Physiological characterization of recombinant inbred lines of barley with contrasting levels of carbon isotope discrimination

Background and Aims

Carbon isotope discrimination (Δ¹³C) in C₃ plants used as an indirect measure of water-use efficiency (WUE) provides a tool for selecting crops with high WUE under dry environments.

Methods

We evaluated the physiology and Δ¹³C of a set of 8 F₅ recombinant inbred lines (RILs) with contrasting levels of leaf Δ¹³C derived from two parents, ‘W89001002003’ (low Δ¹³C) and ‘I60049’ (high Δ¹³C) of six-row barley (Hordeum vulgare L.) in a greenhouse and under field conditions in three locations (Lacombe, Vegreville and Castor). In the greenhouse experiment, seven days of water deficit was imposed at the stem elongation stage followed by re-watering to pre-deficit level.

Results

A significant negative relationship between WUE and leaf Δ¹³C was observed. Under water-deficit conditions, both photosynthetic rate (A) and stomatal conductance (g _s ) were significantly reduced with a strong positive correlation (r = 0.89) between the two, and the variation in g _s was proportionally greater than A. The low leaf-Δ¹³C RIL ‘147’ maintained the highest A and g _s among ten genotypes (RILs and parents) under water-deficit conditions. Leaf Δ¹³C was positively correlated with biomass and grain yield in the field trials. Multivariate analysis of leaf Δ¹³C, harvest index and plant height discriminated genotypes into three clusters: drought sensitive, drought tolerant and an intermediate type.

Conclusions

The study suggests that it is possible to select low Δ¹³C lines such as RIL ‘147’, which is able to maintain or produce high yields under low moisture conditions on the Canadian Prairies     

Genetic Analysis of Carbon Isotope Discrimination and its Relation to Yield in a Wheat Doubled Haploid Population

Carbon isotope discrimination (Δ¹³C) is considered a useful indicator for indirect selection of grain yield (GY) in cereals. Therefore, it is important to evaluate the genetic variation in Δ¹³C and its relationship with GY. A doubled haploid (DH) population derived from a cross of two common wheat varieties, Hanxuan 10 (H10) and Lumai 14 (L14), was phenotyped for Δ¹³C in the flag leaf, GY and yield associated traits in two trials contrasted by water availability, specifically, rain‐fed and irrigated. Quantitative trait loci (QTLs) were identified by single locus and two locus QTL analyses. QTLs for Δ¹³C were located on chromosomes 1A, 2B, 3B, 5A, 7A and 7B, and QTLs for other traits on all chromosomes except 1A, 4D, 5A, 5B and 6D. The population selected for high Δ¹³C had an increased frequency of QTL for high Δ¹³C, GY and number of spikes per plant (NSP) when grown under rain‐fed conditions and only for high Δ¹³C and NSP when grown under irrigated conditions, which was consistent with agronomic performance of the corresponding trait values in the high Δ¹³C progeny; that is, significantly greater than that in the low Δ¹³C. Therefore, selection for Δ¹³C was beneficial in increasing grain yield in rain‐fed environments.     

Isotopes reveal contrasting water use strategies among coexisting plant species in a Mediterranean ecosystem

Variation in the stable carbon and oxygen isotope composition (δ(13) C, Δ(18) O) of co-occurring plant species may reflect the functional diversity of water use strategies present in natural plant communities. We investigated the patterns of water use among 10 coexisting plant species representing diverse taxonomic groups and life forms in semiarid southeast Spain by measuring their leaf δ(13) C and Δ(18) O, the oxygen isotope ratio of stem water and leaf gas exchange rates. Across species, Δ(18) O was tightly negatively correlated with stomatal conductance (g(s) ), whereas δ(13) C was positively correlated with intrinsic water use efficiency (WUE(i) ). Broad interspecific variation in Δ(18) O, δ(13) C and WUE(i) was largely determined by differences in g(s) , as indicated by a strong positive correlation between leaf δ(13) C and Δ(18) O across species The 10 co-occurring species segregated along a continuous ecophysiological gradient defined by their leaf δ(13) C and Δ(18) O, thus revealing a wide spectrum of stomatal regulation intensity and contrasting water use strategies ranging from 'profligate/opportunistic' (high g(s) , low WUE(i) ) to 'conservative' (low g(s) , high WUE(i) ). Coexisting species maintained their relative isotopic rankings in 2?yr with contrasting rainfall, suggesting the existence of species-specific 'isotopic niches' that reflect ecophysiological niche segregation in dryland plant communities.     

