Quantitative Trait Loci For Heading Date Research Articles

Exploring the SiCCT Gene Family and Its Role in Heading Date in Foxtail Millet.

CCT transcription factors are involved in the regulation of photoperiod and abiotic stress in Arabidopsis and rice. It is not clear that how CCT gene family expand and regulate heading date in foxtail millet. In this study, we conducted a systematic analysis of the CCT gene family in foxtail millet. Thirty-nine CCT genes were identified and divided into four subfamilies based on functional motifs. Analysis showed that dispersed duplication played a predominant role in the expansion of CCT genes during evolution. Nucleotide diversity analysis suggested that genes in CONSTANS (COL)-like, CCT MOTIF FAMILY (CMF)-like, and pseudoresponse response regulator (PRR)-like subfamilies were subjected to selection. Fifteen CCT genes were colocalized with previous heading date quantitative trait loci (QTL) and genome-wide association analysis (GWAS) signals. Transgenic plants were then employed to confirm that overexpression of the CCT gene SiPRR37 delayed the heading date and increased plant height. Our study first investigated the characterization and expansion of the CCT family in foxtail millet and demonstrated the role of SiPRR37. These results lay a significant foundation for further research on the function of CCT genes and provide a cue for the regulation of heading date.

Detection of quantitative trait loci for heading date and temperature responsiveness in a re‐sequenced, recombinant inbred line of japonica rice from Heilongjiang province, china

AbstractThe hereditary basis and identification of novel genes of heading date have significant implications for japonica rice improvement in northeast China, especially in Heilongjiang province. A re‐sequenced recombinant inbred line (RIL) population derived from the cross between Lijiangxintuanheigu (LTH) and Shennong 265 (SN265) was used to detect the genetic basis for the RIL in 2017 and 2018. Fourteen heading date quantitative trait loci (QTLs), including nine in 2017 and thirteen in 2018, were detected with a linkage map containing 2,818 bin markers. They were distributed on chromosomes 3, 4, 6 and 9–11 with 9.34%–25.26% phenotypic variations. The QTLs qHD3a, qHD4a, qHD4b, qHD4c, qHD9b, qHD10, qHD11c and qHD11d were identified in both years. The qTRS1, qTRS3a (qHD3a), qTRS3b (qHD3b) and qTRS9 (qHD9a) alleles from LTH and the qTRS4 allele from SN265 were identified by controlling the temperature responsiveness in the RIL population. The explained phenotypic variation in these five QTLs varied from 14.52% to 26.31%. In order to accurately determine the difference in heading date under different temperature conditions, the RILs and two parents were grown in a phytotron. Four QTLs controlling temperature responsiveness were identified on chromosomes 3, 6 and 9, including qTRS3a (qHD3a), qTRS3b (qHD3b), qTRS6 and qTRS9 (qHD9a). In a different environment, qTRS3a (qHD3a), qTRS3b (qHD3b) and qTRS9 (qHD9a) were detected. A comparison of chromosomal locations between the QTLs detected in this study and heading date genes previously cloned indicated that DTH3, Hd16, RFL, HAF1, Ehd2 and RBS1 might be candidate genes for them. The four major heading date genes (Hd1, Ghd7, Ghd7.1 and Ghd8) affecting ecogeographical adaptation were sequenced between SN265 and LTH. SN265 carried a functional Hd1 haplotype, a weak functional Ghd7 haplotype, a weak functional Ghd7.1 haplotype and a weak functional Ghd8 haplotype. LTH also carried functional Hd1 haplotype, a weak functional Ghd7 haplotype, a non‐functional Ghd7.1 haplotype and a non‐functional Ghd8 haplotype. The combinations of the Hd1, Ghd7, Ghd7.1 and Ghd8 alleles in SN265 and LTH largely defined their short heading date under long‐day conditions. The selection of heading date gene combinations with functional Hd1 alleles and non‐functional alleles or weak functional alleles of Ghd7, Ghd7.1 and Ghd8 would be an effective way to improve japonica rice with proper heading days in Northeast China. The novel QTLs detected in this study could also become a valuable source for designing the appropriate heading date in Northeast China japonica rice.

Genome-wide association study of yield components in spring wheat collection harvested under two water regimes in Northern Kazakhstan.

