Identification and validation of QTLs for green plant percentage in barley (<Emphasis Type="Italic">Hordeum vulgare</Emphasis> L.) anther culture

In cereals, albinism is a major obstacle to produce doubled haploids (DH) for breeding programs. In order to identify QTLs for green plant percentage in barley anther culture, a specific population was developed. This population, consisting of 100 DH lines, was generated by crossing the model cultivar for anther culture “Igri” with an albino-producing DH line (DH46) selected from Igri × Dobla, in search of a maximum segregation for the trait and minimum for the other anther culture variables. A combination of bulked segregant analysis and AFLP methodology was used to identify markers linked to the trait. A linkage map was constructed using these AFLPs, together with RAPD, STS and SSR markers. This study identified a new QTL for green plant percentage on chromosome 3H and confirmed the previously reported one on chromosome 5H. Up to 65.2% of the phenotypic variance for this trait was explained by the additive effects of these two QTLs. Thirty elite cultivars of barley from different origin, row type, growth habit and end use, were selected to validate these QTLs. Since two of the markers linked to the QTLs were AFLPs, we successfully converted them into simple PCR-based SCAR markers. Only the SSR HVM60, on chromosome 3H, was significantly associated with the trait, explaining near 20% of the phenotypic variance. Among the allelic variants identified for this marker, HVM60-120bp was associated with the highest values of green plant percentage.     

The effect of semi-dwarf genes on root system size in field-grown barley

Root system size (RSS) was measured in 12 diverse barley genotypes and 157 double-haploid lines (DHs), using electric capacitance. The parents of the DHs, Derkado and B83-12/21/5, carry different semi-dwarfing genes, sdw1 and ari-e.GP, respectively. Estimates of RSS were taken in the field thrice during plant development: stem elongation (RSS1), heading (RSS2) and grain filling (RSS3). The 12 barley genotypes were assessed over 3 years and at two or three locations each year; the DH mapping population was assessed at two locations in 2002. Among the 12 barley genotypes, those with the semi-dwarf genes had greater RSS values in all 3 years (28.9, 24.6 and 15.0% in years 1, 2 and 3, respectively) compared to non-semi-dwarf controls. The DH population showed transgressive segregation on both sides of the parent means, indicating polygenic control of RSS. Quantitative trait loci (QTLs) for RSS were found on five of the seven chromosomes: 1H, 3H, 4H, 5H and 7H and these were compared with previously mapped agronomic traits. The TotalRSS QTL on 3H was associated with sdw1 and QTLs for height, plant yield and plant weight. The RSS3 QTL on 5H was associated with ari-e.GP and QTLs for height, plant yield, plant weight, harvest index and tiller number. The RSS3 QTL on 7H was also associated with a TotalRSS QTL and QTLs for plant weight and harvest index. Other RSS QTLs were not associated with any other trait studied. RSS is considered to be a polygenic trait linked to important traits, in particular to yield. The study highlights the effects of semi-dwarfing genes and discusses the potential for breeding for root traits.     

Comprehensive genetic analyses reveal differential expression of spot blotch resistance in four populations of barley

Spot blotch, caused by Cochliobolus sativus, is an important disease of barley in the Upper Midwest region of the United States. The resistance of six-rowed malting cultivars like Morex has remained effective for over 40 years and is considered durable. Previous research on Steptoe/Morex (S/M), a 6×6-rowed doubled haploid (DH) population, showed that seedling resistance is controlled by a single gene (Rcs5) on chromosome 1(7H) and adult plant resistance by two quantitative trait loci (QTL): one of the major effect on chromosome 5(1H) explaining 62% of the phenotypic variance and a second of minor effect on chromosome 1(7H) explaining 9% of the phenotypic variance. To corroborate these results in a 2×6-rowed DH population, composite interval mapping (CIM) was performed on Harrington/Morex (H/M). As in the S/M population, a single major gene (presumably Rcs5) on chromosome 1(7H) conferred resistance at the seedling stage. However, at the adult plant stage, the results were markedly different as no chromosome 5(1H) effect whatsoever was detected. Instead, a QTL at or near Rcs5 on chromosome 1(7H) explained nearly all of the phenotypic variance (75%) for disease severity. To determine whether this result might be due to the genetic background of the two-rowed susceptible parent Harrington, we analyzed another DH population that included the same resistance donor (Morex) and another six-rowed susceptible cultivar Dicktoo (D/M). Three QTL conferred seedling resistance in the D/M population: one near Rcs5 on chromosome 1(7H) explaining 30%, a second near the centromere of chromosome 1(7H) explaining 9%, and a third on the short arm of chromosome 3(3H) explaining 19% of the phenotypic variation. As in the H/M population, no chromosome 5(1H) QTL was detected for adult plant resistance in the D/M population. Instead, three QTL on other chromosomes explained most of the variation: one on the short arm of chromosome 3(3H) explaining 36%, a second on the long arm of chromosome 3(3H) explaining 11%, and a third at or near Rcs5 on chromosome 1(7H) explaining 20% of the phenotypic variation. These data demonstrate the complexity of expression of spot blotch resistance in different populations and have important implications in breeding for durable resistance.     

