A Genetic linkage map of Pinyon pine (Pinus edulis) based on amplified fragment length polymorphisms

 Amplified fragment length polymorphisms (AFLP) were used to rapidly generate a dense linkage map for pinyon pine (Pinus edulis). The map population consisted of 40 megagametophytes derived from one tree at Sunset Crater, Arizona. A total of 78 primer combinations, each with three to five selective nucleotides, amplified 542 polymorphic markers. Of these, 33 markers showed significant deviation from the expected Mendelian genotypic segregation ratio of 1 : 1, and 164 showed complete linkage with another marker. This resulted in 338 unique markers mapping to 25 linkage groups, each of which ranged from 2 to 22 markers, averaging 80 centiMorgans (cM) in size and covering 2,012 cM (2,200 cM with the inclusion of 25 cM for each of 7 unlinked markers). Pairwise linkage values gave a genome size estimate of 2,390 cM, suggesting comprehensive coverage of the genome. A search for subsets of primer combinations giving the best map coverage found 10 primer combinations which together marked 72% of the linkage map to within 10 cM; an additional 10 primer combinations increased this percentage to 85%. Our map represents an initial step towards the identification of quantitative trait loci associated with pest resistance and water stress in pinyons and will further allow us to examine introgression rates between P. edulis and P. californiarum. Received: 14 October 1997 / Accepted: 29 April 1998     

Construction of genetic linkage map of the medicinal and ornamental plant <Emphasis Type="Italic">Catharanthus roseus</Emphasis>

An integrated genetic linkage map of the medicinal and ornamental plant Catharanthus roseus, based on different types of molecular and morphological markers was constructed, using a F₂ population of 144 plants. The map defines 14 linkage groups (LGs) and consists of 131 marker loci, including 125 molecular DNA markers (76 RAPD, 3 RAPD combinations; 7 ISSR; 2 EST-SSR from Medicago truncatula and 37 other PCR based DNA markers), selected from a total of 472 primers or primer pairs, and six morphological markers (stem pigmentation, leaf lamina pigmentation and shape, leaf petiole and pod size, and petal colour). The total map length is 1131.9 cM (centiMorgans), giving an average map length and distance between two markers equal to 80.9 cM and 8.6 cM, respectively. The morphological markers/genes were found linked with nearest molecular or morphological markers at distances varying from 0.7 to 11.4 cM. Linkage was observed between the morphological markers concerned with lamina shape and petiole size of leaf on LG1 and leaf, stem and petiole pigmentation and pod size on LG8. This is the first genetic linkage map of C. roseus.     

A genetic linkage map of the sea cucumber, Apostichopus japonicus (Selenka), based on AFLP and microsatellite markers

We present the first genetic maps of the sea cucumber ( Apostichopus japonicus ), constructed with an F₁ pseudo-testcross strategy. The 37 amplified fragment length polymorphism (AFLP) primer combinations chosen identified 484 polymorphic markers. Of the 21 microsatellite primer pairs tested, 16 identified heterozygous loci in one or other parent, and six were fully informative, as they segregated in both parents. The female map comprised 163 loci, spread over 20 linkage groups (which equals the haploid chromosome number), and spanned 1522.0 cM, with a mean marker density of 9.3 cM. The equivalent figures for the male map were 162 loci, 21 linkage groups, 1276.9 and 7.9 cM. About 2.5% of the AFLP markers displayed segregation distortion and were not used for map construction. The estimated coverage of the genome was 84.8% for the female map and 83.4% for the male map. The maps generated will serve as a basis for the construction of a high-resolution genetic map and mapping of the functional genes and quantitative trait loci, which will then open the way for the application of a marker-assisted selection breeding strategy in this species.     

