Construction of the First High-Density Genetic Linkage Map and Analysis of Quantitative Trait Loci for Growth-Related Traits in <Emphasis Type="Italic">Sinonovacula constricta</Emphasis>

The razor clam (Sinonovacula constricta) is an important aquaculture species, for which a high-density genetic linkage map would play an important role in marker-assisted selection (MAS). In this study, we constructed a high-density genetic map and detected quantitative trait loci (QTLs) for Sinonovacula constricta with an F₁ cross population by using the specific locus amplified fragment sequencing (SLAF-seq) method. A total of 315,553 SLAF markers out of 467.71 Mreads were developed. The final linkage map was composed of 7516 SLAFs (156.60-fold in the parents and 20.80-fold in each F₁ population on average). The total distance of the linkage map was 2383.85 cM, covering 19 linkage groups with an average inter-marker distance of 0.32 cM. The proportion of gaps less than 5.0 cM was on average 96.90%. A total of 16 suggestive QTLs for five growth-related traits (five QTLs for shell height, six QTLs for shell length, three QTLs for shell width, one QTL for total body weight, and one QTL for soft body weight) were identified. These QTLs were distributed on five linkage groups, and the regions showed overlapping on LG9 and LG13. In conclusion, the high-density genetic map and QTLs for S. constricta provide a valuable genetic resource and a basis for MAS.     

SSR-based genetic linkage map construction in pistachio using an interspecific F<Subscript>1</Subscript> population and QTL analysis for leaf and shoot traits

Pistachio is one of the most commercially important nut trees in the world. To characterize the genetic controls of horticultural traits and facilitate marker-assisted breeding in pistachio, we constructed an SSR-based linkage map using an interspecific F₁ population derived from a cross between the cultivar “Siirt” (Pistacia vera L.) and the monoecious Pa-18 genotype of Pistacia atlantica Desf. This population was also used for the first QTL analysis in pistachio on leaf and shoot characters. In total, 1312 SSR primers were screened, and 388 loci were successfully integrated into parental linkage maps. The Siirt maternal map contained 306 markers, while the “Pa-18” paternal map included 285 markers along the 15 linkage groups. The Siirt map spanned 1410.4 cM, with an average marker distance of 4.6 cM; the Pa-18 map covered 1362.5 cM with an average marker distance of 4.8 cM. Phenotypic data were collected during the growing seasons of 2015 and 2016 for four traits: leaf length (LL), leaf width (LW), leaf length/leaf width ratio (LWR), number of leaflet pairs (NLL), and young shoot color (YSC). A total of 17 QTLs were identified in the parental maps. Four QTLs for LL and LW were located on LG2 and LG4, while four QTLs for LWR ratio on LG13 and LG14, two QTLs for NLL and two QTLs for YSC were on LG7 and LG9, respectively, with similar positions in both parental maps. The SSR markers, linkage maps, and QTLs reported here will provide a valuable resource for future molecular and genetic studies in pistachio.     

SSR-based genetic mapping and QTL analysis for timing of spring bud flush,young shoot color,and mature leaf size in tea plant (<Emphasis Type="Italic">Camellia sinensis</Emphasis>)

Tea plant (Camellia sinensis) is a major beverage crop across the world. To uncover the genetic controls of agronomic traits and facilitate marker-assisted breeding (MAB) in tea plant, we constructed a saturated SSR-based linkage map using an F₁ population derived from the crossing of ‘Longjin43’ × ‘Baihaozao’. A total of 483 SSR markers, consisting of 117 novel loci, 129 transferred from other tea plant maps, and 237 previously mapped, were successfully integrated into a new consensus map. The map has 15 linkage groups, covering 1226.2 cM in total with an average marker distance of 2.5 cM. The 126 markers in common enabled us to align this map to the reference genetic maps of tea plant. Phenotype data were collected in 2014 and 2015 for five traits: timing of spring bud flush (TBF), young shoot color (YSC), mature leaf length (MLL), mature leaf width (MLW), and leaf shape index (LSI, i.e., MLL/MLW). QTL analyses were performed for the five traits using the new consensus map and 15 QTLs were identified. The SSR markers, linkage map, and QTLs reported here are useful resources for future QTL mining, identification of causal genes, and MAB in tea plant.     

Analysis of an intraspecific RIL population uncovers genomic segments harbouring multiple QTL for seed relevant traits in lentil (<Emphasis Type="Italic">Lens culinaris</Emphasis> L.)

