Karyotypes of Elymus scabrifolius (Poaceae: Triticeae) from South America studied by banding techniques and in situ hybridization.

Karyotypes of 4 accessions of Elymus scabrifolius (2n = 4x = 28) were investigated by Giemsa C- and N-banding, GAA-banding (one accession), AgNO3-staining and in situ hybridization with the rDNA probe pTa71. Two additional accessions were studied in less detail. The chromosomes were large (9-14 microns). The complements included 11 pairs of metacentrics, one with conspicuous satellites on the short arms, and 3 pairs of submetacentrics. Two of 4 accessions from Eastern Argentina and Uruguay had minute or small satellites on a submetacentric pair. No such satellites were observed in the other two accessions. In two accessions from the Cordoba province, a non-homologous submetacentric pair had very long satellites. AgNO3-staining established the presence of 4 nucleoli, two larger and two small ones, in 5 accessions. The C-banding patterns comprised from one to 12 conspicuous bands per chromosome at no preferential positions. The amount of constitutive heterochromatin (19-21%) was the highest hitherto established in the Triticeae. Similarities in banding patterns and chromosome morphology identified homologous and discriminated between non-homologous chromosomes within and, except for two chromosomes, between plants. Heteromorphic chromosome pairs were identified in satellite-carrying chromosomes only. N-banding produced conspicuous bands overall at the same positions as C-banding. GAA-banding patterns were similar to N-banding patterns. The rDNA probe hybridized to chromosome segments at nucleolar constrictions only. The production of C- and N-banding patterns in both genomes of E. scabrifolius suggests the presence of two H genomes and the absence of the pivotal St genome of Elymus. On account of the uncertain identity of one genome, and the overall similar gross morphology of E. scabrifolius and other tetraploid South American species referred to Elymus, E. scabrifolius is retained in Elymus.

Effect of rye A and B chromosomes on meiotic association of Hordeum marinum ssp. gussoneanum (4x) chromosomes in intergeneric hybrids.

Chromosome association at metaphase I was studied in PMCs of eight H. marinum ssp. gussoneanum (4x) x rye hybrids. Differences in the levels of association separated six hybrids with 2n = 23 including 14 Hordeum, 7 rye A and 2 rye B chromosomes into two groups of three plants each, a "low association" group with means of 0.03III + 4.43II (1.55 rings + 2.88 rods) + 5.10I and 6.03 chiasmata/cell, and a "high association" group with means of 0.01IV + 0.03III + 6.40II (3.55 rings + 2.85 rods) + 1.13I and 10.04 chiasmata/cell. The low number of plants studied prevents a safe estimate of the number of genes involved, but the significant difference between groups suggests the presence in the rye genome of two major genes, or two genotypes, for control of meiotic chromosome association. In two additional hybrids with 2n = 25, one of each above-mentioned group, the presence of two extra rye B chromosomes raised chiasma frequencies by ca 1.5, indicating a promoting effect on chromosome association. The level of Hordeum chromosome association in the "high association" group and the observation of up to 7 Hordeum ring bivalents in some cells agree with an autoploid origin of H. marinum ssp. gussoneanum (4x). Hordeum and rye chromosomes formed a few heterogenomic bi- and trivalents. Most rye A chromosomes formed univalents, but 2.7% were included in associations. Rye B chromosomes generally formed rod bivalents. The use of genome analysis in its traditional sense is discussed.

Genome and chromosome identification in cultivated barley and related species of the Triticeae (Poaceae) by in situ hybridization with the GAA-satellite sequence.

The satellite sequence studied was primarily composed of GAA repeats organized in long tracts of heterochromatic DNA. Fluorescent in situ hybridization (FISH) with the GAA satellite (GAA banding) to the chromosomes of barley, wheat, rye, and other Triticeae species produced banding patterns similar to those obtained by N-banding. The GAA-banding patterns of barley are described in detail and those of 12 other Triticeae species are described briefly. In situ hybridization with the GAA-satellite sequence permits identification of all the chromosomes of barley. It is a valuable alternative to other banding techniques, especially in connection with physical gene mapping by FISH. The application of the GAA-satellite sequence for the characterization of genomes in phylogenetic studies of genera containing the sequence is discussed.

