Pseudo-testcross Mapping Strategy Research Articles

Constructing the wolfberry (Lycium spp.) genetic linkage map using AFLP and SSR markers

Genetic linkage maps are important for quantitative trait locus (QTL) and marker-assisted selection breeding. The wolfberry (Lycium spp.) is an important food and traditional medicine in China. However, few construction genetic linkage maps have been reported because of the lack of genomic and genetic resources. In this study, a population of 89 F1 seedings was derived from a cross between two heterozygous parents, L. chinense var. potaninii ‘BF-01’ (female) and L. barbarum var. auranticarpum ‘NH-01’ (male), in order to construct a genetic linkage map using simple sequence repeat (SSR) and amplified fragment length polymorphism (AFLP) markers based on the double pseudo-test cross mapping strategy. The resulting genetic map consisted of 165 markers (74 AFLPs and 91 SSRs) distributed across 12 linkage groups and spanned a total length of 557.6 cM with an average distance of 3.38 cM between adjacent markers. The 12 linkage groups contained 3 to 21 markers and ranged in length from 8.6 to 58.3 cM. Twenty-nine segregated markers distributed in the map were mainly located on LG4 and LG9 linkage groups at P<0.05. This is the first linkage map of Lycium species using SSR and AFLP markers, which can serve as basis for improving genes and selective breeding of the genome assembly.

Isolating QTL controlling sugarcane leaf blight resistance using a two-way pseudo-testcross strategy

Sugarcane leaf blight (SLB), caused by Stagonospora tainanensis, is one of the most harmful fungal diseases, threatening the sugarcane industry and causing high losses of cane yield and sugar in susceptible cultivars. Using a two-way pseudo-testcross mapping strategy in combination with array genotyping, two high-density genetic maps were constructed for sugarcane cultivars YT93-159 and ROC22 with mean densities of respectively 3.0 and 3.5 cM per marker, and covering respectively 4485 and 2720 cM of genetic distance. The maps showed highly conserved colinearity with the genome of the ancestral species Saccharum officinarum, supporting the reliability of the linkage configurations of the maps. Quantitative trait loci (QTL) analysis of SLB resistance revealed six QTL (qSLB-1–qSLB-6). The major QTL qSLB-1 explaining 16.4% of phenotypic variance was assigned as the main QTL, and the total percentages of phenotypic variance explained in YT93-159 and ROC22 were 37.9% and 17.6%, respectively. Nine transcription factor and seven pathogen receptor genes lying in the qSLB-1 interval were highly expressed and are proposed as candidate causal genes for SLB resistance.

Mapping quantitative trait loci conferring resistance to Marssonina leaf spot disease in Populus deltoides

Two large-effect QTLs and 14 candidate genes conferring resistance to Marssonina leaf spot disease were identified in an F1Populus deltoides pedigree, which provided valuable information for cloning the particular underlying genes in future. Marssonina leaf spot disease (MLSD), which is caused by Marssonina brunnea, is a devastating threat to poplar plantations. To map quantitative trait loci (QTLs) underlying resistance to MLSD, an F1P. deltoides pedigree has been established and genetic maps were constructed for the mapping parents according to the two-way pseudo-testcross mapping strategy. The female map contained 913 markers spanning a total genetic distance of 3132 cM, with linkage groups (LGs) corresponding to the 19 haploid chromosomes in poplar, whereas the paternal map contained 252 markers distributed on 22 LGs and covered a genetic length of 1809 cM. The established maps were further aligned to the poplar consensus genetic map based on the integrated SSR markers. The resistance to MLSD was recorded as a complex binary trait based on the black spot symptom on leaves. Analyses of QTLs revealed two large-effect QTLs in LGs VI and XVI, namely qMLSD-VI-1 and qMLSD-XVI-2, which explained 50.3% and 34.5% of the total phenotypic variance, respectively. A significant interaction between these two QTLs was detected based on a two-way ANOVA. In this mapping pedigree, the female parent contributed all of the QTL alleles conferring resistance to M. brunnea. Genome sequences in the target regions were obtained by aligning the QTL intervals to the poplar genome sequence with the mapped SSR markers. The importance and utility of the 14 candidate genes associated with disease resistance identified in the QTL intervals should be more thoroughly characterized in future studies.