Development of two loquat [Eriobotrya japonica (Thunb.) Lindl.] linkage maps based on AFLPs and SSR markers from different Rosaceae species

Loquat [Eriobotrya japonica (Thunb.) Lindl.] is a Rosaceae fruit species of growing interest as an alternative to the main fruit crops. However, only a few genetic studies have been carried out on this species. This paper reports the construction of the first genetic maps of two loquat cultivars based on AFLP and microsatellite markers from Malus, Eriobotrya, Pyrus and Prunus genera. An F₁ population consisting of 81 individuals, derived from the cross between ‘Algerie’ and ‘Zaozhong-6’ cultivars, was used to construct both maps. A total of 111 scorable simple sequence repeat (SSR) loci resulted from the testing of 440 SSR primer pairs in the analyzed progeny and the SSR transferability to Eriobotrya was found to be 74% from apple, 58% from pear and 49% from Prunus spp. In addition, 183 AFLP polymorphic bands were produced using 42 primer combinations. The ‘Algerie’ map was organized in 17 linkage groups covering a distance of 900 cM and comprising 177 loci (83 SSRs and 94 AFLPs) with an average marker distance of 5.1 cM. Self-incompatibility trait was mapped at the distal part of the LG17 linkage group, as previously reported in Malus and Pyrus. The ‘Zaozhong-6’ map covered 870 cM comprising 146 loci (64 SSRs and 82 AFLPs) with an average marker distance of 5.9 cM. The 44 SSRs and the 48 AFLPs share in common by both maps were essentially collinear and, moreover, the order of the 75% of apple and pear SSRs mapped in Eriobotrya was shown to be consistent across the Maloideae subfamily. As a whole, these maps represent a useful tool to facilitate loquat breeding and an interesting framework for map comparison in the Rosaceae.     

AFLP genetic maps of Eucalyptus globulus and E. tereticornis

 Amplified fragment length polymorphism (AFLP) analysis is a rapid and efficient technique for detecting large numbers of DNA markers in eucalypts. We have used AFLP markers in a two-way pseudo-testcross strategy to generate genetic maps of two clones of different Eucalyptus species (E. tereticornis and E. globulus). Of 606 polymorphic fragments scored, 487 segregated in a 1 : 1 ratio, corresponding to DNA polymorphisms heterozygous in one parent and null in the other. In the maternal E. tereticornis map, 268 markers were ordered in 14 linkage groups (919 cM); the paternal E. globulus map had 200 markers in 16 linkage groups (967 cM). Results from PGRI software were compared with MAPMAKER. The average density of markers was approximately 1 per 3.9 cM. Framework markers were ordered with an average confidence level of 90%, covering 80–100% of the estimated Eucalyptus genome size. In order to investigate the homologies between the E. tereticornis and the E. globulus genetic linkage maps, we included 19 markers segregating 3 : 1 in the analysis. Some homeologous linkage groups were recognized. The linkage data developed in these maps will be used to detect loci controlling commercially important traits. Received: 17 July 1997 / Accepted: 13 October 1997     

Genetic and physical mapping of new EST-derived SSRs on the A and B genome chromosomes of wheat

The availability of genetic maps and phenotypic data of segregating populations allows to localize and map agronomically important genes, and to identify closely associated molecular markers to be used in marker-assisted selection and positional cloning. The objective of the present work was to develop a durum wheat intervarietal genetic and physical map based on genomic microsatellite or genomic simple sequence repeats (gSSR) markers and expressed sequence tag (EST)-derived microsatellite (EST-SSR) markers. A set of 122 new EST-SSR loci amplified by 100 primer pairs was genetically mapped on the wheat A and B genome chromosomes. The whole map also comprises 149 gSSR markers amplified by 120 primer pairs used as anchor chromosome loci, two morphological markers (Black colour, Bla1, and spike glaucousness, Ws) and two seed storage protein loci (Gli-A2 and Gli-B2). The majority of SSR markers tested (182) was chromosome-specific. Out of 275 loci 241 loci assembled in 25 linkage groups assigned to the chromosomes of the A and B genome and 34 remained unlinked. A higher percentage of markers (54.4%), localized on the B genome chromosomes, in comparison to 45.6% distributed on the A genome. The whole map covered 1,605 cM. The B genome accounted for 852.2 cM of genetic distance; the A genome basic map spanned 753.1 cM with a minimum length of 46.6 cM for chromosome 5A and a maximum of 156.2 cM for chromosome 3A and an average value of 114.5 cM. The primer sets that amplified two or more loci mapped to homoeologous as well as to non-homoeologous sites. Out of 241 genetically mapped loci 213 (88.4%) were physically mapped by using the nulli-tetrasomic, ditelosomic and a stock of 58 deletion lines dividing the A and B genome chromosomes in 94 bins. No discrepancies concerning marker order were observed but the cytogenetic maps revealed in some cases small genetic distance covered large physical regions. Putative function for mapped SSRs were assigned by searching against GenBank nonredundant database using TBLASTX algorithms.     

