淀粉含量不同的玉米自交系籽粒淀粉积累及其关键酶活性

以2个高淀粉和2个低淀粉玉米自交系为材料,分析了玉米籽粒淀粉的动态积累规律,同时对高低淀粉玉米籽粒灌浆过程中淀粉生物合成关键酶活性的动态变化及其与淀粉积累动态的相关性进行讨论分析。研究结果表明:灌浆过程中4个自交系淀粉含量变化趋势均呈sigmoid型曲线。灌浆过程中ADPG-PPase(腺苷二磷酸葡萄糖焦磷酸化酶)、SSS(可溶性淀粉合成酶)、GBSS(颗粒结合淀粉合成酶)活性均呈单峰曲线变化,峰值都出现在20～30DAP(授粉后天数)。2个高淀粉自交系的Q酶(淀粉分支酶)活性也呈单峰曲线变化,峰值也出现在20DAP,而2个低淀粉自交系的Q酶活性则呈双峰曲线变化,2个峰值分别出现在15～20DAP和30～35DAP。4个自交系籽粒淀粉的积累速率与各自交系ADPG-PPase、SSS和GBSS的活性变化呈极显著正相关。各自交系关键酶活性之间,ADPG-PPase、SSS和GBSS三者间活性变化呈极显著正相关,这3种酶活性变化与Q酶活性变化也呈不同程度的正相关。     

Relationship between activities of key enzymes involved in starch synthesis and accumulation in maize inbred lines during grain filling

Time course of starch production and the key enzyme activities in the grains of four maize inbred lines (two high-starch and two low-starch lines) were studied. Accumulation of grain starch and its components in four maize inbred lines rose continuously after pollination and increased as a sigmoid curve during grain filling. The accumulation rates showed single-peak curves. The accumulation rates of starch and its components reached their peaks on 25–32 days after pollination (DAP), respectively. Activities of adenosine diphosphoglucose pyrophosphorylase (AGPPase) and starch synthase in the grains of four lines followed single-peak curves with the peaks on 24–31 DAP. The highest activity of the starch-branching enzyme (Q-enzyme) in the grains of both high-starch lines appeared on 23 DAP, but that of both low-starch inbred lines showed double-peak curves, the peaks being at 15–20 DAP and 30–35 DAP. There was significant positive correlation between AGPPase, soluble starch synthase (SSS), and starch granule-bound synthase (GBSS) activities. The results indicated the Q-enzyme had different expression patterns in the high-and the low-starch maize inbred lines, and that AGPPase, SSS, and GBSS activities were significantly and positively correlated with amylose, amylopectin, and starch accumulation rates in all lines. This text was submitted by the authors in English     

Detection and integration of quantitative trait loci for grain yield components and oil content in two connected recombinant inbred line populations of high-oil maize

Improvement in grain yield is an important objective in high-oil maize breeding. In this study, one high-oil maize inbred was crossed with two normal maize inbreds to produce two connected recombinant inbred line (RIL) populations with 282 and 263 F_7:8 families, respectively. The field experiments were conducted under four environments, and eight grain yield components and grain oil content were evaluated. Two genetic linkage maps were constructed using 216 and 208 polymorphic SSR markers. Quantitative trait loci (QTL) were detected for all traits under each environment and in combined analysis. Meta-analysis was used to integrate genetic maps and detected QTL in both populations. A total of 199 QTL were detected, 122 in population 1 and 87 in population 2. Seven, 11 and 19 QTL showed consistency across five environments, across two RIL populations and with respective F_2:3 generations, respectively. 183 QTL were integrated in 28 meta-QTL (mQTL). QTL with contributions over 15% were consistently detected in 3–4 cases and integrated in mQTL. Each mQTL included 3–19 QTL related to 1–4 traits, reflecting remarkable QTL co-location for grain yield components and oil content. Further research and marker-assisted selection (MAS) should be concentrated on 37 consistent QTL and four genetic regions of mQTL with more than 10 QTL at bins 3.04–3.05, 7.02, 8.04–8.05 and 9.04–9.05. Near-isogenic lines for 100-grain-weight QTL at bin 7.02–7.03, for ear-length QTL at bin 7.02–7.03 and for rows-per-ear QTL at bin 3.08 are now in construction using MAS. Co-located candidate genes could facilitate the identification of candidate genes for grain yield in maize.     

