A linkage map of hexaploid oat based on grass anchor DNA clones and its relationship to other oat maps.

A cultivated oat linkage map was developed using a recombinant inbred population of 136 F6:7 lines from the cross 'Ogle' x 'TAM O-301'. A total of 441 marker loci, including 355 restriction fragment length polymorphism (RFLP) markers, 40 amplified fragment length polymorphisms (AFLPs), 22 random amplified polymorphic DNAs (RAPDs), 7 sequence-tagged sites (STSs), 1 simple sequence repeat (SSR), 12 isozyme loci, and 4 discrete morphological traits, was mapped. Fifteen loci remained unlinked, and 426 loci produced 34 linkage groups (with 2-43 loci each) spanning 2049 cM of the oat genome (from 4.2 to 174.0 cM per group). Comparisons with other Avena maps revealed 35 genome regions syntenic between hexaploid maps and 16-34 regions conserved between diploid and hexaploid maps. Those portions of hexaploid oat maps that could be compared were completely conserved. Considerable conservation of diploid genome regions on the hexaploid map also was observed (89-95%); however, at the whole-chromosome level, colinearity was much lower. Comparisons among linkage groups, both within and among Avena mapping populations, revealed several putative homoeologous linkage group sets as well as some linkage groups composed of segments from different homoeologous groups. The relationships between many Avena linkage groups remain uncertain, however, due to incomplete coverage by comparative markers and to complications introduced by genomic duplications and rearrangements.     

Quantitative trait loci influencing β-glucan content in oat (Avena sativa, 2n=6x=42)

The β-glucan content of oat grain is of inter-est due to its positive human health role as a dietary component influencing serum cholesterol levels and its relation to the energy intake of livestock feed. Two recombinant inbred populations sharing a common parent (Kanota × Ogle and Kanota × Marion), and containing 137 individual lines each, were used to identify genomic regions that influence the β-glucan content in cultivated oat. Single-factor ANOVA, a backward elimination process, simple interval mapping (SIM) and simplified composite interval mapping (sCIM) were used to identify quantitative trait loci (QTLs). Regions on linkage groups 11 and 14 of the hexaploid oat RFLP map influenced β-glucan levels in both populations and over environments. Other genomic regions were identified whose effects varied depending on the genetic background, but were significant over measurements for a given population. Kanota and Ogle exhibit similar β-glucan levels and each parent contributed about the same number of positive β-glucan alleles in the Kanota × Ogle cross. Marion is higher in β-glucan content than Kanota and contributed all of the positive alleles in the Kanota × Marion cross. Three of the β-glucan QTL regions identified have been previously implicated as having a significant influence on the groat oil content in oat. These correlated QTL regions were either in coupling phase, with a region from one parent having the same effect on both traits, or were in repulsion phase. Identification of coupling- and repulsion-phase QTL regions for β-glucan and oil content facilitates the use of markers in manipulating these traits in oat breeding. Received: 8 September 1999 / Accepted: 25 March 2000     

A genetic linkage map for hexaploid,cultivated oat (Avena sativa L.) based on an intraspecific cross 'Ogle/MAM17-5'

Genetic research and breeding of oat ( Avena sativa L.) would be aided by development of a genetic linkage map for a breeding population. Such a map could be used for localization of qualitative and quantitative trait loci, marker-assisted selection and other genetic analysis in an adapted, agronomically useful background. The objectives of this research were to develop a genetic linkage map of hexaploid cultivated oat, to identify homoeologous relationships of linkage groups, and to compare homologous linkage groups between this map and the previously published hexaploid oat map from the cross 'Kanota/Ogle' (KO). A total of 510 markers, including 172 restriction fragment length polymorphisms (RFLP), 324 amplified fragment length polymorphisms (AFLP) and 14 simple sequence repeats (SSR), were assessed on a recombinant inbred population of 152 F(5:6) lines derived from the cross, 'Ogle/MAM17-5' (OM). Twenty eight linkage groups of 5 cM or longer were formed using 476 of the markers, while 34 markers remained either unlinked or in small fragments less than 5 cM. The 28 linkage groups contained from 3 to 33 markers, and varied in size from 5.2 to 123.0 cM, representing a total map length of 1,396.7 cM. Three putative homoeologous groups (OM7, OM8 and OM18; OM2 and OM23; OM13 and OM16) were identified. Comparison with the published KO map indicated that nine OM linkage groups could be determined to be homologous to linkage groups in the KO map. Further comparison of the homologous linkage groups revealed that residual differences in genomic rearrangements existed between the two hexaploid oat populations. Some linkage groups were significantly extended compared with the KO map. Since the OM mapping population is segregating for a number of agronomically important traits, this genetic map will provide a useful tool for identification of qualitative and quantitative loci for these traits.     

