Relationship between oviposition,virulence gene expression and parasitism success in <Emphasis Type="Italic">Cotesia typhae</Emphasis> nov. sp. parasitoid strains

Studying mechanisms that drive host adaptation in parasitoids is crucial for the efficient use of parasitoids in biocontrol programs. Cotesia typhae nov. sp. (Fernández-Triana) (Hymenoptera: Braconidae) is a newly described parasitoid of the Mediterranean corn borer Sesamia nonagrioides (Lefebvre) (Lepidoptera: Noctuidae). Braconidae are known for their domesticated bracovirus, which is injected with eggs in the host larva to overcome its resistance. In this context, we compared reproductive success traits of four Kenyan strains of C. typhae on a French and a Kenyan populations of its host. Differences were found between the four strains and the two most contrasted ones were studied more thoroughly on the French host population. Parasitoid offspring size was correlated with parasitism success and the expression of bracovirus virulence genes (CrV1 and Cystatin) in the host larva after parasitism. Hybrids between these two parasitoid strains showed phenotype and gene expression profiles similar to the most successful parental strain, suggesting the involvement of dominant alleles in the reproductive traits. Ovary dissections revealed that the most successful strain injected more eggs in a single host larva than the less successful one, despite an equal initial ovocyte number in ovaries. It can be expected that the amount of viral particles increase with the number of eggs injected. The ability to bypass the resistance of the allopatric host may in consequence be related to the oviposition behaviour (eggs allocation). The influence of the number of injected eggs on parasitism success and on virulence gene expression was evaluated by oviposition interruption experiments.     

Identification of QTLs related to cocoa resistance to three species of<Emphasis Type="Italic"> Phytophthora</Emphasis>

This study aimed to compare the genetic control of cacao resistance to three species of Phytophthora: Phytophthora palmivora, Phytophthora megakarya and Phytophthora capsici. The study was conducted on 151 hybrid progenies created in Côte d'Ivoire and grown in a green-house in Montpellier. Phytophthora resistance was screened by leaf-test inoculation with two different strains per species. Selection of the best individuals for resistance to P. palmivora at a 10% selection rate, would lead to a genetic progress of 47% in the disease evaluation for this species and a genetic progress of 42% and 21% for the two other species. A genetic map with a total length of 682 cM was built with 213 markers, 190 AFLPs and 23 microsatellites. QTLs were identified using composite interval mapping. QTLs were found located in six genomic regions. One of these was detected with five strains belonging to the three Phytophthora species. Two other regions were detected with two or three strains of two different species. Three additional QTLs were detected for only one species of Phytophthora. Each QTL explained between 8 to 12% of the phenotypic variation. For each strain, between 11.5% to 27.5% of the total phenotypic variation could be explained by the QTLs identified. The identification of multiple QTLs involved in resistance to Phytophthora offers the possibility to improve durability of resistance in cocoa by a possible cumulation of many different resistance genes located in different chromosome regions using marker-aided selection.Communicated by H.F. Linskens     

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.     

Genetic Mapping and QTL Analysis of Growth-Related Traits in the Pacific Oyster

The Pacific oyster (Crassostrea gigas) is one of the most important oysters cultured worldwide. To analyze the oyster genome and dissect growth-related traits, we constructed a sex-averaged linkage map by combining 64 genomic simple sequence repeats, 42 expressed sequence tag-derived SSRs, and 320 amplified fragment length polymorphism markers in an F₁ full-sib family. A total of 426 markers were assigned to 11 linkage groups, spanning 558.2 cM with an average interval of 1.3 cM and 94.7% of genome coverage. Segregation distortion was significant for 18.8% of the markers (P < 0.05), and distorted markers tended to occur on some genetic regions or linkage groups. Most growth-related quantitative traits were highly significantly (P < 0.01) correlated, and principal component analysis obtained four principal components. Quantitative trait locus (QTL) analysis identified three significant QTLs for two principal components, which explained 0.6–13.9% of the phenotypic variation. One QTL for sex was detected on linkage group 6, and the inheritabilities of sex for parental alleles and maternal alleles on that locus C15 are 39.8% and 0.01%, respectively. The constructed linkage map and determined QTLs can provide a tool for further genetic analysis of the traits and be potential for marker-assisted selection in C. gigas breeding.     

