Chromosome Substitution Lines Research Articles

Genetic changes in plant growth and their associations with chromosomes from Gossypium barbadense L. in G. hirsutum L

Cotton (Gossypium spp.) plant growth is an important time-specific agronomic character that supports the development of squares, flowers, boll retention, and yield. With the use of a mixed linear model approach, we investigated 14 cotton chromosome substitution (CS-B) lines and their chromosome-specific F(2) hybrids for genetic changes in plant growth that was measured during the primary flowering time under two environments. The changes in additive and dominance variances for plant height and number of mainstem nodes are reported, showing that additive effects for these two traits were a key genetic component after initial flowering occurred in the field. Time-specific genetic variance components were also detected where phenotypic values observed at time t were conditioned on the events occurring at time t - 1, demonstrating new genetic variations arising at several time intervals during plant growth. Results also revealed that plant height and number of nodes shared some common influence due to additive effects during plant development. With the comparative analyzes, chromosomes associated with the genetic changes in plant growth were detected. Therefore, these results should add new understanding of the genetics underlying these time-specific traits.

Development and mapping of DArT markers within the Festuca - Lolium complex

BackgroundGrasses are among the most important and widely cultivated plants on Earth. They provide high quality fodder for livestock, are used for turf and amenity purposes, and play a fundamental role in environment protection. Among cultivated grasses, species within the Festuca-Lolium complex predominate, especially in temperate regions. To facilitate high-throughput genome profiling and genetic mapping within the complex, we have developed a Diversity Arrays Technology (DArT) array for five grass species: F. pratensis, F. arundinacea, F. glaucescens, L. perenne and L. multiflorum.ResultsThe DArTFest array contains 7680 probes derived from methyl-filtered genomic representations. In a first marker discovery experiment performed on 40 genotypes from each species (with the exception of F. glaucescens for which only 7 genotypes were used), we identified 3884 polymorphic markers. The number of DArT markers identified in every single genotype varied from 821 to 1852. To test the usefulness of DArTFest array for physical mapping, DArT markers were assigned to each of the seven chromosomes of F. pratensis using single chromosome substitution lines while recombinants of F. pratensis chromosome 3 were used to allocate the markers to seven chromosome bins.ConclusionThe resources developed in this project will facilitate the development of genetic maps in Festuca and Lolium, the analysis on genetic diversity, and the monitoring of the genomic constitution of the Festuca × Lolium hybrids. They will also enable marker-assisted selection for multiple traits or for specific genome regions.

Genetic analysis of seed dormancy QTL in barley

Seed dormancy in wild barley enables drought escape by preventing germination during the hot summer in arid environments. Dormancy in cultivated barley has different effects: it can delay the malting process and/or it can prevent pre-harvest sprouting. Thus, cloning dormancy genes in barley will contribute to understanding the domestication process and it will facilitate optimizing the trait for efficient agronomic and industrial uses. Rates of seed germination were used to evaluate dormancy on physiologically matured grain samples that were dried and stored frozen until use. With this phenotypic scoring procedure, many genetic factors controlling seed dormancy has been reported as quantitative trait loci (QTL). Of these QTL, one at the centrometic region of chromosome 5H (Qsd1) has been most frequently identified and shows the largest effect across mapping populations. We also identified this QTL using the EST map based on Haruna Nijo (H. vulgare ssp. vulgare) crossed with wild barley H602 (H. vulgare ssp. spontaneum). We have derived both doubled haploid and recombinant chromosome substitution lines (RCSLs) from this cross. At least four QTLs are segregating in this germplasm. RCSLs having only the Qsd1 segment of wild barley in a Haruna Nijo genetic background were identified and 910 BC3F2 plants were scored for dormancy. In these lines, segregation for dormancy fit a mono-factorial ratio. These germplasm resources are appropriate for map based cloning of Qsd1. Strategies for cloning Qsd1 with these resources are discussed.

Molecular mapping of SKr for crossability in common wheat

The crossability of common wheat with alien species, e.g., rye, wild and cultivated barley, is known to be controlled by the Kr gene family. The reproduction barrier caused by Kr genes decreases hybrid seed set; however, the molecular mechanism is still unclear. We attempted to localize the QTLs controlling the crossability of wheat in wheat-rye crosses by using molecular markers on wheat chromosome 5B on which the most effective Kr gene is known to be located. QTL mapping was carried out using the F7 population derived from a cross between Chinese Spring (high crossability) and a chromosome substitution line of Chinese Spring which has its chromosome 5B of Cheyenne (low crossability), and pollinated with rye cv. Petkus. In this population, a major QTL region controlling crossability with rye was detected on the locus closely linked to a SSR marker, Xgwm443, on the short arm of chromosome 5B which was supposed to be Skr locus.