玉米相对饱和遗传连锁图谱构建与一种新的AFLPs共显性分析方法探讨

利用一个F2作图群体(X178×B73),首先构建了一个含有130个SSRs的玉米连锁框架图,然后用119个AFLPs位点增加图谱密度,得到一个全长1659·3cM,标记间平均间距6·66cM的玉米相对饱和连锁图。同时,对SSRs和AFLPs的一些遗传特性进行了分析,探讨了AFLP标记进行共显性分析的一种新方法。分析表明SSRs和AFLPs分子标记具有多态性和可靠性高等特点,是构建高密度分子标记遗传连锁图的有效技术。加密的玉米遗传连锁图谱为比较基因组研究、数量性状位点(quantitativetraitloci,QTLs)克隆、杂种优势机理研究以及标记辅助选择等提供了技术基础。     

A consensus linkage map for rapeseed (Brassica napus L.): construction and integration of three individual maps from DH populations

A framework consensus map for rapeseed (Brassica napus L.) was constructed from the integration of three DH mapping populations derived from crosses between or within spring- and winter-type parents. Several sources of genetic markers were used: isozymes, RFLPs, RAPDs, and AFLPs. A total of 992 different markers were mapped to at least one population, of which 540 were included in the consensus map and 253 were common to at least two populations. Markers were distributed over 19 linkage groups, thus reflecting the basic chromosome number of rapeseed and covered 2,429 cM, which was in the mean confidence-interval estimates of genome length (2,127–2,480) cM. Markers were evenly spaced on the entire genome even if, for several linkage groups, both RAPD and AFLP markers were not uniformly distributed. In the population resulting from a cross between two spring lines, a higher recombination rate was observed and a translocation was identified. The consensus approach allowed to map a larger number of markers, to obtain a near-complete coverage of the rapeseed genome, to fill the number of gaps, and to consolidate the linkage groups of the individual maps. Received: 19 July 2000 / Accepted: 31 October 2000     

Genetic linkage maps of two apricot cultivars ( Prunus armeniaca L.), and mapping of PPV (sharka) resistance

Genetic linkage maps for two apricot cultivars have been constructed using AFLP, RAPD, RFLP and SSR markers in 81 F1 individuals from the cross 'Goldrich' x 'Valenciano'. This family segregated for resistance to 'plum pox virus' (PPV), the most-important virus affecting Prunus species. Of the 160 RAPD arbitrary primers screened a total of 44 were selected. Sixty one polymorphic RAPD markers were scored on the mapping population: 30 heterozygous in 'Goldrich', 19 heterozygous in 'Valenciano', segregating 1:1, and 12 markers heterozygous in both parents, segregating 3:1. A total of 33 and 19 RAPD markers were mapped on the 'Goldrich' and 'Valenciano' maps respectively. Forteen primer combinations were used for AFLPs and all of them detected polymorphism. Ninety five markers segregating 1:1 were identified, of which 62 were heterozygous in the female parent 'Goldrich' and 33 in the male parent 'Valenciano'. Forty five markers were present in both parents and segregated 3:1. A total of 82 and 48 AFLP markers were mapped on the 'Goldrich' and 'Valenciano' maps. Twelve RFLPs probes were screened in the population, resulting in five loci segregating in the family, one locus heterozygous for 'Valenciano' and four heterozygous for both, segregating 1:2:1. Of the 45 SSRs screened 17 segregated in the mapping family, resulting in seven loci heterozygous for the maternal parent and ten heterozygous for both, segregating 1:2:1 or 1:1:1:1. A total of 16 and 13 co-dominant markers were mapped in the female and male parent maps respectively. A total of 132 markers were placed into eight linkage groups on the 'Goldrich' map, defining 511 cM of the total map-length. The average distance between adjacent markers was 3.9 cM. A total of 80 markers were placed into seven linkage groups on the 'Valenciano' map, defining 467.2 cM of the total map-distance, with an average interval of 5.8 cM between adjacent markers. Thirty six marker loci heterozygous in both parents revealed straightforward homologies between five linkage groups in both maps. The sharka resistance trait mapped on linkage group 2. The region containing sharka resistance is flanked by two co-dominant markers that will be used for targeted SSR development employing a recently constructed complete apricot BAC library. SSRs tightly linked to sharka resistance will facilitate MAS in breeding for resistance in apricot.     