BackgroundBread wheat is the most important cereal in Kazakhstan, where it is grown on over 12 million hectares. One of the major constraints affecting wheat grain yield is drought due to the limited water supply. Hence, the development of drought-resistant cultivars is critical for ensuring food security in this country. Therefore, identifying quantitative trait loci (QTLs) associated with drought tolerance as an essential step in modern breeding activities, which rely on a marker-assisted selection approach.MethodsA collection of 179 spring wheat accessions was tested under irrigated and rainfed conditions in Northern Kazakhstan over three years (2018, 2019, and 2020), during which data was collected on nine traits: heading date (HD), seed maturity date (SMD), plant height (PH), peduncle length (PL), number of productive spikes (NPS), spike length (SL), number of kernels per spike (NKS), thousand kernel weight (TKW), and kernels yield per m2 (YM2). The collection was genotyped using a 20,000 (20K) Illumina iSelect SNP array, and 8,662 polymorphic SNP markers were selected for a genome-wide association study (GWAS) to identify QTLs for targeted agronomic traits.ResultsOut of the total of 237 discovered QTLs, 50 were identified as being stable QTLs for irrigated and rainfed conditions in the Akmola region, Northern Kazakhstan; the identified QTLs were associated with all the studied traits except PH. The results indicate that nine QTLs for HD and 11 QTLs for SMD are presumably novel genetic factors identified in the irrigated and rainfed conditions of Northern Kazakhstan. The identified SNP markers of the QTLs for targeted traits in rainfed conditions can be applied to develop new competitive spring wheat cultivars in arid zones using a marker-assisted selection approach.

Genetic Mapping by Integration of 55K SNP Array and KASP Markers Reveals Candidate Genes for Important Agronomic Traits in Hexaploid Wheat.

Agronomic traits such as heading date (HD), plant height (PH), thousand grain weight (TGW), and spike length (SL) are important factors affecting wheat yield. In this study, we constructed a high-density genetic linkage map using the Wheat55K SNP Array to map quantitative trait loci (QTLs) for these traits in 207 recombinant inbred lines (RILs). A total of 37 QTLs were identified, including 9 QTLs for HD, 7 QTLs for PH, 12 QTLs for TGW, and 9 QTLs for SL, which explained 3.0–48.8% of the phenotypic variation. Kompetitive Allele Specific PCR (KASP) markers were developed based on sequencing data and used for validation of the stably detected QTLs on chromosomes 3A, 4B and 6A using 400 RILs. A QTL cluster on chromosome 4B for PH and TGW was delimited to a 0.8 Mb physical interval explaining 12.2–22.8% of the phenotypic variation. Gene annotations and analyses of SNP effects suggested that a gene encoding protein Photosynthesis Affected Mutant 68, which is essential for photosystem II assembly, is a candidate gene affecting PH and TGW. In addition, the QTL for HD on chromosome 3A was narrowed down to a 2.5 Mb interval, and a gene encoding an R3H domain-containing protein was speculated to be the causal gene influencing HD. The linked KASP markers developed in this study will be useful for marker-assisted selection in wheat breeding, and the candidate genes provide new insight into genetic study for those traits in wheat.

Genetic dissection of Fusarium head blight resistance in spring wheat cv. ‘Glenn’

Fusarium head blight (FHB) is a major disease of wheat in many wheat-growing regions affecting wheat yield and quality. Glenn is arguably the most FHB-resistant spring wheat cultivar in the USA. To decipher the genetics of FHB resistance in Glenn, a population of 112 recombinant inbred lines was developed from the cross Glenn × MN00261-4 and evaluated for various FHB related traits at multiple locations in two states (North Dakota and Minnesota) over 3 years. Quantitative trait loci (QTL) analysis detected 15 QTL for FHB resistance related traits and heading date (HD). One QTL for FHB incidence (INC; type I resistance), six QTL for FHB severity (SEV; type II resistance), one QTL for Fusarium damaged kernels (FDK; type IV resistance), four QTL for disease index (DI), and three QTL for HD were detected. Major QTL defined as those consistent across multiple environments and explaining > 10% of the phenotypic variation were detected on chromosomes 5BL, 6BS, and 7AS. They were associated with multiple FHB variables and HD. The stable 6BS QTL with a large effect for FHB SEV resistance corresponded to the Fhb2 gene in Sumai 3. In addition, potentially novel QTL were identified on 1AS, 5BL and 7DS. Our study showed that FHB resistance in the GM population was contributed by loci other than Fhb1. The major QTL detected for FHB resistance have potential for use in marker-assisted breeding for FHB resistance.

