Quantitative Trait Loci For Days Research Articles

Genetic Analysis Of Seed Yield And Its Contributing Characters In F2 Population Of Soybean Genotypes, Glycine Max (L) Merrill Using Morphological and SNP Markers

This study was carried out on the genetic analysis of seed yield and its contributing characters in F2 population of soybean genotypes, Glycine max (l). Merrill genotypes using morphological and SNP markers. The aim of this study is to determine the extent of genetic variability for seed yield and its contributing characters among the F2 population of soybean genotypes and to determine quantitative trait loci (QTL) associated with seed yield in the soybean genotypes with a view of being utilized in soybean breeding programme. The field experiment was laid out in a randomized complete block design (RCBD) with three replications. Heritability in the broad sense ranged from 40.00% to 99.97% for number of seeds and number of pods respectively. The genetic advance mean ranged between 10.03 and 130.17 for days to maturity and seed yield respectively. Nine QTLs were identified (3 QTLs for days to flowering (DTF), 3 QTLs for days to maturity (DTM), 2 QTLs for total pod weight (TPW) and 1 QTL for seed yield (SYP)) and located on the linkage group A1 (chromosome 5). However, two stable QTLs for days to flowering (DTF) and days to maturity (DTM) and two novel QTLs for days to flowering (DTF) and total pod weight (TPW) were identified in the present study.

Dissection of quantitative trait loci for root characters and day length sensitivity in SynOpDH wheat (Triticum aestivum L.) bi-parental mapping population

AbstractThe genetics of the root system is still not dissected for wheat and lack of knowledge prohibits the use of marker-assisted selection in breeding. To understand the genetic mechanism of root development, Synthetic W7984 × Opata M85 doubled-haploid (SynOpDH) mapping population was evaluated for root and shoot characteristics in PVC tubes until maturity. Two major quantitative trait loci (QTLs) for total root biomass were detected on homoeologous chromosomes 2A and 2D with logarithm of the odds scores between 6.25–10.9 and 11.8–20.86, and total phenotypic effects between 12.7–17.7 and 26.6–40.04% in 2013 and 2014, respectively. There was a strong correlation between days to anthesis and root and shoot biomass accumulation (0.50–0.81). The QTL for biomass traits on chromosome 2D co-locates with QTL for days to anthesis. The effect of extended vegetative growth, caused by photoperiod sensitivity (Ppd) genes, on biomass accumulation was always hypothesized, this is the first study to genetically support this theory.

RAD-seq-Based High-Density Linkage Map Construction and QTL Mapping of Biomass-Related Traits in Sorghum using the Japanese Landrace Takakibi NOG

Sorghum [Sorghum bicolor (L.) Moench] grown locally by Japanese farmers is generically termed Takakibi, although its genetic diversity compared with geographically distant varieties or even within Takakibi lines remains unclear. To explore the genomic diversity and genetic traits controlling biomass and other physiological traits in Takakibi, we focused on a landrace, NOG, in this study. Admixture analysis of 460 sorghum accessions revealed that NOG belonged to the subgroup that represented Asian sorghums, and it was only distantly related to American/African accessions including BTx623. In an attempt to dissect major traits related to biomass, we generated a recombinant inbred line (RIL) from a cross between BTx623 and NOG, and we constructed a high-density linkage map based on 3,710 single-nucleotide polymorphisms obtained by restriction-site-associated DNA sequencing of 213 RIL individuals. Consequently, 13 fine quantitative trait loci (QTLs) were detected on chromosomes 2, 3, 6, 7, 8 and 9, which included five QTLs for days to heading, three for plant height (PH) and total shoot fresh weight and two for Brix. Furthermore, we identified two dominant loci for PH as being identical to the previously reported dw1 and dw3. Together, these results corroborate the diversified genome of Japanese Takakibi, while the RIL population and high-density linkage map generated in this study will be useful for dissecting other important traits in sorghum.

High-density genetic map development and QTL mapping for concentration degree of floret flowering date in cultivated peanut (Arachis hypogaea L.)

