Improving the efficiency of isolated microspore culture in six-row spring barley: II-exploring novel growth regulators to maximize embryogenesis and reduce albinism

Key message

Two alternative cytokinins, thidiazuron and meta-topoline, were tested in isolated microspore culture on recalcitrant barley genotypes (six-row, spring), and green plant regeneration was improved substantially.

Abstract

Doubled-haploid (DH) plants are coveted in plant breeding and in genetic studies, since they are rapidly obtained and perfectly homozygous. In barley, DHs are produced mainly via androgenesis, and isolated microspore culture (IMC) constitutes the method offering the greatest potential efficiency. However, IMC can often be challenging in some genotypes because of low yield of microspores, low regeneration and high incidence of albinism. Six-row spring-type barleys, the predominant type grown in Eastern Canada, are considered recalcitrant in this regard. Our general objective was to optimize an IMC protocol for DH production in six-row spring barley. In particular, we explored the use of alternative hormones in the induction medium (thidiazuron and dicamba), and in the regeneration medium (meta-topoline). This optimization was performed on two typical six-row spring (ACCA and Léger), a two-row spring (Gobernadora) and a two-row winter (Igri) barley cultivar. When 6-benzyl-aminopurine (BAP) was replaced by a combination of thidiazuron and dicamba in the induction medium, a 5.1-fold increase (P < 0.01) in the production of green plants resulted. This increase was mainly achieved by a reduction of albinism. Moreover, a 2.9-fold increase (P < 0.01) in embryo differentiation into green plants was obtained using meta-topoline instead of BAP in the regeneration medium. Together, these innovations allowed us to achieve a substantial improvement in the efficiency of IMC in this recalcitrant type of barley. These results were later successfully validated using sets of F1s from a six-row spring barley breeding program.     

A genome-wide association study of malting quality across eight U.S. barley breeding programs

Key message

We report malt quality QTLs relevant to breeding with greater precision than previous mapping studies. The distribution of favorable alleles suggests strategies for marker-assisted breeding and germplasm exchange.

Abstract

This study leverages the breeding data of 1,862 barley breeding lines evaluated in 97 field trials for genome-wide association study of malting quality traits in barley. The mapping panel consisted of six-row and two-row advanced breeding lines from eight breeding populations established at six public breeding programs across the United States. A total of 4,976 grain samples were subjected to micro-malting analysis and mapping of nine quality traits was conducted with 3,072 SNP markers distributed throughout the genome. Association mapping was performed for individual breeding populations and for combined six-row and two-row populations. Only 16 % of the QTL we report here had been detected in prior bi-parental mapping studies. Comparison of the analyses of the combined two-row and six-row panels identified only two QTL regions that were common to both. In total, 108 and 107 significant marker-trait associations were identified in all six-row and all two-row breeding programs, respectively. A total of 102 and 65 marker-trait associations were specific to individual six-row and two-row breeding programs, respectively indicating that most marker-trait associations were breeding population specific. Combining datasets from different breeding program resulted in both the loss of some QTL that were apparent in the analyses of individual programs and the discovery of new QTL not identified in individual programs. This suggests that simply increasing sample size by pooling samples with different breeding history does not necessarily increase the power to detect associations. The genetic architecture of malting quality and the distribution of favorable alleles suggest strategies for marker-assisted selection and germplasm exchange.

     

Cefotaxime prevents microbial contamination and improves microspore embryogenesis in wheat and triticale

Key message

Cefotaxime (100 mg/l) mitigate occasional gram negative bacterial contamination in wheat and triticale microspore culture and most importantly it increases cell growth and green plant production.

Abstract

Isolated microspore culture is a promising option to rapidly fix the product of meiotic recombination of F₁ hybrids, in the process of varietal development. Clean culture and high embryogenesis rate are essential to commercial triticale and wheat microspore cultures. So, this study investigated (1) contaminants from isolated microspores cultures, (2) two antibiotics to control bacterial growth, and (3) the contribution of antibiotics to increased microspore-derived embryo-like structures (ELS), green and albino plants. Five species of bacteria were identified in contaminated cultures (Erwinia aphidicola, Pantoea agglomerans, Pseudomonas sp., Staphylococcus epidermis and Staphylococcus warneri) using fatty acid analysis and 16S ribosomal RNA sequences analysis, and yeast. Antibacterial susceptibility test using Cefotaxime and Vancomycin resulted in strong inhibition of 24 bacterial isolates, using Cefotaxime at 100 mg/l, but not Pseudomonas sp. Other antibiotic treatments inhibited bacterial growth at least partially. Microspore induction medium supplemented with the same antibiotics treatments resulted in successful microspore embryogenesis and green plant production. Antibiotic treatments were first tested in triticale and then validated in wheat cultivars AC Carberry and AC Andrew. Induction medium supplemented with Cefotaxime at 50 and 100 mg/l substantially increased the formation of ELS and green plants in triticale and wheat, respectively. Incidentally, it also affected the occurrence of albinism in all genotypes. Our results demonstrated dual purpose of Cefotaxime for isolated microspore culture, most importantly it increases cell growth and success of microspore cultures in triticale and wheat genotypes, but would also prevent accidental loss of cultures with most common bacterial contaminants.     