Wild barley shows a wider diversity in genes regulating heading date compared with cultivated barley

Heading date (HD) is an important agronomic trait that influences plant adaptability to varying environment and, ultimately, grain yield. In this study, two doubled haploid (DH) populations were used to identify new QTL for HD. One of the DH populations is originated from a cross between an Australian malting barley cv. Franklin and a wild barley accession TAM407227 and the other one is from the cross between a Syrian wild barley SYR01 and an Australian malting barley cv. Gairdner. Using three times of sowing (TOS) differing in daylength and temperature, we investigated quantitative trait loci (QTL) controlling HD from both populations. Fourteen QTL were identified for HD from different populations and sowing dates. The expression of HD related genes varied with the TOS, suggesting a significant QTL × environment interaction. By comparing the positions of previously mapped HD genes and those of QTL detected in this population, we found that eleven of the fourteen QTL identified in this study were located at similar positions to those reported genes for HD. Among the three new potential QTL, one was located at 73.5 cM on chromosome 2H, explaining 19.2% and 4.6% HD of DH lines in spring and summer growing, respectively. The wild barley parent TAM407227 contributed the early maturity allele. HORVU2Hr1G088460 within the interval of QTL could be the candidate gene. The second new QTL was identified on chromosome 3H from a summer sowing trial and the third one on chromosome 4H affected HD of DH lines only under spring sowing condition. These new QTL identified will provide alternative genetic resources for plant breeders developing barley varieties with improved HD adaptability to varying environments.

Genetic dissection of QTLs and differentiation analysis of alleles for heading date genes in rice.

Heading date is an important agronomic trait in rice (Oryza sativa L.); it determines the geographical and seasonal adaptability of the crop. Single segment substitution lines (SSSLs) have become the preferred experimental materials in mapping functional genetic variations as the particular chromosome segments from donor genotypes can be evaluated for their impact on the phenotype in a recurrent recipient background. The phenotypic differences can be attributed to the control of quantitative trait loci (QTLs). Here, we evaluated a library consisting of 1,123 SSSLs in the same genetic background of an elite rice variety, Huajingxian74 (HJX74), and revealed four SSSLs, W05-1-11-2-7-6 (W05), W08-16-3-2 (W08), W12-28-58-03-19-1 (W12), and W22-9-5-2-4-9-3 (W22), which had a significantly different heading date compared to HJX74. To further genetically dissect the QTLs controlling heading date on chromosomes 3, 6, and 10, four SSSLs were used to develop 15 secondary SSSLs with the smaller substituted segments. The qHD-3 heading date QTL detected in W05 and W08 was delimited to an interval of 4.15 cM, whereas qHD-6-1 and qHD-6-2 heading date QTLs dissected from the substituted segments in W12 were mapped to the intervals of 2.25-cM and 2.55-cM, respectively. The qHD-10 QTL detected on the substituted segment in W22 was mapped to an interval of 6.85-cM. The nucleotide and amino acid sequence changes for those genes in the secondary SSSLs were also revealed. The allele variations of those genes might contribute to the heading date QTLs on chromosome 3 (DTH3, OsDof12, and EHD4), chromosome 6 (Hd3a, Hd17, and RFT1), and chromosome 10 (Ehd1 and Ehd2). These sequence variations in heading date genes would be useful resources for further studying the function of genes, and would be important for rice breeding. Overall, our results indicate that secondary SSSLs were powerful tools for genetic dissection of QTLs and identification of differentiation in the genes.

QTLs for heading date and plant height under multiple environments in rice.