The concentration degree of floret flowering date (CDFFD) is an important selection index for earliness breeding of peanut, while the genetic basis of CDFFD-related traits in peanut is poorly understood. The aim of this study was to develop a high-density genetic linkage map of cultivated peanut by combining SLAF-seq (specific locus amplified fragment sequencing) with SSR (simple sequence repeat) techniques and to identify QTL (quantitative trait loci) controlling CDFFD. A RIL population derived from a cross between Silihong and Jinonghei 3 was sequenced by the HiSeq 2500 platform. A total of 1262.02 M high-quality paired-end reads were obtained, and 1,328,966 SNPs (single nucleotide polymorphisms) were developed from parents and progenies, of which 754,499 SNPs were successfully encoded and genotyping. The resulting map consisted of 3326 genetic markers (2996 SNPs and 330 SSRs) distributed in 20 linkage groups (LGs), spanning 1822.83 cM with an average distance of 0.55 cM between adjacent markers. These assigned SNP markers had average sequencing depths of 16.94-, 15.66-, and 20.94-fold in the male parent, female parent, and their progenies, respectively. Based on phenotyping in 4 environments, 15 significant QTL for the CDFFD were identified. And one major QTL for days to accumulation of 25 flowers (DA25F), qDA25F6.2, located on chromosome 6 was obtained, with a phenotypic variance explanation (PVE) of 12.49%. This map exhibited higher resolution and accuracy, which will facilitate more QTL discovery for interested agronomic and quality traits in cultivated peanut.

Development of temperate basmati rice: a multi-year study on performance and adaptation under high altitude conditions of Northern Himalayas

AbstractIn the present study, an effective secondary selection of transgressive variants from a homozygous population of Pusa Sugandh 3 (PS3) has led to the development of basmati variant SKUA 494. SKUA 494 exhibited a grain yield (7.9 t/ha) with superiority of 21.5% over its progenitor (6.5 t/ha). Besides, the genotype revealed an earliness of about 13 and 15 days for flowering and maturity, respectively. Hulling, milling and head rice recovery traits of SKUA 494 were comparatively better over the controls PS3 and Pusa Basmati 1509. No significant differences in the cooking quality were observed in SKUA 494 over its parental line. Quality traits of SKUA 494 revealed an intermediate score for alkali spreading value, besides similar values for gel consistency and amylose content in comparison to PS3. On the basis of stability variables, stability index and overall mean for most of the traits, SKUA 494 depicted stable performance across the locations and over the years. Molecular analysis based on simple sequence repeat markers revealed polymorphism at locus flanking the quantitative trait loci for days to heading (Hd6) between SKUA 494 and its parent (PS3). Based on overall superiority in the performance and adaptability of SKUA 494, the variety has been recommended to farmers for general cultivation under temperate ecology.

Construction of high-density linkage maps for mapping quantitative trait loci for multiple traits in field pea (Pisum sativum L.)

BackgroundThe objective of this research was to map quantitative trait loci (QTLs) of multiple traits of breeding importance in pea (Pisum sativum L.). Three recombinant inbred line (RIL) populations, PR-02 (Orb x CDC Striker), PR-07 (Carerra x CDC Striker) and PR-15 (1–2347-144 x CDC Meadow) were phenotyped for agronomic and seed quality traits under field conditions over multiple environments in Saskatchewan, Canada. The mapping populations were genotyped using genotyping-by-sequencing (GBS) method for simultaneous single nucleotide polymorphism (SNP) discovery and construction of high-density linkage maps.ResultsAfter filtering for read depth, segregation distortion, and missing values, 2234, 3389 and 3541 single nucleotide polymorphism (SNP) markers identified by GBS in PR-02, PR-07 and PR-15, respectively, were used for construction of genetic linkage maps. Genetic linkage groups were assigned by anchoring to SNP markers previously positioned on these linkage maps. PR-02, PR-07 and PR-15 genetic maps represented 527, 675 and 609 non-redundant loci, and cover map distances of 951.9, 1008.8 and 914.2 cM, respectively. Based on phenotyping of the three mapping populations in multiple environments, 375 QTLs were identified for important traits including days to flowering, days to maturity, lodging resistance, Mycosphaerella blight resistance, seed weight, grain yield, acid and neutral detergent fiber concentration, seed starch concentration, seed shape, seed dimpling, and concentration of seed iron, selenium and zinc. Of all the QTLs identified, the most significant in terms of explained percentage of maximum phenotypic variance (PVmax) and occurrence in multiple environments were the QTLs for days to flowering (PVmax = 47.9%), plant height (PVmax = 65.1%), lodging resistance (PVmax = 35.3%), grain yield (PVmax = 54.2%), seed iron concentration (PVmax = 27.4%), and seed zinc concentration (PVmax = 43.2%).ConclusionWe have identified highly significant and reproducible QTLs for several agronomic and seed quality traits of breeding importance in pea. The QTLs identified will be the basis for fine mapping candidate genes, while some of the markers linked to the highly significant QTLs are useful for immediate breeding applications.

