Genetic diversity and population structure of wild and cultivated barley from West Asia and North Africa

Population structure and relationships within and among 185 accessions of wild (Hordeum vulgare ssp. spontaneum) and cultivated barley (H. v. ssp. vulgare) from five countries in the West Asia and North Africa (WANA) region were studied using 36 simple sequence repeat (SSR) markers. The accessions were divided into subspecies/origin (S/O)‐groups and marker results were analysed in relation to genetic diversity and genetic structure. Wild barley from WANA was found to be highly diverse. The landraces from different countries of the Near East showed genetic diversity that was nearly as high as the wild barley from the same country. Further analyses showed that wild barley from Palestine/Israel represented the group with the highest diversity and the most complex structure. However, this group was distantly related to the cultivated barley in WANA, while the wild barley from the rest of the WANA region was closely related to the cultivated WANA barley. The high diversity and the close relationship to the wild barley make the WANA landraces an interesting genetic resource for both conservation and exploitation.     

Diversity and geographical distribution of seed lipoxygenase‐1 thermostability types in barley

To understand the diversity in the thermostability of the seed lipoxygenase‐1 (LOX‐1), 1040 cultivars of worldwide barley (Hordeum vulgare ssp. vulgare) genetic resources were investigated. The relative thermostability of LOX‐1 (LOX‐RTS) in these lines showed a bimodal frequency distribution and these lines were categorized into the high and low thermostability types (H‐type and L‐type, respectively). The H‐type lines predominated in the wild progenitor, ssp. spontaneum. The geographical distribution of these types in the cultivars was surveyed. The frequencies of the H‐ and L‐types were almost equal to one another in southwestern Asia. The occurrence of the H‐type predominated in eastern Asia and Africa, whereas in Europe and Turkey, the L‐type did. The predominance of the L‐type in Europe and Turkey can be understood through the hypothesis that the Fertile Crescent domestication contributed the majority of diversity in Europe. The uneven geographical distribution of the LOX‐1 thermostability types in the cultivars may reflect a polyphyletic origin of barley.     

A novel barley scald resistance gene: genetic mapping of the Rrs15 scald resistance gene derived from wild barley, Hordeum vulgare ssp. spontaneum

Most genes for resistance to barley leaf scald map either to the Rrs1 locus on the long arm of chromosome 3H, or the Rrs2 locus on the short arm of chromosome 7H. Other loci containing scald resistance genes have previously been identified using lines derived from wild barley, Hordeum vulgare ssp. spontaneum. A single dominant gene conditioning resistance to scald was identified in a third backcross (BC3F3) line derived from an Israeli accession of wild barley. The resistance gene is linked to three microsatellite markers that map to the long arm of chromosome 7H; the closest of these loci, HVM49, maps 11.5 cM from the resistance gene. As no other scald resistance genes have been mapped to this chromosome arm, it is considered to be a novel scald resistance locus. As the Acp2 isozyme locus is linked to this scald resistance locus, at 17.7 cM, Acp2 is assigned to chromosome 7H. Molecular markers linked to the novel scald resistance gene, designated Rrs15, can be used in breeding for scald resistance.     

Screening for resistance in the primary and secondary gene pool of barley against the root-lesion nematode Pratylenchus neglectus

Root-lesion nematodes of the genus Pratylenchus are significant pests in crop cultivation throughout many parts of the world. A study was initiated to determine the resistance of Hordeum vulgare and H. vulgare ssp. spontaneum (wild barley) against one major representative of the genus Pratylenchus , P. neglectus . A glasshouse test was first established. Barley seedlings were grown in 20 cm³ tubes filled with sand. Each plant was inoculated with 400 P. neglectus juveniles. After 12 weeks of cultivation nematodes were isolated from roots and sand using a misting chamber. The nematodes were counted under a microscope. A representative collection of 565 barley and wild barley accessions was tested in this way. The average number of nematodes per accession ranged from 350 to 12 000. In a verification experiment, 35 accessions with low and high infection rates were tested. This experiment identified a number of accessions with low infection rates. The perspectives for future breeding of barley cultivars resistant to root-lesion nematodes are discussed.     