Both heading date and plant height are important traits related to grain yield in rice. In this study, a recombinant inbred lines (RILs) population was used to map quantitative trait loci (QTLs) for both traits under 3 long-day (LD) environments and 1 short-day (SD) environment. A total of eight QTLs for heading date and three QTLs for plant height were detected by composite interval mapping under LD conditions. Additional one QTL for heading date and three QTLs for plant height were identified by Two-QTL model under LD conditions. Among them, major QTLs qHd7.1, qHd7.2 and qHd8 for heading date, and qPh1 and qPh7.1 for plant height were commonly detected. qHd7.1 and qHd7.2 were mapped to small regions of less than 1cM. Genome position comparison of previously cloned genes with QTLs detected in this study revealed that qHd5 and qPh3.1 were two novel QTLs. The alleles of these QTLs increasing trait values were dispersed in both parents, which well explained the transgressive segregation observed in this population. In addition, the interaction between qHd7.1 and qHd8 was detected under all LD conditions. Multiple-QTL model analysis revealed that all QTLs and their interactions explained over 80% of heading date variation and 50% of plant height variation. Two heading date QTLs were detected under SD condition. Of them, qHd10 were commonly identified under LD condition. The difference in QTL detection between LD and SD conditions indicated most heading date QTLs are sensitive to photoperiod. These findings will benefit breeding design for heading date and plant height in rice.

Quantitative Trait Locus Mapping for End‐Use Quality Traits in Hard Winter Wheat Under Contrasting Soil Moisture Levels

ABSTRACTImproved end‐use quality is an essential goal of many wheat (Triticum aestivum L.) breeding programs. Besides genetic factors, environmental conditions are known to influence wheat quality. Our objective was to identify quantitative trait loci (QTL) for quality traits in a winter wheat population under different soil moisture levels. A population of 185 doubled haploid (DH) lines was derived from a cross between hard white winter wheats CO940610 and ‘Platte’. The population was grown in four environments (two limited irrigation and two fully irrigated) in Colorado in 2007/2008 and 2008/2009, and the grain was evaluated for 14 end‐use quality traits. A linkage map was constructed with 250 molecular markers, including five glutenin protein markers. Composite interval mapping detected clusters of QTL for multiple traits near the glutenin loci Glu‐A1, Glu‐B1, and Glu‐D1. Other QTL clusters were located on chromosomes 2B, 6A, 7B, and 7D; the 2B and 7D QTL may reflect the presence of heading date QTL in the same regions. An epistatic interaction for mixograph traits was found between the chromosome 7B QTL and Glu‐B1, consistent with the presence of a regulatory gene on 7B. An apparently novel QTL for kernel weight and diameter was detected on chromosome 3B. Our results confirm similar genetic control of quality traits, especially for large‐effect QTL, for the levels of moisture stress in this study. These results may guide breeding programs in choosing parents and conducting marker‐assisted selection for improved end‐use quality.

Identification and validation of fusarium head blight and Fusarium-damaged kernel QTL in a Frontana/Remus DH mapping population

Fusarium head blight (FHB) is a devastating disease of wheat (Triticum aestivum L.). This study investigated a ‘Frontana/Remus’ doubled haploid population (n = 210 lines) to map and validate the ‘Frontana’ resistance quantitative trait loci (QTL) focusing on Fusarium-damaged kernels (FDK). The plant material was evaluated in six epidemic situations for Fusarium resistance in inoculated field experiments, with either Fusarium graminearum or F. culmorum. Other studies have focused on FHB QTL, but it is important to evaluate how far these QTL determine FDK values. The data show that the genetic regulation of FHB resistance is more complex than earlier proposed. FHB resistance QTL were identified on chromosomes 3A, 4A and 6B. Markers showed association with FDK resistance on chromosomes 3D and at the marker Xs12m15_4. QTL on 2B, 4B, 5A and 7B chromosomes were responsible for both FHB and FDK resistance; in this case, the same QTL influenced both traits and possibly other traits during disease development. These QTL are very important, because they can be considered to be real Fusarium resistance QTL. The use of markers in breeding programmes, which are associated only with FHB or FDK resistance may be questionable and require further research. Heading date QTL were detected on chromosomes 1A, 2D and 7B overlapping with neither FHB nor FDK resistance QTL. The QTL identified in the ‘Frontana/Remus’ population were in good agreement with earlier results from the literature.