Variation at the vernalisation genes Vrn-H1 and Vrn-H2 determines growth and yield stability in barley (Hordeum vulgare) grown under dryland conditions in Syria

Key message

Spring growth in barley controlled by natural variation at Vrn-H1 and Vrn-H2 improved yield stability in marginal Syrian environments.

Abstract

The objective of the present study was to identify QTL influencing agronomic performance in rain-fed Mediterranean environments in a recombinant inbred line (RIL) population, ARKE derived from the Syrian barley landrace, Arta and the Australian feed cultivar, Keel. The population was field tested for agronomic performance at two locations in Syria for 4 years with two sowing dates, in autumn and winter. Genotypic variability in yield of the RIL population was mainly affected by year-to-year variation presumably caused by inter-annual differences in rainfall distribution. The spring growth habit and early flowering inherited from the Australian cultivar Keel increased plant height and biomass and improved yield stability in Syrian environments. QTL for yield and biomass coincided with the map location of flowering time genes, in particular the vernalisation genes Vrn-H1 and Vrn-H2. In marginal environments with terminal drought, the Vrn-H1 allele inherited from Keel improved final biomass and yield. Under changing climate conditions, such as shorter winters, reduced rainfall, and early summer drought, spring barley might thus outperform the traditional vernalisation-sensitive Syrian landraces. We present the ARKE population as a valuable genetic resource to further elucidate the genetics of drought adaptation of barley in the field.     

A quantitative trait locus for long photoperiod response mapped on chromosome 4H in barley

Photoperiod response is a key determinant for barley adaptation to diverse environments. A major quantitative trait locus (QTL) for response to long photoperiod was identified in Australia (Perth, 31°56??S) and China (Wuhan, 30°33??N) using 178 doubled haploid lines derived from a cross of an Australian barley, Baudin, and a Canadian barley, AC Metcalfe. The QTL was detected as a major QTL in the 18-h photoperiod glasshouse experiments and mapped to the Xp12m50B199?CXp13m47B399 interval on chromosome 4H with a LOD score of 57 in Australia and confirmed in China. The single QTL accounted for 77.48 and 37.81% of phenotypic variation for long photoperiod response in Australia and China, respectively. The same QTL also controlled heading date in Australia, under normal and extended photoperiod conditions, and in China, under extended photoperiod and late-sown conditions. The QTL advanced heading date by 27.8?days in Australia and 42.5?days in China under a 18-h photoperiod. In addition, QTL for heading date were identified on chromosomes 2H and 3H. The chromosome 3H QTL was associated with the denso gene and detected in all conditions, but the chromosome 2H QTL was only detected in Australia. The new photoperiod response QTL, Qhea.BM.4-13/Qpho.BM.4-13, on chromosome 4H and its associated markers will provide an alternative for plant breeders developing new varieties for different environments using marker-assisted selection.     

QTLs for earliness and yield-forming traits in the Lubuski × CamB barley RIL population under various water regimes

Drought has become more frequent in Central Europe causing large losses in cereal yields, especially of spring crops. The development of new varieties with increased tolerance to drought is a key tool for improvement of agricultural productivity. Material for the study consisted of 100 barley recombinant inbred lines (RILs) (LCam) derived from the cross between Syrian and European parents. The RILs and parental genotypes were examined in greenhouse experiments under well-watered and water-deficit conditions. During vegetation the date of heading, yield and yield-related traits were measured. RIL population was genotyped with microsatellite and single nucleotide polymorphism markers. This population, together with two other populations, was the basis for the consensus map construction, which was used for identification of quantitative trait loci (QTLs) affecting the traits. The studied lines showed a large variability in heading date. It was noted that drought-treatment negatively affected the yield and its components, especially when applied at the flag leaf stage. In total, 60 QTLs were detected on all the barley chromosomes. The largest number of QTLs was found on chromosome 2H. The main QTL associated with heading, located on chromosome 2H (Q.HD.LC-2H), was identified at SNP marker 5880–2547, in the vicinity of Ppd-H1 gene. SNP 5880–2547 was also the closest marker to QTLs associated with plant architecture, spike morphology and grain yield. The present study showed that the earliness allele from the Syrian parent, as introduced into the genome of an European variety could result in an improvement of barley yield performance under drought conditions.     

