Morphological variation inLolium (Poaceae) as a measure of species relationships

Analysis of morphological and phenological data for determining the genetic variation within sevenLolium species led to the recognition of two groups within this genus. One group, containing the two inbreeding speciesL. temulentum andL. persicum, was clearly distinct from all other species. Strong morphological and phenological intergradation was found between both species. The cross-breeding species,L. perenne, L. rigidum, andL. multiflorum, formed another group. Little differentiation was found between these species, though they were distinct. Two inbreeding species,L. loliaceum andL. remotum, were clearly distinct from each other and the two groups.L. loliaceum had an isolated position and was most related toL. rigidum. L. remotum had an intermediate position between the cross-breeding and inbreeding species, and was almost equally distant from all three cross-breeding species.Genetic variation inLolium spp. I.     

Allozyme variation within and between populations inLolium (Poaceae)

Isozyme analysis was used to determine genetic variation within and between populations of sevenLolium species. All populations from the inbreeding species (L. temulentum, L. remotum, L. loliaceum, andL. persicum) were completely fixed for all enzymes scored. They also contained, for four of the five enzyme systems studied, exactly the same allelic variant. The three cross-breeding species showed large within-population variation and much less between-population variation. The great similarity of the allozymic variants found in all species, made the division of the genusLolium into species on basis of allozymic data difficult. It was not possible to separate the different inbreeding species from each other. Within the cross-breeding groupL. multiflorum andL. rigidum could be distinguished fromL. perenne. L. multiflorum, andL. rigidum could, with more difficulty, also be separated from each other. Allelic variation could have more relation with the provenance of the populations than with taxonomic classification.Genetic variation inLolium spp. II. For first part see Pl. Syst. Evol. 188: 87–99.     

Relationships between five species ofLolium (Poaceae)

Morphological analysis and electrophoresis of seed proteins of fiveLolium species disclosed that they form two distinct groups corresponding to those recognized from compatibility data.Lolium temulentum andL. remotum of the self-pollinated group were shown to be distinct but closely related species. Morphological intergradation and high similarities between protein profiles ofL. perenne, L. multiflorum andL. rigidum (cross-pollinated species) suggest little genetic differentiation between these taxa. This implies that treatment at the infraspecific level might better accomodate the data.     

A phenetic analysis on the genus Lolium (Poaceae) in Iran

In this study, 68 specimens of the genus Lolium were scored for 27 characters, comprising 12 vegetative, 12 inflorescence and 3 seed characters. The aim of the study was to investigate the species relationships within the genus in Iran. The data were analysed using principal components analysis (PCA) and cluster analysis. Both analyses separated L. perenne, L. persicum, L. temulentum, L. multiflorum from each other. According to previous authors, L. rigidum and L. loliaceum show little difference from each other and are not separable to a species level. In this study these two species separated clearly from the other species, but were most closely related to L. perenne following cluster analysis and to L. multiflorum following PCA. L. persicum was found to be the most distinct species within the genus Lolium in Iran.     

The genetics of meiotic chromosome pairing in Lolium temulentum x Lolium perenne tetraploids

Summary The degree of preferential pairing of homologous chromosomes was estimated in a series of tetraploid hybrids of Lolium temulentum x Lolium perenne by means of cytological and genetic analyses. The correlations between the frequency of bivalents at first metaphase of meiosis in the hybrid tetraploids and the degree of preferential pairing calculated from the segregation pattern of isozyme alleles in a test cross was extremely high. The results showed clearly that suppression of heterogenetic pairing in these Lolium tetraploids is achieved by a genetic system involving the A chromosomes as well as the B chromosome system which has been known for some time. Certain similarities with the genetic system controlling pairing in polyploid wheats are discussed.     

Synaptonemal complex formation in hybrids of Lolium temulentum × Lolium perenne (L.)

Chromosome pairing and synaptonemal complex formation at zygotene and pachytene are described from serial section reconstructions of pollen mother cell nuclei in a triploid hybrid containing two haploid sets of Lolium perenne chromosomes, one of L. temulentum and two acces-sory B chromosomes. At pachytene the homologous L. perenne chromosomes form complete and continuous synaptonemal complexes while the L. temulentum chromosomes show extensive nonhomologous pairing both within and between themselves. At zygotene however, homoeologous pairing in the form of a trivalent and very little non-homologous pairing is observed. Evidently, there exists a mechanism that eliminates homoeologous association during zygotene to ensure strict bivalent formation between homologous chromosomes at pachytene. In Lolium this mechanism is under the influence of the B chromosomes and bears close similarity with that in allohexaploid wheat controlled by the Ph locus.     

