Analysis of factors influencing milling yield and their association to other traits by QTL analysis in two hexaploid oat populations

Milling yield, or the grain weight from which 100 kg of rolled groats is obtained upon milling, is an important quality characteristic of cultivated oat (Avena sativa L.). Kernel morphology and the groat (caryopsis) percentage of the whole kernel including hull are factors that influence milling yield. We mapped QTLs for kernel area, kernel length, kernel width, and groat percentage in two populations of 137 recombinant inbred lines by RFLP and AFLP analysis to evaluate the prospects of marker-assisted selection (MAS). Phenotypic correlations between kernel morphology traits and groat percentage were not significant. For kernel morphology traits and groat percentage, one to five QTLs were detected, explaining 7.0–60.7% of the total phenotypic variance depending on the trait. One QTL for kernel length in each population and one QTL for kernel width in one population were found at the same location as a QTL for groat percentage, indicating that a change in kernel size or shape could have an influence on groat percentage. The positions and effects of QTLs for kernel morphology and groat percentage were compared to QTLs detected previously for chemical grain composition (oil andβ-glucanconcentration) and agronomic traits to evaluate the selection response on these traits through MAS. Several regions of the oat genome were identified that contained clusters of QTLs influencing two or more traits. While the allele from one parent at a QTL could simultaneously improve two or more traits in one population, it could have opposite effects on the same traits at another QTL or in the other population. Associations among traits were complex and will require careful consideration when employing QTL-marker associations in MAS to avoid negative selection response. Future research to discover candidate genes for those QTL clusters could provide information about trait associations and help in designing selection programs. Received: 17 February 2000 / Accepted: 27 October 2000     

QTLs for agronomic traits in the Mediterranean environment identified in recombinant inbred lines of the cross 'Arta' × <Emphasis Type="Italic">H. spontaneum</Emphasis> 41-1

A genetic linkage map has been developed for recombinant inbred lines (RILs) of the cross 'Arta' × Hordeum spontaneum 41-1. One hundred and ninety four RILs, randomly chosen from a population of 494 RILs, were mapped with 189 markers including one morphological trait (btr = brittle rachis locus). The linkage map extended to 890 cM. Agronomic traits such as grain yield, biological yield, days to heading, plant height, cold tolerance and others were evaluated at the ICARDA research stations Tel Hadya and Breda during the years 1996–97 and 1997–98. QTLs for agronomic traits related to drought resistance were localized. For the most-important character 'plant height under drought stress', QTLs on 2H, 3H and 7H were detected. The 'plant height' QTLs, specially the one on 3H, showed pleiotropic effects on traits such as days to heading, grain yield and biological yield. QTLs were also identified for other traits associated with adaptation to the Mediterranean environment such as cold tolerance, days to heading and tiller number. The identification of QTLs for agronomic traits is a first step to analyze and to dissect complex characters such as adaptation to drought tolerance.Comunicated by R. Hagemann     

Marker-assisted introgression of blackmold resistance QTL alleles from wild Lycopersicon cheesmanii to cultivated tomato (L. esculentum) and evaluation of QTL phenotypic effects

Blackmold, caused by the fungus Alternaria alternata, is a major ripe fruit disease of processing tomatoes. Previously, we found blackmold resistance in a wild tomato (Lycopersicon cheesmanii) and quantitative trait loci (QTL) for resistance were mapped in an interspecific population. Five QTLs were selected for introgression from L. cheesmanii into cultivated tomato using marker-assisted selection (MAS). Restriction fragment length polymorphism and PCR-based markers flanking, and within, the chromosomal regions containing QTLs were used for MAS during backcross and selfing generations. BC₁ plants heterozygous at the QTLs, and subsequent BC₁S₁ and BC₁S₂ lines possessing different homozygous combinations of alleles at the target QTLs, were identified using DNA markers. Field experiments were conducted in 1998 (with 80 marker-selected BC₁S₂ lines) and 1999 (with 151 marker-selected BC₁S₂ and BC₁S₃ lines) at three California locations. Blackmold resistance was assessed during both years, and horticultural traits were evaluated in 1999. The BC₁S₂ and BC₁S₃ lines containing L. cheesmanii alleles at the QTLs were associated with a large genetic variance for resistance to blackmold and moderate heritability, suggesting that significant genetic gain may be achieved by selection in this genetic material. L. cheesmanii alleles at three of the five introgressed QTLs showed a significant, positive effect on blackmold resistance. A QTL on chromosome 2 had the largest positive effect on blackmold resistance, alone and in combination with other QTLs, and was also associated with earliness, a positive horticultural trait. The other four QTLs were associated primarily with negative horticultural traits. Fine mapping QTLs using near isogenic lines could help determine if such trait associations are due to linkage drag or pleiotropy.     