Genetic regulation of growth and nutrient content under phosphorus deficiency in the wild barley introgression library S42IL

Phosphorus (P) is an important macronutrient required for plant growth and yield formation. Since decades, breeders aim to optimize P efficiency in crops. We studied a set of 47 wild barley (Hordeum vulgare ssp. spontaneum, Hsp) introgression lines (ILs) in hydroponic culture to identify quantitative trait loci (QTLs) improving growth and nutrient content under P deficiency. Applying a mixed model analysis, a total of 91 independent QTLs were located among 39 ILs, of which 64 QTLs displayed trait‐improving Hsp effects. For example, an unknown Hsp allele on barley chromosome 4H increased shoot dry weight under P deficiency in three overlapping ILs by 25.9%. Likewise, an Hsp allele on barley chromosome 6H increased root dry weight under P deficiency in two overlapping ILs by 27.6%. In total, 31 QTLs confirmed Hsp effects already identified in previous field and glasshouse experiments with the same ILs. We conclude that wild barley contains numerous trait‐improving QTL alleles, which are active under P deficiency. In future, the underlying genes can be subjected to cloning and, simultaneously, used in elite barley breeding.     

Mapping of Malt Endopeptidase, NADH Diaphorase and Esterase Loci on Barley Chromosome 3L

Isoelectric focusing (IEF) and immunoblotting were used to detect genetic variants of malt endopeptidase (MEP1), an enzyme related to malting quality in barley and coded by the CepB locus on barley chromosome 3 (= 3H). A variant was found in a Turkish accession of wild barley (Hordeum vulgare ssp. spontaneum). The self progeny of a hybrid between this accession and the barley cultivar ‘Clipper’ were analyzed for recombination between the CepB locus and other isozyme loci. The estimates of recombination linked the CepB locus to an NADH diaphorase locus (Ndh2), which in turn was linked to the seedling esterase complex (Est1, Est2, and Est4) situated near the distal end of the long arm of chromosome 3. The Ndh2 locus was independent of two other NADH dehydrogenase loci (Ndh3, Ndh5) which were mapped on barley chromosome 5 (= 1H) in relation to the three hordein loci (Hor1, Hor2, and Hor3).     

Variation in utilization efficiency and tolerance to reduced water and nitrogen supply among wild and cultivated barleys

Broad genotypic variation in the response to low soilmoisture and reduced nitrogen supply was found amongthe wild Hordeum spontaneum accessions and thelandraces and modern cultivars of H. vulgare ofdifferent geographic origin. Measurements at the endof vegetative growth in plants grown in soil culturesrevealed genotypically specific responses to the usedenvironmental factors. Cultivars and breeding linesfrom Syria and Ethiopian landraces combined bothdrought resistance and tolerance to low nitrogen. TheSyrian barleys were also distinguished by a highnitrogen utilization efficiency (NUE) under low Nnutrition. European cultivars indicated a pooradaptation to N shortage, but some of them wereresistant to soil drought. No stress resistant barleyswere found among the wild accessions and Sardinianlandraces. Genotypic differences in the relativevalues of NUE and water use efficiency were associatedwith low N-tolerance. Some Syrian selections,Ethiopian landraces and the modern German cv. Maresiwere found to be most drought resistant. Maintenanceof a relatively high photosynthetic activity of theuppermost leaves was associated with droughtresistance. As far as concerning with the vegetativegrowth phase, the modern Syrian germplasm andEthiopian landraces may be recommended as donors ofadaptative characters for local barley breeding.     