Map construction of sequence-tagged sites (STSs) in barley (Hordeum vulgare L.)

 In order to identify sequence-tagged sites (STSs) appropriate for recombinant inbred lines (RILs) of barley cultivars ‘Azumamugi’ × ‘Kanto Nakate Gold’, a total of 43 STS primer pairs were generated on the basis of the terminal sequences of barley restriction fragment length polymorphism (RFLP) clones. Forty one of the 43 primer pairs amplified PCR products in Azumamugi, Kanto Nakate Gold, or both. Of these, two showed a length polymorphism and two showed the presence or absence of polymorphism between the parents. PCR products of the remaining 37 primers were digested with 46 restriction endonucleases, and polymorphisms were detected for 15 primers. A 383.6-cM linkage map of RILs of Azumamugi×Kanto Nakate Gold was constructed from the 19 polymorphic STS primer pairs (20 loci) developed in this study, 45 previously developed STS primer pairs (47 loci), and two morphological loci. Linkage analysis and analysis of wheat-barley chromosome addition lines showed that with three exceptions, the chromosome locations of the STS markers were identical with those of the RFLP markers. Received: 4 August 1998 / Accepted: 8 October 1998     

Identification of QTLs for resistance to powdery mildew and SSR markers diagnostic for powdery mildew resistance genes in melon (Cucumis melo L.)

Powdery mildew caused by Podosphaera xanthii is an important foliar disease in melon. To find molecular markers for marker-assisted selection, we constructed a genetic linkage map of melon based on a population of 93 recombinant inbred lines derived from crosses between highly resistant AR 5 and susceptible ‘Earl’s Favourite (Harukei 3)’. The map spans 877 cM and consists of 167 markers, comprising 157 simple sequence repeats (SSRs), 7 sequence characterized amplified region/cleavage amplified polymorphic sequence markers and 3 phenotypic markers segregating into 20 linkage groups. Among them, 37 SSRs and 6 other markers were common to previous maps. Quantitative trait locus (QTL) analysis identified two loci for resistance to powdery mildew. The effects of these QTLs varied depending on strain and plant stage. The percentage of phenotypic variance explained for resistance to the pxA strain was similar between QTLs (R ² = 22–28%). For resistance to pxB strain, the QTL on linkage group (LG) XII was responsible for much more of the variance (41–46%) than that on LG IIA (12–13%). The QTL on LG IIA was located between two SSR markers. Using an independent population, we demonstrated the effectiveness of these markers. This is the first report of universal and effective markers linked to a gene for powdery mildew resistance in melon.     

A first genetic linkage map of mulberry (Morus spp.) using RAPD, ISSR, and SSR markers and pseudotestcross mapping strategy

To lay the foundation for molecular breeding efforts, the first genetic linkage map of mulberry (2n=2x=28) was constructed with 50 F1 full-sib progeny using randomly amplified polymorphic DNA (RAPD), inter-simple sequence repeat (ISSR), and simple sequence repeat (SSR) markers and two-way pseudotestcross mapping strategy. We selected 100 RAPD, 42 ISSR, and 9 SSR primers that amplified 517 markers, of which 188 (36.36%) showed a test-cross configuration, corresponding to the heterozygous condition in one parent and null in the other. Two separate female and male maps were constructed using 94 each of female- and male-specific testcross markers, containing 12 female linkage groups and 14 male linkage groups. At a minimum logarithm of the odds (LOD) score threshold of 6.0 and at a maximum map distance of 20 cM, the female map covered a 1,196.6-cM distance, with an average distance of 15.75 cM and maximum map distance of 37.9 cM between two loci; the male-specific map covered a 1,351.7-cM distance, with an average distance of 18.78 cM and a maximum map distance between two loci is of 34.7 cM. The markers distributed randomly in all linkage groups without any clustering. All 12 linkage groups in the female-specific map consisted of 4–10 loci ranging in length from 0 to 140.4 cM, and in the male-specific map, the 13 largest linkage groups (except linkage group 12, which contained three loci) consisted of 4–12 loci, ranging in length from 53.9 to 145.9 cM and accounting for 97.22% of the total map distance. When mapping, progeny pass through their juvenile phase and assume their adult characters, mapping morphological markers and identification of quantitative trait loci for adaptive traits will be the primary target. In that sense, our map provides reference information for future molecular breeding work on Morus and its relatives.     