Identification of RFLP and NBS/PK profiling markers for disease resistance loci in genetic maps of oats

Two of the domains most widely shared among R genes are the nucleotide binding site (NBS) and protein kinase (PK) domains. The present study describes and maps a number of new oat resistance gene analogues (RGAs) with two purposes in mind: (1) to identify genetic regions that contain R genes and (2) to determine whether RGAs can be used as molecular markers for qualitative loci and for QTLs affording resistance to Puccinia coronata. Such genes have been mapped in the diploid A. strigosa × A. wiestii (Asw map) and the hexaploid MN841801-1 × Noble-2 (MN map). Genomic and cDNA NBS-RGA probes from oat, barley and wheat were used to produce RFLPs and to obtain markers by motif-directed profiling based on the NBS (NBS profiling) and PK (PK profiling) domains. The efficiency of primers used in NBS/PK profiling to amplify RGA fragments was assessed by sequencing individual marker bands derived from genomic and cDNA fragments. The positions of 184 markers were identified in the Asw map, while those for 99 were identified in the MN map. Large numbers of NBS and PK profiling markers were found in clusters across different linkage groups, with the PK profiling markers more evenly distributed. The location of markers throughout the genetic maps and the composition of marker clusters indicate that NBS- and PK-based markers cover partly complementary regions of oat genomes. Markers of the different classes obtained were found associated with the two resistance loci, PcA and R-284B-2, mapped on Asw, and with five out of eight QTLs for partial resistance in the MN map. 53 RGA-RFLPs and 187 NBS/PK profiling markers were also mapped on the hexaploid map A. byzantina cv. Kanota × A. sativa cv. Ogle. Significant co-localization was seen between the RGA markers in the KO map and other markers closely linked to resistance loci, such as those for P. coronata and barley yellow dwarf virus (Bydv) that were previously mapped in other segregating populations.     

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.     

A genetic linkage map of lentil (Lens sp.) based on RAPD and AFLP markers using recombinant inbred lines

 A genetic linkage map of Lens sp. was constructed with 177 markers (89 RAPD, 79 AFLP, six RFLP and three morphological markers) using 86 recombinant inbred lines (F_6:8) obtained from a partially interspecific cross. The map covered 1073 cM of the lentil genome with an average distance of 6.0 cM between adjacent markers. Previously mapped RFLP markers were used as anchor probes. The morphological markers, pod indehiscence, seed-coat pattern and flower-color loci were mapped. Out of the total linked loci, 8.4% showed segregation distortion. More than one-fourth of the distorted loci were clustered in one linkage group. AFLP markers showed more segregation distortion than the RAPD markers. The AFLP and RAPD markers were intermingled and clustering of AFLPs was seldom observed. This is the most extensive genetic linkage map of lentil to-date. The marker density of this map could be used for the identification of markers linked to quantitative trait loci in this population. Received: 6 November 1997 / Accepted: 10 February 1998     

Linkage mapping of AFLP markers in a wild population of great reed warblers: importance of heterozygosity and number of genotyped individuals

Amplified fragment length polymorphisms (AFLP) are dominant markers frequently used to build linkage maps where heterozygosity could be inferred by a backcross breeding strategy. In the present study, we describe the utilization of an unmanipulated great reed warbler, Acrocephalus arundinaceus pedigree to infer heterozygous genotypes of AFLP markers in order to map these markers to a partial linkage map previously based on microsatellites. In total, 50 of the 83 autosomal AFLPs (60%) and 4 of 5 Z-linked AFLPs (80%) were mapped. For each marker, on average, 88% of the expected number of heterozygote parents was detected. The likelihood of map assignment was to a large extent due to the number and density of microsatellite markers already in the map. The 'parsimonious linkage map', that is the map based on the most parsimonious location of all significantly linked markers, consisted of 21 autosomal linkage groups with 2 to 15 markers and had a total map size of 552 cM in males and 858 cM in females. The Z-chromosome linkage group with 12 markers had a size of 155 cM. The autosomal 'framework linkage map', that is the map based only on markers with an unambiguous position, had a total size of 237 cM in males and 440 cM in females, respectively. The inclusion of AFLPs enlarged the previous map substantially (e.g. the autosomal parsimonious linkage map became 441 cM and 621 cM larger for male and female recombination, respectively). The probability that an AFLP became mapped increased with increasing level of heterozygosity, whereas the probability of mapping into a framework position increased with both heterozygosity and number of genotyped individuals. Our results suggest that AFLP provides a fast and inexpensive means of enlarging genetic maps already composed of markers with high polymorphism, also in wild populations with unmanipulated pedigrees.     