Association mapping of plant height, yield, and yield stability in recombinant chromosome substitution lines (RCSLs) using Hordeum vulgare subsp. spontaneum as a source of donor alleles in a Hordeum vulgare subsp. vulgare background

Grain yield and plant height of 80 recombinant chromosome substitution lines (RCSLs) of barley were measured in six environments with contrasting available moisture profiles. Two environments were in OR, USA (Moro and Pendleton) during one growing season (2004), and four in Chile (Cauquenes and Santa Rosa) during two growing seasons (2004/2005 and 2007/2008). From the yield data obtained in the different environments, yield adaptability (Finlay–Wilkinson slope) and stability (deviations from regression) were calculated. Two commercial cultivars (Harrington and Baronesse) were used as checks in all environments. Marker-quantitative trait associations were identified using 47 simple sequence repeats (SSRs) and the general linear model (GLM) implemented in TASSEL. The mean plant height and grain yield of the 80 RCSLs differed greatly across environments, reflecting differences in water availability. In all environments, there were significant differences (P < 0.05) in grain yield among RCSLs. There was also abundant variation in yield adaptability, indicating a differential response of the RCSLs to environmental conditions across environments. Using principal component analysis, it was possible to identify genotypes with better agronomic performance than the recurrent parent cv. Harrington. The association analysis revealed 21 chromosomal regions that were highly correlated with differences in grain yield, plant height and/or yield adaptability (Finlay–Wilkinson slope). In approximately one-fourth of the cases, the H. spontaneum donor contributed favorable alleles. The associations were referenced to the quantitative trait loci (QTL) for the same traits reported in the literature.

Genetic analysis of agronomic and fibre traits using four interspecific chromosome substitution lines in cotton

AbstractBackcrossed chromosome substitution lines (CS‐B) have been developed with a homologous pair of chromosomes or chromosome arms of Gossypium barbadense (3‐79) germplasm substituted for the homologous Gossypium hirsutum(TM‐1) chromosomes or chromosome segments. We report on agronomic and fibre trait performance of four backcrossed chromosome or chromosome arm substitution lines including chromosomes 01, 11sh (chromosome 11 short arm), 12 sh and 26 Lo (chromosome 26 long arm). Data for agronomic and fibre traits were collected from replicated field experiments at two different locations in 2 years, and analysed under an additive dominance genetic model. CS‐B 12sh had higher, while CS‐B 01 and CS‐B 26Lo had lower boll weight than TM‐1. The presence of significant negative additive effects for micronaire with CS‐B 01 and significant positive additive effects for elongation and fibre strength with CS‐B 11sh suggested the substituted chromosome arms of 3‐79 in these CS‐B lines were more likely carrying genes causing these effects. Results revealed that several CS‐B lines had significant homozygous and heterozygous dominance effects for different agronomic and fibre traits suggesting that specific CS‐B lines may be useful for improving agronomic and fibre traits in hybrid cottons. These CS‐B lines also provide novel genetic resources for improving upland cotton germplasm.

Genetic Effect on Yield and Fiber Quality Traits of 16 Chromosome Substitution Lines in Upland Cotton

Evaluation of the genetic effect on yield and fiber quality can provide useful information on cotton breeding. Sixteen CSB lines and TM-1 introduced from USDA/ARS were used as male and top-crossed with three elite cultivars and the 51 F 1 hybrids, 16 CSB lines, TM-1, and 3 elite cultivars were planted at the Cotton Research Institute of CAAS, Anyang, Henan Province and Xiajin, Shandong Province, China. The yield traits and fiber quality data were obtained and additive and dominance effect on each trait were measured by AD model. Boll weight takes the largest additive proration, whereas boll number takes the least additive proration. The largest and the least dominant proration for lint yield and boll weight were measured, respectively. Fiber length has the additive and dominance effect, and dominance effect was slightly more than additive effect. Larger additive and no dominance effect on uniformity, micronaire, and fiber strength were measured. Significantly, positive additive effect on boll weight of CSB06 and CSB12Sh was observed. CSB14Sh and CSB01 have significantly positive additive effect on 4 and 3 traits of fiber quality, respectively. CSB01 has the greatest dominant effect on lint yield among CSB lines. The dominant effect on fiber length of CSB lines showed positive. It is beneficial to use CSB06 and CSB12Sh as parents to improve boll size, to use CSB14Sh and CSB01 as parents to improve fiber quality. As for hybrid cotton breeding, it is reasonable using CSB01 to improve lint yield traits, and using CSB01, CSB11Sh, and CSB06 to improve fiber length.