RAPD-based genetic linkage maps of yellow passion fruit (Passiflora edulis Sims. f. flavicarpa Deg.).

A single cross between two clones of passion fruit (Passiflora edulis Sims. f. flavicarpa Deg., 2n = 18) was selected for genetic mapping. The mapping population was composed of 90 F1 plants derived from a cross between 'IAPAR 123' (female parent) and 'IAPAR 06' (male parent). A total of 380 RAPD primers were analyzed according to two-way pseudo-testcross mapping design. The linkage analysis was performed using Mapmaker version 3.0 with LOD 4.0 and a maximum recombination fraction (theta) of 0.30. Map distances were estimated using the Kosambi mapping function. Linkage maps were constructed with 269 loci (2.38 markers/primer), of which 255 segregated 1:1, corresponding to a heterozygous state in one parent and null in the other. The linkage map for 'IAPAR123' consisted of 135 markers. A total of nine linkage groups were assembled covering 727.7 cM, with an average distance of 11.20 cM between framework loci. The sizes of the linkage groups ranged from 56 to 144.6 cM. The linkage map for 'IAPAR 06' consisted of 96 markers, covering 783.5 cM. The average distance between framework loci was 12.2 cM. The length of the nine linkage groups ranged from 20.6 to 144.2 cM. On average, both maps provided 61% genome coverage. Twenty-four loci (8.9%) remained unlinked. Among their many applications, these maps are a starting point for the identification of quantitative trait loci for resistance to the main bacterial disease affecting passion fruit orchards in Brazil, caused by Xanthomonas campestris pv. passiflorae, because parental genotypes exhibit diverse responses to bacterial inoculation.     

Towards second-generation STS (sequence-tagged sites) linkage maps in conifers: a genetic map of Norway spruce ( Picea abies K.)

Genetic linkage maps have been produced for a wide range of organisms during the last decade, thanks to the increasing availability of molecular markers. The use of microsatellites (or Simple Sequence Repeats, SSRs) as genetic markers has led to the construction of “second-generation” genetic maps for humans, mouse and other organisms of major importance. We constructed a second-generation single-tree genetic linkage map of Norway spruce (Picea abies K.) using a panel of 72 haploid megagametophytes with a total of 447 segregating bands [366 Amplified Fragment Length Polymorphisms (AFLPs), 20 Selective Amplification of Microsatellite Polymorphic Loci (SAMPLs) and 61 SSRs, each single band being treated initially as a dominant marker]. Four hundred and thirteen markers were mapped in 29 linkage groups (including triplets and doublets) covering a genetic length of 2198.3 cM, which represents 77.4% of the estimated genome length of Picea abies (approximately 2839 cM). The map is still far from coalescing into the expected 12 chromosomal linkage groups of Norway spruce (2n = 2x = 24). A possible explanation for this comes from the observed non-random distribution of markers in the framework map. Thirty-eight SSR marker loci could be mapped onto 19 linkage groups. This set of highly informative Sequence Tagged Sites (STSs) can be used in many aspects of genetic analysis of forest trees, such as marker-assisted selection, QTL mapping, positional cloning, gene flow analysis, mating system analysis and genetic diversity studies. Received: 5 November 1997 / Accepted: 16 March 1998     

Genetic Mapping of Laminaria japonica and L. Iongissima Using Amplified Fragment Length Polymorphism Markers in a ＂Two-Way Pseudo- Testcross＂ Strategy

With a ＂two-way pseudo-testcross＂ mapping strategy, we applied the amplified fragment length polymorphism （AFLP） markers to construct two moderate density genetic linkage maps for Laminaria. The linkage maps were generated from the 60 progenies of the F1 cross family （Laminaria iongissima Aresch. × L. Japonica Miyabe） with twenty pairs of primer combinations. Of the 333 polymorphic loci scored in 60 progenies, 173 segregated in a 1：1 ratio, corresponding to DNA polymorphisms heterozygous in a single parent, and the other 58 loci existing in both parents followed a 3：1 Mendelian segregation ratio. Among the loci with 1：1 segregating ratios, 79 loci were ordered in 14 linkage groups （648.6 cM） of the paternal map, and 72 loci were ordered in 14 linkage groups （601.9 cM） of the maternal map. The average density of loci was approximately 1 per 8 cM. To Investigate the homologies between two parental maps, we used 58 loci segregated 3：1 for further analysis, and deduced one homologous linkage group. The linkage data developed in these maps will be useful for detecting loci-controlling commercially important traits for Laminaria.     