Identification of QTLs Associated with Improved Resistance to Ascochyta Blight in an Interspecific Pea Recombinant Inbred Line Population

Ascochyta blight of pea (Pisum sp.), caused by Peyronellaea pinodes, often results in serious yield losses. Some accessions of Pisum fulvum Sibth. & Sm. previously showed high levels of resistance and could be used as sources of new resistance genes. The objectives of this study were to develop a single nucleotide polymorphism (SNP)‐based linkage map and identify genomic regions associated with Ascochyta blight resistance. A population (PR‐19) consisting of 144 recombinant inbred lines (RILs) developed from a cross between P651 (P. fulvum) and Alfetta (Pisum sativum L.) was used. These RILs were evaluated for Ascochyta blight resistance under field conditions in Saskatchewan, as well as under greenhouse conditions. The RILs were genotyped using an Illumina GoldenGate array panel of 1536 SNPs. A wide range of variation was observed in Ascochyta blight scores and other agronomic traits. Disease scores were positively correlated (P < 0.001) with lodging and were negatively correlated (P < 0.001) with days to flower, plant height, days to maturity, and grain yield. A total of 733 SNP markers were assigned to six linkage groups covering 682.1 cM of the pea genome. Nine quantitative trait loci (QTLs) were identified for Ascochyta blight resistance, which individually explained 7.5 to 28% of the total phenotypic variation. In addition, five QTLs each were identified for plant height, days to maturity, and grain yield, four QTLs for days to flower, and two QTLs for lodging. The QTL abIII‐1 was consistent across locations and years, whereas abI‐IV‐2 was significant at both locations in 2014. These QTLs can be utilized for development of molecular markers associated with Ascochyta blight resistance.

Mapping QTLs associated with agronomic and physiological traits under terminal drought and heat stress conditions in wheat (Triticum aestivum L.).

Wheat crops frequently experience a combination of abiotic stresses in the field, but most quantitative trait loci (QTL) studies have focused on the identification of QTLs for traits under single stress field conditions. A recombinant inbred line (RIL) population derived from SeriM82 × Babax was used to map QTLs under well-irrigated, heat, drought, and a combination of heat and drought stress conditions in two years. A total of 477 DNA markers were used to construct linkage groups that covered 1619.6 cM of the genome, with an average distance of 3.39 cM between adjacent markers. Moderate to relatively high heritability estimates (0.60-0.70) were observed for plant height (PHE), grain yield (YLD), and grain per square meter (GM2). The most important QTLs for days to heading (DHE), thousand grain weight (TGW), and YLD were detected on chromosomes 1B, 1D-a, and 7D-b. The prominent QTLs related to canopy temperature were on 3B. Results showed that common QTLs for DHE, YLD, and TGW on 7D-b were validated in heat and drought trials. Three QTLs for chlorophyll content in SPAD unit (on 1A/6B), leaf rolling (ROL) (on 3B/4A), and GM2 (on 1B/7D-b) showed significant epistasis × environment interaction. Six heat- or drought-specific QTLs (linked to 7D-acc/cat-10, 1B-agc/cta-9, 1A-aag/cta-8, 4A-acg/cta-3, 1B-aca/caa-3, and 1B-agc/cta-9 for day to maturity (DMA), SPAD, spikelet compactness (SCOM), TGW, GM2, and GM2, respectively) were stable and validated over two years. The major DHE QTL linked to 7D-acc/cat-10, with no QTL × environment (QE) interaction increased TGW and YLD. This QTL (5.68 ≤ LOD ≤ 10.5) explained up to 19.6% variation in YLD in drought, heat, and combined stress trials. This marker as a candidate could be used for verification in other populations and identifying superior allelic variations in wheat cultivars or its wild progenitors to increase the efficiency of selection of high yielding lines adapted to end-season heat and drought stress conditions.