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.     

QTL mapping of 1000-kernel weight, kernel length, and kernel width in bread wheat (Triticum aestivum L.)

Kernel size and morphology influence the market value and milling yield of bread wheat (Triticum aestivum L.). The objective of this study was to identify quantitative trait loci (QTLs) controlling kernel traits in hexaploid wheat. We recorded 1000-kernel weight, kernel length, and kernel width for 185 recombinant inbred lines from the cross Rye Selection 111 × Chinese Spring grown in 2 agro-climatic regions in India for many years. Composite interval mapping (CIM) was employed for QTL detection using a linkage map with 169 simple sequence repeat (SSR) markers. For 1000-kernel weight, 10 QTLs were identified on wheat chromosomes 1A, 1D, 2B, 2D, 4B, 5B, and 6B, whereas 6 QTLs for kernel length were detected on 1A, 2B, 2D, 5A, 5B and 5D. Chromosomes 1D, 2B, 2D, 4B, 5B and 5D had 9 QTLs for kernel width. Chromosomal regions with QTLs detected consistently for multiple year-location combinations were identified for each trait. Pleiotropic QTLs were found on chromosomes 2B, 2D, 4B, and 5B. The identified genomic regions controlling wheat kernel size and shape can be targeted during further studies for their genetic dissection.     

QTL Analysis in Recombinant Chromosome Substitution Lines and Doubled Haploid Lines Derived from a Cross between Hordeum vulgare ssp. vulgare and Hordeum vulgare ssp. spontaneum

Recombinant chromosome substitution lines (RCSLs) were developed in BC₃ generation to introduce segments of a wild barley strain ‘H602’ (Hordeum vulgare ssp. spontaneum) into a barley cultivar ‘Haruna Nijo’ (H. vulgare ssp. vulgare) genetic background. One hundred thirty four RCSLs were genotyped by 25 SSR and 60 EST markers, which were localized on a linkage map of doubled haploid lines (DHLs) derived from the same cross combination. Graphical genotyping revealed that the observed average substitution ratio of H602 segment (12.9%) agreed with the expected substitution ratio (12.5%), and a minimum set of 19 RCSLs represented the entire H602 genome. Phenotypes of five qualitative and nine quantitative traits were scored in both the RCSLs and DHLs. Five qualitative traits were localized as morphological markers on the linkage map of the DHLs, and these molecular markers were aligned on the respective chromosomal regions in the RCSLs. Simple and composite interval mapping procedures detected a total of 18 and 24 QTLs for nine qualitative traits on the RCSLs and DHLs, respectively. Several QTLs were localized at coincident or very close regions on both linkage maps. In spite of general inferior agronomic performances in wild barley, several H602 QTL alleles showed agronomically positive effects. These RCSLs should contribute to substitution of favorable alleles from wild barley into cultivated barley. These RCSLs are also available as sources of near isogenic lines, with which we can apply advanced genetic analysis methods such as isolation of QTLs and detection of epistatic interactions among QTLs.     

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.     

Genetic analysis of drought tolerance in maize by molecular markers I. Yield components