Molecular mapping and location of QTLs for drought-resistance traits in <Emphasis Type="Italic">indica</Emphasis> rice (<Emphasis Type="Italic">Oryza sativa</Emphasis> L.) lines adapted to target environments

Drought is a major limitation for rice production in rainfed ecosystems. Identifying quantitative trait loci (QTLs) linked to drought resistance provides opportunity to breed high yielding rice varieties suitable for drought-prone areas. Although considerable efforts were made in mapping QTLs associated with drought-resistance traits in rice, most of the studies involved indica × japonica crosses and hence, the drought-resistance alleles were contributed mostly by japonica ecotypes. It is desirable to look for genetic variation within indica ecotypes adapted to target environment (TE) as the alleles from japonica ecotype may not be expressed under lowland conditions. A subset of 250 recombinant inbred lines (RILs) of F₈ generation derived from two indica rice lines (IR20 and Nootripathu) with contrasting drought-resistance traits were used to map the QTLs for morpho-physiological and plant production traits under drought stress in the field in TE. A genetic linkage map was constructed using 101 polymorphic PCR-based markers distributed over the 12 chromosomes covering a total length of 1,529 cM in 17 linkage groups with an average distance of 15.1 cM. Composite interval mapping analysis identified 22 QTLs, which individually explained 4.8–32.2% of the phenotypic variation. Consistent QTLs for drought-resistance traits were detected using locally adapted indica ecotypes, which may be useful for rainfed rice improvement.     

DNA marking of some quantitative trait loci in the cultivated edible mushroom <Emphasis Type="Italic">Pleurotus ostreatus</Emphasis> (Fr.) Kumm.

Fungi of the genus Pleurotus, in particular, species Pleurotus ostreatus (common oyster mushroom) are among most cultivated fungi in the world. Due to intense rates of development of studies in this field, efficient breeding programs are highly required in the search for new P. ostreatus strains. The principal traits used worldwide for selecting strains are intensity of fruitbearing, fruit body cap color (for some consumptive markets), and mycelium growth rate. In this connection, the objective of this work was to study these quantitative traits and to find molecular markers, which could be employed to accomplish breeding programs. In general, we found 12 genomic loci (quantitative trait loci, QTLs) controlling mycelium growth rate of oyster and six QTLs responsible for the fruit body cap color. The genetic map of P. ostreatus was constructed, and all markers of quantitative traits found by us were located on this genetic map. The obtained linkage map can be a useful tool for the accomplishment of breeding programs to improve economically important traits of oyster mushroom.     

AFLP mapping and detection of quantitative trait loci (QTLs) for economically important traits in Pinus sylvestris: a preliminary study

We have applied a two-way pseudo-testcross strategy in an analysis of Pinus sylvestris for genetic mapping and detection of quantitative trait loci (QTLs) associated with economically important traits targeted in the Swedish tree-breeding programme. Based on 94 full-sib progeny of a cross between two plus-trees from northern Sweden we generated two parental maps using AFLP markers. The female map was comprised of 94 markers assigned to 15 linkage groups giving a size of 796 cM. On the male map 155 markers were assigned to 15 linkage groups, giving a total size of 1335 cM. The recombination frequency was found to be sex-dependent, being 29.3% higher in male than in female gametes. On the female map, 12 QTLs were detected (but none for branch diameter or wood density). Three QTLs for tree height accounted for 25.8% of the total phenotypic variation of this trait. When the QTLs detected for all the traits were taken independently, the percentages of phenotypic variance ranged from 9.3% to 22.7%. The highest value was observed for frost hardiness, an important trait in northern Sweden for which a major gene seemed to be involved. A cluster of QTLs for tree height, trunk diameter and volume was located on one linkage group. On the male map, four QTLs for trunk diameter and volume were detected. Due to the reduced number of individuals under study, the results are preliminary and have to be validated on more trees.     