Production of aneuhaploid and euhaploid sporocytes by meiotic restitution in fertile hybrids between durum wheat Langdon chromosome substitution lines and Aegilops tauschii

Fertile F(1) hybrids were obtained between durum wheat (Triticum durum Desf.) Langdon (LDN) and its 10 disomic substitution (LDN DS) lines with Aegilops tauschii accession AS60 without embryo rescue. Selfed seedset rates for hybrids of LDN with AS60 were 36.87% and 49.45% in 2005 and 2006, respectively. Similar or higher selfed seedset rates were observed in the hybrids of 1D (1A), 1D (1B), 3D (3A), 4D (4B), 7D (7A), and 2D (2B) with AS60, while lower in hybrids of 3D (3B) + 3BL, 5D (5A) + 5AL, 5D (5B) + 5B and 6D (6B) + 6BS with AS60 compared with the hybrids of LDN with AS60. Observation of male gametogenesis showed that meiotic restitution, both first-division restitution (FDR) and single-division meiosis (SDM) resulted in the formation of functional unreduced gametes, which in turn produced seeds. Both euhaploid and aneuhaploid gametes were produced in F(1) hybrids. This suggested a strategy to simultaneously transfer and locate major genes from the ancestral species T. turgidum or Ae. tauschii. Moreover, there was no significant difference in the aneuhaploid rates between the F(1) hybrids of LDN and LDN DS lines with AS60, suggesting that meiotic pairing between the two D chromosomes in the hybrids of LDN DS lines with AS60 did not promote the formation of aneuhaploid gametes.

CANADIAN PIONEERS: John Martin Unrau

CANADIAN PIONEERS: John Martin Unrau

Genetic mapping of a new flowering time gene on chromosome 3B of wheat

The single chromosome substitution lines of chromosome 3B of the Czech alternative wheat vari- ety Beska Plesivka (CP 3B) into two spring varieties Zlatka and Sandra, revealed clear diVerences in Xower- ing time compared to the recipient varieties. To map this gene(s), recombinant substitution lines for chromo- some 3B were produced from crosses of the substitu- tion lines with their recipient parents and genetic maps developed using SSR markers. Two populations were mapped, Sandra//Sandra 3B/Sandra (CP 3B) and Zlatka//Zlatka/Zlatka (CP 3B). Combining the geno- type data with phenotype data on Xowering time in Wve independent experiments under natural long day or controlled short day conditions revealed a single Xow- ering time QTL. This gene had an additive eVect of 1- 6 days, depending on environment and genetic back- ground, and was mapped in both populations to a position in the region of marker Xbarc164 near the centromere on the long arm of 3B. Comparisons of the genetic maps with other 3B maps developed by the authors indicated that the QTL may be homologous to a QTL segregating in UK germplasm.

Genetic association of lint yield with its components in cotton chromosome substitution lines

Dissection of the genetic relationship between lint yield and its yield components at the chromosome level may provide an additional avenue for yield enhancement in cotton (Gossypium hirsutum L.). Based on the conditional additive-dominance (AD) genetic model, we investigated the genetic structures of lint yield with its three component traits, lint percentage, boll weight, and boll number, using a two-location data set containing cotton chromosome substitution lines (chromosome or chromosome arm substituted from G. barbadense L. into G. hirsutum L., TM-1) which are defined as CS-B lines and their F2 hybrids with CS-B recurrent parent TM-1. We calculated the conditional variance components, contribution ratios, and contribution effects subject to the additive and dominant components. Our results showed that boll number or boll number with boll weight greatly reduced the conditional variance components and phenotypic variance for lint yield and thus indicated that boll number plays a more important role in lint yield than the other two component traits. We demonstrated that the G. barbadense chromosomes in CS-B16, CS-B18, and CS-B4sh were directly associated with reduced lint yield. Substituted chromosome arms 14sh, 22sh, and 22Lo were associated with reduced additive effects for lint yield through the component of boll weight, thus suggesting that some substituted chromosomes or chromosome arms may be indirectly associated with lint yield through yield component traits. This study provides a better understanding of cotton yield and its component traits at the chromosome level and this information should be useful in cotton breeding.