Variation in heading date conceals quantitative trait loci for other traits of importance in breeding selection of rice

To identify quantitative trait loci (QTLs) associated with the primary target traits for selection in practical rice breeding programs, backcross inbred lines (BILs) derived from crosses between temperate japonica rice cultivars Nipponbare and Koshihikari were evaluated for 50 agronomic traits at six experimental fields located throughout Japan. Thirty-three of the 50 traits were significantly correlated with heading date. Using a linkage map including 647 single-nucleotide polymorphisms (SNPs), a total of 122 QTLs for 38 traits were mapped on all rice chromosomes except chromosomes 5 and 9. Fifty-eight of the 122 QTLs were detected near the heading date QTLs Hd16 and Hd17 and the remaining 64 QTLs were found in other chromosome regions. QTL analysis of 51 BILs having homozygous for the Koshihikari chromosome segments around Hd16 and Hd17 allowed us to detect 40 QTLs associated with 27 traits; 23 of these QTLs had not been detected in the original analysis. Among the 97 QTLs for the 30 traits measured in multiple environments, the genotype-by-environment interaction was significant for 44 QTLs and not significant for 53 QTLs. These results led us to propose a new selection strategy to improve agronomic performance in temperate japonica rice cultivars.

Heading date QTL in rice derived from an analysis of chromosome segment substitution lines

With 5 figures and 3 tables Abstract The inheritance of heading date (HD) in rice was investigated using a set of lines in which chromosome segments of the photoperiod- and temperature-sensitive male sterile line Peiai 64S had been incorporated into a genetic background of the cv. 9311. The flowering time of each line was contrasted with that of cv. 9311 in four distinct environments: natural long days (13.2–14.2 h photoperiod) and artificially shortened days (9 h photoperiod) at Nanjing; and natural (low) temperature and enhanced temperature at Hainan. A set of 21 heading date quantitative trait loci (QTL) was identified, covering eight of the 12 rice chromosomes, and their dependence on photoperiod and/or temperature was characterized. Two of the QTL were photoperiod-sensitive, and eight were insensitive; while two were temperature-sensitive and four insensitive; the remaining five QTL were independent of both temperature and photoperiod. Based on its segregation in an F2 population bred from the cross CSSL C053 × cv. 9311, the temperature- and photoperiod-insensitive QTL qHd-8-4 was mapped within a segment of chromosome 8 flanked by the SSR marker RM22469 (1.9 cM) and RM72 (2.4 cM).

Yield QTL affected by heading date in Mediterranean grown barley

AbstractKnowledge regarding quantitative trait loci (QTL) has led to remarkable advances in breeding for a variety of traits, some of which have an effect on yield under particular environmental conditions. However, the same yield QTL are not usually found, even in the same population tested in different environments, as a result of large genotype‐by‐environment interactions. In this study, we aimed at identifying yield QTL in a series of experiments carried out in Spain. We used a barley doubled haploid population derived from a spring by winter cross. The relationship between heading date and yield, and between the principal heading date QTL and yield, changed depending on the environment. Allelic combinations causing early or late heading dates usually did not favour high yield, whereas intermediate heading dates were associated with not only higher variability but also higher yield potential. To identify QTL for grain yield independent of heading date, the population was divided into three classes: Early, Intermediate and Late. We found three new QTL affecting yield only at specific maturity groups. The implications of these findings in relation to barley breeding are discussed.

Mapping QTL for Seed Dormancy in Weedy Rice

The objective of the study is to dissect the genetic basis of seed dormancy. The weedy rice “Ludao” ( Oryza sp.) with strong seed dormancy was crossed with the rice variety Akihikari ( O. sativa subsp. japonica) and 215 lines of BC 1F 1 were developed for QTL mapping. A total of 4 quantitative trait loci (QTLs) associated with seed dormancy were located on chromosomes 1, 2, 6, and 6, explaining 7.8, 7.1, 5.5, and 4.5% of the overall phenotypic variance, respectively. The QTL, qSD-2, on chromosome 2 appeared to represent a novel source of genetic variation for seed dormancy. A multi-way analysis of variance indicated that the gene action of the 4 QTLs was additive. There was significant negative correlation between the germination rate and the flowering time. A single heading date QTL was identified to be either pleiotropic or linked to a seed dormancy QTL on chromosome 6, thereby accounting for the observed correlation between seed dormancy and flowering time.