Isolation and mapping of resistance gene analogs from the Avena strigosa genome

Degenerate primers based on conserved regions of the nucleotide binding site (NBS) domain (encoded by the largest group of cloned plant disease resistance genes) were used to isolate a set of 15 resistance gene analogs (RGA) from the diploid species Avena strigosa Schreb. These were grouped into seven classes on the basis of 60% or greater nucleic acid sequence identity. Representative clones were used for genetic mapping in diploid and hexaploid oats. Two RGAs were mapped at two loci of the linkage group AswBF belonging to the A. strigosa × A. wiestii Steud map, and ten RGAs were mapped at 15 loci in eight linkage groups belonging to the A. byzantina C. Koch cv. Kanota × A. sativa L. cv. Ogle map. A similar approach was used for targeting genes encoding receptor-like kinases. Three different sequences were obtained and mapped to two linkage groups of the hexaploid oat map. Associations were explored between already known disease resistance loci mapped in different populations and the RGAs. Molecular markers previously linked to crown rust and barley yellow dwarf resistance genes or quantitative trait loci were found in the Kanota × Ogle map linked to RGAs at a distance ranging from 0 cM to 20 cM. Homoeologous RGAs were found to be linked to loci either conferring resistance to different isolates of the same pathogen or to different pathogens. This suggests that these RGAs identify genome regions containing resistance gene clusters.     

Towards a saturated sorghum map using RFLP and AFLP markers

 A near-saturated sorghum genetic linkage map was produced using RFLP, AFLP and morphological markers. First a composite, essentially RFLP-based genetic linkage map was obtained from analyses of two recombinant inbred populations. This map includes 343 loci for 11 linkage groups spanning 1352 cM. Since this map was constructed with many previously mapped heterologous probes, it offers a good basis for synteny studies. Separately, an AFLP map was obtained from the analysis of 168 bands revealed from 12 primer pair combinations. It includes 137 loci for 11 linkage groups spanning 849 cM. Taking into account the different data sets, we constructed a combined genetic linkage map including 443 loci spanning 1899 cM. Two main features are to be noted: (1) the distribution of AFLPs along the genome is not uniform; (2) an important stretching of the former core map is induced after adding the AFLPs. Received: 10 May 1998 / Accepted: 13 July 1998     

An apricot (Prunus armeniaca L.) F2 progeny linkage map based on SSR and AFLP markers,mapping plum pox virus resistance and self-incompatibility traits

A genetic linkage map of apricot ( Prunus armeniaca L.) was constructed using AFLP and SSR markers. The map is based on an F(2) population (76 individuals) derived from self-pollination of an F(1) individual ('Lito') originated from a cross between 'Stark Early Orange' and 'Tyrinthos'. This family, designated as 'Lito' x 'Lito', segregated for two important agronomical traits: plum pox virus resistance (PPV) and self-incompatibility. A total of 211 markers (180 AFLPs, 29 SSRs and two agronomic traits) were assigned to 11 linkage groups covering 602 cM of the apricot genome. The average distance (cM/marker) between adjacent markers is 3.84 cM. The PPV resistance trait was mapped on linkage group G1 and the self-incompatibility trait was mapped on linkage group G6. Twenty two loci held in common with other Prunus maps allowed us to compare and establish homologies among the respective linkage groups.     

An integrated molecular linkage map of diploid wheat based on a <Emphasis Type="Italic">Triticum boeoticum</Emphasis> × <Emphasis Type="Italic">T. monococcum</Emphasis> RIL population