不同发育阶段水稻苗高的QTL分析

分析了不同发育阶段控制水稻苗高的QTL,用5个阶段和4个净增长量的数据共检测到9个QTL,分别位于染色体1,4,6,7,8,11,和12号上。SH－4是主基因,它在各个阶段都表达,对苗高的贡献率在20％以上。结果表明,数量性状的发育或形态建成是由数量性状位点基因选择性表达的结果。     

Mapping of quantitative trait loci for partial resistance to<Emphasis Type="Italic"> Mycosphaerella pinodes</Emphasis> in pea (<Emphasis Type="Italic">Pisum sativum</Emphasis> L.), at the seedling and adult plant stages

The inheritance of resistance to Ascochyta blight, an economically important foliar disease of field pea (Pisum sativum L.) worldwide, was investigated. Breeding resistant pea varieties to this disease, caused by Mycosphaerella pinodes, is difficult due to the availability of only partial resistance. We mapped and characterized quantitative trait loci (QTLs) for resistance to M. pinodes in pea. A population of 135 recombinant inbred lines (RILs), derived from the cross between DP (partially resistant) and JI296 (susceptible), was genotyped with morphological, RAPD, SSR and STS markers. A genetic map was elaborated, comprising 206 markers distributed over eight linkage groups and covering 1,061 cM. The RILs were assessed under growth chamber and field conditions at the seedling and adult plant stages, respectively. Six QTLs were detected at the seedling stage, which together explained up to 74% of the variance. Ten QTLs were identified at the adult plant stage in the field, and together these explained 56.6–67.1% of the variance, depending on the resistance criteria and the organ considered. Four QTLs were detected under both growth chamber and field conditions, suggesting they were not plant-stage dependent. Three QTLs for flowering date and three QTLs for plant height were also identified in the RIL population, some of which co-located with QTLs for resistance. The relationship between QTLs for resistance to M. pinodes, plant height and flowering date is discussed.Communicated by H.C. Becker     

Detection and analysis of QTLs for resistance to the brown planthopper, Nilaparvata lugens, in a doubled-haploid rice population

 We used a mapping population of 131 doubled-haploid lines, produced from a cross between an improved indica rice variety (IR64) and a traditional japonica variety (Azucena), to detect quantitative trait loci (QTLs) for resistance to the brown planthopper (BPH), Nilaparvata lugens. We evaluated the parents and mapping population with six tests that measure varying combinations of the three basic mechanisms of insect host plant resistance, i.e., antixenosis, antibiosis, and tolerance. To factor-out the effect of the major resistance gene Bph1 from IR64, the screening was done with two BPH populations from Luzon Island, The Philippines, that are almost completely adapted to this gene. A total of seven QTLs associated with resistance were identified, located on 6 of the 12 rice chromosomes. Individual QTLs accounted for between 5.1 and 16.6% of the phenotypic variance. Two QTLs were predominantly associated with a single resistance mechanism: one with antixenosis and one with tolerance. Most of the QTLs were derived from IR64, which has been shown to have a relatively durable level of moderate resistance under field conditions. The results of this study should be useful in transferring this resistance to additional rice varieties. Received: 10 May 1998 / Accepted: 4 June 1998     

QTL Analysis of Head Splitting Resistance in Cabbage (Brassica oleracea L. var. capitata) Using SSR and InDel Makers Based on Whole-Genome Re-Sequencing