Gene action for surrogate traits of water-use efficiency and harvest index in peanut (Arachis hypogaea)

Low peanut productivity in the semi‐arid tropics is attributed mainly to drought caused by low and erratic rainfall. Genetic improvement in water‐use efficiency (WUE) could potentially lead to improved yield under limited moisture availability. In peanut, WUE is correlated with SPAD chlorophyll meter reading (SCMR), specific leaf area (SLA), and carbon isotope discrimination (Δ¹³C). These traits can be used as surrogates for selecting for WUE. Partitioning of assimilates as measured by the harvest index (HI) has the greatest effect on pod yield. To improve these traits for tailoring peanut genotypes well matched for water‐limited conditions, a good knowledge of genetic systems controlling the expression of these traits is essential. This study was undertaken to work out the gene action for the surrogates of WUE and HI in a 6 × 6 full diallel mating design. Two of the studied surrogates (SCMR and Δ¹³C) for WUE were found to be under the influence of both additive and nonadditive gene effects with preponderance of the former. SLA and HI were controlled by genes that are mainly additive in nature. Selection for these traits can be effective in the early generations. Maternal effects observed for SLA and Δ¹³C are suggestive of the crucial role of selection of female parent in improvement of these traits. The parental lines, TMV 2 NLM (for SCMR, SLA and Δ¹³C) and ICGV 86031 (for SCMR and SLA), were found to be good general combiners each for more than one character. TAG 24 and Chico (for HI) and CSMG 84‐1 (for SLA) were the other good general combiners.     

Water use efficiency in C3 cereals under Mediterranean conditions: a review of physiological aspects

In this review, we will discuss physiological traits of C₃ cereals related to water use efficiency (WUE) in Mediterranean environments, from leaf (WUE_{instantaneous}) to crop level (WUE_yield or ‘water productivity’). First, we analyse the WUE_{instantaneous} and the possible trade‐off between improving this parameter and growth/yield performance. Ways to ameliorate WUE without penalties are discussed. We also analyse in what cases breeding by high or low WUE_{instantaneous} is a suitable criterion to maintain grain yield under drought (Mediterranean) conditions. This question is approached in the framework of carbon isotope discrimination, (Δ¹³C), the main indirect parameter used to integrate (at time and space scale) the WUE_{instantaneous} in C₃ plants. A negative correlation between these two parameters has been confirmed by several studies. The relationship between Δ¹³C and grain yield, however, is more complex, and may differ from one environment to another. In Mediterranean conditions with moderate or no water stress, a positive correlation between Δ¹³C and grain yield is found in barley and wheat, whereas in ‘stored‐water’ crops (such as in some regions of Australia), lower Δ¹³C (i.e. higher WUE_{instantaneous}) is associated with higher grain yield, particularly in more stressful conditions. These apparent inconsistencies and their possible implications for plant breeding are discussed. One physiological trait that has received minor attention in attempts to improve WUE_{instantaneous} is the role of ear photosynthesis. Ears of barley and durum wheat have a higher WUE_{instantaneous} than the flag leaf, both in well‐watered and in drought conditions. The underlying causes of the higher WUE_{instantaneous} of ears are not fully understood, but their refixation capacity (i.e. the capacity to re‐assimilate respired carbon dioxide) could be important. Although the genotypic variability of this trait has not been extensively studied, some data support the idea that variation in refixation capacity may be attributable to genetic factors. At the crop level, decreasing soil evaporation is a crucial factor in efforts to improve the WUE_yield in Mediterranean conditions, and fast initial growth of the crop (i.e. early vigour) seems to be relevant. In wheat, modern varieties with dwarfing genes (giberellic acid – insensitive) have higher yields but, concomitantly, they have lower initial growth performance. Recently, semi‐dwarf cultivars (giberellic acid – sensitive) with high grain yield and simultaneously high early vigour were found, opening new avenues to increase WUE_yield in wheat. The negative effects of futile water loss by cuticular and nocturnal transpiration are also commented. Finally, we discuss some agronomic practices (in particular, ‘deficit irrigation’ systems) linked to physiological traits that confer higher WUE_yield,, in particular, in the cases of Mediterranean regions.     

