Morphological, yield, cytological and molecular characterization of a bread wheat X tritordeum F1 hybrid

The morphological, yield, cytological and molecular characteristics of bread wheat X tritordeum F₁ hybrids (2n =6x = 42; AABBDH^ch) and their parents were analysed. Morphologically, these hybrids resembled the wheat parent. They were slightly bigger than both parents, had more spikelets per spike, and tillered more profusely. The hybrids are self-fertile but a reduction of average values of yield parameters was observed. For the cytological approach we used a double-target fluorescencein situ hybridization performed with total genomic DNA fromHordeum chilense L. and the ribosomal sequence pTa71. This technique allowed us to confirm the hybrid nature and to analyse chromosome pairing in this material. Our results showed that the expected complete homologous pairing (14 bivalents plus 14 univalents) was only observed in 9.59% of the pollen mother cells (PMCs) analysed. Some PMCs presented autosyndetic pairing of Hch and A, B or D chromosomes. The average number of univalents was higher in the wheat genome (6.8) than in the Hch genome (5.4). The maximum number of univalents per PMC was 20. We only observed wheat multivalents (one per PMC) but the frequency of trivalents (0.08) was higher than that of quadrivalents (0.058). We amplified 50 RAPD bands polymorphic between the F₁ hybrid and one of its parents, and 31 ISSR polymorphic bands. Both sets of markers proved to be reliable for DNA fingerprinting. The complementary use of morphological and yield analysis, molecular cytogenetic techniques and molecular markers allowed a more accurate evaluation and characterization of the hybrids analysed here.     

Cytology of inbreds and f 1 hybrids of pearl millet

Summary The meiotic behaviour of chromosomes was studied in four inbred lines and their F ₁ hybrids of P. typhoides. The inbred lines showed a decrease in mean chiasma frequency when compared with the population plants, but differed from one another in their mean chiasma frequencies. Together with the decrease in mean chiasma frequency the inbreds showed variation in mean chiasma frequencies. The inbred lines showed a number of meiotic abnormalities such as extra chromosomes, extra fragments, desynapsis, persistent nucleoli and differential condensation of chromosomes. The F ₁ hybrids of these inbreds exhibited heterosis for chiasma frequency. All the F ₁'s had mean chiasma frequencies higher than the means of the respective participating parents. The F ₁'s, however, differed in the degree of heterosis exhibited. In the F ₁ hybrids, the variation in mean chiasma frequency, both between plants and between PMC's within plants, was significantly lower than that of the inbred lines. The effect of environment was studied in the inbred lines and their F ₁ hybrids. The mean chiasma frequencies of the inbred lines were significantly lower, and the variation in mean chiasma frequencies was greater, in the stress season. The mean chiasma frequencies of F ₁'s did not show any significant differences between the two seasons. The F ₁'s exhibited less variation in mean chiasma frequency than the inbred lines, showing that F ₁'s were developmentally more stable. The F ₁'s did not show any meiotic abnormalities in either season.     

Relationships between frequency,localization and errors in chiasma formation in desynaptic rye

Four inbred lines of rye (Secale cereale) and the F₁ and F₂ from the cross between two of them have been studied. The results indicate that the genotypes used show variation in chiasma frequency, chiasma error frequency and chiasma localization. Significant correlations between these characters have been found: as chiasma frequency decreases both chiasma error frequency and distal localization increase. These correlations lead us to the assumption that these anomalies are in fact secondary effects of the failure of some preconditions for exchange. It is suggested that one such exchange precondition may be effective pairing.     