Quantitative trait loci and underlying candidate genes controlling agronomical and fruit quality traits in octoploid strawberry <Emphasis Type="Italic">(Fragaria</Emphasis> × <Emphasis Type="Italic">ananassa</Emphasis>)

Breeding for fruit quality traits in strawberry (Fragaria × ananassa, 2n = 8x = 56) is complex due to the polygenic nature of these traits and the octoploid constitution of this species. In order to improve the efficiency of genotype selection, the identification of quantitative trait loci (QTL) and associated molecular markers will constitute a valuable tool for breeding programs. However, the implementation of these markers in breeding programs depends upon the complexity and stability of QTLs across different environments. In this work, the genetic control of 17 agronomical and fruit quality traits was investigated in strawberry using a F₁ population derived from an intraspecific cross between two contrasting selection lines, ‘232’ and ‘1392’. QTL analyses were performed over three successive years based on the separate parental linkage maps and a pseudo-testcross strategy. The integrated strawberry genetic map consists of 338 molecular markers covering 37 linkage groups, thus exceeding the 28 chromosomes. 33 QTLs were identified for 14 of the 17 studied traits and approximately 37% of them were stable over time. For each trait, 1–5 QTLs were identified with individual effects ranging between 9.2 and 30.5% of the phenotypic variation, indicating that all analysed traits are complex and quantitatively inherited. Many QTLs controlling correlated traits were co-located in homoeology group V, indicating linkage or pleiotropic effects of loci. Candidate genes for several QTLs controlling yield, anthocyanins, firmness and l-ascorbic acid are proposed based on both their co-localization and predicted function. We also report conserved QTLs among strawberry and other Rosaceae based on their syntenic location.     

Quantitative trait loci analysis of morphological traits in Citrus

The objectives of this study were to understand the genetic basis of morphological variation observed in the genus Citrus and its relatives and to identify genomic regions associated with certain morphological traits using genetic linkage mapping and quantitative trait loci (QTLs) analysis with random amplified polymorphic DNA (RAPD) markers. First, a genetic linkage map was constructed with RAPD markers obtained by screening 98 progeny plants from a {Citrus grandis × [C. paradisi × Poncirus trifoliata]} × {[(C. paradisi × P. trifoliata) × C. reticulata] × [(C. paradisi × Poncirus trifoliata) × C. sinensis]} intergeneric cross. The map contains 69 RAPD markers distributed into nine linkage groups. Then, 17 different morphological traits, including six tree and two leaf characters of 98 progeny plants and six floral and three fruit characters of about half of the same progeny plants were evaluated for 2 years and statistically analyzed for variation. Statistical analysis of individual traits indicated that trunk diameter and growth, tree height, canopy width, tree vigor and growth, leaf length and width, petal and anther numbers, petal length and width, length of pistil and style, fruit length and diameter, and fruit segment number showed normal or close to normal distribution, suggesting that these traits may be inherited quantitatively. Quantitative data from the morphological traits were analyzed to detect markers and putative QTLs associated with these traits using interval mapping method. QTL analysis revealed 18 putative QTLs of LOD > 3.0 associated with 13 of the morphological traits analyzed. The putative QTLs were distributed in several different linkage groups, and QTLs associated with similar traits were mostly mapped to the same LG or similar locations in the linkage group, indicating that the same genomic region is involved in the inheritance of some of the morphological traits.     

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   

Identification of QTLs affecting traits of agronomic importance in a recombinant inbred population derived from a subspecific rice cross

To detect QTLs controlling traits of agronomic importance in rice, two elite homozygous lines 9024 and LH422, which represent the indica and japonica subspecies of rice (Oryza sativa), were crossed. Subsequently a modified single-seed-descent procedure was employed to produce 194 recombinant inbred lines (F₈). The 194 lines were genotyped at 141 RFLP marker loci and evaluated in a field trial for 13 quantitative traits including grain yield. Transgressive segregants were observed for all traits examined. The number of significant QTLs (LOD 2.0) detected affecting each trait ranged from one to six. The percentage of phenotypic variance explained by each QTL ranged from 5.1% to 73.7%. For those traits for which two or more QTLs were detected, increases in the traits were conditioned by indica alleles at some QTLs Japonica alleles at others. No significant evidence was found for epistasis between markers associated with QTLs and all the other markers. Pleitropic effects of single QTLs on different traits are suggested by the observation of clustering of QTLs. No QTL for traits was found to map to the vicinity of major gene loci governing the same traits qualitatively. Evidence for putative orthologous QTLs across rice, maize, oat, and barley is discussed.     

The genetic basis of flowering time and photoperiod sensitivity in rapeseed <Emphasis Type="Italic">Brassica napus</Emphasis> L.