Improving seed related traits remains key objective in lentil breeding. In recent years, genomic resources have shown great promise to accelerate crop improvement. However, limited genomic resources in lentil greatly restrict the use of genomics assisted breeding. The present investigation aims to build an intraspecific genetic linkage map and identify the QTL associated with important seed relevant traits using 94 recombinant inbreds (WA 8649090 × Precoz). A total of 288 polymorphic DNA markers including simple sequence repeat (SSR), inter simple sequence repeat (ISSR) and random amplified polymorphic DNA (RAPD) were assayed on mapping population. The resultant genetic linkage map comprised 220 loci spanning 604.2 cM of the lentil genome, with average inter-marker distance of 2.74 cM. QTL mapping in this RIL population uncovered a total of 18 QTL encompassing nine major and nine minor QTL. All major QTL were detected for seed related traits viz., seed diameter (SD), seed thickness (ST), seed weight (SW) and seed plumpness (SP) across two locations. A considerable proportion of the phenotypic variation (PV) was accounted to these QTL. For instance, one major QTL on LG5 controlling SW (QTL 15) explained 50% PV in one location, while the same QTL accounted for 34.18% PV in other location. Importantly, the genomic region containing multiple QTL for different seed traits was mapped to a 17-cM region on LG5. The genomic region harbouring QTL for multiple traits opens up exciting opportunities for genomics assisted improvement of lentil.     

Genetic mapping of local adaptation along the altitudinal gradient in <Emphasis Type="Italic">Abies sachalinensis</Emphasis>

Understanding the genetic bases of local adaptation in dominant conifer species is critical in predicting the impacts of rapid climate change on forest ecosystems. However, the genetic basis of adaptation is not yet fully understood due to the huge and complex genomes of conifers and the unavailability to date of suitable crossing material. In this study, we constructed a linkage map for Abies sachalinensis (2n = 24) and investigated quantitative trait loci (QTLs) associated with local adaptation along an altitudinal gradient. A segregating population of 239 seedlings was produced from a cross between two F₁ hybrids (high-altitude × low-altitude genotypes). QTL mapping of phenological and growth traits was performed using a pseudo-testcross strategy with linkage maps based on 1251 single-nucleotide polymorphism (SNP) and three simple sequence repeat (SSR) markers. Two maps consisting of 12 linkage groups with an average marker interval of ca. 3 cM were constructed for each parent. The total lengths of the maps were 1861 and 1949 cM. A permutation test identified four significant QTLs and 11 additional suggestive QTLs, with high logarithm of odds (LOD) scores (> 3.0). This is the first highly saturated linkage map produced for Abies taxa. Our results suggest that spring bud phenology is controlled by several QTLs with moderate effects. The use of the mapping population created by crossing two hybrids (high × low altitude genotypes) and numerous SNP markers enabled us to investigate the genetic basis of adaptive traits in conifer species.     

Genetic mapping and QTL analysis of agronomic traits in Indian <Emphasis Type="Italic">Mucuna pruriens</Emphasis> using an intraspecific F<Subscript>2</Subscript> population

Mucuna pruriens is a well-recognized agricultural and horticultural crop with important medicinal use. However, antinutritional factors in seed and adverse morphological characters have negatively affected its cultivation. To elucidate the genetic control of agronomic traits, an intraspecific genetic linkage map of Indian M. pruriens has been developed based on amplified fragment length polymorphism (AFLP) markers using 200 F ₂ progenies derived from a cross between wild and cultivated genotypes. The resulting linkage map comprised 129 AFLP markers dispersed over 13 linkage groups spanning a total distance of 618.88 cM with an average marker interval of 4.79 cM. For the first time, three QTLs explaining about 6.05–14.77% of the corresponding total phenotypic variation for three quantitative (seed) traits and, eight QTLs explaining about 25.96% of the corresponding total phenotypic variation for three qualitative traits have been detected on four linkage groups. The map presented here will pave a way for mapping of genes/QTLs for the important agronomic and horticultural traits contrasting between the parents used in this study.     