Construction of a high-density genetic linkage map and QTL analysis for hazelnut breeding

Hazelnut breeding is a slow activity due to the long lifecycle of the plant, the long time between pollination and reliable phenotype observation in the progeny, the presence of self-incompatibility and the high level of heterozygosity. Improved knowledge on the hazelnut genome and the development of marker-assisted selection would greatly facilitate breeding programs. Objective of this study was the construction of high-density genetic maps and the detection of QTL (quantitative trait loci) related to phenological, vegetative and productive traits, by using an F1 progeny obtained by crossing ‘Tonda Gentile delle Langhe’ (female parent, hereafter TGdL) with ‘Merveille de Bollwiller’ (syn. ‘Hall’s Giant’ male parent, MB). Genotyping-by-sequencing (GBS), followed by SNP mining using a Samtools-based pipeline, yielded 7,980 SNP markers. Independent linkage maps were constructed for each parent on the basis of the double pseudo-testcross mapping strategy. The linkage map for TGdL consisted of 1,236 markers covering a total genetic length of 900.4 cM, with a mean inter-marker distance of 0.83 cM. A reciprocal translocation was detected in TGdL between two non-homologous chromosomes. The linkage map for MB was based on segregation at 1,211 markers covering a total genetic length of 899.1 cM, with a mean inter-marker distance of 0.82 cM. Plant and nut traits were recorded during five years and statistically analyzed with molecular data to identify marker/QTL associations for flowering and bud burst time, sucker habit and nut traits, such as nut and seed size, roundness index, percent kernel and ease of pellicle removal.

High density SNP mapping and QTL analysis for time of leaf budburst in Corylus avellana L.

The growing area of European hazelnut (Corylus avellana L.) is increasing, as well as the number of producing countries, and there is a pressing need for new improved cultivars. Hazelnut conventional breeding process is slow, due to the length of juvenile phase and the high heterozygosity level. The development of genetic linkage maps and the identification of molecular markers tightly linked to QTL (quantitative trait loci) of agronomic interest are essential tools for speeding up the selection of seedlings carrying desired traits through marker-assisted selection. The objectives of this study were to enrich a previous linkage map and confirm QTL related to time of leaf budburst, using an F1 population obtained by crossing Tonda Gentile delle Langhe with Merveille de Bollwiller. Genotyping-by-Sequencing was used to identify a total of 9,999 single nucleotide polymorphism markers. Well saturated linkage maps were constructed for each parent using the double pseudo-testcross mapping strategy. A reciprocal translocation was detected in Tonda Gentile delle Langhe between two non-homologous chromosomes. Applying a bioinformatic approach, we were able to disentangle ‘pseudo-linkage’ between markers, removing markers around the translocation breakpoints and obtain a linear order of the markers for the two chromosomes arms, for each linkage group involved in the translocation. Twenty-nine QTL for time of leaf budburst were identified, including a stably expressed region on LG_02 of the Tonda Gentile delle Langhe map. The stability of these QTL and their coding sequence content indicates promise for the identification of specific chromosomal regions carrying key genes involved in leaf budburst.

QTLs for Woolly Poplar Aphid (Phloeomyzus passerinii L.) Resistance Detected in an Inter-Specific Populus deltoides x P. nigra Mapping Population.