The objective of this study was to dissect the genetic control of days to flowering (DTF) and photoperiod sensitivity (PS) into the various components including the main-effect quantitative trait loci (QTLs), epistatic QTLs and QTL-by-environment interactions (QEs). Doubled haploid (DH) lines were produced from an F₁ between two spring Brassica napus cultivars Hyola 401 and Q2. DTF of the DH lines and parents were investigated in two locations, one location with a short and the other with a long photoperiod regime over two years. PS was calculated by the delay in DTF under long day as compared to that under short day. A genetic linkage map was constructed that comprised 248 marker loci including SSR, SRAP, and AFLP markers. Further QTL analysis resolved the genetic components of flowering time and PS into the main-effect QTLs, epistatic QTLs, and QEs. A total of 7 main-effect QTLs and 11 digenic interactions involving 21 loci located on 13 out of the 19 linkage groups were detected for the two traits. Three main-effect QTLs and four pairs of epistatic QTLs were involved in QEs conferring DTF. One QTL on linkage group (LG) 18 was revealed to simultaneously affect DTF and PS and explain for the highest percentage of the phenotypic variation. The implications of the results for B. napus breeding have been discussed. The text was submitted by the authors in English.     

Mapping of post-flowering drought resistance traits in grain sorghum: association between QTLs influencing premature senescence and maturity

The identification of genetic factors underlying the complex responses of plants to drought stress provides a solid basis for improving drought resistance. The stay-green character in sorghum (Sorghum bicolor L. Moench) is a post-flowering drought resistance trait, which makes plants resistant to premature senescence under drought stress during the grainfilling stage. The objective of this study was to identify quantitative trait loci (QTLs) that control premature senescence and maturity traits, and to investigate their association under post-flowering drought stress in grain sorghum. A genetic linkage map was developed using a set of recombinant inbred lines (RILs) obtained from the cross B35 × Tx430, which were scored for 142 restriction fragment length polymorphism (RFLP) markers. The RILs and their parental lines were evaluated for post-flowering drought resistance and maturity in four environments. Simple interval mapping identified seven stay-green QTLs and two maturity QTLs. Three major stay-green QTLs (SGA, SGD and SGG) contributed to 42% of the phenotypic variability (LOD 9.0) and four minor QTLs (SGB, SGI.1, SGI.2, and SGJ) significantly contributed to an additional 25% of the phenotypic variability in stay-green ratings. One maturity QTL (DFB) alone contributed to 40% of the phenotypic variability (LOD 10.0), while the second QTL (DFG) significantly contributed to an additional 17% of the phenotypic variability (LOD 4.9). Composite interval mapping confirmed the above results with an additional analysis of the QTL × Environment interaction. With heritability estimates of 0.72 for stay-green and 0.90 for maturity, the identified QTLs explained about 90% and 63% of genetic variability for stay-green and maturity traits, respectively. Although stay-green ratings were significantly correlated (r=0.22, P ≤ 0.05) with maturity, six of the seven stay-green QTLs were independent of the QTLs influencing maturity. Similarly, one maturity QTL (DFB) was independent of the stay-green QTLs. One stay-green QTL (SGG), however, mapped in the vicinity of a maturity QTL (DFG), and all markers in the vicinity of the independent maturity QTL (DFB) were significantly (P ≤ 0.1) correlated with stay-green ratings, confounding the phenotyping of stay-green. The molecular genetic analysis of the QTLs influencing stay-green and maturity, together with the association between these two inversely related traits, provides a basis for further study of the underlying physiological mechanisms and demonstrates the possibility of improving drought resistance in plants by pyramiding the favorable QTLs. Received: 10 October 1998 / Accepted: 12 July 1999     

QTL Analysis of High Thermotolerance with Superior and Downgraded Parental Yeast Strains Reveals New Minor QTLs and Converges on Novel Causative Alleles Involved in RNA Processing