Genetic basis of soybean adaptation to North American vs. Asian mega-environments in two independent populations from Canadian × Chinese crosses

One of the goals of plant breeding is to increase yield with improved quality characters. Plant introductions (PI) are a rich source of favorable alleles that could improve different characters in modern soybean [Glycine max (L.) Merril] including yield. The objectives of this study were to identify yield QTL underlying the genetic basis for differential adaptation of soybeans to the Canadian, United States or Chinese mega-environments (ME) and to evaluate the relationship and colocalization between yield and agronomic traits QTL. Two crosses between high-yielding Canadian cultivars and elite Chinese cultivars, OAC Millennium × Heinong 38 and Pioneer 9071 × #8902, were used to develop two recombinant inbred line (RIL) populations. Both populations were evaluated at different locations in Ontario, Canada; Minnesota, United States (US), Heilongjiang and Jilin, China, in 2009 and 2010. Significant variation for yield was observed among the RILs of both populations across the three hypothetical ME. Two yield QTL (linked to the interval Satt364–Satt591 and Satt277) and one yield QTL (linked to marker Sat_341) were identified by single-factor ANOVA and interval mapping across all ME in populations 1 and 2, respectively. The most frequent top ten high-yielding lines across all ME carried most of the high-yielding alleles of the QTL that were identified in two and three ME. Both parents contributed favorable alleles, which suggests that not only the adapted parent but also the PI parents are potential sources of beneficial alleles in reciprocal environments. Other QTL were detected also at two and one ME. Most of the yield QTL were co-localized with a QTL associated with an agronomic trait in one, two, or three ME in just one or in both populations. Results suggested that most of the variation observed in seed yield can be explained by the variation of different agronomic traits such a maturity, lodging and height. Novel alleles coming from PI can favorably contribute, directly or indirectly, to seed yield and the utilization of QTL detected across one, two or three ME would facilitate the new allele introgression into breeding populations in both North America and China.     

Physiological mechanisms contributing to the increased water-use efficiency in winter wheat under deficit irrigation

Deficit irrigation in winter wheat has been practiced in the areas with limited irrigation water resources. The objectives of this study were to (i) understand the physiological basis for determinations of grain yield and water-use efficiency in grain yield (WUE) under deficit irrigation; and (ii) investigate the effect of deficit irrigation on dry matter accumulation and remobilization of pre-anthesis carbon reserves during grain filling. A field experiment was conducted in the Southern High Plains of the USA and winter wheat (cv. TAM 202) was grown on Pullman clay loam soil (fine mixed thermic Torretic Paleustoll). Treatments consisted of rain-fed, deficit irrigation from jointing to the middle of grain filling, and full irrigation. The physiological measurements included leaf water potential, net photosynthetic rate (Pn), stomatal conductance (Gs), and leaf area index. The rain-fed treatment had the lowest seasonal evapotranspiration (ET), biomass, grain yield, harvest index (HI) and WUE as a result of moderate to severe water stress from jointing to grain filling. Irrigation application increased seasonal ET, and ET increased as irrigation frequency increased. The seasonal ET increased 20% in one-irrigation treatments between jointing and anthesis, 32-46% in two-irrigation treatments, and 67% in three- and full irrigation treatments. Plant biomass, grain yield, HI and WUE increased as the result of increased ET. The increased yield under irrigation was mainly contributed by the increased number of spikes, and seeds per square meter and per spike. Among the irrigation treatments, grain yield increased significantly but the WUE increased slightly as irrigation frequency increased. The increased WUE under deficit irrigation was contributed by increased HI. Water stress during grain filling reduced Pn and Gs, and accelerated leaf senescence. However, the water stress during grain filling induced remobilization of pre-anthesis carbon reserves to grains, and the remobilization of pre-anthesis carbon reserves significantly contributed to the increased grain yield and HI. The results of this study showed that deficit irrigation between jointing and anthesis significantly increased wheat yield and WUE through increasing both current photosynthesis and the remobilization of pre-anthesis carbon reserves.     