QTL consistency and meta-analysis for grain yield components in three generations in maize

Grain yield is the most important and complex trait in maize. In this study, a total of 258 F₉ recombinant inbred lines (RIL), derived from a cross between dent corn inbred Dan232 and popcorn inbred N04, were evaluated for eight grain yield components under four environments. Quantitative trait loci (QTL) and their epistatic interactions were detected for all traits under each environment and in combined analysis. Meta-analysis was used to integrate genetic maps and detected QTL across three generations (RIL, F_2:3 and BC₂F₂) derived from the same cross. In total, 103 QTL, 42 pairs of epistatic interactions and 16 meta-QTL (mQTL) were detected. Twelve out of 13 QTL with contributions (R ²) over 15% were consistently detected in 3–4 environments (or in combined analysis) and integrated in mQTL. Only q100GW-7-1 was detected in all four environments and in combined analysis. 100qGW-1-1 had the largest R ² (19.3–24.6%) in three environments and in combined analysis. In contrast, 35 QTL for 6 grain yield components were detected in the BC₂F₂ and F_2:3 generations, no common QTL across three generations were located in the same marker intervals. Only 100 grain weight (100GW) QTL on chromosome 5 were located in adjacent marker intervals. Four common QTL were detected across the RIL and F_2:3 generations, and two between the RIL and BC₂F₂ generations. Each of five important mQTL (mQTL7-1, mQTL10-2, mQTL4-1, mQTL5-1 and mQTL1-3) included 7–12 QTL associated with 2–6 traits. In conclusion, we found evidence of strong influence of genetic structure and environment on QTL detection, high consistency of major QTL across environments and generations, and remarkable QTL co-location for grain yield components. Fine mapping for five major QTL (q100GW-1-1, q100GW-7-1, qGWP-4-1, qERN-4-1 and qKR-4-1) and construction of single chromosome segment lines for genetic regions of five mQTL merit further studies and could be put into use in marker-assisted breeding.     

QTLs for enzyme activities and soluble carbohydrates involved in starch accumulation during grain filling in maize

ADPglucose, the essential substrate for starch synthesis, is synthesized in maize by a pathway involving at least invertases, sucrose synthase, and ADPglucose pyrophosphorylase, as shown by the starch-deficient mutants, mn1, sh1, and bt2 or sh2, respectively. To improve understanding of the relationship between early grain-filling traits and carbohydrate composition in mature grain, QTLs linked to soluble invertase, sucrose synthase, and ADPglucose pyrophosphorylase activities and to starch, sucrose, fructose, and glucose concentrations were investigated. In order to take into account the specific time-course of each enzyme activity during grain filling, sampling was carried out at three periods (15, 25, and 35 d after pollination) on 100 lines from a recombinant inbred family, grown in the field. The MQTL method associated with QTL interaction analysis revealed numerous QTLs for all traits, but only one QTL was consistently observed at the three sampling periods. Some chromosome zones were heavily labelled, forming clusters of QTLs. Numerous possible candidate genes of the starch synthetic pathway co-located with QTLs. Four QTLs were found close to the locus Sh1 (bin 9.01) coding for the sucrose synthase. In order to confirm the importance of this locus, the CAPS polymorphism of the Sh1 gene was analysed in 45 genetically unrelated maize lines from various geographical origins. The DNA polymorphism was significantly associated with phenotypic traits related to grain filling (starch and amylose content, grain matter, and ADPglucose pyrophosphorylase activity at 35 DAP). Thus, the Sh1 locus could provide a physiologically pertinent marker for maize selection.     