Diploid A genome species of wheat harbour immense variability for biotic stresses and productivity traits, and these could be transferred efficiently to hexaploid wheat through marker assisted selection, provided the target genes are tagged at diploid level first. Here we report an integrated molecular linkage map of A genome diploid wheat based on 93 recombinant inbred lines (RILs) derived from Triticum boeoticum × Triticum monococcum inter sub-specific cross. The parental lines were analysed with 306 simple sequence repeat (SSR) and 194 RFLP markers, including 66 bin mapped ESTs. Out of 306 SSRs tested for polymorphism, 74 (24.2%) did not show amplification (null) in both the parents. Overall, 171 (73.7%) of the 232 remaining SSR and 98 (50.5%) of the 194 RFLP markers were polymorphic. Both A and D genome specific SSR markers showed similar transferability to A genome of diploid wheat species. The 176 polymorphic markers, that were assayed on a set of 93 RILs, yielded 188 polymorphic loci and 177 of these as well as two additional morphological traits mapped on seven linkage groups with a total map length of 1,262 cM, which is longer than most of the available A genome linkage maps in diploid and hexaploid wheat. About 58 loci showed distorted segregation with majority of these mapping on chromosome 2A^m. With a few exceptions, the position and order of the markers was similar to the ones in other maps of the wheat A genome. Chromosome 1A^m of T. monococcum and T. boeoticum showed a small paracentric inversion relative to the A genome of hexaploid wheat. The described linkage map could be useful for gene tagging, marker assisted gene introgression from diploid into hexaploid wheat as well as for map based cloning of genes from diploid A genome species and orthologous genes from hexaploid wheat.     

Inheritance and mapping of a powdery mildew resistance gene introgressed from Avena macrostachya in cultivated oat

The powdery mildew resistance from Avena macrostachya was successfully introgressed into hexaploid oat (A. sativa). Genetic analysis of F₁, F₂, F₃ and BC₁ populations from two powdery-mildew resistant introgression lines revealed that the resistance is controlled by a dominant gene, tentatively designated Eg-5. Molecular marker analysis was conducted using bulked-segregant analysis in two segregating F₃ populations. One codominant simple sequence repeats (SSR) marker AM102 and four AFLP-derived PCR-based markers were successfully developed. The SSR marker AM102 and the STS marker ASE41M56 were linked to the gene Eg-5, with genetic distances of 2 and 0.4 cM, respectively, in both mapping populations. Three STS markers (ASE45M56, ASE41M61, ASE36M55) co-segregated with Eg-5 in one population while two (ASE45M56, ASE36M55) of them linked to Eg-5 with a genetic distance of 1 cM in another population. The gene was further mapped to be in a region corresponding to linkage group 22_44+18 in the Kanota × Ogle (KO) hexaploid oat map by comparative mapping. To our knowledge, this is the first report of mapping powdery-mildew resistance in hexaploid oat. The new resistance source of A. macrostachya, together with the tightly linked markers identified here, could be beneficial in oat breeding programmes.     

RFLP genetic linkage maps from four F(2.3) populations and a joinmap of Gossypium hirsutum L

An RFLP genetic linkage joinmap was constructed from four different mapping populations of cotton (Gossypium hirsutum L.). Genetic maps from two of the four populations have been previously reported. The third genetic map was constructed from 199 bulk-sampled plots of an F_2.3 (HQ95–6×’MD51ne’) population. The map comprises 83 loci mapped to 24 linkage groups with an average distance between markers of 10.0 centiMorgan (cM), covering 830.1 cM or approximately 18% of the genome. The fourth genetic map was developed from 155 bulk-sampled plots of an F_2.3 (119– 5 sub-okra×’MD51ne’) population. This map comprises 56 loci mapped to 16 linkage groups with an average distance between markers of 9.3 cM, covering 520.4 cM or approximately 11% of the cotton genome. A core of 104 cDNA probes was shared between populations, yielding 111 RFLP loci. The constructed genetic linkage joinmap from the above four populations comprises 284 loci mapped to 47 linkage groups with the average distance between markers of 5.3 cM, covering 1,502.6 cM or approximately 31% of the total recombinational length of the cotton genome. The linkage groups contained from 2 to 54 loci each and ranged in distance from 1.0 to 142.6 cM. The joinmap provided further knowledge of competitive chromosome arrangement, parental relationships, gene order, and increased the potential to map genes for the improvement of the cotton crop. This is the first genetic linkage joinmap assembled in G. hirsutum with a core of RFLP markers assayed on different genetic backgrounds of cotton populations (Acala, Delta, and Texas plain). Research is ongoing for the identification of quantitative trait loci for agronomic, physiological and fiber quality traits on these maps, and the identification of RFLP loci lineage for G. hirsutum from its diploid progenitors (the A and D genomes). Received: 23 February 2001 / Accepted: 8 June 2001     

Segregation distortion and linkage analysis in eggplant (Solanum melongena L.)

