 and NCPGR48 showed expected monogenic ratios in the selected F₂ population. The results demonstrated that the gametophytic selection for wilt resistance increase the frequency of resistance alleles and resistant plants in the progeny. Deviation from the expected segregation ratio of the marker closely linked to resistance loci suggests the presence of linkage drag in gametophytic selection for resistance. The significant deviation from monogenic ratio was also observed for the linked marker A07C₄₁₇ in the selected F₂ population of second cross BG256 × WR315. On the contrary, the segregation of markers in a different linkage not linked to resistance loci was not affected. Thus demonstrating the utility of gamete selection for resistance is increasing the frequency of resistant plant in the progeny independent of the parental genotype. Gametophytic selection can be applied in plant breeding programmes to develop wilt resistant genotypes in a short period.     

Development of an interspecific Vigna linkage map between Vigna umbellata (Thunb.) Ohwi & Ohashi and V. nakashimae (Ohwi) Ohwi & Ohashi and its use in analysis of bruchid resistance and comparative genomics

To facilitate transfer of bruchid resistance to azuki bean (Vigna angularis) from its relatives an interspecific mapping population was made between rice bean, V. umbellata, and the related wild species V. nakashimae. The V. umbellata parent is completely resistant and V. nakashimae is completely susceptible to the bruchid beetle pests, azuki bean weevil (Callosobruchus chinensis) and cowpea weevil (C. maculatus). There is very low cross compatibility between V. umbellata and azuki bean. Therefore, V. nakashimae, that crosses with both V. umbellata and V. angularis without the need for embryo rescue, is used as a bridging species. A genetic linkage map was constructed based on an interspecific F₂ mapping population between V. umbellata and V. nakashimae consisting of 74 plants. A total of 175 DNA marker loci (74 RFLPs and 101 SSRs) were mapped on to 11 linkage groups spanning a total length of 652 cM. Segregation distortion was observed but only three markers were not linked to any linkage group due to severe segregation distortion. This interspecific genome map was compared with the genome map of azuki bean. Of 121 common markers on the two maps, 114 (94.2%) were located on the same linkage groups in both maps. The marker order was highly conserved between the two genome maps. Fifty F₂ plants that produced sufficient seeds were used for quantitative trait locus (QTL) analysis and locating gene(s) for C. chinensis and C. maculatus resistance in V. umbellata. The resistance reaction of these F₂ plants differed between C. chinensis and C. maculatus. Both resistances were quantitatively inherited with no F₂ plants completely susceptible to C. chinensis or C. maculatus. One putative QTL for resistance to each of these bruchid species was located on different linkage groups. Other putative QTLs associated with resistance to both C. chinensis and C. maculatus were localized on the same linkage group 1. Linked markers associated with the bruchid‐resistant QTL will facilitate their transfer to azuki bean breeding lines.     

Mapping of quantitative trait loci controlling partial resistance against rust incited by <Emphasis Type="Italic">Uromyces pisi</Emphasis> (Pers.) Wint. in a <Emphasis Type="Italic">Pisum fulvum</Emphasis> L. intraspecific cross

A quantitative trait loci (QTL) associated with resistance to pea rust, caused by the fungus Uromyces pisi (Pers.) Wint., has been identified in a F₂ population derived from an intraspecific cross between two wild pea (Pisum fulvum L.) accessions, IFPI3260 (resistant) and IFPI3251 (susceptible). Both parental lines and all the segregating population displayed a fully compatible interaction (high infection type), which indicates absence of hypersensitive response. Nevertheless, differences on the percentage of symptomatic area of the whole plant (disease severity) were observed. A genetic map was developed covering 1283.3 cM and including 146 markers (144 random amplified polymorphic DNA (RAPDs) and two sequence tagged sites (STSs) markers) distributed in 9 linkage groups. A QTL explaining 63% of the total phenotypic variation was located in linkage group 3. RAPDs markers (OPY11₁₃₁₆ and OPV17₁₀₇₈) flanking this QTL should allow, after their conversion in SCARs, a reliable marker-assisted selection for rust resistance.     

Mapping of QTLs controlling epicotyl length in adzuki bean (Vigna angularis)

Epicotyl length (ECL) of adzuki bean (Vigna angularis) affects the efficiency of mechanized weeding and harvest. The present study investigated the genetic factors controlling ECL. An F₂ population derived from a cross between the breeding line ‘Tokei1121’ (T1121, long epicotyls) and the cultivar ‘Erimo167’ (common epicotyls) was phenotyped for ECL and genotyped using simple sequence repeats (SSRs) and single-nucleotide polymorphism (SNP) markers. A molecular linkage map was generated and fifty-two segregating markers, including 27 SSRs and 25 SNPs, were located on seven linkage groups (LGs) at a LOD threshold value of 3.0. Four quantitative trait loci (QTLs) for ECL, with LOD scores of 4.0, 3.4, 4.8 and 6.4, were identified on LGs 2, 4, 7 and 10, respectively; together, these four QTLs accounted for 49.3% of the phenotypic variance. The segregation patterns observed in F₅ residual heterozygous lines at qECL10 revealed that a single recessive gene derived from T1121 contributed to the longer ECL phenotype. Using five insertion and deletion markers, this gene was fine mapped to a ~255 kb region near the end of LG10. These findings will facilitate marker-assisted selection for breeding in the adzuki bean and contribute to an understanding of the mechanisms associated with epicotyl elongation.     

Identification of SSR markers linked to the Phytophthora resistance gene Rps1-d in soybean

To identify markers for the Phytophthora resistance gene, Rps1‐d, 123 F_{2 : 3} families were produced from a cross between Glycine max (L.) Merr. ‘Tanbakuro’ (a Japanese traditional black soybean) and PI103091 (Rps1‐d) as an experimental population. The results of virulence tests produced 33 homozygous resistant, 61 segregating and 29 homozygous susceptible F_{2 : 3} families. The chi‐squared test gave a goodness‐of‐fit for the expected ratio of 1 : 2 : 1 for resistant, segregating and susceptible traits, suggesting that the inheritance of Rps1‐d is controlled by a monogenic dominant gene. Simple sequence repeat (SSR) analyses of this trait were carried out using the cultivars ‘Tanbakuro’ and PI103091. Sixteen SSR primers, which produced 19 polymorphic fragments between the two parents, were identified from 41 SSR primers in MLG N. Eight SSR markers were related to Rps1‐d, based on 32 of the 123 F_{2 : 3} families, consisting of 16 homozygous resistant and 16 homozygous susceptible lines. The remaining 91 families were analysed for these eight markers, and a linkage map was constructed using all 123 F_{2 : 3} families. The length of this linkage group is 44.0 cM. The closest markers, Sat_186 and Satt152, are mapped at 5.7 cM and 11.5 cM, respectively, on either side of the Rps1‐d gene. Three‐way contingency table analysis indicates that dual‐marker‐assisted selection using these two flanking markers would be efficient.