Grain yield is a complex trait, strongly influenced by the environment: severe losses can be caused by drought, a stress common in most maize-growing areas, including temperate climatic zones. Accordingly, drought tolerance is one of the main components of yield stability, and its improvement is a major challenge to breeders. The aim of the present work was the identification, in maize genotypes adapted to temperate areas, of genomic segments responsible for the expression of drought tolerance of yield components: ear length, ear weight, kernel weight, kernel number and 50-kernel weight. A linkage analysis between the expression of these traits and molecular markers was performed on a recombinant inbred population of 142 families, obtained by repeated selfing of the F₁ between lines B73 and H99. The population, genotyped at 173 loci (RFLPs, microsatellites and AFLPs), was evaluated in well-watered and water-stressed conditions. A drought tolerance index was calculated as the ratio between the mean value of the trait in the two environments. For the traits measured, a highly positive correlation was found over the two water regimes, and more than 50% of the quantitative trait loci (QTLs) detected were the same in both; moreover, the direction of the allelic contribution was always consistent, the allele increasing the trait value being mostly from line B73. Several QTLs were common to two or more traits. For the tolerance index, however, most of the QTLs were specific for a single component and different from those controlling the basic traits; in addition, a large proportion of the alleles increasing tolerance were provided by line H99. The data suggest that drought tolerance for yield components is largely associated with genetic and physiological factors independent from those determining the traits per se. The implications of these results for developing an efficient strategy of marker-assisted selection for drought tolerance are discussed. Received: 19 October 1998 / Accepted: 28 December 1998     

Detection of quantitative trait loci influencing growth trajectories of adventitious roots in Populus using functional mapping

The capacity to root from cuttings is a key factor for the mass deployment of superior genotypes in clonal forestry. We studied the genetic basis of rooting capacity by mapping quantitative trait loci (QTLs) that control growth rate and form of root traits in a full-sib family of 93 hybrids derived from an interspecific cross between two Populus species, P. deltoides and P. euramericana. The hybrid family was typed for different marker systems (including SSRs, AFLPs, RAPDs, ISSRs, and SNPs), leading to the construction of two linkage maps based on the female P. deltoides (D map) and male P. euramericana (E map) with a pseudotestcross mapping strategy. The two maps were scanned by functional mapping to detect QTLs that control early growth trajectories of two rooting traits, maximal single-root length and the total number of roots per cutting, measured at five time points in water culture. Of the six QTLs detected for these two growth traits, only one is segregating in P. deltoides with poor rooting capacity, while the other five are segregating in P. euramericana showing good rooting capacity. Tests with functional mapping suggest different developmental patterns of the genetic effects of these root QTLs in time course. Five QTLs were detected to change their effects on root growth trajectories with time, whereas one detected to affect root growth consistently in time course. Knowledge about the genetic and developmental control mechanisms of root QTLs will have important implications for the genetic improvement of vegetative propagation traits in Populus.     

Identification and verification of QTLs for agronomic traits using wild barley introgression lines

A set of 39 wild barley introgression lines (hereafter abbreviated with S42ILs) was subjected to a QTL study to verify genetic effects for agronomic traits, previously detected in the BC₂DH population S42 (von Korff et al. 2006 in Theor Appl Genet 112:1221–1231) and, in addition, to identify new QTLs and favorable wild barley alleles. Each line within the S42IL set contains a single marker-defined chromosomal introgression from wild barley (Hordeum vulgare ssp. spontaneum), whereas the remaining part of the genome is exclusively derived from elite spring barley (H. vulgare ssp. vulgare). Agronomic field data of the S42ILs were collected for seven traits from three different environments during the 2007 growing season. For detection of putative QTLs, a two-factorial mixed model ANOVA and, subsequently, a Dunnett test with the recurrent parent as a control were conducted. The presence of a QTL effect on a wild barley introgression was accepted, if the trait value of a particular S42IL was significantly (P < 0.05) different from the control, either across all environments and/or in a particular environment. A total of 47 QTLs were localized in the S42IL set, among which 39 QTLs were significant across all tested environments. For 19 QTLs (40.4%), the wild barley introgression was associated with a favorable effect on trait performance. Von Korff et al. (2006 in Theor Appl Genet 112:1221–1231) mapped altogether 44 QTLs for six agronomic traits to genomic regions, which are represented by wild barley introgressions of the S42IL set. Here, 18 QTLs (40.9%) revealed a favorable wild barley effect on the trait performance. By means of the S42ILs, 20 out of the 44 QTLs (45.5%) and ten out of the 18 favorable effects (55.6%) were verified. Most QTL effects were confirmed for the traits days until heading and plant height. For the six corresponding traits, a total of 17 new QTLs were identified, where at six QTLs (35.3%) the exotic introgression caused an improved trait performance. In addition, eight QTLs for the newly studied trait grains per ear were detected. Here, no QTL from wild barley exhibited a favorable effect. The introgression line S42IL-107, which carries an introgression on chromosome 2H, 17–42 cM is an example for S42ILs carrying several QTL effects simultaneously. This line exhibited improved performance across all tested environments for the traits days until heading, plant height and thousand grain weight. The line can be directly used to transfer valuable Hsp alleles into modern elite cultivars, and, thus, for breeding of improved varieties.     