Transmission of chromosomes through the eggs and pollen of triticale × wheat F1 hybrids

Summary The substitution patterns of rye chromosomes in hexaploid triticale × wheat F₂ hybrids, along with the transmission patterns of rye chromosomes through egg cells and pollen when several of the F₁ hybrids were test crossed to triticale and wheat were investigated. The data indicated that the rye chromosome transmission through both the egg and pollen was random in number and in composition. The test crosses suggested that it was best to use wheat pollen for the transmission of rye chromosomes through the egg cells of the F₁ hybrids and triticale egg cells for the transmission of rye chromosomes through F₁ hybrid pollen. A deviation from random segregation in the F₂ and the transmission rate was observed for rye chromosomes 1R, 4R/7R, and 6R. The transmission rates of 1R and 6R varied depending on the direction in which the cross was made. The results also indicated that there was little or no compensation between the R- and D-genomes and that the chromosomes of these two genomes appeared to be transmitted independently of each other.     

Chromosome pairing in meiosis of partially fertile wheat/rye hybrids

The normal course of meiosis depends on regular pairing of homologous chromosomes. In intergeneric hybrids, including those of wheat, there is no chromosome pairing because there are no homologs. In F₁ wheat/rye hybrids, pairing is largely prevented by the pairing homoeologous1 (Ph1) gene. In its presence, there are only rare instances of pairing; most chromosomes are univalent, and their orientation at metaphase I initiates different pathways of the meiotic cycle. The meiotic-like pathway includes a combination of the reductional and the equational + reductional steps at AI followed by the second division. The resulting gametes are mostly non-functional. The mitotic-like pathway involves equational division of univalents at AI and the absence of the second division. Any fertility of wheat/rye hybrids depends on the production of unreduced gametes arising from meiotic restitution (mitotic-like division). We examined the meiotic pairing in wheat/rye hybrids created from wheat lines with single rye chromosome substitutions and Ph1 present. This guaranteed F₁ meiosis with one pair of rye homologs. All hybrids formed bivalents, but proportions of meiocytes with bivalents varied. In the meiocytes where bivalents were present, there was a higher tendency for the meiotic-like pathway, while in meiocytes where bivalent pairing failed, the tendency was stronger for the mitotic-like pathway. Among the equationally dividing cells, we observed more than 90 % of meiocytes without bivalents, where rye homologs did not form bivalents, too. The data indicate a potential application of wheat/rye lines in producing genetic stocks of amphidiploids with designated genomic constitutions.     

Gene mutations in rye causing embryo lethality in hybrids with wheat: allelism and chromosomal localisation

In crosses between hexaploid wheat and inbred lines of rye, a small number of rye genotypes produce seeds carrying undifferentiated, non-viable embryos. Hybrids between such lines and those not showing this phenotype were used as pollen donors in crosses with bread wheat in order to determine the genetic basis of disturbed embryo development. A single gene, designated Eml-R1b, is causing this character. Molecular markers associated with F₂ genotypes derived from a contrasting rye inbred progeny were used for a linkage study. Recombinant inbred lines of an F₅ population served as testers. Eml-R1b maps to chromosome arm 6RL, along with two co-segregating microsatellite loci, Xgwm1103 and Xgwm732. Complementary interactions of deleterious genes in wheat and rye are discussed.     

Meiotic pairing in hybrids between tetraploid Triticale and related species: new elements concerning the chromosome constitution of tetraploid Triticale

Summary Two F5 strains of tetraploid triticale (2n= 4x=28), obtained from 6x triticaleX2 rye progenies, were crossed with diploid and tetraploid rye, some durum and bread wheats, and various 8x and 6x triticale lines. Meiosis in the different hybrid combinations was studied. The results showed that the haploid complement of these triticales consists of seven chromosomes from rye and seven chromosomes from wheat. High frequencies of PMCs showing trivalents were observed in hybrids involving the reference genotypes of wheat and triticale. These findings proved that several chromosomes from the wheat component have chromosome segments coming from two parental wheat chromosomes. The origin of these heterogeneous chromosomes probably lies in homoeologous pairing occurring at meiosis in the 6x triticaleX2x rye hybrids from which 4x triticale lines were isolated. A comparison among different hybrids combinations indicated that the involvement of D-genome chromosomes in homoeologous pairing is quite limited. In contrast, meiotic patterns in 4x triticale X 2x rye hybrids showed a quite high pairing frequency between some R chromosomes and their A and B homoeologues.     