The first genetic map of pigeon pea based on diversity arrays technology (DArT) markers

With an objective to develop a genetic map in pigeon pea (Cajanus spp.), a total of 554 diversity arrays technology (DArT) markers showed polymorphism in a pigeon pea F₂ mapping population of 72 progenies derived from an interspecific cross of ICP 28 (Cajanus cajan) and ICPW 94 (Cajanus scarabaeoides). Approximately 13% of markers did not conform to expected segregation ratio. The total number of DArT marker loci segregating in Mendelian manner was 405 with 73.1% (P > 0.001) of DArT markers having unique segregation patterns. Two groups of genetic maps were generated using DArT markers. While the maternal genetic linkage map had 122 unique DArT maternal marker loci, the paternal genetic linkage map has a total of 172 unique DArT paternal marker loci. The length of these two maps covered 270.0 cM and 451.6 cM, respectively. These are the first genetic linkage maps developed for pigeon pea, and this is the first report of genetic mapping in any grain legume using diversity arrays technology.     

Triticum turgidum L. 6A and 6B recombinant substitution lines: extended linkage maps and characterization of residual background alien genetic variation

  Triticum turgidum L. var ‘durum’ cv ‘Langdon’-T. t. var ‘dicoccoides’ chromosome 6A and 6B recombinant substitution lines (RSLs) and a F₂ population derived from a ‘Langdon’-T. t. var ‘dicoccoides’ disomic chromosome 6A substitution lineבLangdon’ cross were analyzed with the objective of markedly increasing the number of markers assigned to and the resolution of previously constructed 6A and 6B linkage maps. Fifty-seven markers were added to the 6A RSL-population map, which now consists of 73 markers that span 111 cM, and 40 markers were added to the 6B RSL-population map, which now consists of 56 markers that span 123 cM. With the exception of 2 6B loci, all of the loci on the two RSL-population maps were ordered at a LOD score ≥3.0. Thirty-seven orthologous markers were mapped in the two chromosomes and colinearity between them is strongly indicated. The 6A RSL-population map and the F₂-population map are highly similar, indicating that the former population, which consists of 66 lines, can be reliably used for mapping, as was previously demonstrated for the 6B RSL population. In the absence of selection and genetic drift, the lines in a RSL population, except at loci in the substituted/recombined chromosome, should be near-isogenic. An unexpected finding was that at least 26 and possibly 29 of the RFLPs detected in the RSL populations (18% of the markers analyzed) are not located in the substituted/recombined chromosomes. Linkage analysis of the markers disclosed that at least 19 of them are located in six or seven segments that span approximately 10 cM and 17 cM of the genetic lengths of 6B and 6A, respectively, in the 6A and 6B RSL populations, respectively, a finding that suggests that 40 or more alien segments spanning 8–15% of the genetic length of the 13 unsubstituted chromosomes are present in both of the RSL populations. Alien alleles are fixed in many RSLs for most of the markers, in most cases at a frequency consistent with theoretical expectations. Highly distorted segregation favoring the alien allele was detected for all of the markers in 2 of the segments, however. Nine of the markers were among those mapped in the substituted/recombined chromosomes; the linkage data obtained for the other 10 was sufficient to assign them to approximate map positions. Received: 12 June 1997 / Accepted: 6 October 1997     

Mapping QTLs for submergence tolerance in rice by AFLP analysis and selective genotyping