Endogenous ABA concentration and cytoplasmic membrane fluidity in microspores of oilseed rape (Brassica napus L.) genotypes differing in responsiveness to androgenesis induction

Key message

A better understanding of androgenesis with a focus on the changes in plasma membrane fluidity and endogenous ABA content affecting embryogenesis induction in microspore suspension of B. napus.

Abstract

Changes in plasma membrane fluidity (MF) and ABA content associated with androgenesis induction were under the study. Both parameters were monitored in microspores of two Brassica napus L. genotypes differing in their response to androgenic induction under heat (1 day at 32 °C). MF was assessed by DPH method. ABA content was evaluated by ELISA. Heat caused microspores’ plasma membrane to become more rigid. Lower MF in microspores of ‘DH 4079’ (of high androgenic potential) seems to maintain proper cell protection and leads to efficient embryogenesis induction. Plasma membrane remodelling coincided with changes of ABA content in microspores and in the culture medium in both genotypes. ABA concentration (μM) and ABA content (fmol per 10⁴ microspores or pmol g^?1 FW) were for the first time measured in microspores. ABA concentration (μM) in microspores and in the culture medium (nM) differed significantly for the genotype and the treatment. The interaction between both variables was also significant. In general, ABA content ranged from <3.5 to 87.1 fmol per 10⁴ microspores. The highest content of ABA was detected in ‘DH 4079’ microspores at 32 °C. Assuming a mean microspores’ radius of 10 μm, it corresponds to ABA concentration of 2.1 μM. Heat shock resulted in quantum of medium pH reduction (0.1–0.2) and increased levels of ABA in microspores and in the medium of both tested genotypes. However, heat induced increase of ABA content in microspores of non-responsive ‘Campino’ had no clear-cut impact, on androgenesis induction efficiency, which suggests a more complex mechanism of process initiation.     

Association mapping of grain hardness,polyphenol oxidase,total phenolics,amylose content,and β-glucan in US barley breeding germplasm

A renewed interest in breeding barley specifically for food end-uses is being driven by increased consumer interest in healthier foods. We conducted association mapping on physicochemical properties of barley that play a role in food quality and processing including grain hardness, polyphenol oxidase activity, total phenolics, amylose content, and β-glucan. We used 3,069 elite two-row and six-row spring barley breeding lines from eight US breeding programs and 2,041 SNP markers for association mapping. Marker–trait associations were identified using a mixed model that incorporated population structure and kinship. We detected two previously identified QTL for grain hardness on chromosome 2H in the telomeric region of 5H along with two novel regions on 4H and 6H. For amylose content, we detected marker–trait associations on 7H from 0.63 to 30 cM. We detected four regions on chromosomes 1H, 2H, 3H, and 4H associated with polyphenol oxidase activity. The chromosome 2H region co-localized with the two previously mapped polyphenol oxidase genes PPO1 and PPO2, and the regions on chromosomes 1H, 3H, and 4H QTL were novel. For total phenolics, we identified three significant regions on 3H, 4H, and 5H. Two regions on 2H and 7H were associated with β-glucan. Both previously identified and novel QTL are segregating in elite US breeding germplasm. Only three of the 24 SNPs that were associated with traits using either the two-row or six-row mapping panel were identified in both panels. Nine SNPs were detected in the individual two-row or six-row panels that were not detected in the analysis using the complete panel and accounting for population structure. The distribution of favorable alleles at these loci that underpin food quality across the breeding programs suggests several strategies to use markers to improve barley for food uses.     

Archaeogenetic Evidence of Ancient Nubian Barley Evolution from Six to Two-Row Indicates Local Adaptation

Background

Archaeobotanical samples of barley (Hordeum vulgare L.) found at Qasr Ibrim display a two-row phenotype that is unique to the region of archaeological sites upriver of the first cataract of the Nile, characterised by the development of distinctive lateral bracts. The phenotype occurs throughout all strata at Qasr Ibrim, which range in age from 3000 to a few hundred years.