An anther-derived doubled haploid (DH) population and an F2 mapping population were developed from an intraspecific hybrid between the eggplant breeding lines 305E40 and 67/3. The former incorporates an introgressed segment from Solanum aethiopicum Gilo Group carrying the gene Rfo-sa1, which confers resistance to Fusarium oxysporum; the latter is a selection from an intraspecific cross involving two conventional eggplant varieties and lacks Rfo-sa1. Initially, 28 AFLP primer combinations (PCs) were applied to a sample of 93 F2 individuals and 93 DH individuals, from which 170 polymorphic AFLP fragments were identified. In the DH population, the segregation of 117 of these AFLPs as well as markers closely linked to Rfo-sa1 was substantially distorted, while in the F2 population, segregation distortion was restricted to just 10 markers, and thus the latter was chosen for map development. A set of 141 F2 individuals was genotyped with 73 AFLP PCs (generating 406 informative markers), 32 SSRs, 4 tomato RFLPs, and 3 CAPS markers linked to Rfo-sa1. This resulted in the assignment of 348 markers to 12 major linkage groups. The framework map covered 718.7?cM, comprising 238 markers (212 AFLPs, 22 SSRs, 1 RFLP, and the Rfo-sa1 CAPS). Marker order and inter-marker distances in this eggplant map were largely consistent with those reported in a recently published SSR-based map. From an eggplant breeding perspective, DH populations produced by anther culture appear to be subject to massive segregation distortion and thus may not be very efficient in capturing the full range of genetic variation present in the parental lines.     

Comparison off genetic distance and order off DNA markers in five populations of rice.

A group of about 300 evenly distributed DNA markers from a high density RFLP linkage map of rice constructed using an F2 population derived from a japonica variety, Nipponbare, and an indica variety, Kasalath, were used to evaluate gene order and genetic distance in four other rice mapping populations. The purpose of this study was to determine the degree to which information gained from the high density linkage map could be applied to other mapping populations, particularly with regard to its utility in bridging quantitative traits and molecular and physical mapping information. The mapping populations consisted of two F2 populations derived from Dao Ren Qiao/Fl-1084 and Kinandangputi/Fl-1007, recombinant inbred lines from Asominori/IR24, and a backcross population from Sasanishiki/Habataki//Sasanishiki. All DNA markers commonly mapped in the four populations showed the same linkage groups as in the Nipponbare/Kasalath linkage map with conserved linkage order. The genetic distance between markers among the different populations did not vary to a significant level in any of the 12 chromosomes. The differences in some markers could be attributed to the size of the population used in the construction of the linkage maps. Furthermore, the conservation of linkage order found in the distal region of chromosomes 11 and 12 was also confirmed in the RFLP maps based on the four populations of rice. These suggest that any major genetic information from the Nipponbare/Kasalath map can be expected to be approximately the same in other crosses or populations. This high density RFLP linkage map, which is being utilized in constructing a physical map of rice, can be very useful in interpreting genome structure with great accuracy in other populations. Key words : linkage map, japonica, indica, gene order, genetic distance.     

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     

AFLP and CAPS linkage maps of Cryptomeria japonica

We have used two DNA marker systems, AFLP and CAPS, in a two-way pseudo-testcross strategy applied to an F₁ population to construct genetic linkage maps of two local sugi cultivars. The AFLP markers detected about eight polymorphisms per parent per primer combination. Using 38 primer combinations, 612 AFLPs were detected in ’Haara 4’ and ’Kumotooshi’, of which 305 segregated in a 1:1 ratio (P>0.05). A total of 91 markers (83 AFLP and 8 CAPS) in ’Haara 4’ and 132 (123 AFLP and 9 CAPS) in ’Kumotooshi’ were distributed among 19 and 23 linkage groups, respectively, each of which included 2–17 markers. Maps of ’Haara 4’ and ’Kumotooshi’ spanned 1266.1 cM and 1992.3 cM, and covered approximately 50% and 80% of the sugi genome, respectively. Sequences derived from cDNA, which were previously used to construct a sugi linkage map, were also placed on our linkage maps as CAPS markers. Where a ’two-way pseudo-testcross’ is used, more than half of the sugi CAPS developed can be used to construct linkage maps for each parental family. The saturation of mapped markers, and the integration of several linkage maps derived from different mapping populations, is anticipated in the near future. Received: 15 August 1999 / Accepted: 27 August 1999