Endosperm protein accumulation in wild and cultivated barley and their cross grown in spike culture

Summary The high protein wild relatives of cultivated cereals have proven difficult to utilize in plant breeding by direct selection for high grain protein percentage, and hence alternative selection criteria are needed. In this study, a spike culture method was used to measure differences in protein accumulation between wild and cultivated barley, and their cross, at different levels of nitrogen supply. Three genotypes, barley cultivar Hordeum vulgare L. cv. Clipper, a wild barley accession H. spontaneum Koch line 363, and a high protein F₅ line (38.4) derived from their cross, were grown from 8 to 27 days after flowering in in vitro spike culture. Nitrogen supply in the culture medium was either 0.4 g/l or 2.0 g/l of N supplied as NH₄NO₃. Spikes were harvested at approximately 3 day intervals during grain development, and salt soluble and hordein protein fractions were measured. Lines 363 and 38.4 differed from Clipper in having extremely high initial rates of protein accumulation, even at 0.4 g/l N. In high nitrogen conditions all three genotypes reached similar salt soluble plus hordein protein levels. Hordein-1 and hordein-2 fractions were measured separately; the percent of hordein-1 was higher in lines 363 and 38.4 than in Clipper at 0.4 g/l N. For all parameters measured, pot-grown spikes of matching age were harvested and were shown to be similar to the 0.4 g/l N treatment. The possible utilization of spike culture for identification of critical protein accumulation parameters is discussed, in relation to their possible utilization in breeding.     

Associations of simple sequence repeats with quantitative trait variation including biotic and abiotic stress tolerance in Hordeum spontaneum

A total of 33 simple sequence repeats (SSRs) was analyzed in 52 genotypes of Hordeum spontaneum originally collected from two different soil types (Terra rossa and Basalt) at Tabigha in Israel. Data on the performance of developmental, morphological, and yield‐related traits under well‐watered control and water‐stress conditions were available from previous experimentation, and powdery mildew susceptibility was scored. Regression analyses based on SSR allele class differences were performed. Highly significant associations were detected at the SSR loci Bmac181 (on chromosome 4H) and Bmac316 (6H) for water ‐stress tolerance and powdery mildew resistance, respectively. The study shows that association mapping using SSRs and genetically diverse germplasm provides an effective means of relating genotypes to complex quantitative phenotypes.     

Genetic mapping of the barley Rrs14 scald resistance gene with RFLP, isozyme and seed storage protein markers

The scald susceptible barley cultivar ‘Clipper’ and a third‐backcross (BC₃) line homozygous for the Rrs14 scald resistance gene that originally came from Hordeum vulgare ssp. spontaneum were grown in replicated field trials. The level of resistance that Rrs14 confers against field populations of the pathogen Rhynchosporium secalis, the causal agent of scald disease, was evaluated. The Rrs14 BC₃ line exhibited 80% and 88% less leaf damage than ‘Clipper’ in 1995 and 1996, respectively. Given this effectiveness of Rrs14, research was undertaken to identify a linked marker locus suitable for indirect selection of Rrs14. Based on linkage to a set of previously mapped loci, Rrs14 was positioned to barley chromosome 1H between the seed storage protein (hordein) loci Hor1 and Hor2, approximately 1.8 cM from the latter locus. The Hor2 locus is thus an ideal codominant molecular marker for Rrs14. The tight linkage between Rrs14 and Hor2 and the availability of alternative biochemical and molecular techniques for scoring Hor2 genotypes, permits simple indirect selection of Rrs14 in barley scald resistance breeding programmes.     

Characterization and mapping of gene Rph19 conferring resistance to Puccinia hordei in the cultivar 'Reka 1' and several Australian barleys