Genome-wide association mapping of agronomic traits in relevant barley germplasm in Uruguay

The genetic basis of agronomic traits determining adaptation to specific production conditions is a key factor for the improvement of crops, including malting barley (Hordeum vulgare L.). The aim of this study was to determine the genome-wide genetic components associated with agronomic phenotypes of local and global significance in a population of 76 barley genotypes that have been introduced into Uruguay in different chronological periods. The phenotypic database was obtained from five field experiments, planted in 2 years and in two locations, where a total of 13 agronomic traits were determined. The population was genotyped with 1,033 single nucleotide polymorphisms. We found a total of 41 quantitative trait loci (QTL) in a combined analysis using all datasets and 79 QTL if we considered all the trait/experiment combinations analyzed. The highest concentration of QTL was detected on chromosomes 2H and 4H. Most QTL were detected for grain plumpness and weight. Two linkage disequilibrium (LD) blocks associated with a large number of traits were detected on 2HS. The largest LD block was composed of three haplotypes, possibly derived from three ancestors of different geographical origin. We also detected three genomic regions in different chromosomes (2H, 5H and 7H) in LD between them, associated with agronomic traits. This study provides a contribution to the understanding of the genetics of barley adaptation in the southern cone of South America. Our results showed that elite varieties have favorable alleles at different QTL, indicating that gains can be made through plant breeding.     

QTL in mega-environments: II. Agronomic trait QTL co-localized with seed yield QTL detected in a population derived from a cross of high-yielding adapted × high-yielding exotic soybean lines

Seed yield mega-environment-universal and specific QTL (QTL_U and QTL_SP, respectively) linked to Satt100, Satt130, Satt162, Satt194, Satt259 Satt277 and Sat_126, have been identified in a population derived from a cross between a Chinese and a Canadian soybean [Glycine max (L.) Merrill] elite line. The variation observed in yield could be the consequence of the variation of agronomic traits. Yield-component traits have been reported in the literature, but a better understanding of their impact at the molecular level is still lacking. Therefore, the objectives of this study were to identify traits correlated with yield and to determine if the yield QTL_U and QTL_SP were co-localized with QTL_U and QTL_SP associated with an agronomic trait. A recombinant inbred line (RIL) population was developed from a cross between a high-yielding adapted Canadian and a high-yielding exotic Chinese soybean elite line. The RIL were evaluated in multiple environments in China and Canada during the period from 2004 to 2006. Four yield QTL_U, tagged by markers Satt100, Satt277, Satt162 and Sat_126, were co-localized with a QTL associated with an agronomic trait, behaving as either QTL_U or QTL_SP for the agronomic trait. For example, the yield QTL_U, tagged by marker Satt100 was associated also with 100 seed weight, pods per plant, pods per node, plant height, R1, R5, R8, oil content and protein content in all Canadian environments, but only with pods per plant, pods per node, plant height, R1, R5, R8 and oil content in two or more Chinese environments. No agronomic traits QTL were co-localized with the yield QTL_U tagged by the marker Satt139 or the yield QTL_SP tagged by Satt259, suggesting a physiological basis of the yield in these QTL. The results suggest that a successful introgression of crop productivity alleles from plant introductions into an adapted germplasm could be facilitated by the use of both the QTL_U and QTL_SP because each type of QTL contributed either directly or indirectly through yield-component traits to seed yield of RILs.     

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

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

Genetic Control of Water Use Efficiency and Leaf Carbon Isotope Discrimination in Sunflower (Helianthus annuus L.) Subjected to Two Drought Scenarios

High water use efficiency (WUE) can be achieved by coordination of biomass accumulation and water consumption. WUE is physiologically and genetically linked to carbon isotope discrimination (CID) in leaves of plants. A population of 148 recombinant inbred lines (RILs) of sunflower derived from a cross between XRQ and PSC8 lines was studied to identify quantitative trait loci (QTL) controlling WUE and CID, and to compare QTL associated with these traits in different drought scenarios. We conducted greenhouse experiments in 2011 and 2012 by using 100 balances which provided a daily measurement of water transpired, and we determined WUE, CID, biomass and cumulative water transpired by plants. Wide phenotypic variability, significant genotypic effects, and significant negative correlations between WUE and CID were observed in both experiments. A total of nine QTL controlling WUE and eight controlling CID were identified across the two experiments. A QTL for phenotypic response controlling WUE and CID was also significantly identified. The QTL for WUE were specific to the drought scenarios, whereas the QTL for CID were independent of the drought scenarios and could be found in all the experiments. Our results showed that the stable genomic regions controlling CID were located on the linkage groups 06 and 13 (LG06 and LG13). Three QTL for CID were co-localized with the QTL for WUE, biomass and cumulative water transpired. We found that CID and WUE are highly correlated and have common genetic control. Interestingly, the genetic control of these traits showed an interaction with the environment (between the two drought scenarios and control conditions). Our results open a way for breeding higher WUE by using CID and marker-assisted approaches and therefore help to maintain the stability of sunflower crop production.     