Complex genetic interactions underlying expression differences between Drosophila races: Analysis of chromosome substitutions

Regulation of gene expression is usually separated into cis and trans components. The separation may become artificial if much of the variation in expression is under multigenic and epistatic (e.g., cis-by-trans) control. There is hence a need to quantify the relative contribution of cis, trans, and cis-by-trans effects on expression divergence at different levels of evolution. To do so across the whole genome, we analyzed the full set of chromosome-substitution lines between the two behavioral races of Drosophila melanogaster. Our observations: (i) Only approximately 3% of the genes with an expression difference are purely cis regulated. In fact, relatively few genes are governed by simple genetics because nearly 80% of expression differences are controlled by at least two chromosomes. (ii) For 14% of the genes, cis regulation does play a role but usually in conjunction with trans regulation. This joint action of cis and trans effects, either additive or epistatic, is referred to as inclusive cis effect. (iii) The percentage of genes with inclusive cis effect increases to 32% among genes that are strongly differentiated between the two races. (iv) We observed a nonrandom distribution of trans-acting factors, with a substantial deficit on the second chromosome. Between Drosophila racial groups, trans regulation of expression difference is extensive, and cis regulation often evolves in conjunction with trans effects.

Characterization of inter-varietal chromosome substitution lines of wheat using molecular markers

Several sets of wheat inter-varietal chromosome substitution lines (SLs) have been produced over the last fifty years at the CRI (formerly RICP) in Prague-Ruzyně, based on cytogenetic manipulations using aneuploids. Lines with defined genes have been obtained which significantly influence growth habit and flowering time and these have been used particularly in the study of the genetics and physiology of flowering. The sets of lines include substitutions of homoeologous group 5 chromosomes carrying Vrn genes that control vernalisation response, homoeologous group 2 chromosomes with Ppd genes controlling photoperiodic sensitivity, and some other substitutions, particularly those with chromosome 3B of the Czech alternative variety Česk&amp;aacute; Přes&amp;iacute;vka where a novel flowering time effect was located. Although the phenotypic and cytological analysis of substitution lines has been continually carried out during backcrossing generations, only the use of molecular markers can allow an unambiguous characterization to verify that substitutions are correct and complete. This analysis has allowed incorrect substitutions or partial substitutions to be identified and discarded. This paper summarizes the results of recent molecular checks of the substitution line collections at CRI.

Plant survival after freezing in wheat ‘Cappelle Desprez’ (‘Bezostaya 1’) intervarietal chromosome substitution lines

AbstractThe effect of individual chromosomes of the wheat variety ‘Bezostaya 1’ on plant resistance to low temperatures was studied using the available set of intervarietal ‘Cappelle Desprez’ (‘Bezostaya 1’) chromosome substitution lines. The number of plants surviving after freezing at −12, −15 and −17°C was determined for both parents and lines in trials in 2004/2005 and 2005/2006. Significant differences between the three temperature treatments and between lines were found, implying that two factors, the level of temperature stress and chromosome substitutions, were influencing plant survival. Improved frost resistance in both trials was associated with genes located on five chromosomes: 5A, 2D, 4A, 5D and 6A. An increase in the plant frost resistance because of the effects of 7A and 1A chromosomes was also observed in the 2005/2006 trial, when the overall autumn and winter (January) temperatures were lower than in 2004/2005.

Comparative mapping of HKT genes in wheat, barley, and rice, key determinants of Na+ transport, and salt tolerance