Behaviour of rye univalents in hybrids of 6x-triticale with Triticum turgidum (L.) ssp. turgidum conv. durum (Desf.)

In a cytological analysis of the meiotic behaviour in PMCs of five hybrids between hexaploid triticale and durum wheat, Triticum turgidum L., chromosome association at meiotic first metaphase and the behaviour of rye univalents at first anaphase were analyzed. The chromosomes of the B genome, chromosomes 4A and 7A (disomic condition), and the seven rye chromosomes, could be distinguished by their C-banding pattern. No wheat-rye paring was detected at metaphase I. Rye univalents were observed as laggards which disjoined either predominantly equationaly (2R, 3R, 4R, 5R and 7R) or predominantly reductionaly (1R and 6R). Misdivision occurred in up to 3% of rye univalents.     

Introgression of the reduced height gene <Emphasis Type="Italic">Rht10</Emphasis> from the wheat cultivar Ai-Bian 1 into the triticale genotype

A gene determining reduced height, Rht10, from the wheat cultivar Ai-Bian 1 was introgressed into the triticale genotype. Initially, Ai-Bian 1 was crossed with the wheat cultivar Chinese Spring (CS), a carrier of Kr genes, to overcome the uncrossability of this cultivar with rye. Amphidiploids were produced by hybridizing the F₂ (CS × Ai-Bian 1) plants displaying reduced height (at the level of Ai-Bian 1) with rye. Free pollination of F₁ (F₂ of CS × Ai-Bian 1) × Saratovskaya 7 with triticale pollen gave fertile viable hybrids; the majority of hybrids were phenotypically closer to octoploid triticale; however, the variants intermediate between octo-and hexaploids were also present. The height of amphidiploids varied from 40 to 90 cm, and the grain yield per spike amounted on the average to 11.7–24.7 grains, which exceeded essentially this value in F₁ plants.     

SEMISTERILITY IN THE INTERSPECIFIC HYBRID MELILOTUS POLONICA × M. ALBA

Jaranowski , J. K. (Coll. of Agriculture, ul. Wojska Polskiego 71c, Poznan, Poland.) Semisterility in the interspecific hybrid Melilotus polonica × M. alba. Amer. Jour. Bot. 48(1): 28–35. Illus. 1961.—Interspecific hybrids between Melilotus polonica (n = 8) and M. alba (n = 8) are readily secured. The F₁ hybrids are intermediate between the parents and partially sterile with a mean percentage of 58.8 (ranging from 46.8 to 72.6) defective pollen grains. Six bivalents and a chain or ring of 4 chromosomes occur at diakinesis and metaphase-I of microsporogenesis. A crossshaped configuration characteristic of a reciprocal translocation is present at pachytene, indicating that one of the parents is homozygous for an interchange of relatively large section between two of the members of the chromosome complex. Chromosome bridges, lagging chromosomes, movement of the univalents to the same pole and precocious division of the univalents lead to aberrant chromosome distribution during the course of meiosis. Reduction in self-fertility indicates a corresponding aberrant distribution of chromosomes during megasporogenesis. Pollen sterility in the F₂ generation ranged from 24.8% to 72.5% with a mean value of 54.6%. Two plants in the F₂ generation which had relatively low pollen sterility proved to be aneuploids (2n + 1). Meiotic irregularities in the F₂ plants were comparable to those exhibited by the F₁ plants.     