Molecular detection of genomic regions associated with grain yield and yield-related components in an elite bread wheat cross evaluated under irrigated and rainfed conditions

Grain yield and grain weight of wheat are often decreased by water-limitation in the north-eastern cropping belt of Australia. Based on knowledge that CIMMYT lines are well-adapted in this region, a recombinant inbred line (RIL) population between two elite CIMMYT bread wheats (Seri M82 and Babax) was evaluated under water-limited environments. Fourteen productivity traits were evaluated in 192 progeny in up to eight trials. For three aggregations of the environments (all, high yield or low yield), multiple quantitative trait loci (QTL) were detected, each explaining <15% of variation. Co-location of multiple trait QTL was greatest on linkage groups 1B-a, 1D-b, 4A-a, 4D-a, 6A-a, 6B-a, 7A-a and an unassigned linkage group. Two putative QTL (LOD > 3) from Seri (6D-b and UA-d) increased grain yield and co-located with a suggestive (2 < LOD < 3) and a putative QTL for increased stem carbohydrate content (WSC), respectively; the latter QTL also co-located with a putative anthesis QTL for earlier flowering. Both QTL were detected only in high yield (>4t ha⁻¹) environments. A third increased grain yield QTL (7A-a) from Babax co-located with QTL for increased grain number. Six putative QTL increased grain weight and co-located with QTL for harvest index, grains per spike and spike number. Three putative QTL for increased grains per spike co-located with strong QTL for earlier flowering, increased grain weight and fewer spikes. A group of progeny that exceeded the mean grain yield and grain weight of commercial checks had an increased frequency of QTL for high WSC, large grain size, increased harvest index and greater height, but fewer stems, when compared to low yielding (20% less), low grain weight progeny. These findings were consistent with agronomic analyses of the germplasm and demonstrate that there should be opportunities to independently manipulate grain number and grain size which is typically difficult due to strong negative correlations.     

Mapping of QTLs associated with cytosolic glutamine synthetase and NADH-glutamate synthase in rice (Oryza sativa L.).

Ninety-eight backcross inbred lines (BC1F6) developed between Nipponbare, a japonica rice, and Kasalath, an indica rice were employed to detect putative quantitative trait loci (QTLs) associated with the contents of cytosolic glutamine synthetase (GS1; EC 6.3.1.2) and NADH-glutamate synthase (NADH-GOGAT; EC 1.4.1.14) in leaves. Immunoblotting analyses showed transgressive segregations toward lower or greater contents of these enzyme proteins in these backcross inbred lines. Seven chromosomal QTL regions for GS1 protein content and six for NADH-GOGAT protein content were detected. Some of these QTLs were located in QTL regions for various biochemical and physiological traits affected by nitrogen recycling. These findings suggested that the variation in GS1 and NADH-GOGAT protein contents in this population is related to the changes in the rate of nitrogen recycling from senescing organs to developing organs, leading to changes in these physiological traits. Furthermore, a structural gene for GS1 was mapped between two RFLP markers, C560 and C1408, on chromosome 2 and co-located in the QTL region for one-spikelet weight. A QTL region for NADH-GOGAT protein content was detected at the position mapped for the NADH-GOGAT structural gene on chromosome 1. A QTL region for soluble protein content in developing leaves was also detected in this region. Although fine mapping is required to identify individual genes in the future, QTL analysis could be a useful post-genomic tool to study the gene functions for regulation of nitrogen recycling in rice.     

不同类型玉米发育籽粒中淀粉合成及相关酶活性比较

以普通玉米、爆裂玉米、甜玉米和糯玉米为试材,分析和比较不同类型的玉米品种之间籽粒发育过程中淀粉合成及相关酶活性的变化。结果表明,淀粉合成速率和蔗糖合成酶(SS)、可溶性淀粉合成酶(SSS)、束缚态淀粉合成酶(GBSS)、淀粉分支酶(SBE)、去分支酶(DBE)活性都呈单峰曲线变化。30～40 DAP,普通玉米的SS活性显著高于其他3种类型;类型间平均和最大SSS活性水平的顺序为普通玉米>糯玉米>爆裂玉米>甜玉米;30～40 DAP,普通玉米GBSS活性最高,糯玉米GBSS活性最低;20～40 DAP,糯玉米SBE活性最高;甜玉米的DBE活性很低,并且在40 DAP完全丧失。淀粉合成速率与SS、SSS、GBSS和SBE活性相关程度比较高,与腺苷二磷酸葡萄糖焦磷酸化酶(AGP酶)和DBE活性相关不显著。推测AGP酶虽然为淀粉合成提供直接前体ADPG,但可能SS活性过低致使其限速作用比AGP酶的还强,AGP酶潜在的限速作用无法表现,SS成为玉米籽粒淀粉合成的限速因子。GBSS对直链淀粉积累起重要的促进作用;SSS和SBE对支链淀粉积累起重要的促进作用。     