Previous studies established that the Australian barley cultivar ‘Prior’ possessed resistance to Puccinia hordei (RphP), displaying the same specificity as an uncharacterized resistance in the differential cultivar ‘Reka 1’ (also possessing Rph2). Multipathotype tests confirmed the presence RphP in nine additional barley cultivars and indicated that RphP differed in specificity to the genes Rph1 to Rph15 and Rph18, plus the gene RphX present in the barley cultivar ‘Shyri’. RphP was inherited as a single dominant gene. Mapping studies using a doubled haploid population derived from ‘Chebec’/‘Harrington’ located RphP to the long arm of chromosome 7H, and demonstrated linkage with an restriction fragment length polymorphism marker (pTAG732), a resistance gene analogue marker (RLch4(Nc)), and two microsatellite markers (HVM11 and HVM49) at genetic distances of about 4‐10 cM. RphP showed linkage of 28 ± 4.3 cM with Rph3. RphP was designated Rph19, with the allele designation Rph19.ah. Previous studies have established that virulence for Rph19 occurs in many barley growing regions of the world.     

Genetic variation for dry matter and nitrogen accumulation and translocation in two-rowed spring barley: I. Dry matter translocation

A 4-year field study was carried out to determine dry matter and nitrogen accumulation until anthesis and at grain filling period and dry matter translocation and utilization in grain filling of barley. Twenty two-rowed spring barley (Hordeum vulgare ssp. distichum L.) cultivars originated from different countries (Yugoslavia, Germany, Australia, the Czeck Republic, Netherlands, France and USA) were grown during 1995–1998 on a non-calcareous chernozem soil near Novi Sad (45° 20′N, 15° 51′E, 86 m asl). Dry matter and nitrogen accumulation depended on the cultivar and year. In a year with favorable weather conditions, 58% of dry matter was accumulated during pre-anthesis, while in a year with less favorable weather the amount was 48%. In the favorable year 91% and in unfavorable year 65% of nitrogen was accumulated until anthesis. The results indicated that the greater amount of dry matter and nitrogen accumulated before anthesis. Dry matter translocation efficiency depended on the cultivar and ranged from 3 to 16.4%, while the contribution of pre-anthesis assimilates to kernel varied from 4 to 24.2%. Cultivars that have been developed for the growing conditions of the area where the experimental site was located, i.e. adapted ones, did not use pre-anthesis dry matter for grain filling. High positive correlations (P<0.01) were found between biomass at anthesis and biological yield, dry matter translocation efficiency, contribution of translocated dry matter to grain yield, and total plant nitrogen at maturity. Accumulated nitrogen at anthesis was positively correlated (P<0.01) with growing degree–days until anthesis, dry matter at anthesis and dry matter translocation parameters. Heritability for the investigated characters was rather high, over 0.60.     

Regional distribution of resistances to powdery mildew in winter and spring barley cultivars grown in the northern part of France

The spatio-temporal distribution of race-specific resistances to powdery mildew was analysed in northern France (the east, the north and the west of Paris). Resistances were identified in 26 winter and six spring barley cultivars. Seedling leaf segments were inoculated with 20 powdery mildew isolates, chosen to identify 14 resistance alleles. As opposed to other European countries, the resistance alleles differed between winter and spring cultivars grown in the three regions. Most of the winter cultivars had no resistance allele, or only the widespread resistance alleles Mlra and/or Mlh, plus Mlg in the west. Mla9 and Mla13 were also present in the north, but at a low frequency. Spring cultivars carried the alleles Mla7, Mla9, Mla12, Mlk, Mlg or MlLa in the east, where a diversification of resistances has occurred since 1987, particularly because of the use of ‘Volga’ (Mla7, Mlk, Mlg and MlLa). In the north and the west, Mla12 dominated after a decrease in the frequency of Mla7, Mla13 has recently been introduced in the north and the west with the cultivar ‘Vodka’.     