Chiasma distribution in rye chromosomes of diploid rye and in wheat/rye addition lines in relation to C-heterochromatin

Summary In five genetically different inbred lines of rye and in the seven Chinese Spring/Imperial wheatrye addition lines, chiasma distribution in rye chromosomes was studied with respect to the amount and position of constitutive heterochromatin (Giemsa C-bands). In all inbred lines, rye chromosomes with one primary terminal band were more frequently found as univalents than those with primary bands on both telomeres. These chromosomes were most probably 5R and/or 6R. In the addition lines a highly significant reduction in the number of arms bound by chiasmata was found for rye chromosomes 5R and 6R. Because of the similar chiasma distribution in the inbred lines and in the rye chromosomes of the addition lines, no effect of the wheat genome on the number of chiasmata in the rye chromosomes can be ascertained. However, a relationship between chiasma frequency and chromosome arm length seems to exist, since under reduced chiasma conditions the two shortest arms of the rye complement, those of chromosomes 5R and 6R, frequently fail to form a chiasma. No effect of the large blocks of constitutive heterochromatin in the telomeres of the rye chromosomes on the position of chiasmata within a bivalent could be established.This study was financially supported by the Deutsche Forschungsgemeinschaft     

The genus Argemone

Summary Crosses between three diploid (A. mexicana; A. subfusiformis; A. albiflora) and one tetraploid (A. ochroleuca) Argemone species were made. The F₁'s were cytogenetically analysed. All the triploid hybrids were sterile and did not set any seed. In the species there was predominantly bivalent pairing (14II; 28II) and high pollen and seed fertility. The F₁'s displayed different configurations, e.g. I, II and III, and pollen fertility was low; the capsules were shrunken and did not contain any seed.In the two combinations mexicana X ochroleuca and subfusiformis X ochroleuca, pairing was identical and both auto- and allosyndesis were observed. The number of univalents, bivalents and trivalents varied in the three combinations but the number of associations did not differ significantly. In the albiflora X ochroleuca combination as many as 13 trivalents were observed.In general a negative correlation was observed between univalents and chiasmata per cell. However, chiasma frequency and paired associations displayed a positive correlation.It is deduced that sufficient similarities existed between one of the ochroleuca and the three diploid species genomes; the remainder of the ochroleuca genome had homologous chromosomes. Apparently A. ochroleuca carried enough cryptic intergenomal homologies which ordinarily remained unexposed. In the hemizygous state however, as in the F₁'s, there was intergenomal pairing. In an attempt to resolve the conflict between homology and bivalent pairing in the species, a diploidizing genetic mechanism is envisaged. Alternatively an acute propensity to preferential pairing caused bivalent formation. Such a system or systems caused meiotic isolation of various genomes and instituted normal fertility. Furthermore, the segmental allotetraploid nature of A. ochroleuca is concluded. The cytogenetic relationship between mexicana and ochroleuca is appraised.     

Meiotic studies of wheat,rye and 42-chromoaome-Triticales

In 42-chromosome — triticales, chromosome pairing was extremely erratic with very low frequency (60–63 %) of regular bivalents per pollen mother cell. The frequency of univalents was very low or nil in the wheat and rye parents.     

Thinopyrum distichum addition lines: production,morphological and cytological characterisation of 11 disomic addition lines and stable addition-substitution line

Plants of the partial amphiploid Inia 66/Thinopyrum distichum (2n = 70)//Inia 66 (2n = 56) were used as male parents in crosses with the monosomic series in the common wheat cultivar Inia 66. The genome and homoeologous group of the monosomic used in the cross affected the distribution of chromosome number of the progeny plants in the F₂ and F₄. Meiosis in the pollen mother cells of the B₁F₇ partial amphiploids was not stable, and not different from that of the B₁F₁ in which univalents and multivalents were observed. Disomic addition lines were selected on the basis of morphology and meiotic stability in the F₂, F₄ and F₅. Eleven of the fourteen possible wheat-Th. distichum disomic addition lines were identified using chromosome C-band pattern, as well as size and arm ratio, as genetic markers. Addition of T. distichum chromosome J ^dll produced a phenotype indicating homoeology with wheat group-2 chromosomes. Clear indications of homoeology based on morphological characteristics were not obtained in any of the other addition lines, probably due to the mixed homoeology of the Th. distichum chromosomes relative to wheat. The addition lines were all susceptible to leaf rust, unlike the germplasm-line Indis which carries a leaf rust resistance gene on a translocation segment derived from Th. distichum. Instability of meiotic pairing was observed in all addition lines. The stability, or not, of progeny chromosome counts did not reflect the level of chromosome pairing instability in the parental plants. SDS-PAGE for gliadin-type seed proteins revealed two addition lines which expressed seed storage proteins uncommon to Inia 66 but typical of Th. distichum.     