Salt tolerance of plants depends on HKT transporters (High-affinity K(+) Transporter), which mediate Na(+)-specific transport or Na(+)-K(+) co-transport. Gene sequences closely related to rice HKT genes were isolated from hexaploid bread wheat (Triticum aestivum) or barley (Hordeum vulgare) for genomic DNA southern hybridization analysis. HKT gene sequences were mapped on chromosomal arms of wheat and barley using wheat chromosome substitution lines and barley-wheat chromosome addition lines. In addition, HKT gene members in the wild diploid wheat ancestors, T. monococcum (A(m) genome), T. urartu (A(u) genome), and Ae. tauschii (D(t) genome) were investigated. Variation in copy number for individual HKT gene members was observed between the barley, wheat, and rice genomes, and between the different wheat genomes. HKT2;1/2-like, HKT2;3/4-like, HKT1;1/2-like, HKT1;3-like, HKT1;4-like, and HKT1;5-like genes were mapped to the wheat-barley chromosome groups 7, 7, 2, 6, 2, and 4, respectively. Chromosomal regions containing HKT genes were syntenic between wheat and rice except for the chromosome regions containing the HKT1;5-like gene. Potential roles of HKT genes in Na(+) transport in rice, wheat, and barley are discussed. Determination of the chromosome locations of HKT genes provides a framework for future physiological and genetic studies investigating the relationships between HKT genes and salt tolerance in wheat and barley.

Influence of alien chromosomes on the resistance of soft wheat to biotrophic fungal pathogens

The resistance of 77 disomic chromosome-addition and chromosome-substitution lines of soft wheat that had been created on the base of the Chinese Spring variety to Belorussian populations of powdery mildew and brown leaf rust is studied. The lines possess a chromosome pair introduced from 13 species of cereals as well as three amphiploids. New genes that express resistance to biotrophic fungal pathogens in chromosomes 2Ss and 5Ss from the Aegilops searsii species and chromosome 6Rm from the Secale montanum species were discovered. We do not exclude the possibility that the new resistance gene against powdery mildew is carried by chromosome 6S1 from the species Aegilops longissima (line No. 4), and that the new resistance gene against brown leaf rust is carried by chromosome 3E from the species Elytrigia elongata.

Fine scale genetic and physical mapping using interstitial deletion mutants of Lr34 /Yr18: a disease resistance locus effective against multiple pathogens in wheat

The Lr34/Yr18 locus has contributed to durable, non-race specific resistance against leaf rust (Puccinia triticina) and stripe rust (P. striiformis f. sp. tritici) in wheat (Triticum aestivum). Lr34/Yr18 also cosegregates with resistance to powdery mildew (Pm38) and a leaf tip necrosis phenotype (Ltn1). Using a high resolution mapping family from a cross between near-isogenic lines in the "Thatcher" background we demonstrated that Lr34/Yr18 also cosegregated with stem rust resistance in the field. Lr34/Yr18 probably interacts with unlinked genes to provide enhanced stem rust resistance in "Thatcher". In view of the relatively low levels of DNA polymorphism reported in the Lr34/Yr18 region, gamma irradiation of the single chromosome substitution line, Lalbahadur(Parula7D) that carries Lr34/Yr18 was used to generate several mutant lines. Characterisation of the mutants revealed a range of highly informative genotypes, which included variable size deletions and an overlapping set of interstitial deletions. The mutants enabled a large number of wheat EST derived markers to be mapped and define a relatively small physical region on chromosome 7DS that carried Lr34/Yr18. Fine scale genetic mapping confirmed the physical mapping and identified a genetic interval of less than 0.5 cM, which contained Lr34/Yr18. Both rice and Brachypodium genome sequences provided useful information for fine mapping of ESTs in wheat. Gene order was more conserved between wheat and Brachypodium than with rice but these smaller grass genomes did not reveal sequence information that could be used to identify a candidate gene for rust resistance in wheat. We predict that Lr34/Yr18 is located within a large insertion in wheat not found at syntenic positions in Brachypodium and rice.

Utilisation of Aegilops (goatgrass) species to widen the genetic diversity of cultivated wheat