Methodology and Findings

We extracted ancient DNA from barley samples from the entire range of occupancy of the site, and studied the Vrs1 gene responsible for row number in extant barley. Surprisingly, we found a discord between the genotype and phenotype in all samples; all the barley had a genotype consistent with the six-row condition. These results indicate a six-row ancestry for the Qasr Ibrim barley, followed by a reassertion of the two-row condition. Modelling demonstrates that this sequence of evolutionary events requires a strong selection pressure.

Conclusions

The two-row phenotype at Qasr Ibrim is caused by a different mechanism to that in extant barley. The strength of selection required for this mechanism to prevail indicates that the barley became locally adapted in the region in response to a local selection pressure. The consistency of the genotype/phenotype discord over time supports a scenario of adoption of this barley type by successive cultures, rather than the importation of new barley varieties associated with individual cultures.     

Isolated microspore culture of oat (Avena sativa L.) for the production of doubled haploids: effect of pre-culture and post-culture conditions

The production of doubled haploid (DH) plants from microspores is an important technique used in plant breeding programs and basic research. Although doubled haploidy efficiencies in wheat and barley are sufficient for breeding purposes, oat (Avena sativa L.) is considered recalcitrant. The objective of this project was to develop a protocol for the production of microspore-derived embryos of oat and further develop these embryos into fertile DH plants. A number of experiments were conducted evaluating the factors influencing microspore embryogenesis, i.e. donor plant conditions, pretreatments, media composition, and culture conditions. The initial studies yielded little response, and it was not until high microspore densities (10⁶ microspores/mL and greater) were used that embryogenesis was achieved. Depending on the treatment, yields of over 5,000 embryos/10⁶ microspores were obtained for breeding line 2000QiON43. The doubled haploidy protocol includes: a 0.3 M mannitol pretreatment of the tillers for 7 days, culture in W14 basal medium with a pH of 6.5–7.5, a microspore density of 10⁶ microspores/mL, and continuous incubation at 28 °C incubation. The resulting embryos observed after 28 days were plated onto solidified W14 medium with 0.8 or 1.0 g/L activated charcoal. A colchicine treatment of 0.2 % colchicine for 4 h resulted in conversion of 80 % of the plants from haploid to DH. This protocol was successful for the production of oat microspore-derived embryos and DH green plants with minimal albinism. DH seed was produced and planted for evaluation in a field nursery.     

Population structure and linkage disequilibrium in barley assessed by DArT markers

Diversity Array Technology (DArT) markers were used to investigate the genetic diversity, population structure, and extent of linkage disequilibrium (LD) on a genome-wide level in Canadian barley (Hordeum vulgare L.). Approximately 1,000 DArT markers were polymorphic and scored with high confidence among a collection of 170 barley lines composed mostly of Canadian cultivars and breeding lines. The reproducibility of DArT markers proved very high, as 99.9% of allele calls were identical among seven replicated samples. The polymorphism information content (PIC) of DArT markers ranged between 0.04 and 0.50 with an average of 0.38. Using principal coordinate analysis (PCoA), most lines fell into one of two major groups reflecting inflorescence type (two-row versus six-row). Within these two large groups, evidence of geographic clustering of genotypes was also observed. A cluster analysis Unweighted Pair Group Method with Algorithmic Mean suggested the existence of three subgroups within the two-row group and four subgroups within the six-row group. An analysis of molecular variance (AMOVA) revealed highly significant (P < 0.001) genetic variance within subgroups, among subgroups, and among groups. Values of LD, expressed as r ², declined with increasing genetic distance, and mean values of r ² fell below 0.2 for markers located 2.6 cM apart. Approximately 8% of marker pairs located on the same chromosome and 3.4% of pairs located on different chromosomes were in LD (r ²  > 0.2). Within both the subsets of two-row and six-row lines, LD extended slightly further (3.5 cM) than for the entire set, while 7.5% of intra-chromosomal locus pairs and <2% of inter-chromosomal pairs were in LD. We discuss the implications of these findings with regard to the prospects of association mapping of complex traits in barley.     

Stress treatments and in vitro culture conditions influence microspore embryogenesis and growth of callus from anther walls of sweet pepper (Capsicum annuum L.)