QTLs CONTROLLING SEED WEIGHT AND DAYS TO FLOWERING IN MUNGBEAN (Vigna radiata (L.) Wilczek), THEIR CONSERVATION IN AZUKI BEAN (V. angularis (Ohwi) Ohwi & Ohashi) AND RICE BEAN (V. umbellata (Thunb.) Ohwi & Ohashi)

Mungbean ( Vigna radiata (L.) Wilczek) is a socio-economically important legume crop of Asia. Varieties with large seed size and early maturity are preferred in commercial production. In this study, we identified quantitative trait loci (QTL) controlling seed weight and days to flowering in mungbean. The mapping population comprises 155 F 2 -derived lines from a cross between Kamphaeng Saen 1 (large-seeded and early flowering) and V4718 (small-seeded and late flowering). The F 2 population was analyzed with 67 simple sequence repeat markers. The F2:3 families were evaluated for 100-seed weigh and days to flowering in two years, 2008 (one season) and 2011 (two seasons). Composite interval mapping identified six QTLs for 100-seed weight and 5 QTLs for days to flowering. Three genomic regions harbored QTLs for both seed weight and days to flowering, revealing association between the two traits. Comparison of QTLs for both traits found in this study with those reported in azuki bean ( Vigna angularis (Willd.) Ohwi & Ohashi) and rice bean ( Vigna umbellata (Thunb.) Ohwi & Ohashi) revealed that several QTLs are conserved among the three Vigna species.

QTLs CONTROLLING SEED WEIGHT AND DAYS TO FLOWERING IN MUNGBEAN [Vigna radiata (L.) Wilczek], THEIR CONSERVATION IN AZUKI BEAN [V. angularis (Ohwi) Ohwi & Ohashi] AND RICE BEAN [V. umbellata (Thunb.) Ohwi & Ohashi

Mungbean ( Vigna radiata (L.) Wilczek) is a socio-economically important legume crop of Asia. Varieties with large seed size and early maturity are preferred in commercial production. In this study, we identified quantitative trait loci (QTL) controlling seed weight and days to flowering in mungbean. The mapping population comprises 155 F 2 -derived lines from a cross between Kamphaeng Saen 1 (large-seeded and early flowering) and V4718 (small-seeded and late flowering). The F 2 population was analyzed with 67 simple sequence repeat markers. The F2:3 families were evaluated for 100-seed weigh and days to flowering in two years, 2008 (one season) and 2011 (two seasons). Composite interval mapping identified six QTLs for 100-seed weight and 5 QTLs for days to flowering. Three genomic regions harbored QTLs for both seed weight and days to flowering, revealing association between the two traits. Comparison of QTLs for both traits found in this study with those reported in azuki bean ( Vigna angularis (Willd.) Ohwi & Ohashi) and rice bean ( Vigna umbellata (Thunb.) Ohwi & Ohashi) revealed that several QTLs are conserved among the three Vigna species.

QTL mapping for maize resistance and yield under infestation with Sesamia nonagrioides

The Mediterranean corn borer (MCB) is the most important maize insect pest in the Mediterranean region. The main objective was to map quantitative trait loci (QTL) for yield performance under infestation with MCB, resistance and agronomic traits in a maize RIL population derived from an inbred cross European flint × Reid. Six QTL for resistance traits were located: one QTL for tunnel length (bin 9.03; p = 19.8 %), one QTL for stalk lodging (bin 3.07, p = 11.5 %), and four QTL for ear resistance (bins 1.07, 5.03/5.05, and 8.04; p = 25–63 %). Twelve QTL for agronomic traits were located: a QTL for yield under infestation (bin 5.03, p = 15 %); two QTL for grain moisture (bins 1.07 and 8.05); two QTL for days to anthesis (bin 1.07 and 8.05); two QTL for days to silking (bins 8.04 and 10.02); three QTL for plant height (bins 5.04, 8.05 and 9.03); and two QTL for ear height (bins 8.05 and 9.03). No genetic correlations between yield and other traits were observed. The cross validation (CV) approach showed that the estimation biases for QTL for resistance traits were higher than those for agronomic traits. This work stresses the importance of the region 9.03 for controlling corn borer resistance and suggests the presence of QTL with small effect on ear-resistance traits. At the same genomic region, there are also genes that control plant and ear height and future works could elucidate whether these genes are the same or are closely linked. The QTL for yield seem to play an important role in MCB tolerance in this genetic background. Large biases observed for QTL effects by CV were mainly due to the small sample size used and were higher for resistance traits due to their larger genetic complexity. We consider that it is more appropriate to select for grain yield under infestation instead of selecting for resistance traits because resistance to MCB could have unfavorable associations with agronomic traits.