The genus Populus represents one of the most economically important groups of forest trees. It is composed by approximately 30 species used for wood and non-wood products, phytoremediation and biomass. Poplar is subjected to several biological and environmental threats although, compared to annual crops, we know far less about the genetic bases of biotic stress resistance. Woolly poplar aphid (Phloeomyzus passerinii) is considered a main pest of cultivated poplars in European and American countries. In this work we present two high density linkage maps in poplar obtained by a genotyping by sequencing (GBS) approach and the identification of QTLs involved in Ph. passerinii resistance. A total of 5,667 polymorphic markers (5,606 SNPs and 61 SSRs) identified on expressed sequences have been used to genotype 131 plants of an F1 population P ×canadensis obtained by an interspecific mate between Populus deltoides (resistant to woolly poplar aphid) and Populus nigra (susceptible to woolly poplar aphid). The two linkage maps, obtained following the two-way pseudo-testcross mapping strategy, have been used to investigate the genetic bases of woolly poplar aphid resistance. One major QTL and two QTLs with minor effects (mapped on LGV, LGXVI and LG XIX) explaining the 65.8% of the genetic variance observed in the progeny in response to Ph. passerinii attack were found. The high density coverage of functional markers allowed the identification of three genes belonging to disease resistance pathway as putative candidates for P. deltoides resistance to woolly poplar aphid. This work is the first report on genetic of woolly poplar aphid genetic resistance and the resistant loci associated markers identified represent a valuable tool in resistance poplar breeding programs.

Heterozygosities and genetic relationship of tea cultivars revealed by simple sequence repeat markers and implications for breeding and genetic mapping programs.

Genetic maps are essential tools for quantitative trait locus analysis and marker-assisted selection breeding. In order to select parents that are highly heterozygous for genetic mapping, the heterozygosity (HS) of 24 tea cultivars (Camellia sinensis) was analyzed with 72 simple sequence repeat markers. In total, 359 alleles were obtained with an average of 4.99 per marker. The HS varied greatly from 37.5 to 71.0% with an average of 51.3%. On average, tea cultivars from Fujian Province showed a higher level of heterozygosity (59.8%) than those from Zhejiang (48.5%) and Yunnan (44.5%), and the 12 national tea cultivars were generally more heterozygous than the 12 provincial cultivars. Unweighted pair-group analysis using the arithmetic average grouping divided the 24 cultivars into 2 groups that are consistent with the morphological classification. All dual combinations of the 24 cultivars were studied to calculate the percentage of mappable markers when using pseudo-testcross mapping strategy, and results showed that this value also varied greatly from 51.4 to 90.3%. The genetic relationships and HS differences among different cultivars were discussed, and tea cultivars with high HS were recommended as cross parents for genetic mapping programs.

Preliminary genetic linkage maps of Chinese herb Dendrobium nobile and D. moniliforme

Dendrobium is an endangered genus in the orchid family with medicinal and horticultural value. Two preliminary genetic linkage maps were constructed using 90 F1 progeny individuals derived from an interspecific cross between D. nobile and D. moniliforme (both, 2n = 38), using random amplified polymorphic DNA (RAPD) and intersimple sequence repeat (ISSR). A total of 286 RAPD loci and 68 ISSR loci were identified and used for genetic linkage analysis. Maps were constructed by double pseudo-testcross mapping strategy using the software Mapmaker/EXP ver. 3.0, and Kosambi map distances were constructed using a LOD score greater than or equal to 4 and a recombination threshold of 0.4. The resulting frame map of D. nobile was 1474 cM in total length with 116 loci distributed in 15 linkage groups; and the D. moniliforme linkage map had 117 loci placed in 16 linkage groups spanning 1326.5 cM. Both maps showed 76.91% and 73.59% genome coverage for D. nobile and D. moniliforme, respectively. These primary maps provide an important basis for genetic studies and further medicinal and horticultural traits mapping and marker-assisted selection in Dendrobium breeding programmes.

First genetic linkage map in pistachio constructed using an interspecific cross between Pistacia vera L. and monoecious Pistacia atlantica Desf.