Constructing a genetic linkage map and mapping quantitative trait loci for skeletal traits in Japanese flounder

A genetic linkage map of Japanese flounder was constructed using 165 doubled haploids (DHs) derived from a single female. A total of 574 genomic microsatellites (type II SSRs) and expressed sequence tag (EST)-derived markers (EST-SSRs) were mapped to 24 linkage groups. The length of linkage map was estimated as 1270.9 centiMorgans (cM), with an average distance between markers of 2.2 cM. The EST-SSRs were used together with type II SSR markers to construct the Japanese flounder genetic linkage map which will facilitate identify quantitative trait locus (QTL) controlling important economic traits in Japanese flounder. Thus, twelve skeletal traits at 2 years of age were measured for all DHs. Forty-one QTLs were detected on 14 linkage groups and totally account for a small proportion of phenotypic variation (4.5 to 17.3%). Most of QTLs detected distribute on linkage groups 5 (9 QTLs), 8 (9 QTLs), 9 (5 QTLs) and 20 (4 QTLs), in which, some QTLs perform the pleiotropy.     

Oil palm (Elaeis guineensis Jacq.) linkage map,and quantitative trait locus analysis for sex ratio and related traits

Sex ratio and shell-thickness type are among the main components determining yield in oil palm. An integrated linkage map of oil palm was constructed based on 208 offspring derived from a cross between two tenera palms differing in inherited sex ratio. The map consisted of 210 genomic simple sequence repeats (SSRs), 28 expressed sequence tag SSRs, 185 amplified fragment length polymorphism markers, and the Sh locus, which controls shell-thickness phenotype, distributed across 16 linkage groups covering 1,931 cM, with an average marker distance of 4.6 cM. Quantitative trait locus (QTL) analysis identified eight QTLs across six linkage groups associated with sex ratio and related traits. These QTLs explained 8.1–13.1 % of the total phenotypic variance. The QTL for sex ratio on linkage group 8 overlapped with a QTL for number of male inflorescences. In most cases a specific QTL allele combination was responsible for genotype class mean differences, suggesting that most QTLs in heterozygous oil palm are likely to be segregating for multiple alleles with different degrees of dominance. In addition, two new SSRs were shown to flank the major Sh locus controlling the fruit variety type in oil palm.     

Construction of genetic linkage maps and QTL mapping for X-disease resistance in tetraploid chokecherry (Prunus virginiana L.) using SSR and AFLP markers

Chokecherry (Prunus virginiana L.) (2n = 4x = 32) is a unique Prunus species for both genetics and disease resistance research due to its tetraploid nature and known variations in X-disease resistance. X-disease is a destructive disease of stone fruit trees, causing yield loss and poor fruit quality. However, genetic and genomic information on chokecherry is limited. In this study, simple sequence repeat (SSR) and amplified fragment length polymorphism (AFLP) markers were used to construct genetic linkage maps and to identify quantitative trait loci (QTLs) associated with X-disease resistance in chokecherry. A segregating population (101 progenies) was developed by crossing an X-disease-resistant chokecherry line (RC) with a susceptible chokecherry line (SC). A total of 498 DNA markers (257 SSR and 241 AFLP markers) were mapped on the two genetic maps of the two parental lines (RC and SC). The map of RC contains 302 markers assigned to 14 linkage groups covering 2,089 cM of the genome. The map of SC has 259 markers assigned to 16 linkage groups covering 1,562.4 cM of the genome. The average distance between two markers was 6.9 cM for the RC map and 6.0 cM for the SC map. One QTL located on linkage group 15 on the map of SC was found to be associated with X-disease resistance. Genetic linkage maps and the identified QTL linked to X-disease resistance will further facilitate genetic research and breeding of X-disease resistance in chokecherry and other Prunus species.     

Linkage analysis and identification of quantitative trait loci associated with freeze tolerance and turf quality traits in St. Augustinegrass

St. Augustinegrass [Stenotaphrum secundatum (Walt.) Kuntze] is a warm-season turfgrass commonly grown in the southern USA. In this study, the first linkage map for all nine haploid chromosomes of the species was constructed for cultivar ‘Raleigh’ and cultivar ‘Seville’ using a pseudo-F₂ mapping strategy. A total of 160 simple sequence repeat markers were mapped to nine linkage groups (LGs) covering a total distance of 1176.24 cM. To demonstrate the usefulness of the map, quantitative trait loci (QTL) were mapped controlling field winter survival, laboratory-based freeze tolerance, and turf quality traits. Multiple genomic regions associated with these traits were identified. Moreover, overlapping QTL were found for winterkill and spring green up on LG 3 (99.21 cM); turf quality, turf density, and leaf texture on LG 3 (68.57–69.50 cM); and surviving green tissue and regrowth on LGs 1 (38.31 cM), 3 (77.70 cM), 6 (49.51 cM), and 9 (34.20 cM). Additional regions, where QTL identified in both field and laboratory-based/controlled environment freeze testing co-located, provided strong support that these regions are good candidates for true gene locations. These results present the first complete linkage map produced for St. Augustinegrass, providing a template for further genetic mapping. Additionally, markers linked to the QTL identified may be useful to breeders for transferring these traits into new breeding lines and cultivars.     