The relationship between physical and genetic distances at the Hor1 and Hor2 loci of barley estimated by two-colour fluorescent in situ hybridization.

The hordeins are the major class of storage proteins in barley. They are encoded by multigene families. The B- and C-hordein loci have been mapped physically to the distal end of chromosome 5 (1I) of cultivated barley by fluorescent in situ hybridization. Based on measurements of chromosomal distances between the two hordein loci, the relationship between genetic and physical distances has been estimated to be about 1 mega base pairs per centiMorgan. This is four times higher than the mean value for the barley genome as a whole and confirms the tendency to increased recombination in distal chromosome regions. The resolving power of two-colour FISH is discussed. It is concluded that the method is suitable for estimating the relationship between genetic and physical distances of regions of about 10 Mbp or larger.

Chromosomal locations of four minor rDNA loci and a marker microsatellite sequence in barley.

Four minor rDNA loci have been mapped physically to barley (Hordeum vulgare L.) chromosomes 1 (7l), 2 (2l), 4 (4l), and 5 (1l) by a two-step in situ hybridization procedure including a GAA microsatellite sequence. Reprobing with the microsatellite resulted in a distinct banding pattern, resembling the C-banding pattern, which enabled unequivocal chromosome identification. This study suggests that gene mapping accuracy may be improved by using probes with well-characterized and narrow hybridization sites as cytological markers which are situated close to the gene locus. One of the rDNA loci is located about 54% out on the short arm of chromosome 4 and it has not previously been reported in barley. We have designated the new locus Nor-l6. rDNA loci on homoeologous group 4 chromosomes have not yet been reported in other Triticeae species. The origin of these 4 minor rDNA loci is discussed in relation to their equilocal distribution on the chromosomes.

Triple hybridization with cultivated barley (Hordeum vulgare L.).

A crossing programme for trispecific hybridization including cultivated barley (Hordeum vulgare L.) as the third parent was carried out. The primary hybrids comprised 11 interspecific combinations, each of which had either H. jubatum or H. lechleri as one of the parents. The second parent represented species closely or distantly related to H. jubatum and H. lechleri. In trispecific crosses with diploid barley, the seed set was 5.7%. Crosses with tetraploid barley were highly unsuccessful (0.2% seed set). Three lines of diploid barley were used in the crosses, i.e. 'Gull', 'Golden Promise' and 'Vada'. Generally, cv 'Gull' had high crossability in crosses with related species in the primary hybrid. It is suggested that 'Gull' has a genetic factor for crossability not present in cv 'Vada' and cv 'Golden Promise'. One accession of H. brachyantherum used in the primary hybrid had a very high crossability (seed set 54.7%) in combination with cv 'Vada' but no viable offspring was produced. In all, two trispecific hybrids were raised, viz. (H. lechleri x H. brevisubulatum) x 'Gull' (2n=7-30) and (H. jubatum x H. lechleri) x 'Gull' (2n=20-22). The first combination invariably had a full complement of seven barley chromosomes plus an additional chromosome no. 7, but a varying number of chromosomes (19-22) of the wild-species hybrid. The second combination had a full set of barley chromosomes. The meiotic pairing was low in both combinations.

Complex interspecific hybridization in barley (Hordeum vulgare L.) and the possible occurrence of apomixis.

Several complex hybrids were produced from the combination [(Hordeum lechleri, 6x xH. procerum, 6 x) × H. vulgare, 2 x]. Crosses with six diploid barley lines resulted in triple hybrids, most of which had a full complement of barley chromosomes (no. 1-7), but were mixoploid with respect to alien chromosomes (19-22). In one combination, chromosome no. 7 was duplicated. Meiosis in triple hybrids showed low, but variable pairing (1.3-5.5 chiasmata per cell). The syndesis probably did not include the barley chromosomes. Direct back-crosses to di- and tetraploid barley lines were unsuccessful. Chromosome doubling of the triple hybrid based on cv 'Pallas' resulted in a plant with 2n = 53-56, which had an increased fertility. Backcrosses to one di- and one tetraploid barley line resulted in offspring. The cross made with the tetraploid line ('Haisa II'), produced a 28-chromosomic plant in which the male parental genome was absent. We suspect that this plant may have arisen through parthenogenetic development of a reduced female gamete. The other cross with a diploid line ('9208/9') resulted in plant with 2n = 51-53. The most likely explanation for this second plant is that an unreduced gamete from the amphiploid was fertilized by a normal gamete from the backcross parent, and during early embryo development, some chromosomes were eliminated.