Identifying genetic components controlling fertility in the outcrossing grass species perennial ryegrass (Lolium perenne) by quantitative trait loci analysis and comparative genetics

Mutational load and resource allocation factors and their effects on limiting seed set were investigated in ryegrass by comparative mapping genomics and quantitative trait loci (QTL) analysis in two perennial ryegrass (Lolium perenne) mapping families sharing common genetic markers. Quantitative trait loci for seed-set were identified on chromosome (LG) 7 in both families and on LG4 of the F2/WSC family. On LG7, seed-set and heading date QTLs colocalized in both families and cannot be unequivocally resolved. Comparative genomics suggests that the LG7 region is syntenous to a region of rice LG6 which contains both fertility (S5(n)) and heading date (Hd1, Hd3a) candidate genes. The LG4 region is syntenous to a region of rice LG3 which contains a fertility (S33) candidate gene. QTL maxima for seed-set and heading date on LG4 in the F2/WSC family are separated by c. 8 cm, indicating distinct genetic control. Low seed set is under the control of recessive genes at both LG4 and LG7 locations. The identification of QTLs associated with seed set, a major component of seed yield in perennial ryegrass, indicates that mutational load associated with these genomic regions can be mitigated through marker-assisted selection.

QTLs for drought escape and tolerance identified in a set of random introgression lines of rice

A large set of 254 introgression lines in an elite indica genetic background were evaluated for grain yield (GY) and related traits under the irrigated (control) and drought (stress) conditions in two consecutive years for genetic dissection of adaptive strategies of rice to water stress. A total of 36 quantitative trait loci (QTLs) affecting heading date (HD), plant height (PH), GY and yield components were identified and most QTLs showed pronounced differential expression either qualitatively or quantitatively in response to drought. These QTLs could be grouped into three major types based on their behaviors under control and stress conditions. Type I included 12 QTLs that expressed under both the stress and non-stress conditions. Type II comprised 17 QTLs that expressed under irrigation but not under stress. Type III included seven QTLs that were apparently induced by stress. The observation that the Lemont (japonica) alleles at all HD QTLs except QHd5 resulted in early heading under stress appeared to be responsible for the putative adaptation of Lemont to drought by escaping, whereas the Teqing (indica) alleles at most PH/GY QTLs were consistently associated with increased yield potential and trait stability and thus contributed to DT. Our result that most DT QTLs were non-allelic with QTLs for drought escaping suggests that the two adaptive strategies in the parental lines are under possible negative regulation of two largely non-overlapping genetic systems.

Heritable basis for some genotype–environment stability statistics: Inferences from QTL analysis of heading date in two-rowed barley

The genetic basis for some stability statistics used in plant breeding was investigated in this study by quantitative trait loci (QTLs) analysis. The mapping population comprised 180 doubled haploid lines from a cross between Australian (VB9524) and North American (ND11231-12) two-rowed barley lines. Using a 211-point genetic linkage map, we identified six QTLs segregating for heading date in the population. These mapped to the approximate position of the major earliness genes ( Ppd-H1 and Ppd-H2), and several genes for earliness in a narrow sense (earliness per se). By aligning the QTL positions with those for calculated stability statistics, we used the co-location of QTL positions to infer genetic basis. The stability statistics considered were Wricke's [Wricke, G., 1962. Über eine Methode zur Erfassung der oekologischen Streubreite in Feldversuchen. Zeitschr f Pflanzenz 47, 92–96] Ecovalence ( W i ), Eberhart and Russell's [Eberhart, S.A., Russell, W.A., 1966. Stability parameters for comparing varieties. Crop Sci. 6, 36–40] regression coefficient (SLOPE) and deviation from regression (MSDEV), Lin and Binns’ [Lin, C.S., Binns, M.R., 1988. A superiority measure of cultivar performance for cultivar × location data. Can. J. Plant Sci. 68, 193–198] cultivar superiority measure ( P i ) and the first two principal component axis scores (IPCA1 and IPCA2) from the additive main effect and multiplicative interaction (AMMI) model. Based on a genome-wide LOD threshold of 3.0, we found little evidence for genetic control of MSDEV. However, W i was considered to be under genetic control, due to a significant linkage (peak LOD = 4.85) to a locus on chromosome 2H where the Ppd-H1 gene is located. For SLOPE and IPCA1, strong evidence of genetic control was indicated by linkage to three unlinked loci. Two of these occurred at regions on chromosomes 2HS and 5HL, close to the approximate locations of Ppd-H1 and eps5HL, and where heading date QTLs showed significant ( P < 0.001) QTL × E interactions. For P i , the genome-wide LOD profile matched that for heading date QTLs, with peak LOD scores at all regions where the QTLs were identified. The pattern of co-localisation of QTLs for stability parameters with those for heading date suggests that, in this population, G × E interactions might be largely controlled by allelic sensitivity.