Genetic mapping and QTL analysis for yield and agronomic traits with an F2:3 population derived from a waxy corn × sweet corn cross

We constructed a framework map using SSR markers in the F₂ population derived from a cross between a waxy corn inbred line and a sweet corn inbred line. We constructed a genetic linkage map of the F_2:3 population employing 295 SSR markers on 158 F₂ individuals produced from the cross. The map comprised a total genomic length of 2,626.5 cM in 10 linkage groups and an average distance between markers of 8.9 cM. The number of loci per linkage group ranged from 27 (chr. 5) to 34 (chr. 7). The genetic distance per linkage group ranged from 213.6 cM (chr. 10) to 360.6 cM (chr. 2). Χ ² tests revealed that 254 markers (86.1 %) distributed over all 10 chromosomes exhibited a Mendelian segregation ratio of 1:2:1. A total of 14 quantitative trait loci (QTLs) for days to silking (DTS), plant height (PH), ear height (EH), ear height ratio (ER), ear length (L-ear), and setted ear length (L-sear) were found in the 158 F₂ progeny. They were mapped to chromosomes 1, 2, 3, 7, 8, and 10. Among them, one QTL was associated with DTS, three with PH, six with EH, one with ER, two with L-ear, and one QTL was related to L-sear. In our study, we found that four QTLs: qDTS1, qEH1a, qEH1b, and qPH1, were clustered between umc2390 and umc1603 on chromosome 1. These new QTLs identified by the present study could serve as useful molecular markers in selecting for yield and agronomic traits in maize. The results of this study may improve the identification and characterization of genes responsible for yield and agronomic traits in waxy corn and sweet corn.     

Genetic mapping of yield traits using RIL population derived from Fuchuan Dahuasheng and ICG6375 of peanut (<Emphasis Type="Italic">Arachis hypogaea</Emphasis> L.)

The genetic architecture determinants of yield traits in peanut (Arachis hypogaea L.) are poorly understood. In the present study, an effort was made to map quantitative trait loci (QTLs) for yield traits using recombinant inbred lines (RIL). A genetic linkage map was constructed containing 609 loci, covering a total of 1557.48 cM with an average distance of 2.56 cM between adjacent markers. The present map exhibited good collinearity with the physical map of diploid species of Arachis. Ninety-two repeatable QTLs were identified for 11 traits including height of main stem, total branching number, and nine pod- and seed-related traits. Of the 92 QTLs, 15 QTLs were expressed across three environments and 65 QTLs were newly identified. Twelve QTLs for the height of main stem and the pod- and seed-related traits explaining more than 10 % of phenotypic variation showed a great potential for marker-assisted selection in improving these traits. 相似文献   

Construction of a SNP-based genetic linkage map for kiwifruit using next-generation restriction-site-associated DNA sequencing (RADseq)

Kiwifruit is a perennial horticultural crop species of the Actinidiaceae family and has high nutritional value. For a species with a long generation time, traditional breeding and genetic improvement is predicted to take more than 20 years to obtain superior cultivars. Thus, marker-assisted selection (MAS) should be used to accelerate the breeding process. Development of a genetic linkage map and molecular markers are pre-requisites for MAS of crop species. Here, we report a genome-wide SNP-based genetic map of kiwifruit by analysing next-generation restriction-site-associated DNA sequencing (RADseq) reads. To construct a genetic linkage map, a 102 F1 line mapping population of Actinidia chinensis (2n = 58) was derived by combining parents that had contrasting phenotypic traits. The maternal map contained 4112 SNP loci and spanned a distance of 3821 cM, with an average adjacent-marker interval length of 0.929 cM. The map length of the 29 linkage groups ranged from 78.3 to 169.9 cM, with an average length of 131.8 cM. High levels of collinearity between the 29 genetic maps with the kiwifruit reference genome were found. The genetic map developed in this study can serve as an important platform to improve kiwifruit research, including anchoring unmapped scaffolds of the kiwifruit genome sequence and mapping QTLs (quantitative trait loci) that control economically important traits.     