Genomewide Association Mapping of Flowering Time, Kernel Composition, and Disease Resistance in Historical Minnesota Maize Inbreds

ABSTRACTAssociation mapping in maize (Zea mays L.) has been effective at identifying major quantitative trait loci (QTL) for less‐complex traits, and historical inbreds are a potential source of useful variation. Our objectives were to (i) characterize genomewide linkage disequilibrium, (ii) assess variation for flowering time, kernel composition, and resistance to northern corn leaf blight (NCLB) (caused by Setosphaeria turcica) and Goss's wilt and blight (GWB) (caused by Clavibacter michiganensis subsp. nebraskensis), and (iii) identity major QTL for these traits in a collection of 284 historical maize inbreds mostly developed at the University of Minnesota. Linkage disequilibrium (LD) was high, decaying (r2 = 0.1) in 802 kb, among 39,166 single nucleotide polymorphism (SNP) markers on the Illumina MaizeSNP50 Beadchip. The mean LD between adjacent markers was r2 = 0.38. The A321 subpopulation, to which 60% of the Minnesota inbreds belonged, had inbreds with either or both the minimum and maximum inbred mean value for all traits except protein concentration. We identified QTL for days to anthesis (eight QTL), days to silking (11 QTL), oil concentration (11 QTL), starch concentration (two QTL), NCLB (13 QTL), and GWB (nine QTL). The Minnesota inbreds were enriched for favorable QTL alleles for days to flowering and oil concentration but not for starch concentration and disease resistance. These QTL identified in historical maize inbreds may be useful in modern breeding programs.

QTLs for resistance to Phomopsis seed decay are associated with days to maturity in soybean (Glycine max)

Phomopsis seed decay (PSD), primarily caused by Phomopsis longicolla, is a major contributor to poor soybean seed quality and significant yield loss, particularly in early maturing soybean genotypes. However, it is not yet known whether PSD resistance is associated with early maturity. This study was conducted to identify quantitative trait loci (QTLs) for resistance to PSD and days to maturity using a recombinant inbred line (RIL) population derived from a cross between the PSD-resistant Taekwangkong and the PSD-susceptible SS2-2. Based on a genetic linkage map incorporating 117 simple sequence repeat markers, QTL analysis revealed two and three QTLs conferring PSD resistance and days to maturity, respectively, in the RIL population. Two QTLs (PSD-6-1 and PSD-10-2) for PSD resistance were identified in the intervals of Satt100-Satt460 and Sat_038-Satt243 on chromosomes 6 and 10, respectively. Two QTLs explained phenotypic variances in PSD resistance of 46.3 and 14.1%, respectively. At the PSD-6-1 QTL, the PSD-resistant cultivar Taekwangkong contributed the allele with negative effect decreasing the infection rate of PSD and this QTL does not overlap with any previously reported loci for PSD resistance in other soybean genotypes. Among the three QTLs for days to maturity, two (Mat-6-2 and Mat-10-3) were located at positions similar to the PSD-resistance QTLs. The identification of the QTLs linked to both PSD resistance and days to maturity indicates a biological correlation between these two traits. The newly identified QTL for resistance to PSD associated with days to maturity in Taekwangkong will help improve soybean resistance to P. longicolla.

Genetic Analysis of Yield Components in the PI 438489B by ‘Hamilton’ Recombinant Inbred Line (RIL) Population of Soybean [Glycine max (L.) Merr.

Yield is a multi-factorial trait determined by several genetic traits and highly correlated with important agronomic traits in many crops including soybean. [Glycine max (L.)]. Plant height, seed and pod numbers, and seed weight are all components of yield and polygenic in nature. The objective of this study was to identify quantitative trait loci (QTL) for days to germination, days to flowering, plant height, pod number, seed number, 100-seed weight, and total seed weight in soybean using the using the PI 438489B by ‘Hamilton’ recombinant inbred line (RIL) population (PIxH, n=50). A total of 18 QTL were found on 10 different chromosomes. Three QTL for days to germination (qDG001-qDG003) have been identified on chromosomes 5b, 6, and 13b. Two QTL (qDF001 and qDF002) have been identified on chromosomes 9 and 13b, respectively. On QTL for plant height (qPH001) have been identified on chromosome 6. Four QTL for pod number (qPN001-qPN004) had been identified on chromosomes 2, 6, and 8 (2 QTL), respectively. Two QTL for seed number (qSN001 and qSN002) have been identified on chromosomes 5b and 11b, respectively. Five QTL for 100-seed weight (qSW001 to qSW005) have been identified on chromosomes 5a, 6, 8, 9, and 11c, respectively. Two QTL for total seed weight (qTSW001 and qTSW002) have been identified on chromosomes 5b and 17c, respectively. The QTL identified here may be introduced in breeding programs to develop soybean cultivars with high yield potential.