Head splitting resistance (HSR) in cabbage is an important trait closely related to both quality and yield of head. However, the genetic control of this trait remains unclear. In this study, a doubled haploid (DH) population derived from an intra-cross between head splitting-susceptible inbred cabbage line 79–156 and resistant line 96–100 was obtained and used to analyze inheritance and detect quantitative trait loci (QTLs) for HSR using a mixed major gene/polygene inheritance analysis and QTL mapping. HSR can be attributed to additive-epistatic effects of three major gene pairs combined with those of polygenes. Negative and significant correlations were also detected between head Hsr and head vertical diameter (Hvd), head transverse diameter (Htd) and head weight (Hw). Using the DH population, a genetic map was constructed with simple sequence repeat (SSR) and insertion–deletion (InDel) markers, with a total length of 1065.9 cM and average interval length of 4.4 cM between adjacent markers. Nine QTLs for HSR were located on chromosomes C3, C4, C7, and C9 based on 2 years of phenotypic data using both multiple-QTL mapping and inclusive composite interval mapping. The identified QTLs collectively explained 39.4 to 59.1% of phenotypic variation. Three major QTLs (Hsr 3.2, 4.2, 9.2) showing a relatively larger effect were robustly detected in different years or with different mapping methods. The HSR trait was shown to have complex genetic mechanisms. Results from QTL mapping and classical genetic analysis were consistent. The QTLs obtained in this study should be useful for molecular marker-assisted selection in cabbage breeding and provide a foundation for further research on HSR genetic regulation.     

Mapping of quantitative trait loci and development of allele-specific markers for seed weight in Brassica napus

Seed weight is an important component of grain yield in oilseed rape (Brassica napus L.), but the genetic basis for the important quantitative trait is still not clear. In order to identify the genes for seed weight in oilseed rape, QTL mapping for thousand seed weight (TSW) was conducted with a doubled haploid (DH) population and an F₂ population. A complete linkage map of the DH population was constructed using 297 simple sequence repeat (SSR) markers. Among nine TSW QTLs detected, two major QTLs, TSWA7a and TSWA7b, were stably identified across years and collectively explained 27.6–37.9% of the trait variation in the DH population. No significant epistatic interactions for TSW detected in the DH population indicate that the seed weight variation may be primarily attributed to additive effects. The stability and significance of TSWA7a and TSWA7b were further validated in the F₂ population with different genetic backgrounds. By cloning BnMINI3a and BnTTG2a, two B. napus homologous genes to Arabidopsis thaliana, allele-specific markers were developed for TSWA5b and TSWA5c, two TSW QTLs on A5, respectively. The importance of the major and minor QTLs identified was further demonstrated by analysis of the allelic effects on TSW in the DH population.     

Genetic analysis of resistance to septoria tritici blotch in the French winter wheat cultivars Balance and Apache

The ascomycete Mycosphaerella graminicola is the causal agent of septoria tritici blotch (STB), one of the most destructive foliar diseases of bread and durum wheat globally, particularly in temperate humid areas. A screening of the French bread wheat cultivars Apache and Balance with 30 M. graminicola isolates revealed a pattern of resistant responses that suggested the presence of new genes for STB resistance. Quantitative trait loci (QTL) analysis of a doubled haploid (DH) population with five M. graminicola isolates in the seedling stage identified four QTLs on chromosomes 3AS, 1BS, 6DS and 7DS, and occasionally on 7DL. The QTL on chromosome 6DS flanked by SSR markers Xgpw5176 and Xgpw3087 is a novel QTL that now can be designated as Stb18. The QTLs on chromosomes 3AS and 1BS most likely represent Stb6 and Stb11, respectively, and the QTLs on chromosome 7DS are most probably identical with Stb4 and Stb5. However, the QTL identified on chromosome 7DL is expected to be a new Stb gene that still needs further characterization. Multiple isolates were used and show that not all isolates identify all QTLs, which clearly demonstrates the specificity in the M. graminicola–wheat pathosystem. QTL analyses were performed with various disease parameters. The development of asexual fructifications (pycnidia) in the characteristic necrotic blotches of STB, designated as parameter P, identified the maximum number of QTLs. All other parameters identified fewer but not different QTLs. The segregation of multiple QTLs in the Apache/Balance DH population enabled the identification of DH lines with single QTLs and multiple QTL combinations. Analyses of the marker data of these DH lines clearly demonstrated the positive effect of pyramiding QTLs to broaden resistance spectra as well as epistatic and additive interactions between these QTLs. Phenotyping of the Apache/Balance DH population in the field confirmed the presence of the QTLs that were identified in the seedling stage, but Stb18 was inconsistently expressed and might be particularly effective in young plants. In contrast, an additional QTL for STB resistance was identified on chromosome 2DS that is exclusively and consistently expressed in mature plants over locations and time, but it was also strongly related with earliness, tallness as well as resistance to Fusarium head blight. Although to date no Stb gene has been reported on chromosome 2D, the data provide evidence that this QTL is only indirectly related to STB resistance. This study shows that detailed genetic analysis of contemporary commercial bread wheat cultivars can unveil novel Stb genes that can be readily applied in marker-assisted breeding programs.     