Revealing QTLs with a minor effect in complex traits remains difficult. Initial strategies had limited success because of interference by major QTLs and epistasis. New strategies focused on eliminating major QTLs in subsequent mapping experiments. Since genetic analysis of superior segregants from natural diploid strains usually also reveals QTLs linked to the inferior parent, we have extended this strategy for minor QTL identification by eliminating QTLs in both parent strains and repeating the QTL mapping with pooled-segregant whole-genome sequence analysis. We first mapped multiple QTLs responsible for high thermotolerance in a natural yeast strain, MUCL28177, compared to the laboratory strain, BY4742. Using single and bulk reciprocal hemizygosity analysis we identified MKT1 and PRP42 as causative genes in QTLs linked to the superior and inferior parent, respectively. We subsequently downgraded both parents by replacing their superior allele with the inferior allele of the other parent. QTL mapping using pooled-segregant whole-genome sequence analysis with the segregants from the cross of the downgraded parents, revealed several new QTLs. We validated the two most-strongly linked new QTLs by identifying NCS2 and SMD2 as causative genes linked to the superior downgraded parent and we found an allele-specific epistatic interaction between PRP42 and SMD2. Interestingly, the related function of PRP42 and SMD2 suggests an important role for RNA processing in high thermotolerance and underscores the relevance of analyzing minor QTLs. Our results show that identification of minor QTLs involved in complex traits can be successfully accomplished by crossing parent strains that have both been downgraded for a single QTL. This novel approach has the advantage of maintaining all relevant genetic diversity as well as enough phenotypic difference between the parent strains for the trait-of-interest and thus maximizes the chances of successfully identifying additional minor QTLs that are relevant for the phenotypic difference between the original parents.     

Genotypic and phenotypic variation in transmission traits of a complex life cycle parasite

Characterizing genetic variation in parasite transmission traits and its contribution to parasite vigor is essential for understanding the evolution of parasite life‐history traits. We measured genetic variation in output, activity, survival, and infection success of clonal transmission stages (cercaria larvae) of a complex life cycle parasite (Diplostomum pseudospathaceum). We further tested if variation in host nutritional stage had an effect on these traits by keeping hosts on limited or ad libitum diet. The traits we measured were highly variable among parasite genotypes indicating significant genetic variation in these life‐history traits. Traits were also phenotypically variable, for example, there was significant variation in the measured traits over time within each genotype. However, host nutritional stage had no effect on the parasite traits suggesting that a short‐term reduction in host resources was not limiting the cercarial output or performance. Overall, these results suggest significant interclonal and phenotypic variation in parasite transmission traits that are not affected by host nutritional status.     

Identification of quantitative trait loci for agronomically important traits and their association with genic-microsatellite markers in sorghum

The identification of quantitative trait loci (QTLs) affecting agronomically important traits enable to understand their underlying genetic mechanisms and genetic basis of their complex interactions. The aim of the present study was to detect QTLs for 12 agronomic traits related to staygreen, plant early development, grain yield and its components, and some growth characters by analyzing replicated phenotypic datasets from three crop seasons, using the population of 168 F₇ RILs of the cross 296B × IS18551. In addition, we report mapping of a subset of genic-microsatellite markers. A linkage map was constructed with 152 marker loci comprising 149 microsatellites (100 genomic- and 49 genic-microsatellites) and three morphological markers. QTL analysis was performed by using MQM approach. Forty-nine QTLs were detected, across environments or in individual environments, with 1–9 QTLs for each trait. Individual QTL accounted for 5.2–50.4% of phenotypic variance. Several genomic regions affected multiple traits, suggesting the phenomenon of pleiotropy or tight linkage. Stable QTLs were identified for studied traits across different environments, and genetic backgrounds by comparing the QTLs in the study with previously reported QTLs in sorghum. Of the 49 mapped genic-markers, 18 were detected associating either closely or exactly as the QTL positions of agronomic traits. EST marker Dsenhsbm19, coding for a key regulator (EIL-1) of ethylene biosynthesis, was identified co-located with the QTLs for plant early development and staygreen trait, a probable candidate gene for these traits. Similarly, such exact co-locations between EST markers and QTLs were observed in four other instances. Collectively, the QTLs/markers identified in the study are likely candidates for improving the sorghum performance through MAS and map-based gene isolations.     