QTLs for days to silking in a recombinant inbred line maize population subjected to high and low nitrogen regimes

Days to silking (DTS) is one of the most important traits in maize (Zea mays). To investigate its genetic basis, a recombinant inbred line population was subjected to high and low nitrogen (N) regimes to detect quantitative trait loci (QTLs) associated with DTS. Three QTLs were identified under the high N regime; these explained 25.4% of the phenotypic variance. Due to additive effects, the QTL on chromosome 6 increased DTS up to 0.66 days; while the other two QTLs mapped on chromosome 9 (one linked with Phi061 and the other linked with Nc134) decreased DTS 0.89 and 0.91 days, respectively. Under low N regime, two QTLs were mapped on chromosomes 6 and 9, which accounted for 25.9% of the phenotypic variance. Owing to additive effects, the QTL on chromosome 6 increased DTS 0.67 days, while the other QTL on chromosome 9 decreased it 1.48 days. The QTL on chromosome 6, flanked by microsatellite markers Bnlg1600 and Phi077, was detected under both N regimes. In conclusion, we identified four QTLs, one on chromosome 6 and three on chromosome 9. These results contribute to our understanding of the genetic basis of DTS and will be useful for developing marker-assisted selection in maize breeding programs.

Identification of novel quantitative trait loci for days to ear emergence and flag leaf glaucousness in a bread wheat (Triticum aestivum L.) population adapted to southern Australian conditions

In southern Australia, where the climate is predominantly Mediterranean, achieving the correct flowering time in bread wheat minimizes the impact of in-season cyclical and terminal drought. Flag leaf glaucousness has been hypothesized as an important component of drought tolerance but its value and genetic basis in locally adapted germplasm is unknown. From a cross between Kukri and RAC875, a doubled-haploid (DH) population was developed. A genetic linkage map consisting of 456 DArT and SSR markers was used to detect QTL affecting time to ear emergence and Zadoks growth score in seven field experiments. While ear emergence time was similar between the parents, there was significant transgressive segregation in the population. This was the result of segregation for the previously characterized Ppd-D1a and Ppd-B1 photoperiod responsive alleles. QTL of smaller effect were also detected on chromosomes 1A, 4A, 4B, 5A, 5B, 7A and 7B. A novel QTL for flag leaf glaucousness of large, repeatable effect was detected in six field experiments, on chromosome 3A (QW.aww-3A) and accounted for up to 52 percent of genetic variance for this trait. QW.aww-3A was validated under glasshouse conditions in a recombinant inbred line population from the same cross. The genetic basis of time to ear emergence in this population will aid breeders' understanding of phenological adaptation to the local environment. Novel loci identified for flag leaf glaucousness and the wide phenotypic variation within the DH population offers considerable scope to investigate the impact and value of this trait for bread wheat production in southern Australia.

Quantitative trait analysis of transplanting time and other root-growth-related traits in tomato

Transplanting time is determined by factors such as the field conditions, the age of the seedlings, and the size of the container, but little information is available on the effect of the genetic background on transplanting time. Here, we examined root dry weight (RDW), shoot dry weight, root/shoot ratio (RSR), time at which 50% of the germinated seedlings have expanded cotyledons (CE50), root ball formation (RBW), the length of time from the cotyledon expansion from the first to the last germinated seedling (ES) and transplanting time (TRD) in a BC 1F 6 population derived from Solanum lycopersicum and Solanum pimpinellifolium. All traits exhibited significant correlation with each other, except for RSR, which was only significantly correlated to RDW. A total of eight additive quantitative trait loci (QTLs) were detected for the five traits, i.e., RSR, RBW, CE50, ES, and TRD. One epistatic (QTL × QTL) interaction each was identified for RSR and TRD. QTLs for RSR, RBW, CE50, ES and TRD clustered near marker LEOH37 on chromosome 4. Clustering of ce50-4, rsr4, rbw4, and es4 with trd4 reflected the dependence of transplanting time on root ball formation, growth uniformity and early seedling growth, especially root growth. In addition, several QTLs in this study were mapped to regions where QTLs for days to flowering or number of leaves before the first inflorescence had been identified previously. This suggests that the roots may exert some influence on the flowering time in tomato.