Dynamic gene action at QTLs for resistance to Setosphaeria turcica in maize

 Cultivars with quantitative resistance are widely used to control Setosphaeria turcica (Luttrell) Leonard & Suggs, the causal organism of northern corn leaf blight (NCLB). Here the effectiveness of quantitative trait loci (QTLs) for NCLB resistance was investigated over the course of host plant development in inoculated field trials. A population of 194–256 F_2:3 lines derived from a cross between a susceptible Italian (Lo951) and a highly resistant African inbred line (CML202) was tested in three environments in Kenya. The traits assessed were the incubation period (IP), the percentage disease severity (DS 1 to 5, taken biweekly), and the area under the disease progress curve (AUDPC). Considering all resistance traits and environments, a total of 19 putative QTLs were detected by composite interval mapping using a linkage map with 110 RFLP markers. In the combined analysis across environments, nine QTLs were significant (LOD >3.0) for DS 3, recorded around flowering time, explaining 71% of the genotypic variance. Four of these nine QTLs displayed significant (P<0.05) QTL×environment (QTL×E) interaction. Most QTLs were already significant in the juvenile stage (IP) and became less effective after flowering. Across environments, three QTLs conditioned adult-plant resistance, in the sense that they were only significant after flowering. Six QTL alleles on chromosomes 2, 4, 5, 8, and 9 of CML202 should be useful for marker-assisted backcrossing. Received: 24 August 1998 / Accepted: 29 September 1998     

Strain-specific and recessive QTLs involved in the control of partial resistance to Fusarium oxysporum f. sp. melonis race 1.2 in a recombinant inbred line population of melon

Fusarium oxysporum f. sp. melonis (FOM) causes serious economic losses in melon (Cucumis melo L.). Two dominant resistance genes have been identified, Fom-1 and Fom-2, which provide resistance to races 0 and 2 and races 0 and 1, respectively, however FOM race 1.2 overcomes these resistance genes. A partial resistance to FOM race 1.2 that has been found in some Far East accessions is under polygenic control. A genetic map of melon was constructed to tag FOM race 1.2 resistance with DNA markers on a recombinant inbred line population derived from a cross between resistant (Isabelle) and susceptible (cv. Védrantais) lines. Artificial root inoculations on plantlets of this population using two strains, one that causes wilting (FOM 1.2w) and one that causes yellowing (FOM 1.2y), resulted in phenotypic and genotypic data that enabled the identification of nine quantitative trait loci (QTLs). These QTLs were detected on five linkage groups by composite interval mapping and explained between 41.9% and 66.4% of the total variation. Four digenic epistatic interactions involving seven loci were detected and increased the total phenotypic variation that was explained. Co-localizations between QTLs and resistance gene homologs or resistance genes, such as Fom-2 and Vat, were observed. A strain-specific QTL was detected, and some QTLs appeared to be recessive.     

Potential of doubled-haploid lines and localization of quantitative trait loci (QTL) for partial resistance to bacterial leaf streak (Xanthomonas campestris pv. hordei) in barley