Production of doubled haploids (DHs) is a convenient tool to obtain pure lines for breeding purposes. Until now, the easiest and most useful approach to obtain pepper DHs is via anther culture. However, this method has an associated possibility of producing calli from anther wall tissues that would be coexisting in the anther locule with embryos derived from microspores. Using two established protocols for anther culture, Dumas de Vaulx et al. (Agronomie 2:983–988, 1981) and Supena et al. (Sci Hort 107:226–232, 2006a; Plant Cell Rep 25:1–10, 2006b) callus and embryo development was assessed in four sweet pepper cultivars. For all genotypes tested, the protocol of Dumas de Vaulx et al. (Agronomie 2:983–988, 1981) promoted both embryo development and callus growth, whereas the protocol of Supena et al. (Sci Hort 107:226–232, 2006a; Plant Cell Rep 25:1–10, 2006b) produced no callus but only embryos. However, differences in embryo production were observed among these genotypes. In parallel, anthers were exposed to a 35 °C inductive heat shock for 4, 8, 12 and 16 days, prior to culture at 25 °C. The duration of the heat shock had significant effects in embryo production, but also in callus generation. Callus generation increased with prolonged exposures to 35 °C. Embryo and callus origin was analyzed by flow cytometry, light microscopy and molecular markers. Tests conducted demonstrated a gametophytic origin for all of the embryos tested, and a sporophytic origin for all of the calli. Together, our results reveal that culture conditions have a significant influence on the presence of calli derived from anther walls, which could be minimized by reducing heat shock exposure and/or using a shed-microspore approach.     

Organelle antioxidants improve microspore embryogenesis in wheat and triticale

Low frequency of green plant production and albinism limits the use of isolated microspore culture (IMC) in cereal breeding programs. The present study was conducted in triticale and bread wheat IMC to increase the production of green plants and minimize albinism. NPB-99?+?10% Ficoll induction medium was supplemented with mitochondrial or plastid antioxidants, in a completely random design, to evaluate their contribution to successful microspore embryogenesis and green plant production. Each group of antioxidants was tested independently: first in triticale and then validated in various spring wheat genotypes. While the response differed by wheat genotype, induction medium supplemented with proline (10 mM) yielded a greater number of embryos/embryo-like structures and green plants in both triticale and wheat. No differences were found with respect to albinism in triticale or wheat except for the cv. Sadash. Among plastid antioxidants tested, glutathione (2 μM) proved to be the best antioxidant to increase embryo and green plant production. Salicylic acid also helped to reduce the number of albino plants in triticale and the wheat genotype SWS366. Overall, induction medium supplemented with proline or glutathione enhanced microspore embryogenesis in both triticale and wheat and increased the number of green plants in the recalcitrant genotypes.     

Micronucleation by mitosis inhibitors in developing microspores of Spathiphyllum wallisii Regel

Key message

We developed an efficient protocol for chromosome scattering in Spathiphyllum microspores. The effects of plant material, developmental age, genotype and antimicrotubular toxin type, exposure and concentration were evaluated.

Abstract

Asymmetric hybridization through microprotoplast-mediated chromosome transfer (MMCT) is a known method for overcoming sexual breeding barriers between distantly related plant species. To obtain microprotoplasts, it is necessary to induce mass micronucleation either in somatic or gametic cells. We have tested the efficiency for micronuclei induction of five mitosis inhibitors, amiprophos-methyl (APM), butamiphos (BUT), chlorpropham (CIPC), oryzalin (ORY) and propyzamide (PRO), on developing microspores of diploid Spathiphyllum wallisii Regel. Besides the used toxins, also the effect of their concentrations and incubation period as well as plant genotypes and material was tested. We observed micronuclei (MNi) in pollen mother cells, dyads and tetrads as well as other abnormalities such as ball metaphases and chromosome bridges. The flower position on the spadix and the type of starting material (dissected anthers vs. complete spadices) did not significantly influence micronucleation frequencies. The highest micronucleation index of 86 % was obtained in microspores treated with 10 μM ORY during 72 h. All six genotypes tested formed micronuclei after this particular treatment, although the efficiency varied between cultivars. Next to ORY, CIPC was also a very efficient MNi inducer. The average number of MNi found in micronucleated cells varied between 1.67–6.44 for CIPC and 0.83–5.50 for ORY. The maximal number of MNi observed was 12 for CIPC and 9 for ORY. Our results demonstrate that CIPC and ORY can be applied for mass micronucleation on developing microspores of S. wallisii as a first step of MMCT in aroid interspecific or intergeneric breeding.     