A genetic linkage map based on AFLP and SSR markers and mapping of QTL for dry-matter content in sweetpotato

We developed a genetic linkage map of sweetpotato using amplified fragment length polymorphism (AFLP) and simple sequence repeat (SSR) markers and a mapping population consisting of 202 individuals derived from a broad cross between Xushu 18 and Xu 781, and mapped quantitative trait loci (QTL) for the storage root dry-matter content. The linkage map for Xushu 18 included 90 linkage groups with 2077 markers (1936 AFLP and 141 SSR) and covered 8,184.5 cM with an average marker distance of 3.9 cM, and the map for Xu 781 contained 90 linkage groups with 1954 markers (1824 AFLP and 130 SSR) and covered 8,151.7 cM with an average marker distance of 4.2 cM. The maps described herein have the best coverage of the sweetpotato genome and the highest marker density reported to date. These are the first maps developed that have 90 complete linkage groups, which is in agreement with the actual number of chromosomes. Duplex and triplex markers were used to detect the homologous groups, and 13 and 14 homologous groups were identified in Xushu 18 and Xu 781 maps, respectively. Interval mapping was performed first and, subsequently, a multiple QTL model was used to refine the position and magnitude of the QTL. A total of 27 QTL for dry-matter content were mapped, explaining 9.0–45.1 % of the variation; 77.8 % of the QTL had a positive effect on the variation. This work represents an important step forward in genomics and marker-assisted breeding of sweetpotato.     

High density SNP mapping and QTL analysis for fruit quality characteristics in peach (Prunus persica L.)

Single nucleotide polymorphisms (SNPs) were used to construct an integrated SNP linkage map of peach (Prunus persica (L.) Batsch). A set of 1,536 SNPs were evaluated with the GoldenGate® Genotyping assay in two mapping populations, Pop-DF, and Pop-DG. After genotyping and filtering, a final set of 1,400 high quality SNPs in Pop-DF and 962 in Pop-DG with full map coverage were selected and used to construct two linkage maps with JoinMap®4.0. The Pop-DF map covered 422 cM of the peach genome and included 1,037 SNP markers, and Pop-DG map covered 369 cM and included 738 SNPs. A consensus map was constructed with 588 SNP markers placed in eight linkage groups (n?=?8 for peach), with map coverage of 454 cM and an average distance of 0.81 cM/marker site. Placements of SNPs on the “peach v1.0” physical map were compared to placement on the linkage maps and several differences were observed. Using the SNP linkage map of Pop-DG and phenotypic data collected for three harvest seasons, a QTL analysis for fruit quality traits and chilling injury symptoms was carried out with the mapped SNPs. Significant QTL effects were detected for mealiness (M) and flesh bleeding (FBL) QTLs on linkage group 4 and flesh browning (FBr) on linkage group 5. This study represents one of the first examples of QTL detection for quality traits and chilling injury symptoms using a high-density SNP map in a single peach F1 family.     

Construction of a high-density SNP genetic map in flue-cured tobacco based on SLAF-seq

Tobacco (Nicotiana tabacum L., 2n = 48) is an important agronomic crop and model plant. Flue-cured tobacco is the most important type and accounts for approximately 80 % of tobacco production worldwide. The low genetic diversity of flue-cured tobacco impedes the construction of a high-density genetic linkage map using simple sequence repeat (SSR) markers and warrants the exploitation of single nucleotide polymorphic (SNP) markers from genomic regions. In this article, initially using specific locus-amplified fragment sequencing, we discovered 10,891 SNPs that were subsequently used as molecular markers for genetic map construction. Combined with SSR markers, a final high-density genetic map was generated containing 4215 SNPs and 194 SSRs distributed on 24 linkage groups (LGs). The genetic map was 2662.43 cM in length, with an average distance of 0.60 cM between adjacent markers. Furthermore, by mapping the SNP markers to the ancestral genomes of Nicotiana tomentosiformis and Nicotiana sylvestris, a large number of genome rearrangements were identified as occurring after the polyploidization event. Finally, using this novel integrated map and mapping population, two major quantitative trait loci (QTLs) were identified for flue-curing and mapped to the LG6 of tobacco. This is the first report of SNP markers and a SNP-based linkage map being developed in tobacco. The high-density genetic map and QTLs related to tobacco curing will support gene/QTL fine mapping, genome sequence assembly and molecular breeding in tobacco.     