Wild Aegilops species related to cultivated wheat (Triticum spp.) possess numerous genes of agronomic interest and can be valuable sources of resistance to diseases, pests and extreme environmental factors. These genes can be incorporated into the wheat genome via intergeneric crossing, following, where necessary, the development of chromosome addition and substitution lines from the resulting hybrids. The transfer of a single segment from an alien chromosome can be achieved by translocations. The Aegilops (goatgrass) species, which are the most closely related to wheat, exhibit great genetic diversity, the exploitation of which has been the subject of experimentation for more than a century. The present paper gives a survey of the results achieved to date in the field of wheat–Aegilops hybridisation and gene transfer. The Aegilops genus consists of 11 diploid, 10 tetraploid and 2 hexaploid species. Of these 23 Aegilops species, most of the diploids (Ae. umbellulata Zhuk., Ae. mutica Boiss., Ae. bicornis (Forssk.) Jaub. & Spach, Ae. searsii Feldman & Kislev ex Hammer, Ae. caudata L., Ae. sharonensis Eig, Ae. speltoides Tausch, Ae. longissima Schweinf. & Muschl.) and several polyploids (Ae. ventricosa Tausch, Ae. peregrina (Hack. In J. Fraser) Marie & Weiller, Ae. geniculata Roth, Ae. kotschyi Boiss., Ae. biuncialis L.) have been used to develop wheat–Aegilops addition lines. Wheat–Aegilops substitution lines were developed using several species, including Ae. umbellulata, Ae. caudata, Ae. tauschii, Ae. speltoides, Ae. sharonensis, Ae. longissima and Ae. geniculata. Translocations carrying genes responsible for useful agronomic traits were developed with Ae. umbellulata, Ae. comosa, Ae. ventricosa, Ae. longissima, Ae. speltoides and Ae. geniculata. A large number of genes were transferred from Aegilops species to cultivated wheat, including those for resistance to leaf rust, stem rust, yellow rust and powdery mildew, and various pests (cereal cyst nematode, root knot nematode, Hessian fly, greenbug). Many molecular markers are linked to these resistance genes. The development of new molecular markers is also underway. There are still many untapped genetic resources in Aegilops species that could be used as resistance sources for plant breeding.

Identification of differentially expressed genes associated with cotton fiber development in a chromosomal substitution line (CS-B22sh)

One of the impediments in the genetic improvement of cotton fiber is the paucity of information about genes associated with fiber development. Availability of chromosome arm substitution line CS-B22sh (chromosome 22 short arm substitution from 3-79 (Gossypium barbadense) into a TM-1 (Gossypium hirsutum) background) provides a novel opportunity to study fiber-associated genes because previous studies revealed this line was associated with some superior fiber quality traits compared to TM-1. We used an integrated approach of suppression subtractive hybridization (SSH), microarray, and real-time reverse transcription-polymerase chain reaction (RT-PCR) technologies to identify the potential genes associated with fiber development. Utilizing mRNAs from 15 days post-anthesis (dpa) fibers, we constructed a SSH cDNA library with chromosome substitution line CS-B22sh as the tester and TM-1 as the driver. The SSH cDNA library was screened using microarrays. Microarray analysis showed that 36 genes were differentially expressed in CS-B22sh 15-dpa fiber compared to TM-1 as confirmed by real time RT-PCR. These genes include two beta-tubulins, an actin, a putative kinesin light chain, a cellulose synthase, glycosyl hydrolase family 3 protein, pyruvate decarboxylase, glycoside hydrolase family 5, GDP-mannose pyrophosphorylase, dynamin-like protein, annexin, and a number of genes involved in signal transduction, and protein, nucleic acid, and lipid metabolisms. To our knowledge, this is the first report on identification of differentially expressed fiber-associated genes in a cotton chromosomal substitution line.

Introgression of wheat chromosome 2D or 5D into tritordeum leads to free-threshing habit

Hexaploid tritordeum is the amphiploid derived from the cross between the diploid wild barley Hordeum chilense and durum wheat. The non-free-threshing habit is a constraint to this species becoming a new crop. Three tritordeum lines (HT374, HT376, and HT382) showing the free-threshing habit were selected from crosses between tritordeum and bread wheat. All three lines were euploids, as revealed by mitotic chromosome counting. Genomic in situ hybridization analysis made it possible to distinguish differences among these lines. While the line HT382 carries only 10 chromosomes from H. chilense, the lines HT374 and HT376 have 12. These results suggest that HT382 is a double chromosome substitution line between H. chilense and the wheat D genome, while HT374 and HT376 each have one pair of H. chilense (Hch) chromosomes substituted by wheat D chromosomes. Molecular characterization revealed that HT382 is a 1D/(1Hch), 2D/(2Hch) chromosome substitution line, whereas HT374 and HT376 have 5D/(5Hch) substitutions. On the basis of previous knowledge, it seems that the absence of chromosome 2Hch or 5Hch is more important for producing the free-threshing habit than the presence of chromosome 2D or 5D, while chromosome 1Hch seems to be unrelated to the trait. These free-threshing tritordeum lines constitute an important advance in the tritordeum breeding program.