Role of male-sterile cytoplasm in resistance to barley yellow mosaic virus and Fusarium head blight in barley

Two types of male‐sterile cytoplasm, designated msm1 and msm2, in barley were investigated to determine whether these cytoplasms confer resistance to barley yellow mosaic virus (Ba YMV) and Fusarium head blight (FHB). Alloplasmic lines and isogenic lines of two cultivars showed the same reaction to each Ba YMV as that of their euplasmic lines. This demonstrates that the barley male‐sterile cytoplasms msm1 and msm2 have no effect on resistance to BaYMV. No significant difference in reactions to FHB was recognized among fertile alloplasmic lines of ‘Adorra’, but the difference in reactions to FHB between fertile and sterile isogenic lines of ‘Adorra’ was significant. The damage caused by FHB in the male‐sterile lines that produced sterile pollen was significantly greater than the damage in a sterile line that did not produce pollen. These results suggest that pollen or anthers are important factors in infection with or spread of FHB. For production of hybrid seeds, male‐sterile lines with no pollen production, such as those with msm1 male‐sterile cytoplasm, would reduce FHB infestation.     

Variation in developmental patterns of wild barley (Hordeum spontaneum L.) and cultivated barley (H. vulgare L.)

Summary Six wild barley (Hordeum spontaneum) accessions, from a diverse range of habitats, and two spring-cultivated barleys, were examined for variation in durations of development phases. The durations of the leaf initiation and spikelet initiation phases were longer and spikelet growth phases shorter, in wild than in cultivated barley. Across all wild and cultivated barleys the rate and duration of spikelet initiation were negatively correlated, but neither was related to the number of spikelets per spike. The number of spikelets was positively correlated with the number of leaves and the ratio of the number of spikelets to the number of leaves declined with increasing time to anthesis, indicating that each successive leaf was associated with a diminishing increase in the number of spikelets. The duration of culm elongation and final culm length were shorter in accessions of cultivated barley compared with wild barley. This paper also discusses the feasibility for increasing the number of spikelets per spike through breeding for genetic changes in lengths of pre-anthesis phases of development.Abbreviations ANOVA Analysis of variance - HV Hordeum vulgare - CE Culm elongation - DR Double ridge - HS Hordeum spontaneu - ° Cd Degree days     

Possibility of exploiting the Yd2 resistance to BYDV in spring barley breeding

The effects of the Yd2 gene on tolerance to barley yellow dwarf virus (BYDV) and other agronomically important characters in spring barley were evaluated in a set of randomly selected doubled haploid (DH) lines of an‘Igri’/‘Atlas 68’ cross and three crosses between CIMMYT Yd2 materials and the Czech malting barley ‘Akcent’. The cleaved amplified polymorphic site (CAPS) diagnostic marker Yd2 was used for identification of the Yd2 gene and this analysis showed high agreement with the results of field infection tests. Yd2 lines exhibited significantly lower symptom scores and lower reductions of some grain yield characters, but their resistance level was not consistent over the years. The presence of secondary stresses (high temperature/drought) in 2000 led to relatively higher sensitivity to BYDV infection, strengthened by the long life cycle of genotypes. In cases where secondary stresses were mild (in 2002), the longer life cycle significantly increased sensitivity to BYDV infection only in the absence of the Yd2 gene (in susceptible genotypes). The examination of different vegetative, grain yield and malting quality characters separately for groups of Yd2 and non‐ Yd2 lines did not show any evidence of adverse effect of the Yd2 gene on any character.     

Inheritance of plant height and allelism tests of the dwarfing genes in Chinese barley

In order to find new dwarfing genes, the inheritance of plant height in 25 Chinese barley dwarf accessions was studied and allelism tests carried out, not only between the dwarfing genes found but also with the known dwarfing genes uz, br, sdw and denso. The results showed that out of the 25 dwarf accessions, 20 were due to monogenic recessiveness and four to digenic recessiveness. Only the short plant character in ‘1974E’ was controlled by a recessive together with a dominant dwarfing gene. In the present study, seven recessive and one dominant new dwarfing genes were identified. Five recessive genes were found in the monogenic mutants ‘91G318’, ‘91D27’ and ‘93‐597’ and in the Tibetan monogenic dwarf landraces ‘Jia Jiu’ and ‘BQK’, respectively. The other two recessives were found in the Tibetan digenic dwarf landraces ‘ZLL’ and ‘ZLLQK’, and the one dominant gene in the digenic mutant ‘1974E’.     