 Genetic variability for partial resistance to bacterial leaf streak in barley, caused by Xanthomonas campestris pv. hordei, was investigated in 119 doubled-haploid lines (DH) developed by the Hordeum bulbosum method from the F₁ progeny of the cross between two cultivars, ‘Morex’ (resistant) and ‘Steptoe’ (susceptible). Two experiments were undertaken in a randomized complete block design with three replicates, in a controlled growth chamber. Twenty seeds per replicate were planted in plastic containers (60×40×8 cm) containing moistened vermiculite. At the two-leaf stage seedlings were inoculated with an Iranian strain of the pathogen. Genetic variability was observed among the 119 DH lines for partial resistance to the disease. Some DH lines were significantly more resistant than ‘Morex’ (resistant parent) to bacterial leaf streak. Genetic gain in percentage of resistant parent for 5% of the selected DH lines was significant (47.70% and 33.72% in the first and the second experiment, respectively). A QTL analysis of bacterial leaf streak resistance showed that three QTLs were detected on chromosomes 3 and 7. Multilocus allelic effects of the three QTLs account for almost 54% of the mean difference between the parents and nearly 30% of the phenotypic variation of the trait in the mean experiment. The resistance locus on chromosome 3, near ABG377, apprears to be a major gene. Received: 15 July 1997 / Accepted: 4 August 1997     

Mapping quantitative and qualitative disease resistance genes in a doubled haploid population of barley (Hordeum vulgare)

Stripe rust, leaf rust, and Barley Yellow Dwarf Virus (BYDV) are important diseases of barley (Hordeum vulgare L). Using 94 doubled-haploid lines (DH) from the cross of Shyri x Galena, multiple disease phenotype datasets, and a 99-marker linkage map, we determined the number, genome location, and effects of genes conferring resistance to these diseases. We also mapped Resistance Gene Analog Polymorphism (RGAP) loci, based on degenerate motifs of cloned disease resistance genes, in the same population. Leaf rust resistance was determined by a single gene on chromosome 1 (7H). QTLs on chromosomes 2 (2H), 3 (3H), 5 (1H), and 6 (6H) were the principal determinants of resistance to stripe rust. Two- locus QTL interactions were significant determinants of resistance to this disease. Resistance to the MAV and PAV serotypes of BYDV was determined by coincident QTLs on chromosomes 1 (7H), 4 (4H), and 5 (1H). QTL interactions were not significant for BYDV resistance. The associations of molecular markers with qualitative and quantitative disease resistance loci will be a useful information for marker-assisted selection. Received: 2 February 1999 / Accepted: 30 December 1999     

QTLs for a component of partial resistance to cucumber mosaic virus in pepper: restriction of virus installation in host-cells

 Ninety four doubled-haploid (DH) lines obtained from the F₁ between Perennial, a cucumber mosaic virus (CMV)-partially resistant Capsicum annuum line, and Yolo Wonder, a CMV-susceptible C. annuum line, were analysed with 138 markers including mostly RFLPs and RAPDs. Clustering of RAPD markers was observed on five linkage groups of the intraspecific linkage map. These clusters could correspond to the centromeric regions of pepper chromosomes. The same progenies were evaluated for restriction of CMV installation in pepper cells in order to map quantitative trait loci (QTLs) controlling CMV resistance. This component of partial resistance to CMV was quantitatively assessed using a CMV strain that induced necrotic local lesions on the inoculated leaves. The number of local lesions gave an estimation of the density of the virus-infection sites. Genotypic variance among the DH lines was highly significant for the number of local lesions, and heritability was estimated to be 0.94. Using both analysis of variance and non-parametric tests, three genomic regions significantly affecting CMV resistance were detected on chromosomes Noir, Pourpre and linkage group 3, together explaining 57% of the phenotypic variation. A digenic epistasis between one locus that controlled significant trait variation and a second locus that by itself had no demonstrable effect on the trait was found to have an effect on CMV resistance. For each QTL, the allele from Perennial was associated with an increased resistance. Implications of QTL mapping in marker-based breeding for CMV resistance are discussed. Received: 16 September 1996     

Molecular markers locate genes for resistance to the Colorado potato beetle,Leptinotarsa decemlineata,in hybrid Solanum tuberosum x S. berthaultii potato progenies

The wild Bolivian potato, Solanum berthaultii Hawkes, has been used as a source of resistance to the Colorado potato beetle (CPB), Leptinotarsa decemlineata Say, one of the most significant pests of potato. In this study, two reciprocal backcross S. tuberosum x S. berthaultii potato progenies, BCB and BCT, were mapped with RFLP markers and screened for resistance to CPB consumption, oviposition and defoliation. The genotypic and phenotypic data were combined and analysed to locate quantitative trait loci (QTLs) for resistance to CPB. Three QTLs on three chromosomes in BCB, and two QTLs on two chromosomes in BCT influenced resistance. The QTLs were generally additive but one instance of epistasis was noted. Each QTL accounted for 4–12% of the phenotypic variation observed in resistance. In the more resistant BCB population, a three QTL model explained ca. 20% of the variation in CPB oviposition. When alleles at the three QTLs were homozygous S. berthaultii, oviposition was reduced ca. 60% compared to the heterozygotes. The QTLs for resistance to CPB were compared to those previously identified for the type A and B glandular trichomes, which have been implicated in resistance in the same progenies. Generally, the QTLs for resistance to CPB coincided with loci associated with the glandular trichomes confirming the importance of the glandular trichomes in mediating resistance. However, a relatively strong and consistent QTL for insect resistance in both BCB and BCT on chromosome 1 was observed that was not associated with any trichome traits, suggesting the trichomes may not account for all of the resistance observed in these progenies.     