This study was performed to construct the first genetic linkage map of pistachio using progeny from a cross between Pistacia vera L. ‘Siirt’ and monoecious Pistacia atlantica Desf. (Pa-18 genotype). In total, 242 primers were screened. Seventy inter-simple sequence repeat (ISSR), sequence-related amplified polymorphism (SRAP), and amplified fragment length polymorphism (AFLP) primer pairs were chosen, and they produced 321 segregating markers. A double pseudo-testcross mapping strategy was applied to construct the ‘Siirt’ and ‘Pa-18’ maps. The ‘Siirt’ map consisted of 144 testcross and 21 intercross markers, and the ‘Pa-18’ map included 134 testcross and 22 intercross markers. The ‘Siirt’ map had 17 linkage groups spanning 1237.3cM with a mean marker density of 7.50cM, while the ‘Pa-18’ map comprised 19 linkage groups covering 1337.5cM, with the average marker density being 8.57cM. One hundred fifty-seven of the segregating markers were distorted, of which 38.2% were in the ‘Siirt’ map, and 60.3% were in the ‘Pa-18’ map. The maps of P. vera and monoecious P. atlantica may help to clarify the genetic basis of sex determination and inheritance in Pistacia, as well as other notable agronomic characters, and in identifying markers for marker-assisted selection.

Linkage map construction and QTL analysis for Betula platyphylla Suk using RAPD, AFLP, ISSR and SSR

AbstractA linkage map for Betula platyphylla Suk was constructed based on RAPD, ISSR, AFLP and SSR markers by a pseudo-testcross mapping strategy. A F1segregating population including 80 progenies was obtained from the cross between two superior trees selected from Qinghai and Wangqing provenance, respectively. The paternal map was constructed with 282 markers consisting of 14 major and 15 minor (5 triplets and 10 doublets) linkage groups and spanning 1131 cM at an average distance of 4.0 cM between adjacent markers. The maternal map has 277 markers consisting of 15 major and 8 minor (5 triplets and 3 doublets) groups covering 1288 cM at an average distance of 4.6 cM between adjacent markers. In the same pedigree we investigated association of genetic markers with seedling stem height and circumference. The composite interval mapping was used to detect the number of quantitative trait loci and their position on the genetic linkage maps. Three QTLs (one on the male map and two on the female map) were found explaining 13.4%, 17.5% and 18.8% of the trait variation, respectively.

Molecular marker-based genetic linkage map of a diploid banana population (Musa acuminata Colla)

A well-saturated genetic linkage map is valuable for fundamental and applied genetic research. Genetic linkage maps of two half-sib diploid banana populations were constructed using allele-specific-polymerase chain reactions (AS-PCRs), diversity array technology (DArT), and simple sequence repeat (SSR) markers. Molecular maps were produced for each parent using the pseudo-testcross mapping strategy. The first maternal map (6142-1, 81 individuals) consisted of 231 markers divided as followed: 121 DArT, 106 SSR and 4 AS-PCR markers in 15 linkage groups (LGs) covering 670 cM. The second maternal map (6142-1-S, 58 individuals) contained a total of 152 markers including 71 DArTs, 79 SSRs, and 2 AS-PCRs mapped to 16 LGs that spanned 698 cM. The combined paternal map (139 individuals) comprised 316 markers (196 DArTs, 117 SSRs and 3 AS-PCRs) distributed over 15 LGs with a total map length of 1,004 cM. While distorted segregation of some markers was observed in all maps, this was much more frequent for the male parent. Homology between maps was assessed using common markers. While there was generally good congruity with regard to marker order across maps, incongruity in other cases may reflect chromosomal rearrangement events such as inversions, translocations, or deletions. The new banana map can provide a better understanding of the Musa genome and could be used for the identification of economically important traits and improvement of breeding strategies.

Construction of a linkage map for quantitative trait loci associated with economically important traits in creeping bentgrass (Agrostis stolonifera L.)