Comparative QTL analysis of root lesion nematode resistance in barley

Key message

This study demonstrates for the first time that resistance to different root lesion nematodes ( P. neglectus and P. penetrans ) is controlled by a common QTL. A major resistance QTL ( Rlnnp6H ) has been mapped to chromosome 6H using two independent barley populations.

Abstract

Root lesion nematodes (Pratylenchus spp.) are important pests in cereal production worldwide. We selected two doubled haploid populations of barley (Igri × Franka and Uschi × HHOR 3073) and infected them with Pratylenchus penetrans and Pratylenchus neglectus. Nematode multiplication rates were measured 7 or 10 weeks after infection. In both populations, continuous phenotypic variations for nematode multiplication rates were detected indicating a quantitative inheritance of resistance. In the Igri × Franka population, four P. penetrans resistance QTLs were mapped with 857 molecular markers on four linkage groups (2H, 5H, 6H and 7H). In the Uschi × HHOR 3073 population, eleven resistance QTLs (P. penetrans and P. neglectus) were mapped with 646 molecular markers on linkage groups 1H, 3H, 4H, 5H, 6H and 7H. A major resistance QTL named Rlnnp6H (LOD score 6.42–11.19) with a large phenotypic effect (27.5–36.6 %) for both pests was mapped in both populations to chromosome 6H. Another resistance QTL for both pests was mapped on linkage group 5H (Igri × Franka population). These data provide first evidence for common resistance mechanisms against different root lesion nematode species. The molecular markers are a powerful tool for the selection of resistant barley lines among segregating populations because resistance tests are time consuming and laborious.     

High-frequency generation and characterization of intergeneric hybrids and haploids from new wheat–barley crosses

Key message

Hybrid plants and a high frequency of maternal haploids were obtained using an efficient wheat–barley hybridization system (with new genotype combinations) and confirmed by several cytological and molecular tools.

Abstract

An efficient hybridization system between wheat (Triticum aestivum L.) and barley (Hordeum vulgare L.) is presented on the basis of three new genotype combinations. A particularly high, 14 % frequency of plant regeneration per florets was achieved in the wheat–barley genotype combination of ‘Sichuan’ × ‘Morex’. The genome composition in 42 of the 95 plants regenerated by embryo rescue was determined using ploidy analysis, genomic in situ hybridization and the application of chromosome arm-specific molecular markers (SSR and STS). A high overall frequency (76 %) of maternal (wheat) haploids was observed in all the tests for all three cross combinations. A major implication of this observation is that this new hybridization system represents a useful tool to study the mechanism of uniparental chromosome elimination in cereals.     

Initiation of embryogenesis from cultured barley microspores: a further investigation into the toxic effects of sucrose and glucose

The toxic effects of sucrose and glucose upon Hordeum vulgare L. ev Igri microspore cultures were investigated. It was concluded from this study that:

-microspores could be cultured in the presence of low concentrations of glucose without any deleterious effects upon cell viability, but the microspores did not form embryos or calluses.

-microspores died when incubated in the presence of 40 mM glucose during the first 2 of days of incubation, but, if glucose was added after this period, cells went on to produce embryos or calluses.

-the toxic effects of sucrose upon cultured microspores were irreversible after 6 h from the start of incubation. Implications of these results on underlying causes of cell death in the presence of sucrose and glucose are discussed.

     

Prehistoric settlement activities changed soil pH, nutrient availability, and growth of contemporary crops in Central Europe

Background and aims

How prehistoric human settlement activities have changed soil chemical properties, plant nutrition and growth of contemporary crops is a question that has not been satisfactorily addressed. The aim of this paper was to study to what extent nutrient availability in the soil, together with nutrition and growth of spring barley (Hordeum vulgare), improved on sites of former sunken buildings (cropmarks) in comparison to their surroundings (controls) 1,700 years after abandonment of the buildings.

Methods

In the Czech Republic, a unique prehistoric settlement with many sunken buildings was discovered during aerial reconnaissance from cropmarks in stands of cereals. Soil and biomass samples were collected from cropmarks and controls in a barley crop in June 2012.

Results

A substantially higher content of organic matter, higher pH and concentrations of plant-available (Mehlich III) P, Ca, Mg, Cu and Zn were recorded in the sub-soil layer in cropmarks compared with controls, indicating the accumulation of wood ash and organic waste. In the arable layer, pH and concentrations of P, Ca and Mg were generally very high in both positions. Cropmarks were characterised by barley plants that were twice as tall as the controls, with significantly higher Ca, Mg and P concentrations.