Identification of metabolic and biomass QTL in Arabidopsis thaliana in a parallel analysis of RIL and IL populations

Plant growth and development are tightly linked to primary metabolism and are subject to natural variation. In order to obtain an insight into the genetic factors controlling biomass and primary metabolism and to determine their relationships, two Arabidopsis thaliana populations [429 recombinant inbred lines (RIL) and 97 introgression lines (IL), derived from accessions Col-0 and C24] were analyzed with respect to biomass and metabolic composition using a mass spectrometry-based metabolic profiling approach. Six and 157 quantitative trait loci (QTL) were identified for biomass and metabolic content, respectively. Two biomass QTL coincide with significantly more metabolic QTL (mQTL) than statistically expected, supporting the notion that the metabolic profile and biomass accumulation of a plant are linked. On the same basis, three out the six biomass QTL can be simulated purely on the basis of metabolic composition. QTL based on analysis of the introgression lines were in substantial agreement with the RIL-based results: five of six biomass QTL and 55% of the mQTL found in the RIL population were also found in the IL population at a significance level of P  ≤ 0.05, with >80% agreement on the allele effects. Some of the differences could be attributed to epistatic interactions. Depending on the search conditions, metabolic pathway-derived candidate genes were found for 24–67% of all tested mQTL in the database AraCyc 3.5. This dataset thus provides a comprehensive basis for the detection of functionally relevant variation in known genes with metabolic function and for identification of genes with hitherto unknown roles in the control of metabolism.     

Gene expression of the biosynthetic enzymes and biosynthesis of starch during Rice Grain development

Amylose and amylopectin are determinants of the physicochemical properties for starch and grain quality in rice. Their biosynthesis is catalyzed by the interplay of ADP-glucose pyrophosphorylase (AGPase), granule-bound starch synthase (GBSS), soluble starch synthase (SSS), a starch branching enzyme (SBE), and a starch debranching enzyme (SDE). In this study, the genes for these enzymes were highly expressed 7 to 28 days after flowering during grain development, and their expression closely matched increases in both starch content and grain weight Among all the tested cultivars, amylose contents in the rice grains remained essentially constant throughout their development The AGPase gene was highly expressed in the high-yield cultivars of both glutinous and non-glutinous rice. The SSS gene was actively expressed when mature GBSS mRNA decreased. Genes responsible for amylopectin biosynthesis were simultaneously expressed in the late stage of grain development. We have now demonstrated that the expression patterns of starch biosynthetic genes differ between glutinous and non-glutinous rice, and between Tongil (a Japonica/ Indica hybrid) and Japonica types.     

From QTLs for enzyme activity to candidate genes in maize

In order to facilitate the search for genes underlying QTLs (Quantitative Trait Loci), the activities of key enzymes of the carbohydrate metabolism in maize, and the concentration of their substrates or products were used as quantitative traits. For each of the chosen enzyme, i.e. ADPglucose pyrophosphorylase, sucrose-phosphate-synthase and invertases, the corresponding cDNA was available. Since biochemical traits are more closely related to gene expression than agronomic traits, co-locations could be expected between an enzyme structural gene and a QTL for its enzyme activity, and/or the corresponding product or substrate content. This approach was applied using recombinant inbred lines on leaves at 3- or 4-leaf stage, under control and water stress conditions and on grain, at maturity. Several QTLs were detected for each trait, particularly for two enzyme activities measured in mature leaves. Apparent co-locations between QTL for activity and structural locus were observed for sucrose-phosphate-synthase (chromosome 8) and acid-soluble invertase (chromosome 2 and 5). Leaf acid-soluble (vacuolar) invertase provided an interesting case since QTL, on chromosome 5, explaining 17% of variability was apparently co-located with the Ivr2 gene encoding a vacuolar invertase protein which was strongly water-stress inducible. Similarly, in grain, an amylose QTL co-located with the Sh2 gene of ADPglucose pyrophosphorylase. The reliability of this candidate was further tested through the examination of Sh2 DNA polymorphism in 46 genetically unrelated lines. A correlation was obtained between this polymorphism and kernel starch content, which further validated Sh2 as a candidate. Some improvements or alternatives to this strategy are briefly discussed.      