Genetic analysis of apomixis in Citrus and Poncirus by molecular markers

Propagation of citrus rootstocks depends upon the production of clonal plants from nucellar seedlings. This makes apomixis one of the host important traits in breeding programs for citrus rootstocks. The genetic control of apomixis was studied in a 50-tree progeny derived from the cross C. volkameriana×P. trifoliata using 69 molecular markers and bulked segregant analysis. The proportion of nucellar seedlings was estimated by isoenzymatic analysis of 25 seedlings per tree for 2 consecutive years. The type of embryony (polyembryonic versus monoembryonic seeds) was also determined for fruit-yielding trees. Separate genetic maps for each parental species were developed. The integration and comparison of these maps could be accomplished using common multiallelic segregant loci. Differences in gene synteny between the two species-specific genetic maps were shown. Important distortions in the segregation of markers at several genomic regions, some of them also involving differences in the C-methylation pattern, have been observed, especially for the pollen parent. Analysis of quantitative trait loci (QTLs) revealed the presence of six genomic positions (two in P. trifoliata and four in C. volkameriana) contributing individually up to 24% of the total variation for apomixis. Within the same species, QTLs with positive and negative allele effects were present, even in the same linkage group. One of the markers associated to apomixis (Apo2) is also associated to embryony type. Therefore, the genetic control of apomictic reproduction found in citrus (nucellar embryony) is quite complex compared to what has been reported for gametophytic apomixis. Molecular markers linked to QTLs governing apomixis will be useful to assist selection of future apomictic rootstocks for citrus varieties. Received: 30 November 1998 / Accepted: 28 December 1998     

No effect of the ectoparasite Crataerina pallida on reproduction of Common Swifts Apus apus

Previous studies have failed to ascertain negative effects of the Swift Lousefly Crataerina pallida parasitism on Common Swifts Apus apus. Abundances of C. pallida were experimentally manipulated to create broods experiencing either enhanced or reduced parasitism, and host life‐history traits were examined. No significant differences in clutch and brood size, rate of growth, asymptotic and fledging mass and size, or the number of fledglings per nest were observed. Reductions in parasite virulence may have developed due to the connection of C. pallida and host success, or costs may be borne by traits not influencing immediate fledging success.     

QTL mapping of ten agronomic traits on the soybean (<Emphasis Type="Italic">Glycine max</Emphasis> L. Merr.) genetic map and their association with EST markers

A set of 184 recombinant inbred lines (RILs) derived from soybean vars. Kefeng No.1 × Nannong 1138-2 was used to construct a genetic linkage map. The two parents exhibit contrasting characteristics for most of the traits that were mapped. Using restricted fragment length polymorphisms (RFLPs), simple sequence repeats (SSRs) and expressed sequence tags (ESTs), we mapped 452 markers onto 21 linkage groups and covered 3,595.9 cM of the soybean genome. All of the linkage groups except linkage group F were consistent with those of the consensus map of Cregan et al. (1999). Linkage group F was divided into two linkage groups, F1 and F2. The map consisted of 189 RFLPs, 219 SSRs, 40 ESTs, three R gene loci and one phenotype marker. Ten agronomic traits—days to flowering, days to maturity, plant height, number of nodes on main stem, lodging, number of pods per node, protein content, oil content, 100-seed weight, and plot yield—were studied. Using winqtlcart, we detected 63 quantitative trait loci (QTLs) that had LOD>3 for nine of the agronomic traits (only exception being seed oil content) and mapped these on 12 linkage groups. Most of the QTLs were clustered, especially on groups B1 and C2. Some QTLs were mapped to the same loci. This pleiotropism was common for most of the QTLs, and one QTL could influence at most five traits. Seven EST markers were found to be linked closely with or located at the same loci as the QTLs. EST marker GmKF059a, encoding a repressor protein and mapped on group C2, accounted for about 20% of the total variation of days to flowering, plant height, lodging and nodes on the main stem, respectively.Communicated by H.F. LinskensW.-K. Zhang, Y.-J. Wang and G.-Z. Luo contributed equally to this investigation.     

Genetic dissection of acetic acid tolerance in <Emphasis Type="Italic">Saccharomyces cerevisiae</Emphasis>

Dissection of the hereditary architecture underlying Saccharomyces cerevisiae tolerance to acetic acid is essential for ethanol fermentation. In this work, a genomics approach was used to dissect hereditary variations in acetic acid tolerance between two phenotypically different strains. A total of 160 segregants derived from these two strains were obtained. Phenotypic analysis indicated that the acetic acid tolerance displayed a normal distribution in these segregants, and suggested that the acetic acid tolerant traits were controlled by multiple quantitative trait loci (QTLs). Thus, 220 SSR markers covering the whole genome were used to detect QTLs of acetic acid tolerant traits. As a result, three QTLs were located on chromosomes 9, 12, and 16, respectively, which explained 38.8–65.9 % of the range of phenotypic variation. Furthermore, twelve genes of the candidates fell into the three QTL regions by integrating the QTL analysis with candidates of acetic acid tolerant genes. These results provided a novel avenue to obtain more robust strains.