The effect of B chromosomes on homoeologous pairing in species hybrids

The effect of B chromosomes on chromosome pairing at meiosis was investigated in the species hybrid Lolium temulentum x L. perenne at both the diploid and tetraploid level. The presence of B chromosomes drastically reduced association of homoeologous chromosomes in both the diploids and tetraploids. This was evident from the high frequency of univalents recorded in PMC's of diploid hybrids with B's and from the predominantly bivalent association of homologous chromosomes in tetraploids of this type. In the absence of B's homoeologous pairing was extensive giving a high frequency of bivalents in the diploids and multivalents as well as bivalents and univalents in the tetraploids.     

Cytological affinities and interfertilities between Lolium temulentum and L. persicum (Poaceae) accessions

Interspecific crossing between L. temulentum L. and L. persicum Boiss. & Hohen. ex Boiss. was performed to clarify their interfertility based on the results of chromosome pairing, pollen fertility and seed set. Both parents were normal with a high percentage of chromosome association of ring bivalents in contrast to rod bivalents at metaphase I, pollen fertility and seed set, but F1 hybrids showed different proportions of them for each crossing combination. Chromosome affinity expressed by pairing was certainly a factor affecting the pollen fertility or seed set in F1 hybrids, but it was not the most important. The positive correlation was generally found between pollen fertility and seed set of F1 hybrids. The L. persicum accession with relatively high interfertility with L. temulentum was supposed to be derived from natural hybridization between L. temulentum and L. persicum. The degree of cytogenetic differentiation between L. temulentum and L. persicum existed because of lower chromosomal pairing, pollen fertility and seed set, but their F1 hybrids were partially fertile.     

Isozyme variation and species relationships in the genus Lolium L. (ryegrasses,Graminaceae)

Thirty-two natural populations belonging to the eight species of the genus Lolium (ryegrass) or to Festuca pratensis (meadow fescue) were recorded for allelic frequencies at 13 isozyme loci. Cultivated ryegrass (L. perenne and L. multiflorum), meadow fescue, and the annual L. rigidum, are true outbreeders. The other species are true inbreeders, except for L. canariense, which shows a moderate level of cross fertilisation (20%). Hierarchical clustering from Nei's unbiased distance leads to four groups. The three self-pollinating, weed species, L. temulentum, L. remotum and L. persicum, belong to the first cluster, which is the most differentiated one. The second cluster comprises L. multiflorum, L. subulatum and most populations of L. rigidum. All L. perenne populations belong to the third cluster, as do two of L. rigidum. The average genetic distance within the L. perenne group is very low. Surprisingly, the fourth cluster groups together L. canariense and Festuca pratensis. The data suggest that L. rigidum is the species with the greatest diversity, and could be a common ancestor of the genus. Knowledge of historical processes of domestication could help to calibrate the molecular clock.     

Interaction between rye B-chromosomes and wheat genetic systems controlling homoeologous pairing

The interactive effect on homoeologous pairing of rye B-chromosomes with the absence of both pairing suppressor (3A, 3D, 5B) and promotor (3B, 5A, 5D) chromosomes of common wheat (Triticum aestivum L.) is analyzed by comparison of pairing at Metaphase I of 27-, 27+2B, 28- and 28+2B-chromosome plants. These plants were obtained from crosses between the respective wheat monosomics (2n=41) and rye plants (Secale cereale L.) carrying or not carrying two B-chromosomes (2n=14 or 14+2Bs). —The effect of rye B-chromosomes on pairing depends on the function of the wheat chromosome which is absent in the appropriate hybrids, i.e., rye B-chromosomes have a suppressor effect on pairing when the pairing suppressing wheat chromosomes 3A, 3D or 5B are absent, while they behave as promotors when the pairing promoting chromosomes 3B, 5A or 5D are absent.     

Genetic control of synapsis and recombination in Lolium amphidiploids

Homologous bivalent formation in amphidiploids of Lolium is promoted during meiosis by diploidising genes carried by A-chromosomes and by supernumerary B-chromosomes. The site and mode of action of these diploidising factors were investigated by comparing the relative frequencies of pairing configurations at meiotic prophase and metaphase I in several different hybrid genotypes. The results indicate that diploidising genes act predominatly by increasing the stringency of synapsis at early stages of meiotic prophase. By contrast, B-chromosomes appear to promote bivalent formation by ensuring that homoeologously paired chromosome segments within multivalents do not crossover. The results show that the additive effects of diploidising genes and B-chromosomes are to a certain extent separable in terms of their mode of action and timing during meiosis.     