Creeping bentgrass (Agrostis stolonifera L.) is the most widely cultivated and high-value turfgrass species. Genetic linkage maps of creeping bentgrass were constructed for quantitative trait loci (QTL) analysis of gray snow mold (Typhula incarnata) resistance, recovery and leaf width. A segregating population of 188 pseudo-F2 progeny was developed by two-way pseudo-testcross mapping strategy. Amplified fragment length polymorphism, new developed Agrostis specific expressed sequence tag-single sequence repeat (SSR), random amplified polymorphic DNA and genomic SSR markers corresponding to DNA polymorphisms heterozygous in one parent and null in the other, were scored and placed on two separate genetic linkage maps, representing each parent. In the male parent map, 100 markers were mapped to 14 linkage groups covering a total length of 793 cM with an average interval of 8.2 cM. In the female parent map, 146 markers were clustered in another 14 linkage groups spanning 805 cM with an average distance of 5.9 cM between adjacent markers. We identified three putative QTL for leaf width and one QTL for snow mold disease resistance. The construction of a linkage map and QTL analysis are expected to facilitate the development of disease resistant creeping bentgrass cultivars by using molecular marker-assisted selection.

Genetic Linkage Map and Diversity Analysis of Tahitian Vanilla (Vanilla ×tahitensis, Orchidaceae)

ABSTRACTThe first vanilla genetic linkage map was constructed by analyzing the progeny of an interspecific cross between Vanilla ×tahitensis J. W. Moore (pro sp.) and Vanilla pompona Schiede. The two‐way pseudotestcross mapping strategy was used and a total of 225 amplified fragment length polymorphism (AFLP) markers were mapped on 18 linkage groups covering 1035.85 cM. Thirteen tahitian vanilla morphotypes, one Vanilla planifolia Andrews and recent hybrids were compared by measuring seven morphological traits and by genotyping, with 539 AFLP fragments. The morphotypes studied showed relatively homogenous stem traits but differed in their bean and leaf traits as in their AFLP pattern. Genetic variability and AFLP genotyping comparison suggest a diversification in French Polynesia based on sexual reproduction and are consistent with the hypothesis of a single introduction event. These results are the first step for vanilla breeding program and will be also useful for tahitian vanilla resource preservation.

Development of DArT markers in olive (Olea europaea L.) and usefulness in variability studies and genome mapping

The present study reports the setting up of Diversity Arrays Technology (DArT) markers in olive (Olea europaea L.). Two genomic representations were generated using the PstI/TaqI combination. A first one was aimed to cover the variability available at the World Olive Germplasm Bank (WOGB) and it was based on DNA from 87 olive cultivars carefully selected from the WOGB to represent the olive variability. The second one was obtained from DNA of the parents of a mapping population, ‘Picual’ and ‘Arbequina’, and was used to increase the number of markers segregating within them. A total of 2031 and 1630 markers were used for diversity and mapping analyses, respectively to test the utility of DArT markers in olive. A set of 62 cultivars was genotyped with olive-specific DArT markers. A dendrogram was constructed confirming the relationships among olive cultivars reported in previous works. Besides, DArT markers permitted the unambiguous discrimination of all 62 genotypes confirming thus their utility for identification studies, an important issue for management of germplasm collections. DArT markers also allowed the construction of a genetic map of olive using the population derived from the cross ‘Picual’בArbequina’ and the pseudo-testcross mapping strategy. This map will be used as a framework map to add new markers derived from olive sequencing originating from the project OLEAGEN. In conclusion, olive-specific DArT markers will enhance identification and genetic studies in olive given their high throughput and low cost per data.