By combining the amplified fragment length polymorphism (AFLP) technique with selective genotyping, we constructed a linkage map for rice and assigned each linkage group to a corresponding chromosome. The AFLP map, consisting of 202 AFLP markers, was generated from 74 recombinant inbred lines (RIL) which were selected from both extremes of the population (250 lines) with respect to the response to complete submergence. Map length was 1756 cM, with an average interval size of 8.5 cM. To assign linkage groups to chromosomes, we used 50 previously mapped AFLP markers as anchor markers distributed over the 12 chromosomes. Other AFLP markers were then assigned to specific chromosomes based on their linkage to anchor markers. This AFLP map is equivalent to the RFLP/AFLP map constructed previously as the anchors were in the same order in both maps. Furthermore, tests with two restriction fragment length polymorphism (RFLP) markers and two sequence-tagged site (STS) markers showed that they mapped in the expected positions. Using this AFLP map, a major gene for submergence tolerance was localized on chromosome 9. Quantitative trait loci (QTL) associated with submergence tolerance were detected on chromosomes 6, 7, 11, and 12. We conclude that the combination of AFLP mapping and selective genotyping provides a much faster and easier approach to QTL identification than the use of RFLP markers. Received: 20 December 1996 / Accepted: 21 January 1997     

Genetic linkage map in sour cherry using RFLP markers

 Restriction fragment length polymorphism (RFLP) linkage maps of two tetraploid sour cherry (Prunus cerasus L., 2n=4x=32) cultivars, Rheinische Schattenmorelle (RS) and Erdi Botermo (EB), were constructed from 86 progeny from the cross RS×EB. The RS linkage map consists of 126 single-dose restriction fragment (SDRF, Wu et al. 1992) markers assigned to 19 linkage groups covering 461.6 cM. The EB linkage map has 95 SDRF markers assigned to 16 linkage groups covering 279.2 cM. Fifty three markers mapped in both parents were used as bridges between both maps and 13 sets of homologous linkage groups were identified. Homoeologous relationships among the sour cherry linkage groups could not be determined because only 15 probes identified duplicate loci. Fifty nine of the markers on the linkage maps were detected with probes used in other Prunus genetic linkage maps. Four of the sour cherry linkage groups may be homologous with four of the eight genetic linkage groups identified in peach and almond. Twenty one fragments expected to segregate in a 1 : 1 ratio segregated in a 2 : 1 ratio. Three of these fragments were used in the final map construction because they all mapped to the same linkage group. Six fragments exhibited segregation consistent with the expectations of intergenomic pairing and/or recombination. Received: 1 April 1998 / Accepted: 9 June 1998     

An integrated restriction fragment length polymorphism--amplified fragment length polymorphism linkage map for cultivated sunflower.

Restriction fragment length polymorphism (RFLP) maps have been constructed for cultivated sunflower (Helianthus annuus L.) using three independent sets of RFLP probes. The aim of this research was to integrate RFLP markers from two sets with RFLP markers for resistance gene candidate (RGC) and amplified fragment length polymorphism (AFLP) markers. Genomic DNA samples of HA370 and HA372, the parents of the F2 population used to build the map, were screened for AFLPs using 42 primer combinations and RFLPs using 136 cDNA probes (RFLP analyses were performed on DNA digested with EcoRI, HindIII, EcoRV, or DraI). The AFLP primers produced 446 polymorphic and 1101 monomorphic bands between HA370 and HA372. The integrated map was built by genotyping 296 AFLP and 104 RFLP markers on 180 HA370 x HA372 F2 progeny (the AFLP marker assays were performed using 18 primer combinations). The HA370 x HA372 map comprised 17 linkage groups, presumably corresponding to the 17 haploid chromosomes of sunflower, had a mean density of 3.3 cM, and was 1326 cM long. Six RGC RFLP loci were polymorphic and mapped to three linkage groups (LG8, LG13, and LG15). AFLP markers were densely clustered on several linkage groups, and presumably reside in centromeric regions where recombination is reduced and the ratio of genetic to physical distance is low. Strategies for targeting markers to euchromatic DNA need to be tested in sunflower. The HA370 x HA372 map integrated 14 of 17 linkage groups from two independent RFLP maps. Three linkage groups were devoid of RFLP markers from one of the two maps.     