Quantitative trait loci for agronomic traits in an elite barley population for Mediterranean conditions

Advances in plant breeding through marker-assisted selection (MAS) are only possible when genes or quantitative trait loci (QTLs) can contribute to the improvement of elite germplasm. A population of recombinant inbred lines (RILs) was developed for one of the best crosses of the Spanish National Barley Breeding Program, between two six-row winter barley cultivars Orria and Plaisant. The objective of this study was to identify favourable QTLs for agronomic traits in this population, which may help to optimise breeding strategies for these and other elite materials for the Mediterranean region. A genetic linkage map was developed for 217 RILs, using 382 single nucleotide polymorphism markers, selected from the barley oligonucleotide pool assay BOPA1 and two genes. A subset of 112 RILs was evaluated for several agronomic traits over a period of 2 years at three locations, Lleida and Zaragoza (Spain) and Fiorenzuola d’Arda (Italy), for a total of five field trials. An important segregation distortion occurred during population development in the region surrounding the VrnH1 locus. A QTL for grain yield and length of growth cycle was also found at this locus, apparently linked to a differential response of the VrnH1 alleles to temperature. A total of 33 QTLs was detected, most of them for important breeding targets such as plant height and thousand-grain weight. QTL × environment interactions were prevalent for most of the QTLs detected, although most interactions were of a quantitative nature. Therefore, QTLs suitable for MAS for most traits were identified.     

δ(13) C of leaf-respired CO(2) reflects intrinsic water-use efficiency in barley

Leaf intrinsic water-use efficiency (WUE), the ratio of photosynthetic rate to stomatal conductance (A/g(s) ), is a key plant trait linking terrestrial carbon and water cycles. A rapid, integrative proxy for A/g(s) is of benefit to crop breeding programmes aiming to improve WUE, but also for ecologists interested in plant carbon-water balance in natural systems. We hypothesize that the carbon isotope composition of leaf-respired CO(2) (δ(13) C(Rl) ), two hours after leaves are transferred to the dark, records photosynthetic carbon isotope discrimination and so provides a proxy for A/g(s) . To test this hypothesis, δ(13) C(Rl) was measured in four barley cultivars grown in the field at two levels of water availability and compared to leaf-level gas exchange (the ratio of leaf intercellular to ambient CO(2) partial pressure, C(i) /C(a) , and A/g(s) ). Leaf-respired CO(2) was more (13) C-depleted in plants grown at higher water availability, varied between days as environmental conditions changed, and was significantly different between cultivars. A strong relationship between δ(13) C(Rl) and δ(13) C of sucrose was observed. δ(13) C(Rl) was converted into apparent photosynthetic discrimination (Δ(13) C(Rl) ) revealing strong relationships between Δ(13) C(Rl) and C(i) /C(a) and A/g(s) during the vegetative stage of growth. We therefore conclude that δ(13) C(Rl) may provide a rapid, integrative proxy for A/g(s) in barley.     

QTL mapping reveals genetic architectures of malting quality between Australian and Canadian malting barley (<Emphasis Type="Italic">Hordeum vulgare</Emphasis> L.)

Australia and Canada are major exporters of malting barley (Hordeum vulgare L.), with Baudin from Australia and AC Metcalfe from Canada being the benchmark varieties for premium malting quality in the past 10 years. We used the barley doubled haploid population derived from a cross of Baudin and AC Metcalfe to map quantitative trait loci (QTLs) for malting quality. The results revealed different genetic architectures controlling malting quality for the two cultivars. Sixteen QTLs were identified and located on chromosomes 1H, 2H, 5H and 7H. The Australian barley Baudin mainly contributed to the malting quality QTL traits of high diastatic power and high β-glucanase on chromosome 1H, while Canadian barley AC Metcalfe mainly contributed to the QTL traits of high hot water extract, high free amino nitrogen, high α-amylase and low malt yield in chromosome 5HL telomere region. This study demonstrated the potential to breed new barley varieties with superior malting quality by integrating genes from Australian and Canadian malting barley varieties. This paper also provides methods to anchor traditional molecular markers without sequence information, such as amplified fragment length polymorphism markers, into the physical map of barley cv. ‘Morex’.     