Linkage mapping of the Mediterranean cypress, Cupressus sempervirens, based on molecular and morphological markers

Gene mapping for a Cupressus species is presented for the first time. Two linkage maps for the Mediterranean cypress (Cupressus sempervirens) varieties, C. sempervirens var. horizontalis and C. sempervirens var. pyramidalis, were constructed following the pseudo-testcross mapping strategy and employing RAPD, SCAR and morphological markers. A total of 427 loci (425 RAPDs, two SCARs) representing parents and F(1) progeny were screened for polymorphism with 32 random decamer and two SCAR primers. A morphological marker defined as "crown form" was also included. Of 274 polymorphic loci, the 188 that presented Mendelian inheritance formed the mapping dataset. Of these loci, 30% were mapped into seven linkage groups for the horizontalis (maternal) and four linkage groups for the pyramidalis (paternal) map. The putative "crown form" locus was included in a linkage group of both maps. The horizontalis and the pyramidalis maps covered 160.1 and 144.5 cM, respectively, while genome length was estimated to be 1696 cM for the former variety and 1373 cM for the latter. The four RAPD markers most tightly linked to crown form were cloned and converted to SCARs. Each of the cloned RAPD markers yielded two to three different sequences behaving as co-migrating fragments. Two SCAR markers, SC-D05(432) and SC-D09(667), produced amplified bands of the expected sizes and maintained linkage with the appropriate phenotype, but to a lesser extent compared to their original RAPD counterparts. These linkage maps represent a first step towards the localization of QTLs and genes controlling crown form and other polygenic traits in cypress.

Comparative genome mapping among Populus adenopoda, P. alba, P. deltoides, P. euramericana and P. trichocarpa

Among the genus Populus, the sections Populus (white poplar), Aigeiros Duby (black poplar) and Tacamahaca Spach contain many tree species of economical and ecological important properties. Two parental maps for the inter-specific hybrid population of Populus adenopoda × P. alba (two species of Populus section) were constructed based on SSR and SRAP markers by means of a two-way pseudo-test cross mapping strategy. The same set of SSR markers developed from the P. trichocarpa (belonging to Tacamahaca section) genome which were used to construct the maps of P. deltoides and P. euramericana (two species of Aigeiros section) was chosen to analyze the genotype of the experimental population of P. adenopoda × P. alba. Using the mapped SSR markers as allelic bridges, the alignment of the white and black poplar maps to each other and to the P. trichocarpa physical map was conducted. The alignment showed high degree of marker synteny and colinearity and the closer relationship between Aigeiros and Tacamahaca sections than that of Populus and Tacamahaca. Moreover, there was evidence for the chromosomal duplication and inter-chromosomal reorganization involving some poplar linkage groups, suggesting a complicated course of fission or fusion in one of the lineages. A poplar consensus map based on the comparisons could be constructed will be useful in practical applications including marker assisted selection.

Construction of Genetic Linkage Maps of Larch (Larix Kaempferi × Larix Gmelini) by Rapd Markers and Mapping of QTLS for Larch

ABSTRACTGenetic linkage mapping was performed with an interspecific mapping pedigree of 145 full-sib hybrids individuals of Japanese larch x Chinese larch (Larix kaempferi x Larix gmelini). A total of 210 random amplification of polymorphic DNA (RAPD) primers were used for mapping, and 581 segregating loci were identified. According to pseudo-testcross mapping strategy, we used mapping software to construct parent-specific linkage maps. The constructed linkage maps consisted of 48 sites in 5 linkage groups (four or more sites per group), 4 triplets, 6 linkage pairs for the maternal parent, and covered the map distance of about 546.5 cM, with the average map distance of 11.9 cM between adjacent markers. In addition, 91 sites in 9 linkage groups (four or more sites per group), 2 triplets, and 5 linkage pairs for the male parent covered the map distance of about 262.0 cM; the average map distance between adjacent markers was 6.1 cM. We detected the quantitative traits of the group by composite interval mapping, and analyzed the quantitative trait loci (QTL) with LOD ≥1.5. During analysis of the relationship between marker loci and traits, we obtained 4 and 20 QTLs, which were related to growth and timber characteristics. We found one QTL each for tracheid length and tracheid Length to Width ratio in Larix Kaempferi and nine, four, and five QTLs for specific gravity of wood, tracheid Length tracheid Width, respectively, in Larix gmelini. The LOD of every QTL was 1.5∼11.9, and the contribution rate was 0.0105∼45.9986%.