QTLs linked to leaf epicuticular wax,physio-morphological and plant production traits under drought stress in rice (<Emphasis Type="Italic">Oryza sativa</Emphasis> L.)

Drought stress is the major constraint to rice (Oryza sativa L.) production and yield stability in rainfed ecosystems. Identifying genomic regions contributing to drought resistance will help to develop rice cultivars suitable for rainfed regions through marker-assisted breeding. Quantitative trait loci (QTLs) linked to leaf epicuticular wax, physio-morphological and plant production traits under water stress and irrigated conditions were mapped in a doubled haploid (DH) line population from the cross CT9993-5-10-1-M/IR62266-42-6-2. The DH lines were subjected to water stress during anthesis. The DH lines showed significant variation for epicuticular wax (EW), physio-morphological and plant production traits under stress and irrigated conditions. A total of 19 QTLs were identified for the various traits under drought stress and irrigated conditions in the field, which individually explained 9.6%–65.6% of the phenotypic variation. A region EM15_10-ME8_4-R1394A-G2132 on chromosome 8 was identified for leaf EW and rate of water loss i.e., time taken to reach 70% RWC from excised leaves in rice lines subjected to drought stress. A large effect QTL (65.6%) was detected on chromosome 2 for harvest index under stress. QTLs identified for EW, rate of water loss from excised leaves and harvest index under stress in this study co-located with QTLs linked to shoot and root-related drought resistance traits in these rice lines and might be useful for rainfed rice improvement.     

Quantitative trait loci controlling barley powdery mildew and scald resistances in two different barley doubled haploid populations

Powdery mildew and scald can cause significant yield loss in barley. In order to identify new resistance genes for powdery mildew and scald in barley, two barley doubled haploid (DH) populations were screened for adult plant resistance in the field and glasshouse under natural infection. The mapping populations included 92 DH lines from the cross of TX9425 × Franklin and 177 DH lines from the cross of Yerong × Franklin. Two quantitative trait loci (QTL) for resistance to powdery mildew were identified in the TX9425 × Franklin population. These QTL were mapped to chromosomes 7H and 5H, respectively. The phenotypic variation explained by the two QTL detected in this population was 22 and 17%, respectively. Three significant QTL were identified from the Yerong × Franklin population for the resistance to powdery mildew; the major one, detected on the short arm of chromosome 1H, explained 66% of phenotypic variation. The major QTL for scald resistance, identified from two different populations which shared a common parent, Franklin, were mapped in the similar position on 3H. However, the Franklin allele provided resistance to one population but susceptibility to the other population. The Yerong allele on 3H showed much better resistance to scald than the Franklin allele, which has not been reported before. Using high-density maps for both populations, some markers which were very close to the resistance genes were identified. Transgression beyond the parents in disease resistances of the DH populations indicates that both small-effect QTLs and genetic background may also have significant contributions towards the resistance.     

苗期水稻根部性状的QTL定位

耐旱是水稻抗逆研究中最重要的性状之一。利用水稻籼粳品种窄叶青8号（ZYQ8）和京系17（JX17）及其通过杂交F1代花药培养获得的127个单株组成的双单倍体分离群体（double haploid,DH)为材料,在营养液中培养10天后,对影响抗旱能力的根部几个主要性状进行了分析,发现最大根长（Maximum root Length,MRL)、根干重（Dry Root Weight,DRW)和根茎干重比（Root/Shoot Ratio of Dry Weight,RSR)3个性状在群体中变异较大,利用该群体建立的水稻分子遗传图谱,对上述3个水稻性状进行数量性状座位（Quantitative Trait Locus,QTL)的分析定位,结果表明,2／1／2个QTLs的亲本JX17等位基因分别控制着最大根长、根干重和茎士重比的表达,对表型变异的解释率分别为16．4％、17．0％、16．4％、10．4％和19．9％;2／1个QTLs的亲本ZYQ8等位基因分别控制着最大根长和根茎干重比的增加,表表型变异的解释率分别为19．6％、13．0％和13．2％。检测到的8个QTLs分别位地水稻的染色体2、3、4、5、6、9和10上。与其他已发表的定位结果比较表现,在3个性状的总共8个QTLs中,各有1个性状的1个QTL（控制最大根长的L169－CT106A,控制根干重的G45－G1314A和控制根茎干重比的G62－G144）与早先报道的结果相吻合。     