AB-QTL analysis in spring barley: III. Identification of exotic alleles for the improvement of malting quality in spring barley (<Emphasis Type="Italic">H. vulgare</Emphasis> ssp. <Emphasis Type="Italic">spontaneum</Emphasis>)

Malting quality is genetically determined by the complex interaction of numerous traits which are expressed prior to and, in particular, during the malting process. Here, we applied the advanced backcross quantitative trait locus (AB-QTL) strategy (Tanksley and Nelson, Theor Appl Genet 92:191–203, 1996), to detect QTLs for malting quality traits and, in addition, to identify favourable exotic alleles for the improvement of malting quality. For this, the BC₂DH population S42 was generated from a cross between the spring barley cultivar Scarlett and the wild barley accession ISR42-8 (Hordeum vulgare ssp. spontaneum). A QTL analysis in S42 for seven malting parameters measured in two different environments yielded 48 QTLs. The exotic genotype improved the trait performance at 18 (37.5%) of 48 QTLs. These favourable exotic alleles were detected, in particular, on the chromosome arms 3HL, 4HS, 4HL and 6HL. The exotic allele on 4HL, for example, improved α-amylase activity by 16.3%, fermentability by 0.8% and reduced raw protein by 2.4%. On chromosome 6HL, the exotic allele increased α-amylase by 16.0%, fermentability by 1.3%, friability by 7.3% and reduced viscosity by 2.9%. Favourable transgressive segregation, i.e. S42 lines exhibiting significantly better performance than the recurrent parent Scarlett, was recorded for four traits. For α-amylase, fermentability, fine-grind extract and VZ45 20, 16, 2 and 26 S42 lines, respectively, surpassed the recurrent parent Scarlett. The present study hence demonstrates that wild barley does harbour valuable alleles, which can enrich the genetic basis of cultivated barley and improve malting quality traits.     

Assessment of differences in morphological and physiological leaf lodging characteristics between two cultivars of Hippeastrum rutilum

Kernel weight and morphology are important traits affecting cereal yields and quality. Dissecting the genetic basis of thousand kernel weight (TKW) and its related traits is an effective method to improve wheat yield. In this study, we performed quantitative trait loci (QTL) analysis using recombinant inbred lines derived from the cross ‘PuBing3228 × Gao8901’ (PG-RIL) to dissect the genetic basis of kernel traits. A total of 17 stable QTLs related to kernel traits were identified, notably, two stable QTLs QTkw.cas-1A.2 and QTkw.cas-4A explained the largest portion of the phenotypic variance for TKW and kernel length (KL), and the other two stable QTLs QTkw.cas-6A.1 and QTkw.cas-7D.2 contributed more effects on kernel width (KW). Conditional QTL analysis revealed that the stable QTLs for TKW were mainly affected by KW. The QTLs QTkw.cas-7D.2 and QKw.cas-7D.1 associated with TKW and KW were delimited to the physical interval of approximately 3.82 Mb harboring 47 candidate genes. Among them, the candidate gene TaFT-D1 had a 1 bp insertions/deletion (InDel) within the third exon, which might be the reason for diversity in TKW and KW between the two parents. A Kompetitive Allele-Specific PCR (KASP) marker of TaFT-D1 allele was developed and verified by PG-RIL and a natural population consisted of 141 cultivar/lines. It was found that the favorable TaFT-D1 (G)-allele has been positively selected during Chinese wheat breeding. Thus, these results can be used for further positional cloning and marker-assisted selection in wheat breeding programs. Seventeen stable QTLs related to kernel traits were identified. The stable QTLs for thousand kernel weight were mainly affected by kernel width. TaFT-D1 could be the candidate gene for QTLs QTkw.cas-7D.2 and QKw.cas-7D.1.     

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.     