A preliminary research of genetic linkage map construction and QTL analysis for growth-related traits in yellow catfish (&lt;I&gt;Pelteobagrus fulvidraco&lt;/I&gt;)

Genetic linkage maps of yellow catfish (Pelteobagrus fulvidraco) were constructed using SSR,SRAP and TRAP markers and a pseudo-testcross mapping strategy. A segregating population including 100 progenies was sampled within the first filial generation obtained by artificial fertilization between a male parent and a female parent from wild and breeding populations respectively. Totally,13 SSR,89 SRAP and 26 TRAP markers were used to construct a genetic map. Female map included 16 linkage groups,covering a total of 585.5 cM in length. Male map included 15 linkage groups,covering a total of 752.3 cM in length. Combined map included 5 linkage groups,covering a total of 231.3 cM in length. This map was used to scan the QTL related to growth traits of yellow catfish. One head length QTLs were identified in female map located in LG7,LOD value is 3.2 and accounted for 13 % of phenotypic variation. A body width and a body length QTLs were identified in male map both located in LG1,LOD value is 2.4 and 2.1 respectively,and accounted for 12% and 11% of phenotypic variation respectively. Three QTLs could be considered to apply in marker-assisted selection for growth-related traits breeding of yellow catfish.

Genetic Linkage Mapping and Analysis of Muscle Fiber-Related QTLs in Common Carp (Cyprinus carpio L.)

A genetic linkage map of common carp (Cyprinus carpio L.) was constructed using Type I and Type II microsatellite markers and a pseudo-testcross mapping strategy. The microsatellite markers were isolated from microsatellite-enriched genomic libraries and tested for their segregation in a full-sib mapping panel containing 92 individuals. A total of 161 microsatellite loci were mapped into 54 linkage groups. The total lengths of the female, male and consensus maps were 2,000, 946, and 1,852cM, with an average marker spacing of approximately 13, 7, and 11cM, respectively. Muscle fiber-related traits, including muscle fiber cross-section area and muscle fiber density, were mapped to the genetic map. Three QTLs for muscle fiber cross-section area and two QTLs for muscle fiber density were identified when considering both significant and suggestive QTL effects. The QTLs with largest effects for muscle fiber cross-section area and muscle fiber density were 21.9% and 18.9%, and they were located in LG3, respectively.

A preliminary genetic linkage map of chrysanthemum ( Chrysanthemum morifolium) cultivars using RAPD, ISSR and AFLP markers

A genetic linkage map of chrysanthemum ( Chrysanthemum morifolium) was constructed by genotyping 142 F 1 progeny of the bi-parental cross ‘Yuhualuoying’ × ‘Aoyunhanxiao’ with a combination of RAPD, ISSR and AFLP markers in a double pseudo-testcross mapping strategy. A total of 567 polymorphic markers, including 153 RAPDs, 61 ISSRs and 353 AFLPs, were used in linkage mapping. 336 of 567 (60%) markers were grouped on the two parental maps, leaving 231 (40%) markers unlinked. In the ‘Yuhualuoying’ linkage map, 210 markers including 116 testcross and 94 intercross markers were placed in 12 major and 32 minor (8 triplets and 24 doublets) linkage groups, covering 1034 cM with an average map distance of 6.2 cM between adjacent markers. In ‘Aoyunhanxiao’ linkage map, 190 markers consisting of 113 testcross and 77 intercross markers were resolved into 9 major and 24 minor linkage groups, with genome coverage of 1095 cM and a mean inter-marker separation of 6.9 cM between adjacent markers. Six pairs of homologous linkage groups were established on the basis of 64 intercross markers shared by the two parental maps. The maps lay a foundation for further quantitative traits loci (QTL) mapping and marker-assisted breeding of chrysanthemum.