Location of genes involved in ear compactness in wheat (Triticum aestivum) by means of molecular markers

Quantitative trait loci (QTLs) for three traits related to ear morphology (spike length, number of spikelets, and compactness as the ratio between number of spikelets and spike length) in wheat (Triticum aestivum L.) were mapped in a doubled-haploid (DH) population derived from the cross between the cultivars Courtot and Chinese Spring. A molecular marker linkage map of this cross that had previously been constructed based on 187 DH lines and 380 markers was used for QTL mapping. The genome was well covered (85%) except chromosomes 1D and 4D and a set of anchor loci regularly spaced (one marker each 15.5 cM) were chosen for marker regression analysis. The presence of a QTL was declared at a significance threshold = 0.001. The population was grown in one location under field conditions during three years (1994, 1995 and 1998). For each trait, 4 to 6 QTLs were identified with individual effects ranging between 6.9% and 21.8% of total phenotypic variation. Several QTLs were detected that affected more than one trait. Of the QTLs 50% were detected in more than one year and two of them (number of spikelets on chromosome 2B, and compactness on chromosome 2D) emerged from the data from the three years. Only one QTL co-segregated with the gene Q known to be involved in ear morphology, namely the speltoid phenotype. However, this chromosome region explained only a minor part of the variation (7.5–11%). Other regions had a stronger effect, especially two previously unidentified regions located on chromosomes 1A and 2B. The region on the long arm of chromosome 1A was close to the locus XksuG34-1A and explained 12% of variation in spike length and 10% for compactness. On chromosome 2B, the QTL was detected for the three traits near the locus Xfbb121-2B. This QTL explained 9% to 22% of variation for the traits and was located in the same region as the gene involved in photoperiod response (Ppd2). Other regions were located at homoeologous positions on chromosomes 2A and 2D.     

Identification of QTLs for partial resistance to leaf rust (Puccinia hordei) in barley

 The partial resistance to leaf rust in barley is a quantitative resistance that is not based on hypersensitivity. To map the quantitative trait loci (QTLs) for partial resistance to leaf rust, we obtained 103 recombinant inbred lines (RILs) by single-seed descent from a cross between the susceptible parent L94 and the partially resistant parent Vada. These RILs were evaluated at the seedling and adult plant stages in the greenhouse for the latent period (LP) of the rust fungus, and in the field for the level of infection, measured as area under the disease progress curve (AUDPC). A dense genetic map based on 561 AFLP markers had been generated previously for this set of RILs. QTLs for partial resistance to leaf rust were mapped using the “Multiple Interval Mapping” method with the putative QTL markers as cofactors. Six QTLs for partial resistance were identified in this population. Three QTLs, Rphq1, Rphq2 and Rphq3, were effective at the seedling stage and contributed approximately 55% to the phenotypic variance. Five QTLs, Rph2, Rphq3, Rphq4, Rphq5, and/or Rphq6 contributed approximtely. 60% of the phenotypic variance and were effective at the adult plant stage. Therefore, only the QTLs Rphq2 and Rhpq3 were not plant-stage dependent. The identified QTLs showed mainly additive effects and only one significant interaction was detected, i.e. between Rphq1 and Rphq2. The map positions of these QTLs did not coincide with those of the race-specific resistance genes, suggesting that genes for partial resistance and genes for hypersensitive resistance represent entirely different gene families. Also, three QTLs for days to heading, of which two were also involved in plant height, were identified in the present recombinant inbred population. These QTLs had been mapped previously on the same positions in different populations. The perspectives of these results for breeding for durable resistance to leaf rust are discussed. Received: 15 July 1997 / Accepted: 30 December 1997