The effect of B chromosomes on homoeologous pairing in species hybrids

Six diploid populations of Lolium rigidum were used in crosses with a standard homozygous line of Lolium temulentum in order to analyse the variation in the effect of B chromosomes on homoeologous pairing in the interspecific hybrid. — Large differences in chiasma frequency were found, both between the progeny of the different populations and, in one case, between the progeny of different plants from the same population. That this variation was due to differences in B chromosome genotype was ruled out by the use of appropriate 1B Lolium rigidum parents. It is concluded therefore that the effect of B's on homoeologous pairing in this interspecific hybrid can be modified quite substantially by the A chromosome genotype of the parents.     

Introgression of chromosomes of Festuca arundinacea var. glaucescens into Lolium multiflorum revealed by genomic in situ hybridisation (GISH)

An F₁ hybrid (n=4x=28) between the tetraploid species Festuca arundinacea var. glaucescens (GGG′G′) and a synthetic tetraploid Lolium multiflorum (LmLmLmLm) was backcrossed to diploid L. multiflorum to produce triploid (2n=3x=21) BC₁ hybrids (LmLmG). At metaphase I of meiosis the triploids had a preponderance of ring bivalents and univalents with some linear and frying-pan trivalents. Genomic in situ hybridisation (GISH) differentiated the Festuca chromosomes from Lolium and revealed that the bivalents were exclusively between Lolium homologues, while the univalents were Festuca. Despite the limited amount of homoeologous chiasmata pairing in the triploids, some recombinant chromosomes were recovered in the second backcross when the hybrids were further crossed to diploid L. multiflorum. The progeny from the second backcross was predominantly diploid. Genotypes with recombinant chromosomes and chromosome additions involving an extra Festuca chromosome were identified using GISH. Changes in plant phenotype were related to the presence of Festuca chromatin. Received: 20 September 2000 / Accepted: 05 January 2001     

CYTOGENETIC STUDIES IN THE GENUS TRIBOLIUM (POACEAE: ARUNDINEAE)

The genus Tribolium Desv. consists of nine species, i.e., T. utriculosum (Nees) Renv., T. ciliare (Stapf) Renv., T. echinatum (Thunb.) Desv., T. hispidum (Thunb.) Desv., T. acutiflorum (Nees) Renv., T. obliterum sensu Davidse, T. glomeratum sensu Davidse, T. uniolae (L.f.) Renv., and T. brachystachyum (Nees) Renv. The genus has a basic chromosome number of 6, and from diploid to hexaploid specimens have been examined. Precocious segregation of metaphase I bivalents were observed in four species. Multivalent formation results in unequal chromosome segregation during anaphase I, and several cells with an 11–13 chromosome distribution have been observed. The presence of univalents and anaphase I bridges in all T. brachystachyum specimens suggests a hybrid origin for the species. B-chromosomes were present in specimens from four species. The B-chromosomes are similar to the euchromosomes with the exception that they do not participate in meiosis. The B-chromosomes have a possible isochromosome origin. The cytogenetic evidence presented supports the combination of Plagiochloa and Lasiochloa into Tribolium and indicates that the genus is closely related to Urochlaena, whereas it is not closely related to Prionanthium.     

Probing meiosis in hybrids of Lolium (Poaceae) with a discriminatory repetitive genomic sequence

A moderately repetitive genomic DNA sequence (designated pLPBB2-123) derived from Lolium perenne L. (Poaceae) is considerably more abundant in the genome of this species than in that of the closely related L. temulentum. The repetitive sequence probe is clearly able to discriminate between the genomic DNA of both species in Southern analysis, and effectively ’paints’ only the chromosome set of L. perenne in diploid and triploid hybrids with L. temulentum. Fluorescence in situ hybridisation of this sequence onto homoeologous chromosomes during meiosis I of the hybrids shows that the sequence is evenly distributed along all of the chromosomes of L. perenne and appears to have little effect on the structural integrity or recombination potential of hybrid bivalents. Discrimination between chromatin of different parental origin in hybrid bivalents shows for the first time a progressive relaxation of relational coiling of homoeologues throughout meiotic prophase. It also highlights structural irregularities that can now be unequivocally assigned to the longer chromosomes of L. temulentum. The advantages of the use of specific differentially amplified sequences instead of whole genome probes are discussed within the context of introgression breeding programmes within the Lolium/Festuca complex. Received: 14 December 1999; in revised form: 15 February 2000 / Accepted: 15 February 2000     