Identification of RAPD markers closely linked to the mlo-locus in barley

Developing resistance to powdery mildew, Erysiphe graminis f.sp. hordei, is a major goal of many barley breeding programmes. Several resistance genes have been tagged or mapped with molecular markers. The mlo gene confers durable resistance towards all known isolates of the pathogen. In this study, RAPD markers and bulked segregant analysis were used to determine PCR-based markers linked to the mlo-locus. Sixty doubled haploid lines from a cross between an isogenic line of ‘Ingrid’ carrying the mlo11 allele and a susceptible cv. ‘Pokko’ were used as plant material. Seven linked RAPD markers were found, the closest lying 1.6 cM away from the resistance gene. When eight barley varieties were assayed for the presence of this band, F4-980, it was found in the resistant varieties but not in the susceptible ones. The linked marker bands could be amplified from DNA-samples prepared by using three different methods, including a quick squash technique. PCR-based markers linked to the resistance gene can be used as tools for selection in breeding programmes.     

Evaluation of quantitative resistance to yellow rust (Puccinia striiformis f. sp. hordei) in the ICARDA/CIMMYT barley breeding programme

The resistance to yellow rust (Puccinia striiformis f. sp. hordei) of 500 advanced barley lines from the ICARDA/CIMMYT breeding programme in Mexico was evaluated on seedlings in the greenhouse and on adult plants in the field. A high frequency of advanced lines (85.8%) showed a susceptible reaction (infection type ≥ 7) on seedlings after inoculation with isolate Mex-1, representing a Mexican variant of race 24. This indicates the absence of effective hypersensitive resistance. In addition, the same advanced lines showed a large variation in disease severity in the field, ranging from 0 to 95%. More than 76% of the advanced lines with a susceptible reaction in the seedling stage demonstrated low disease severity (10% or less in the adult plant). Consequently, these advanced lines possess high levels of quantitative resistance. Two aspects in the ICARDA/CIMMYT barley breeding programme may explain the large number of advanced lines with high levels of quantitative resistance. First, a recurrent selection approach is applied when advanced (F₅) lines reaching homozygosity are intercrossed. Second, low levels of disease are accepted in the selection process instead of selecting the ultimate green plant. Both aspects combined allow the accumulation of quantitative resistance. Certain cultivars released from South-American national programmes in the late 1970s and early 1980s in Peru (UNA-80), Bolivia (IBTA 80) and Ecuador (Teran) are still resistant, demonstrating the durable nature of quantitative resistance to yellow rust.     

Resistance to powdery mildew in a doubled haploid barley population and its association with marker loci

The genetic basis of resistance to powdery mildew (Erysiphe graminis DC. f.sp. hordei Marchal) was analyzed using doubled haploid barley (Hordeum vulgare L.) lines from the cross Harrington/TR306. Based on infection types observed after inoculation with defined single-conidium isolates, the lines were classified into four groups. The observed phenotypic ratio fit a two-locus model. The two putative loci were mapped relative to molecular markers. One coincided with the previously mapped dMlg locus on chromosome 4. Based on the observed infection types, Harrington carries the Mlg resistance allele, and TR306 carries a second locus on chromosome 7 (5H); this was tentatively designated Ml(TR). It is the first reported race-specific powdery mildew resistance gene located on that chromosome. These two loci were also detected by simple interval mapping of disease severity data from naturally infected field plots. Composite interval mapping with the first two resistance loci as co-factors detected an additional locus on chromosome 6, with a minor effect on resistance. Finally, superimposing the race-specific classification onto the field data provided evidence for a minor-effect locus on chromosome 7 (5H). The Mlg locus had the largest effect, the Ml(TR) locus had an intermediate effect and the other two loci had very small effects. This study demonstrates the effectiveness of an integrated approach to identifying and mapping resistance loci using classification data from inoculated experiments and quantitative data from field experiments. This revised version was published online in July 2006 with corrections to the Cover Date.