The genotypic control of homoeologous chromosome association in Lolium temulentum × Lolium perenne interspecific hybrids

Two contrasting genotypes of Lolium perenne and two inbred lines of L. temulentum were examined with regard to their effect on homoeologous chromosome pairing in interspecific hybrids derived from them. Substantial differences in chiasma frequency were observed between the hybrid progeny of the different parental types. The background genes involved were found to operate in the presence and in the absence of B chromosomes. The combination of A chromosome genes present in some of the 0B hybrids was found to result in a considerable suppression of chiasma formation at the diploid level, and the restriction of pairing to strict homologues at the tetraploid level. It appears, therefore, that genes are present within the diploid species of the genus Lolium which are capable of performing a function similar to that of the Ph locus in wheat.     

Cytogenetics of the trigeneric hybrid, (Hordeum vulgare ×Triticum aestivum) ×Secale cereale

Summary Chromosome pairing was studied in hybrids of (Hordeum vulgare ×Triticum aestivum) ×Secale cereale. Chiasma frequency per cell varied from 1.94 to 3.16 between the different hybrids. This variation was attributed to genetic variability in rye parents which affected homoeologous pairing. The pairing of rye chromosomes as revealed by Giemsa C-banding was a combination of nonhomologous association between rye chromosomes and associations with chromosomes of wheat and barley. Contribution No. 634 Ottawa Research Station     

Chromosome pairing in tetraploid rye with monosomic-substitution wheat chromosomes

In tetraploid rye with single-substitution wheat chromosomes - 1A, 2A, 5A, 6A, 7A, 3B, 5B, 7B - chromosome pairing was analysed at metaphase I in PMCs with the C-banding method. The frequency of univalents of chromosome 1A was considerably higher than that of the other four wheat chromosomes of genome A (6A, 5A, 7A and 2A). Among chromosomes of genome B, the lowest mean frequency of univalents was observed for chromosome 5B. In monosomic lines, wheat chromosomes 1A, 2A, 5A, 6A, 7A and 5B paired with rye homoeologues most often in rod bivalents and in chain quadrivalents (also including 3B). The 47% pairing of 5B-5R chromosomes indicate that the rye genomes block the suppressor Ph1 gene activity. In monosomic plants with chromosomes 5A, 2A, 6A, 7A and 5B, a low frequency of rye univalents was observed. It was also found that the wheat chromosomes influenced the pairing of rye genome chromosomes, as well as the frequency of ring and rod bivalents and tri- and quadrivalents. However, the highest number of terminal chiasmata per chromosome occurred in the presence of chromosomes 5A and 2A, and the lowest - in the presence of chromosomes 3B and 7B. In the presence of chromosome 5B, the highest frequency of bivalents was observed. The results of the present study show that the rye genome is closer related to the wheat genome A of than to genome B. The high pairing of wheat-rye chromosomes, which occurs in tetraploid rye with substitution wheat chromosomes, indicates that there is a high probability of incorporating wheat chromosome segments into rye chromosomes.     