Dissection of genotype-phenotype associations in rice grains using metabolome quantitative trait loci analysis

A comprehensive and large‐scale metabolome quantitative trait loci (mQTL) analysis was performed to investigate the genetic backgrounds associated with metabolic phenotypes in rice grains. The metabolome dataset consisted of 759 metabolite signals obtained from the grains of 85 lines of rice (Oryza sativa, Sasanishiki × Habataki back‐crossed inbred lines). Metabolome analysis was performed using four mass spectrometry pipelines to enhance detection of different classes of metabolites. This mQTL analysis of a wide range of metabolites highlighted an uneven distribution of 802 mQTLs on the rice genome, as well as different modes of metabolic trait (m‐trait) control among various types of metabolites. The levels of most metabolites within rice grains were highly sensitive to environmental factors, but only weakly associated with mQTLs. Coordinated control was observed for several groups of metabolites, such as amino acids linked to the mQTL hotspot on chromosome 3. For flavonoids, m‐trait variation among the experimental lines was tightly governed by genetic factors that alter the glycosylation of flavones. Many loci affecting levels of metabolites were detected by QTL analysis, and plausible gene candidates were evaluated by in silico analysis. Several mQTLs profoundly influenced metabolite levels, providing insight into the control of rice metabolism. The genomic region and genes potentially responsible for the biosynthesis of apigenin‐6,8‐di‐C‐α‐l‐ arabinoside are presented as an example of a critical mQTL identified by the analysis.     

Chromosomal location of wheat genes of the carotenoid biosynthetic pathway and evidence for a catalase gene on chromosome 7A functionally associated with flour b* colour variation

Knowledge of molecular and genetic mechanisms controlling wheat grain quality characteristics is significant for improving flour for end-product functionality. Flour b* colour is an important quality trait for breeding wheat varieties to produce grain for specific market requirements. The degree of flour yellowness is due to the accumulation of carotenoids in grain, particularly lutein. Flour b* is under polygenic control and quantitative trait loci (QTL) have frequently been reported on chromosome 7AL. Analysis of carotenoid genes showed that phytoene synthase (PSY) co-located to the QTL on 7AL but other genes at this locus are also thought to contribute flour b* colour variation. This study used the wheat genome survey sequence and identified the chromosomal location of all wheat carotenoid genes, but none other than PSY were located on 7AL and, therefore, other genes may control flour b* colour variation including oxidative genes that degrade carotenoids. An investigation of EST bin mapped to 7AL identified a gene encoding a catalase enzyme (Cat3-A1) that was phylogenetically related to other plant class III enzymes, co-located to the QTL for flour b* colour variation on 7AL in three mapping populations and expressed during seed development. Therefore, Cat3-A1 was functionally associated with flour b* colour variation. Catalase acts upon hydrogen peroxide as a substrate and it was postulated that Cat3-A1 alleles control varying degrees of bleaching action on lutein in developing wheat grain. Markers for Cat3-A1 developed in this study can be used in conjunction with other candidate gene markers including phytoene synthase and lycopene-ε-cylase to develop a molecular signature for selecting lines with specific flour b* colour values in wheat breeding.     

Verification of QTL for Grain Starch Content and Its Genetic Correlation with Oil Content Using Two Connected RIL Populations in High-Oil Maize