DTH8 Suppresses Flowering in Rice, Influencing Plant Height and Yield Potential Simultaneously

The three most important agronomic traits of rice (Oryza sativa), yield, plant height, and flowering time, are controlled by many quantitative trait loci (QTLs). In this study, a newly identified QTL, DTH8 (QTL for days to heading on chromosome 8), was found to regulate these three traits in rice. Map-based cloning reveals that DTH8 encodes a putative HAP3 subunit of the CCAAT-box-binding transcription factor and the complementary experiment increased significantly days to heading, plant height, and number of grains per panicle in CSSL61 (a chromosome segment substitution line that carries the nonfunctional DTH8 allele) with the Asominori functional DTH8 allele under long-day conditions. DTH8 is expressed in most tissues and its protein is localized to the nucleus exclusively. The quantitative real-time PCR assay revealed that DTH8 could down-regulate the transcriptions of Ehd1 (for Early heading date1) and Hd3a (for Heading date3a; a rice ortholog of FLOWERING LOCUS T) under long-day conditions. Ehd1 and Hd3a can also be down-regulated by the photoperiodic flowering genes Ghd7 and Hd1 (a rice ortholog of CONSTANS). Meanwhile, the transcription of DTH8 has been proved to be independent of Ghd7 and Hd1, and the natural mutation of this gene caused weak photoperiod sensitivity and shorter plant height. Taken together, these data indicate that DTH8 probably plays an important role in the signal network of photoperiodic flowering as a novel suppressor as well as in the regulation of plant height and yield potential.

Identification of coincident QTL for days to heading, spike length and spikelets per spike in Lolium perenne L.

Flowering time is a trait which has a major influence on the quality of forage. In addition, flowering and subsequent seed yields are important traits for seed production by grass breeders. In this study, we have identified quantitative trait loci (QTL) for flowering time and morphological traits of the flowering head in an F1 mapping population in Lolium perenne L (perennial ryegrass), a number of which have not previously been identified in L. perenne mapping studies. QTL for days to heading (DTH) were mapped in both outdoor and glasshouse experiments, revealing three and five QTL for DTH which explained 53% and 42% of the total phenotypic variation observed, respectively. Two QTL for DTH were detected in both environments, although they had contrasting relative magnitudes in each environment. One QTL for spike length and three QTL for spikelets per spike were also identified explaining, a total of 32 and 33% of the phenotypic variance, respectively. Furthermore, the QTL for spike length and spikelets per spike generally coincided with QTL for days to heading, implying co-ordinate regulation by underlying genes. Of particular interest was a region harbouring overlapping QTL for days to heading, spike length and spikelets per spike on the top of linkage group 4, containing the major QTL for spike length identified in this population.

QTL analysis of flooding tolerance in soybean at an early vegetative growth stage

AbstractSoybean cultivars are sensitive to flooding stress and their seed yields are substantially reduced in response to the stress. This study was conducted to investigate the genetic basis of flooding tolerance at an early vegetative growth stage. Sixty recombinant inbred lines derived from a cross between a relatively tolerant cv. ‘Misuzudaizu’ and a sensitive cv. ‘Moshidou Gong 503’ were grown in pots in a vinyl plastic greenhouse in 2002 and 2003. At the two‐leaf stage, half of the pots were waterlogged by water placed in plastic containers and adjusted to 5 cm above the soil surface. After 3 weeks of treatment, the pots were returned to the greenhouse and grown until maturity. Flooding tolerance was evaluated by dividing the seed weight of the treated plants by that of the control plants. Quantitative trait loci (QTL) analysis using 360 genetic markers revealed three QTLs for flooding tolerance, ft1 to ft3 in 2002. The ft1 (molecular linkage group C2) was reproducible and an additional four QTLs, ft4 to ft7, were found in 2003. The ft1 had a high LOD score in both years (15.41 and 7.57) and accounted for 49.2% and 30.5% of the total variance, respectively. A large QTL for days to flowering was consistently observed across treatments and years at a similar position to ft1. Comparing the relative location with markers, the maturity gene probably corresponds to E1. Late maturity may have conferred a longer growth period for recovery from flooding stress.