Elimination and duplication of particular Hordeum vulgare chromosomes in aneuploid interspecific Hordeum hybrids.

Seeds formed in crosses Hordeum lechleri (6x) x H. vulgare (2x and 4x), H. arizonicum (6x) x H. v. (2x), H. parodii (6x) x H. v. (2x), and H. tetraploidum (4x) x H. v. (2x) produced plants at high or rather high frequencies through embryo rescue. Giemsa C-banding patterns were used to analyze chromosomal constitutions and chromosomal locations on the methaphase plate. Among 100 plants obtained from H. vulgare (2x) crosses, 32 plants were aneuploid with 2n=29 (1), 28 (3), 27 (13), 26 (5), 25 (4), 24 (4), or 22 (2); 50 were euploid (12 analyzed), and 18 were polyhaploid (5 analyzed). Four plants had two sectors differing in chromosome number. Two of four hybrids with H. vulgare (4x) were euploid and two were aneuploid. Parental genomes were concentrically arranged with that of H. vulgare always found closest to the metaphase centre. Many plants showed a certain level of intraplant variation in chromosome numbers. Except for one H. vulgare (4x) hybrids, this variation was restricted to peripherally located non-H. vulgare genomes. This may reflect a less firm attachment of the chromosomes from these genomes to the spindle. Interplant variation in chromosome numbers was due to the permanent elimination or, far less common, duplication of the centrally located H. vulgare chromosomes in all 34 aneuploids, and in a few also to loss/gain of non-H, vulgare chromosomes. This selective elimination of chromosomes of the centrally located genome contrasts conditions found in diploid interspecific hybrids, which eliminate the peripherally located genome. The difference is attributed to changed "genomic ratios'. Derivatives of various H. vulgare lines were differently distributed among euploid hybrids, aneuploids, and polyhaploids. Chromosomal constitutions of hypoploid hybrids revealed a preferential elimination of H. vulgare chromosomes 1, 5, 6, and 7, but did not support the idea that H. vulgare chromosomes should be lost in a specific order. H. vulgare SAT-chromosomes 6 and 7 showed nucleolar dominance. Aneuploidy is ascribed to the same chromosome elimination mechanism that produces haploids in cross-combinations with H. vulgare (2x). The findings have implications for the utilization of interspecific Hordeum hybrids.

Cytogenetic analysis of structural rearrangements in three varieties of common wheat, Triticum aestivum.

The winter wheat varieties 'Starke' and 'Cappelle Desprez' and the spring wheat 'Chinese Spring' were analysed for structural chromosome rearrangements that resulted in the formation of multivalents in F1 hybrids. The analyses were carried out using hybrids involving euploids, monosomic and ditelosomic stocks, and double-monotelodisomic constructs. The study confirmed that 'Cappelle Desprez' differs from 'Chinese Spring' in a reciprocal translocation between chromosomes 5B and 7B (Riley et al. 1967); a translocation involving chromosomes 3B and 3D could not be verified. Furthermore, the analysis showed that 'Starke' differs from 'Chinese Spring' in a reciprocal translocation between chromosomes 7A and 7D. Both translocations have a coefficient of multivalent realisation of about 0.84. Further multivalents in euploid 'Starke', in euploid and some aneuploid stocks of 'Cappelle Desprez', and in euploid as well as various types of aneuploid hybrids between all three varieties could nearly all be explained hypothesizing that chromosome 2B of both 'Starke' and 'Cappelle Desprez' is a duplication-deficiency chromosome. In the hypothesis a part of the long arm of 2B is missing and replaced by a duplicated part of the long arm of chromosome 2D. The multivalents of this rearrangement showed an average coefficient of realisation of about 0.09.