Genetic analysis of grain and malt quality in an elite barley population

Quantitative trait loci (QTLs) associated with grain weight, grain width, kernel hardness and malting quality were mapped in a doubled haploid population derived from two elite Australian malting barley varieties, Navigator and Admiral. A total of 30 QTLs for grain weight, grain width and kernel hardness were identified in three environments, and 63 QTLs were identified for ten malting quality traits in two environments. Three malting quality traits, namely β-amylase, diastatic power and apparent attenuation limit, were mainly controlled by a QTL linked to the Bmy1 gene at the distal end of chromosome 4H encoding a β-amylase enzyme. Six other malting quality traits, namely α-amylase, soluble protein, Kolbach index, free amino-acid nitrogen, wort β-glucan and viscosity, had coincident QTL clustered on chromosomes 1HS, 4HS, 7HS and 7HL, which demonstrated the interdependence of these traits. There was a strong association between these malt quality QTL clusters on chromosomes 1HS and 7HL and the major QTL for kernel hardness, suggesting that the use of this trait to enable early selection for malting quality in breeding programs would be feasible. In contrast, the majority of QTLs for hot-water extract were not coincident with those identified for other malt quality traits, which suggested differences in the mechanism controlling this trait. Novel QTLs have been identified for kernel hardness on chromosomes 2HL and 7HL, hot-water extract on 7HL and wort β-glucan on 6HL, and the resulting markers may be useful for marker-assisted selection in breeding programs.     

Unconditional and conditional QTL analysis of kernel weight related traits in wheat (Triticum aestivum L.) in multiple genetic backgrounds

Wheat thousand kernel weight (TKW) is a complex trait, and is largely controlled by several kernel traits, including kernel length (KL) and kernel width (KW). In order to reveal the genetic relationship between TKW and these kernel traits (KW and KL) as accurate as possible, we applied both unconditional and conditional mapping analyses to three distinct genetic populations, one DH population and two RIL populations. This report describes the identifications of 36 unconditional and conditional additive QTLs and 30 pairs of unconditional and conditional epistatic QTLs, all of which are closely associated with TKW. While the conditional additive locus Qtkw1B, detected in the RIL2 population, exhibited the largest contribution, explaining 14.12 % of TKW variance, the unconditional epistatic QTLs Qtkw3A-2/Qtkw5B.1, detected in the DH population, accounted for 11.95 % of phenotypic variance. This study also showed that, compared with unconditional mapping, conditional mapping resulted in very different numbers and different extent of effects of additive and epistatic QTLs that were associated with TKW when TKW was conditioned on kernel traits (KW and KL). These data strongly suggest that KW and KL indeed play a significant role in determining TKW. Furthermore, we demonstrated that the effects of the 25 additive QTLs for TKW were either entirely or largely determined by KW, while the effects of the other 25 additive QTLs for TKW were either entirely or largely affected by KL. We conclude that the conditional mapping can be useful for a better understanding of the interrelationship between the yield contributing traits at the QTL level.     

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.     

Detection and verification of malting quality QTLs using wild barley introgression lines

A malting quality quantitative trait locus (QTL) study was conducted using a set of 39 wild barley introgression lines (hereafter abbreviated with S42ILs). Each S42IL harbors a single marker-defined chromosomal segment from the wild barley accession ‘ISR 42-8’ (Hordeum vulgare ssp. spontaneum) within the genetic background of the elite spring barley cultivar ‘Scarlett’ (Hordeum vulgare ssp. vulgare). The aim of the study was (1) to verify genetic effects previously identified in the advanced backcross population S42, (2) to detect new QTLs, and (3) to identify S42ILs exhibiting multiple QTL effects. For this, grain samples from field tests in three different environments were subjected to micro malting. Subsequently, a line × phenotype association study was performed with the S42ILs in order to localize putative QTL effects. A QTL was accepted if the trait value of a particular S42IL was significantly (P < 0.05) different from the recurrent parent as a control, either across all tested environments or in a particular environment. For eight malting quality traits, altogether 40 QTLs were localized, among which 35 QTLs (87.5%) were stable across all environments. Six QTLs (15.0%) revealed a trait improving wild barley effect. Out of 36 QTLs detected in a previous advanced backcross QTL study with the parent BC₂DH population S42, 18 QTLs (50.0%) could be verified with the S42IL set. For the quality parameters α-amylase activity and Hartong 45°C, all QTLs assessed in population S42 were verified by S42ILs. In addition, eight new QTL effects and 17 QTLs affecting two newly investigated traits were localized. Two QTL clusters harboring simultaneous effects on eight and six traits, respectively, were mapped to chromosomes 1H and 4H. In future, fine-mapping of these QTL regions will be conducted in order to shed further light on the genetic basis of the most interesting QTLs.     