QTL Analysis of Morphological, Developmental, and Winter Hardiness‐Associated Traits in Perennial Ryegrass

Quantitative trait loci (QTLs) for a number of agronomically important traits of perennial ryegrass (Lolium perenne L.) were identified by means of a reference molecular marker‐based genetic map. Replicated phenotypic data was obtained for a number of field‐assessed morphological and developmental traits as well as the winter hardiness‐associated characters of winter survival and electrical conductivity. Marker‐trait association analysis was performed by a number of methods, and a high degree of congruence was observed between the respective results. QTLs were detected for morphological traits such as plant height, tiller size, leaf length, leaf width, fresh weight at harvest, plant type, spikelet number per spike and spike length, as well as the developmental traits of heading date and degree of aftermath heading. A number of traits were significantly correlated, and coincident QTL locations were identified. No significant QTLs for winter survival in the field were identified. However, a QTL for electrical conductivity corresponding to frost tolerance was located close to a heading date QTL in a region that may show conserved synteny with chromosomal regions associated with both winter hardiness and flowering time variation in cereals. The QTL analysis of multiple phenotypic traits provides the basis for marker assisted selection (MAS) of important agronomic characters, allowing genetic improvement of yield, quality and adaptation in perennial ryegrass breeding.

QTL Analysis of Morphological, Developmental, and Winter Hardiness-Associated Traits in Perennial Ryegrass

Quantitative trait loci (QTLs) for a number of agronomically important traits of perennial ryegrass (Lolium perenne L.) were identified by means of a reference molecular marker-based genetic map. Replicated phenotypic data was obtained for a number of field-assessed morphological and developmental traits as well as the winter hardiness-associated characters of winter survival and electrical conductivity. Marker-trait association analysis was performed by a number of methods, and a high degree of congruence was observed between the respective results. QTLs were detected for morphological traits such as plant height, tiller size, leaf length, leaf width, fresh weight at harvest, plant type, spikelet number per spike and spike length, as well as the developmental traits of heading date and degree of aftermath heading. A number of traits were significantly correlated, and coincident QTL locations were identified. No significant QTLs for winter survival in the field were identified. However, a QTL for electrical conductivity corresponding to frost tolerance was located close to a heading date QTL in a region that may show conserved synteny with chromosomal regions associated with both winter hardiness and flowering time variation in cereals. The QTL analysis of multiple phenotypic traits provides the basis for marker assisted selection (MAS) of important agronomic characters, allowing genetic improvement of yield, quality and adaptation in perennial ryegrass breeding.

Quantitative trait loci associated with stomatal conductance, leaf rolling and heading date mapped in upland rice (Oryza sativa)

summaryImproving the drought resistance of high yielding rice (Oryza sativa L.) varieties for upland areas is a goal of rice breeders since upland rice relies exclusively on rainfall for water and is generally low yielding. Identifying quantitative trait loci (QTLs) which confer drought resistance promises to speed this goal. We have previously described the use of 82 restriction fragment length polymorphism (RFLP) markers in the genetic mapping of root growth characteristics that are potentially involved in drought resistance in a population of 178 F2 plants derived from a cross of two drought resistant upland varieties, Azucena and Bala. Here we report the characterization and QTL mapping of three other mechanisms of drought resistance, leaf rolling, stomatal behaviour and early flowering, in this population. When the youngest fully expanded leaf was excised from 12 rice varieties,‘IR20’and‘Bala’ were identified as slow at rolling. Although ‘Azucena’ rolled its leaves much faster than ‘Bala’ upon excision, stomatal resistance rose more rapidly in‘Bala’, resulting in a lower rate of water loss. By assessing leaf rolling and stomatal resistance in the F2 population, it was possible to identify QTLs for these traits. A QTL for slow leaf rolling from ‘Bala’ was found on chromosome 1. Two QTLs associated with resting stomatal conductance were found on chromosomes 3 and 12. QTLs for the rate of stomatal closure were found on chromosomes 3 and 7. In addition, it was possible to map QTLs associated with the days to heading which were found on chromosomes 3, 8 and 10. These results identify markers of potential value to breeders and are discussed in the context of previously reported data for heading date QTLs in rice and for stomatal conductance QTLs in maize.