Development of F1 hybrid population and the high-density linkage map for European aspen (<Emphasis Type="Italic">Populus tremula</Emphasis> L.) using RADseq technology

Background

Restriction-site associated DNA sequencing (RADseq) technology was recently employed to identify a large number of single nucleotide polymorphisms (SNP) for linkage mapping of a North American and Eastern Asian Populus species. However, there is also the need for high-density genetic linkage maps for the European aspen (P. tremula) as a tool for further mapping of quantitative trait loci (QTLs) and marker-assisted selection of the Populus species native to Europe.

Results

We established a hybrid F1 population from the cross of two aspen parental genotypes diverged in their phenological and morphological traits. We performed RADseq of 122 F1 progenies and two parents yielding 15,732 high-quality SNPs that were successfully identified using the reference genome of P. trichocarpa. 2055 SNPs were employed for the construction of maternal and paternal linkage maps. The maternal linkage map was assembled with 1000 SNPs, containing 19 linkage groups and spanning 3054.9 cM of the genome, with an average distance of 3.05 cM between adjacent markers. The paternal map consisted of 1055 SNPs and the same number of linkage groups with a total length of 3090.56 cM and average interval distance of 2.93 cM. The linkage maps were employed for QTL mapping of one-year-old seedlings height variation. The most significant QTL (LOD = 5.73) was localized to LG5 (96.94 cM) of the male linkage map, explaining 18% of the phenotypic variation.

Conclusions

The set of 15,732 SNPs polymorphic in aspen and high-density genetic linkage maps constructed for the P. tremula intra-specific cross will provide a valuable source for QTL mapping and identification of candidate genes facilitating marker-assisted selection in European aspen.

     

Identification of quantitative trait loci for resistance to Verticillium wilt and yield parameters in hop (Humulus lupulus L.)

Verticillium wilt (VW) can cause substantial yield loss in hop particularly with the outbreaks of the lethal strain of Verticillium albo-atrum. To elucidate genetic control of VW resistance in hop, an F₁ mapping population derived from a cross of cultivar Wye Target, with the predicted genetic basis of resistance, and susceptible male breeding line BL2/1 was developed to assess wilting symptoms and to perform QTL mapping. The genetic linkage map, constructed with 203 markers of various types using a pseudo-testcross strategy, formed ten major linkage groups (LG) of the maternal and paternal maps, covering 552.98 and 441.1 cM, respectively. A significant QTL for VW resistance was detected at LOD 7 on a single chromosomal region on LG03 of both parental maps, accounting for 24.2–26.0 % of the phenotypic variance. QTL analysis for alpha-acid content and yield parameters was also performed on this map. QTLs for these traits were also detected and confirmed our previously detected QTLs in a different pedigree and environment. The work provides the basis for exploration of QTL flanking markers for possible use in marker-assisted selection.     

QTL analysis of flower and fruit traits in sour cherry

The map locations and effects of quantitative trait loci (QTLs) were estimated for eight flower and fruit traits in sour cherry (Prunus cerasus L.) using a restriction fragment length polymorphism (RFLP) genetic linkage map constructed from a double pseudo-testcross. The mapping population consisted of 86 progeny from the cross between two sour cherry cultivars, Rheinische Schattenmorelle (RS)×Erdi Botermo (EB). The genetic linkage maps for RS and EB were 398.2 cM and 222.2 cM, respectively, with an average interval length of 9.8 cM. The RS/EB linkage map that was generated with shared segregating markers consisted of 17 linkage groups covering 272.9 cM with an average interval length of 4.8 cM. Eleven putatively significant QTLs (LOD >2.4) were detected for six characters (bloom time, ripening time, % pistil death, % pollen germination, fruit weight, and soluble solids concentration). The percentage of phenotypic variation explained by a single QTL ranged from 12.9% to 25.9%. Of the QTLs identified for the traits in which the two parents differed significantly, 50% had allelic effects opposite to those predicted from the parental phenotype. Three QTLs affecting flower traits (bloom time, % pistil death, and % pollen germination) mapped to a single linkage group, EB 1. The RFLP closest to the bloom time QTL on EB 1 was detected by a sweet cherry cDNA clone pS141 whose partial amino acid sequence was 81% identical to that of a Japanese pear stylar RNase. Received: 4 March 1999 / Accepted: 27 August 1999