Marker-trait associations in Virginia Tech winter barley identified using genome-wide mapping

Genome-wide association studies (GWAS) provide an opportunity to examine the genetic architecture of quantitatively inherited traits in breeding populations. The objectives of this study were to use GWAS to identify chromosome regions governing traits of importance in six-rowed winter barley (Hordeum vulgare L.) germplasm and to identify single-nucleotide polymorphisms (SNPs) markers that can be implemented in a marker-assisted breeding program. Advanced hulled and hulless lines (329 total) were screened using 3,072 SNPs as a part of the US. Barley Coordinated Agricultural Project (CAP). Phenotypic data collected over 4 years for agronomic and food quality traits and resistance to leaf rust (caused by Puccinia hordei G. Otth), powdery mildew [caused by Blumeria graminis (DC.) E.O. Speer f. sp. hordei Em. Marchal], net blotch (caused by Pyrenophora teres), and spot blotch [caused by Cochliobolus sativus (Ito and Kuribayashi) Drechsler ex Dastur] were analyzed with SNP genotypic data in a GWAS to determine marker-trait associations. Significant SNPs associated with previously described quantitative trait loci (QTL) or genes were identified for heading date on chromosome 3H, test weight on 2H, yield on 7H, grain protein on 5H, polyphenol oxidase activity on 2H and resistance to leaf rust on 2H and 3H, powdery mildew on 1H, 2H and 4H, net blotch on 5H, and spot blotch on 7H. Novel QTL also were identified for agronomic, quality, and disease resistance traits. These SNP-trait associations provide the opportunity to directly select for QTL contributing to multiple traits in breeding programs.     

Genetic dissection of grain beta-glucan and amylose content in barley (Hordeum vulgare L.)

High beta-glucan (BG) barleys (Hordeum vulgare L.) have major potential as food ingredients due to their well-known health benefits. Quantitative trait loci (QTL) associated with BG have been reported in traditional barley varieties with intermediate levels of BG, but no QTL studies have been reported in hull-less barley varieties with high BG levels. In this study, QTL analysis was performed to identify markers linked to high BG and amylose in the hull-less barley varieties Falcon (4–5 % BG) and Azhul (8–9 % BG) using a newly developed recombinant inbred line (RIL) mapping population. The population was grown over 3 years (2007–2009) at sites in Yuma, AZ, USA; Leeston, New Zealand; Aberdeen, ID, USA; and Tetonia, ID, USA. We identified 17 QTL associated with either BG or amylose content. QTL contributing to high BG were located on chromosomes 3H, 4H, 5H, 6H and 7H, while QTL contributing to amylose were located on chromosomes 1H, 5H and 7H. Additionally, we identified QTL affecting both BG and amylose content located on chromosomes 1H and 7H. Transgressive segregation was observed in some of the RILs and exceptions were discovered contradicting an inverse relationship between BG and amylose. This work will provide the basis for gene cloning and marker-assisted selection in combination with traditional field selection to improve barley breeding for high BG content.     

Quantitative trait loci mapping for yield and its components by using two immortalized populations of a heterotic hybrid in Gossypium hirsutum L.

Quantitative trait loci (QTL) mapping provides a powerful tool for unraveling the genetic basis of yield and yield components as well as heterosis in upland cotton. In this research, a molecular linkage map of Xiangzamian 2 (Gossypium hirsutum L.)-derived recombinant inbred lines (RILs) was reconstructed based on increased expressed sequence tag–simple sequence repeat markers. Both the RILs and immortalized F2s (IF2) developed through intermating between RILs were grown under multiple environments. Yield and yield components including seed-cotton yield, lint yield, bolls/plant, boll weight, lint percentage, seed index, lint index and fruit branch number were measured and their QTL were repeatedly identified across environments by the composite interval mapping (CIM) method. From a total of 111 non-redundant QTL, 23 were detected in both two populations. In the meantime, multi-marker joint analyses showed that 16 of these QTL had significant environmental interaction. QTL for correlated traits tended to be collocated and most of the QTL for seed-cotton yield and lint yield were associated with QTL for at least one yield component, consistent with the results observed in correlation analyses. For many QTL with significant additive effects, positive alleles from CRI12, the inferior parent with lower yield performance, were associated with trait improvement. Trait performance of IF2s and the large number of QTL with positive dominant effects implied that dominance plays an important role in the genetic basis of heterosis in Xiangzamian 2 and that non-additive inheritance is also an important genetic mode for lint percentage in the population. These QTL can provide the bases for marker-assisted breeding programs of upland cotton.