Looking into flowering time in almond (Prunus dulcis (Mill) D. A. Webb): the candidate gene approach

Blooming time is one of the most important agronomic traits in almond. Biochemical and molecular events underlying flowering regulation must be understood before methods to stimulate late flowering can be developed. Attempts to elucidate the genetic control of this process have led to the identification of a major gene (Lb) and quantitative trait loci (QTLs) linked to observed phenotypic differences, but although this gene and these QTLs have been placed on the Prunus reference genetic map, their sequences and specific functions remain unknown. The aim of our investigation was to associate these loci with known genes using a candidate gene approach. Two almond cDNAs and eight Prunus expressed sequence tags were selected as candidate genes (CGs) since their sequences were highly identical to those of flowering regulatory genes characterized in other species. The CGs were amplified from both parental lines of the mapping population using specific primers. Sequence comparison revealed DNA polymorphisms between the parental lines, mainly of the single nucleotide type. Polymorphisms were used to develop co-dominant cleaved amplified polymorphic sequence markers or length polymorphisms based on insertion/deletion events for mapping the candidate genes on the Prunus reference map. Ten candidate genes were assigned to six linkage groups in the Prunus genome. The positions of two of these were compatible with the regions where two QTLs for blooming time were detected. One additional candidate was localized close to the position of the Evergrowing gene, which determines a non-deciduous behaviour in peach.     

QTLs mapping for fruit size and shape in chromosomes 2 and 4 in pepper and a comparison of the pepper QTL map with that of tomato

Quantitative trait locus (QTL) mapping for fruit weight and shape in pepper (Capsicum spp.) was performed using C. chinense and C. frutescens introgression lines of chromosomes 2 and 4. In chromosome 2, a single major fruit-weight QTL, fw2.1, was detected in both populations that explained 62% of the trait variation. This QTL, as well as a fruit-shape QTL, fs2.1, which had a more minor effect, were localized to the tomato fruit-shape gene ovate. The cloned tomato fruit-weight QTL, fw2.2, did not play a major role in controlling fruit size variations in pepper. In chromosome 4, two fruit-weight QTLs, fw4.1 and fw4.2, were detected in the same genomic regions in both mapping populations. In addition, a single fruit-shape QTL was detected in each of the mapping populations that co-localized with one of the fruit-weight QTLs, suggesting pleiotropy or close linkage of the genes controlling size and shape. fw2.1 and fw4.2 represent major fruit-weight QTLs that are conserved in the three Capsicum species analyzed to date for fruit-size variations. Co-localization of the pepper QTLs with QTLs identified for similar traits in tomato suggests that the pepper and tomato QTLs are orthologous. Compared to fruit-shape QTLs, fruit-weight QTLs were more often conserved between pepper and tomato. This implies that different modes of selection were employed for these traits during domestication of the two Solanaceae species.S. Zygier and A. Ben Chaim contributed equally to this work.     

AFLP mapping of QTLs for in vitro organogenesis traits using recombinant inbred lines in sunflower (Helianthus annuus L.)

Genetic control for two in vitro organogenesis traits, the number of shoots per explant plated (S/E) and the number of shoots per regenerating explant (S/RE), was investigated in 75 recombinant inbred lines (RILs) of sunflower and their two parents (PAC-2 and RHA-266). Genetic variability was observed among the 75 RILs for the organogenesis traits studied. Some RILs presented significant differences when compared with the best parental line (RHA-266). Genetic gain, in terms of the percentage of the best parent, for 32% of the selected RILs was significant. A set of 99RILs from the same cross including the 75 mentioned above was screened with 333 AFLP markers and a linkage map was constructed based on 264 linked loci. Six putative QTLs for the S/RE (tentatively named osr) and seven QTLs for the S/E (ose) trait were detected using composite interval mapping. For each trait, the QTLs explained 52% (ose) and 67% (osr) of the total phenotypic variance. These results suggested that additive gene effects predominate in explaining a large proportion of the observed genetic variation associated with regeneration ability. The coincidental location of QTLs for S/E and S/RE is discussed. Received: 20 September 1999 / Accepted: 16 May 2000