Grain oil content is negatively correlated with starch content in maize in general. In this study, 282 and 263 recombinant inbred lines (RIL) developed from two crosses between one high-oil maize inbred and two normal dent maize inbreds were evaluated for grain starch content and its correlation with oil content under four environments. Single-trait QTL for starch content in single-population and joint-population analysis, and multiple-trait QTL for both starch and oil content were detected, and compared with the result obtained in the two related F_2∶3 populations. Totally, 20 single-population QTL for grain starch content were detected. No QTL was simultaneously detected across all ten cases. QTL at bins 5.03 and 9.03 were all detected in both populations and in 4 and 5 cases, respectively. Only 2 of the 16 joint-population QTL had significant effects in both populations. Three single-population QTL and 8 joint-population QTL at bins 1.03, 1.04–1.05, 3.05, 8.04–8.05, 9.03, and 9.05 could be considered as fine-mapped. Common QTL across F_2∶3 and RIL generations were observed at bins 5.04, 8.04 and 8.05 in population 1 (Pop.1), and at bin 5.03 in population 2 (Pop.2). QTL at bins 3.02–3.03, 3.05, 8.04–8.05 and 9.03 should be focused in high-starch maize breeding. In multiple-trait QTL analysis, 17 starch-oil QTL were detected, 10 in Pop.1 and 7 in Pop.2. And 22 single-trait QTL failed to show significance in multiple-trait analysis, 13 QTL for starch content and 9 QTL for oil content. However, QTL at bins 1.03, 6.03–6.04 and 8.03–8.04 might increase grain starch content and/or grain oil content without reduction in another trait. Further research should be conducted to validate the effect of these QTL in the simultaneous improvement of grain starch and oil content in maize.     

QTL for nodal root angle in sorghum (<Emphasis Type="Italic">Sorghum bicolor</Emphasis> L. Moench) co-locate with QTL for traits associated with drought adaptation

Nodal root angle in sorghum influences vertical and horizontal root distribution in the soil profile and is thus relevant to drought adaptation. In this study, we report for the first time on the mapping of four QTL for nodal root angle (qRA) in sorghum, in addition to three QTL for root dry weight, two for shoot dry weight, and three for plant leaf area. Phenotyping was done at the six leaf stage for a mapping population (n = 141) developed by crossing two inbred sorghum lines with contrasting root angle. Nodal root angle QTL explained 58.2% of the phenotypic variance and were validated across a range of diverse inbred lines. Three of the four nodal root angle QTL showed homology to previously identified root angle QTL in rice and maize, whereas all four QTL co-located with previously identified QTL for stay-green in sorghum. A putative association between nodal root angle QTL and grain yield was identified through single marker analysis on field testing data from a subset of the mapping population grown in hybrid combination with three different tester lines. Furthermore, a putative association between nodal root angle QTL and stay-green was identified using data sets from selected sorghum nested association mapping populations segregating for root angle. The identification of nodal root angle QTL presents new opportunities for improving drought adaptation mechanisms via molecular breeding to manipulate a trait for which selection has previously been very difficult.     

Identification of trait-improving quantitative trait loci for grain yield components from a dent corn inbred line in an advanced backcross BC<Subscript>2</Subscript>F<Subscript>2</Subscript> population and comparison with its F<Subscript>2:3</Subscript> population in popcorn

Normal maize germplasm could be used to improve the grain yield of popcorn inbreds. Our first objective was to locate genetic factors associated with trait variation and make first assessment on the efficiency of advanced backcross quantitative trait locus (AB-QTL) analysis for the identification and transfer of favorable QTL alleles for grain yield components from the dent corn inbred. A second objective was to compare the detection of QTL in the BC₂F₂ population with results using F_2:3 lines of the same parents. Two hundred and twenty selected BC₂F₂ families developed from a cross between Dan232 and an elite popcorn inbred N04 were evaluated for six grain yield components under two environments, and genotyped by means of 170 SSR markers. Using composite interval mapping (CIM), a total of 19 significant QTL were detected. Eighteen QTL had favorable alleles contributed by the dent corn parent Dan232. Sixteen of these favorable QTL alleles were not in the same or near marker intervals with QTL for popping characteristics. Six QTL were also detected in the F_2:3 population. Improved N04 could be developed from 210 and 208 families with higher grain weight per plant and/or 100-grain weight, respectively, and 35 families with the same or higher popping expansion volume than N04. In addition, near isogenic lines containing detected QTL (QTL-NILs) for grain weight per plant and/or 100-grain weight could be obtained from 12 families. Our study demonstrated that the AB-QTL method can be applied to identify and manipulate favorable QTL alleles from normal corn inbreds and combine QTL detection and popcorn breeding efficiently.     