Genetic Control of Embryo Lethality in Crosses between Common Wheat and Rye

The phenotypic manifestation and genetic control of embryo lethality observed in crosses between common wheat and rye were studied. It was found that crosses between common wheat and inbred self-fertile rye lines L2 and 535 gave rise to ungerminating grains, in which the development and differentiation of the hybrid embryo are arrested. Study of the degree of embryo development in the hybrid grains obtained by crossing common wheat varieties with inbred rye lines L2 and 535 showed that genotypes of the parents affected the ratio between undifferentiated embryos of various sizes. Analysis of this trait was performed by test crosses according to a novel pedigree program with the use of interlinear hybrids and a set of fourth-generation hybrid recombinant inbred lines. Rye line L2 was shown to bear the Eml (Embryo lethality) gene, which terminates the development of the hybrid embryo in amphihaploids. The suggestion of complementary interaction between wheat and rye genes during formation of a “new” character in wheat-rye F₁ hybrids is discussed. A method of detecting an allele not complementary to the rye Eml allele in wheat is proposed. The proposed test program allows appropriate study of the system of wheat and rye genes involved in complementary interaction in the genotype of a distant hybrid.__________Translated from Genetika, Vol. 41, No. 8, 2005, pp. 1075–1083.Original Russian Text Copyright © 2005 by Tikhenko, Tsvetkova, Voylokov.     

The influence of rye cytoplasm on meiotic stability of tetraploid Secalotriticum

Chromosome pairing in tetraploid Secalotriticum was analysed. In the studied plants wheat chromosomes in PMCs during metaphase I showed a higher degree of pairing, in comparison to the rye genome. This is reflected in a very low frequency of univalents and a higher frequency of ring bivalents. The occurrence of wheat univalents was dependent on wheat mixogenome. In plants with an unstabilized fourth homoeologous group, a heteromorphic bivalent 4A-4B was observed in 39.9% of PMCs, whereas in plants with an unstabilized seventh homoeologous group, chromosome 7A-7B pairing was found in all analysed cells. Rye univalents were present in all plants studied. The highest mean frequency of univalents and rod bivalents, both in wheat and in rye genomes, were recorded in plants whose first homoeologous group contained chromosome 1A. The mean number of terminal chiasmata per chromosome amounted to 1.78 in the wheat genome and 1.36 in the rye genome. It may be concluded that the plasmagenes in Secalotriticum did not increase the meiotic stability of the rye genome and also did not stabilize plant fertility.     

The effect of B chromosomes on meiotic and pre-meiotic spindles and chromosome pairing in Triticum/Aegilops hybrids

Diploid populations of Aegilops mutica and Aegilops speltoides containing B chromosomes have been used as male parents in crosses with aneuploid genotypes of Triticum aestivum to investigate the effect of B chromosomes on meiotic homologous and homoeologous chromosome pairing. F₁ hybrids of T. aestivum/Ae. mutica and T. aestivum/Ae. speltoides segregated into four classes with regard to the degree of meiotic chromosome pairing, irrespective of the presence of B chromosomes. The B chromosomes do not introduce factors altering the level of pairing other than that due to the natural allelic and gene variation occurring in the diploids. Similarly no reduction in pairing of homologous chromosomes was observed in genotypes in which pairs of homologues co-existed with B chromosomes. However, a significant drop in chiasma frequency was observed in F₁ hybrids of T. aestivum × Ae. mutica with B chromosomes and T. aestivum × Ae. mutica nullisomic for wheat chromosome 5D with B chromosomes, in temperature regimes of 12° C. No asynapsis occurred in similar hybrids in the absence of Mutica B chromosomes at low temperatures. The low-temperature sensitive phase lies early in the pre-meiotic interphase. In this instance the Mutica B chromosomes are interacting with specific gene loci of the A chromosomes. Synaptic pairing has been observed between A and B chromosomes in Ae. mutica. A high frequency of pollen mother cells with twice the number of chromosomes was observed in hybrids in the presence of Mutica B chromosomes due to failure of spindle formation at the last pre-meiotic mitosis. Meiotic spindle irregularities occurred in hybrids containing Speltoides B chromosomes. Hybrids of Ae. speltoides + B's X Ae. mutica + B's displayed the mitotic and meiotic spindle abnormalities introduced by the presence of the B chromosomes of each parent.