Conclusions

Prehistoric settlement activity affected nutrient availability and plant growth in the previously settled area even after 1,700 years. We conclude that the chemical signature of prehistoric settlement activity can be detected from chemical analysis of the sub-soil layer as well as analysis of the contemporary arable layer and crop biomass.     

A comparison of barley isolated microspore and anther culture and the influence of cell culture density

Comparisons were made between the efficiency of barley plant regeneration from anther culture (AC) and isolated microspore culture (IMC) for the European winter cultivar `Igri' and the spring F<sub>1</sub> Australian breeder's hybrid Amagi Nijo×WI2585. In both cases, IMC produced a higher number of green regenerant plantlets per anther than AC. For `Igri' there was a 100- to 200-fold improvement and for Amagi Nijo×WI2585 there was a five- to ninefold improvement of IMC over AC. To improve the consistency and reliability of the IMC method, we investigated several parameters, including maltose concentration, subculture protocol, microspore plating density and colony plating density. Subculturing during the liquid culture phase produced no significant improvement in the number of microspores developing into colonies. The optimal concentration of maltose in the liquid induction medium was found to be 90 g l^–1. Both microspore plating density and colony plating density were found to influence plant regeneration. Microspores produced the highest numbers of colonies when plated at densities greater than 5×10⁴ ml^–1, and colonies produced optimal numbers of green plantlets when plated at 12.5–25 colonies/cm². Received: 23 March 1997 / Revision received: 29 May 1997 / Accepted: 25 June 1997     

Golden SusPtrit: a genetically well transformable barley line for studies on the resistance to rust fungi

Key message

We developed ‘Golden SusPtrit’, i.e., a barley line combining SusPtrit’s high susceptibility to non-adapted rust fungi with the high amenability of Golden Promise for transformation.

Abstract

Nonhost and partial resistance to Puccinia rust fungi in barley are polygenically inherited. These types of resistance are principally prehaustorial, show high diversity between accessions of the plant species and are genetically associated. To study nonhost and partial resistance, as well as their association, candidate gene(s) for resistance must be cloned and tested in susceptible material where SusPtrit would be the line of choice. Unfortunately, SusPtrit is not amenable to Agrobacterium-mediated transformation. Therefore, a doubled haploid (DH) mapping population (n = 122) was created by crossing SusPtrit with Golden Promise to develop a ‘Golden SusPtrit’, i.e., a barley line combining SusPtrit’s high susceptibility to non-adapted rust fungi with the high amenability of Golden Promise for transformation. We identified nine genomic regions occupied by resistance quantitative trait loci (QTLs) against four non-adapted rust fungi and P. hordei isolate 1.2.1 (Ph.1.2.1). Four DHs were selected for an Agrobacterium-mediated transformation efficiency test. They were among the 12 DH lines most susceptible to the tested non-adapted rust fungi. The most efficiently transformed DH line was SG062N (11–17 transformants per 100 immature embryos). The level of non-adapted rust infection on SG062N is either similar to or higher than the level of infection on SusPtrit. Against Ph.1.2.1, the latency period conferred by SG062N is as short as that conferred by SusPtrit. SG062N, designated ‘Golden SusPtrit’, will be a valuable experimental line that could replace SusPtrit in nonhost and partial resistance studies, especially for stable transformation using candidate genes that may be involved in rust-resistance mechanisms.     

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.     

Identifying the critical period for waterlogging on yield and its components in wheat and barley

Background and aims

Crop tolerance to waterlogging depends on factors such as species sensitivity and the stage of development that waterlogging occurs. The aim of this study was to identify the critical period for waterlogging on grain yield and its components, when applied during different stages of crop development in wheat and barley.

Methods

Two experiments were carried out (E1: early sowing date, under greenhouse; E2: late sowing date, under natural conditions). Waterlogging was imposed during 15–20 days in 5 consecutive periods during the crop cycle (from Leaf 1 emergence to maturity).

Results

The greatest yield penalties occurred when waterlogging was applied from Leaf 7 appearance on the main stem to anthesis (from 34 to 92 % of losses in wheat, and from 40 to 79 % in barley for E1 and E2 respectively). Waterlogging during grain filling reduced yield to a lesser degree. In wheat, reductions in grain number were mostly explained by reduced grain number per spike while in barley, by variations in the number of spikes per plant.

Conclusions

The time around anthesis was identified as the most susceptible period to waterlogging in wheat and barley. Exposing the crop to more stressful conditions, e.g. delaying sowing date, magnified the negative responses to waterlogging, although the most sensitive stage (around anthesis) remained unchanged.