QTL mapping for grain filling rate and yield-related traits in RILs of the Chinese winter wheat population Heshangmai × Yu8679

A set of 142 winter wheat recombinant inbred lines (RILs) deriving from the cross Heshangmai x Yu8679 were tried in four ecological environments during the seasons 2006 and 2007. Nine agronomic traits comprising mean grain filling rate (GFR(mean)), maximum grain filling rate (GFR(max)), grain filling duration (GFD), grain number per ear (GNE), grain weight per ear (GWE), flowering time (FT), maturation time (MT), plant height (PHT) and thousand grain weight (TGW) were evaluated in Beijing (2006 and 2007), Chengdu (2007) and Hefei (2007). A genetic map comprising 173 SSR markers and two EST markers was generated. Based on the genetic map and phenotypic data, quantitative trait loci (QTL) were mapped for these agronomic traits. A total of 99 putative QTLs were identified for the nine traits over four environments except GFD, PHT and MT, measured in two environments (BJ07 and CD07), respectively. Of the QTL detected, 17 for GFR(mean), 16 for GFR(max), 21 for TGW and 10 for GWE involving the chromosomes 1A, 1B, 2A, 2D, 3A, 3B, 3D, 4A, 4D, 5A, 5B, 6D and 7D were identified. Moreover, 13 genomic regions showing pleiotropic effects were detected in chromosomes 1A, 1B, 1D, 2A, 2B, 2D, 3A, 3B, 4B, 4D, 5B, 6D and 7D; these QTL revealing pleiotropic effects may be informative for a better understanding of the genetic basis of grain filling rate and other yield-related traits, and represent potential targets for multi-trait marker aided selection in wheat.     

Relationships between grain protein content and grain yield components through quantitative trait locus analyses in a recombinant inbred line population derived from two elite durum wheat cultivars

Grain protein content (GPC) in durum wheat (Triticum turgidum var. durum) is negatively correlated with grain yield. To evaluate possible genetic interrelationships between GPC and grain yield per spike, thousand-kernel weight and kernel number per spike, quantitative trait loci (QTL) for GPC were mapped using GPC-adjusted data in a covariance analysis on yield components. Phenotypic data were evaluated in a segregating population of 120 recombinant inbred lines derived from crossing the elite cultivars Svevo and Ciccio. The material was tested at five environments in southern Italy. QTL were determined by composite interval mapping based on the Svevo?×?Ciccio linkage map described in Gadaleta et al. (2009) and integrated with DArT markers. The close relationship between GPC and yield components was reflected in the negative correlation between the traits and in the reduction of variance when GPC values were adjusted to yield components. Ten independent genomic regions involved in the expression of GPC were detected, six of which were associated with QTL for one or more grain yield components. QTL alleles with increased GPC effects were associated with QTL alleles with decreased effects on one or more yield component traits, or vice versa (i.e. the allelic effects were in opposite direction). Four QTL for GPC showed always significant effects, and these QTL should represent genes that influence GPC independently from variation in the yield components. Such genes are of special interest in wheat breeding since they would allow an increase in GPC without a concomitant decrease in grain yield.     

Activities of key enzymes for starch synthesis in relation to growth of superior and inferior grains on winter wheat (Triticum aestivum L.) spike

Weight of individual grains is a major yield component in wheat. The non-uniform distribution of single grain weight on a wheat spike is assumed to be closely associated with starch synthesis in grains. The present study was undertaken to determine if the enzymes involved in starch synthesis cause the differences in single grain weight between superior and inferior grains on a wheat spike. Using two high-yield winter wheat (Triticum aestivum L.) varieties differing in grain weight and three nitrogen rates for one variety, the contents of amylose and amylopectin, and activities of enzymes involved in starch synthesis in both superior and inferior grains were investigated during the entire period of grain filling. Superior grains showed generally higher starch accumulation rates and activities of enzymes including SS (sucrose synthase), UDPGPPase (UDP-glucose pyrophosphorylase), ADPGPPase (ADP-glucose pyrophosphorylase), SSS (soluble starch synthase) and GBSS (starch granule bound starch synthase) and subsequently produced much higher single grain weight than inferior grains. Nitrogen increased enzyme activities and starch accumulation rates, and thus improved individual grain weight, especially for inferior grains. The SS, ADPGPPase and SSS were significantly correlated to amylopectin accumulation, while SS, ADPGPPase, SSS and GBSS were significantly correlated to amylose accumulation. This infers that SS, ADPGPPase and starch synthase play key roles in regulating starch accumulation and grain weight in superior and inferior grains on a wheat spike.