Genetic dissection of sex determinism, inflorescence morphology and downy mildew resistance in grapevine

A genetic linkage map of grapevine was constructed using a pseudo-testcross strategy based upon 138 individuals derived from a cross of Vitis vinifera Cabernet Sauvignon × Vitis riparia Gloire de Montpellier. A total of 212 DNA markers including 199 single sequence repeats (SSRs), 11 single strand conformation polymorphisms (SSCPs) and two morphological markers were mapped onto 19 linkage groups (LG) which covered 1,249 cM with an average of 6.7 cM between markers. The position of SSR loci in the maps presented here is consistent with the genome sequence. Quantitative traits loci (QTLs) for several traits of inflorescence and flower morphology, and downy mildew resistance were investigated. Two novel QTLs for downy mildew resistance were mapped on linkage groups 9 and 12, they explain 26.0–34.4 and 28.9–31.5% of total variance, respectively. QTLs for inflorescence morphology with a large effect (14–70% of total variance explained) were detected close to the Sex locus on LG 2. The gene of the enzyme 1-aminocyclopropane-1-carboxylic acid synthase, involved in melon male organ development and located in the confidence interval of all QTLs detected on the LG 2, could be considered as a putative candidate gene for the control of sexual traits in grapevine. Co-localisations were found between four QTLs, detected on linkage groups 1, 14, 17 and 18, and the position of the floral organ development genes GIBBERELLIN INSENSITIVE1, FRUITFULL, LEAFY and AGAMOUS. Our results demonstrate that the sex determinism locus also determines both flower and inflorescence morphological traits.     

Construction of High-Density Genetic Linkage Maps and Mapping of Growth-Related Quantitative Trail Loci in the Japanese Flounder (Paralichthys olivaceus)

High-density genetic linkage maps were constructed for the Japanese flounder (Paralichthys olivaceus). A total of 1624 microsatellite markers were polymorphic in the reference family. Linkage analysis using JoinMap 4.0 resulted in the mapping of 1487 markers to 24 linkage groups, a result which was consistent with the 24 chromosomes seen in chromosome spreads. The female map was composed of 1257 markers, covering a total of 1663.8 cM with an average interval 1.35 cM between markers. The male map consisted of 1224 markers, spanning 1726.5 cM, with an average interval of 1.44 cM. The genome length in the Japanese flounder was estimated to be 1730.3 cM for the females and 1798.0 cM for the males, a coverage of 96.2% for the female and 96.0% for the male map. The mean recombination at common intervals throughout the genome revealed a slight difference between sexes, i.e. 1.07 times higher in the male than female. High-density genetic linkage maps are very useful for marker-assisted selection (MAS) programs for economically valuable traits in this species and for further evolutionary studies in flatfish and vertebrate species. Furthermore, four quantiative trait loci (QTL) associated with growth traits were mapped on the genetic map. One QTL was identified for body weight on LG 14 f, which explained 14.85% of the total variation of the body weight. Three QTL were identified for body width on LG14f and LG14m, accounting for 16.75%, 13.62% and 13.65% of the total variation in body width, respectively. The additive effects were evident as negative values. There were four QTL for growth traits clustered on LG14, which should prove to be very useful for improving growth traits using molecular MAS.     

Inheritance and usefulness of AFLP markers in channel catfish (Ictalurus punctatus ), blue catfish ( I. furcatus) , and their F1, F2, and backcross hybrids

Eight primer combinations were used to investigate the application of amplified fragment length polymorphism (AFLP) markers in catfish for genetic analysis. Intraspecific polymorphism was low among channel catfish or blue catfish strains. Interspecific AFLP polymorphism was high between the channel catfish and blue catfish. Each primer combination generated from 70 to more than 200 bands, of which 38.6–75.7% were polymorphic between channel catfish and blue catfish. On average, more than 20 polymorphic bands per primer combination were produced as quality markers suitable for genetic analysis. All AFLP markers were transmitted into channel catfish × blue catfish F1 hybrids, except rare markers that were heterozygous in the parents and therefore were segregating in F1 hybrids. The two reciprocal channel catfish × blue catfish F1 hybrids (channel catfish female × blue catfish male; blue catfish female × channel catfish male) produced identical AFLP profiles. The AFLP markers were inherited and segregated in expected Mendelian ratios. At two loci, E8-b9 and E8-b2, markers were found at significantly lower frequencies than expected with F2 and backcross hybrids which had been selected for increased growth rates. The reproducibility of AFLP was excellent. These characteristics of the catfish AFLP markers make them highly useful for genetic analysis of catfish, especially for construction of genetic linkage and quantitative trait loci maps, and for marker-assisted selection. Received: 10 September 1997 / Accepted: 10 December 1997