MEIOTIC CHROMOSOME BEHAVIOR IN SOME INTERGENERIC HYBRIDS OF THE VANDA ALLIANCE

Tanaka , R., and H. Kamemoto . (U. Hawaii, Honolulu.) Meiotic chromosome behavior in some intergeneric hybrids of the Vanda alliance. Amer. Jour. Bot. 48(7): 573–582. Illus. 1961.—Meiotic chromosome behavior of 11 groups of diploid intergeneric hybrids (2n=38) of the Vanda alliance was investigated. Vanda Miss Joaquim × Luisia teretifolia and Ascocentrum curvifolium × Vanda lamellata usually produced 19 bivalents at metaphase I, indicating good homology of the parental chromosomes. Vanda tricolor var. sanderae × Vandopsis lissochiloides, Vandopsis lissochiloides × Vanda sanderiana, Vandopsis lissochiloides × Vanda Tatzeri and Arachnis flos-aeris × Vandopsis lissochiloides showed fair homology of parental genomes with formation of 12–15 bivalents at metaphase I. Trichoglottis brachiata × Vanda sanderiana, Vanda tricolor var. purpurea × Phalaenopsis denevei, Vanda Tatzeri × Aerides lawrenceae, Renanthera monachica × Vanda luzonica, Renanthera storiei × Vanda Clara Shipman Fisher and Aerides lawrenceae × Saccolabium giganteum, formed an average of 2–7 bivalents, thereby indicating poor homology of parental genomes. The hybrids, Renanthera monachica × Phalaenopsis sanderiana and Arachnis hookeriana × Vanda suavis, lacked chromosome pairing. On the basis of chromosome affinity at meiosis, a cytotaxonomic scheme was developed for the several genera of the Vanda alliance studied. Cytotaxonomy, evolution and breeding behavior in the Vanda tribe were briefly discussed.     

Genetic relationships among <Emphasis Type="Italic">Hystrix patula,H. duthiei</Emphasis> and <Emphasis Type="Italic">H. longearistata</Emphasis> according to meiotic studies and genome-specific RAPD assay

Hybrids including Hystrix patula, H. duthiei and H. longearistata were obtained and genetic relationships among them were studied. Meiotic pairing in hybrids of H. duthiei × Psathyrostachys juncea (Ns), H. longearistata × Psa. juncea (Ns), Leymus multicaulis (NsXm) × H. duthiei, L. multicaulis (NsXm) × H. longearistata, Elymus sibiricus (StH) × H. patula, Roegneria ciliaris (StY) × H. patula, R. ciliaris (StY) × H. duthiei and R. ciliaris (StY) × H. longearistata averaged 5.76, 5.44, 11.94, 10.88, 10.08, 3.57, 0.46 and 0.90 bivalents per cell, respectively. The results indicated that H. duthiei and H. longearistata had the NsXm genomes of Leymus, while H. patula contained the StH genomes and had a low genome affinity with the StY genomes of Roegneria. Results of genome-specific RAPD assay were comparable with the chromosome pairing data. According to the genomic system of classification in Triticeae, H. patula should be considered as Elymus hystrix L., while H. duthiei and H. longearistata as Leymus duthiei and Leymus duthiei ssp. longearistata, respectively.     

Chromosome number and genetic system in several Trifolium species related to T. alexandrinum

Chromosome counts have been done in 12 species of Trifolium, closely related to T. alexandrinum L., and the chiasma frequency in meiosis, pollen fertility, and seedset upon selfing was estimated. In all species, the basic number of chromosomes was 2n=16 arranged in eight bivalents. Two species, T. salmoneum Mout, and T. berytheum Boiss., have 0–7 B-chromosomes in eight out of nine plants examined. The frequency of B-chromosomes was somewhat correlated with pollen fertility. Chiasma frequency ranged between 10.8 and 16.1 per cell with specific and ecotypic differentiation. Except for T. alexandrinum, the species analyzed were completely (or, in a few cases, highly) self-incompatible.Contribution from the Volcani Institute of Agricultural Research, Bet Dagan, Israel. 1970 Series, No. 1677 E. This research was financed by a grant from the U.S.D.A. under P.L. 480, Contract A10-CR-56.     

Chromosome pairing in triploid intergeneric hybrids ofFestuca pratensis withLolium multiflorum, revealed by GISH

Genomic in situ hybridisation (GISH) was used to reveal chromosome pairing in two partly fertile, triploid (2n = 3x = 21) hybrids obtained by crossing the diploid (2n = 2x = 14) Festuca pratensis Huds. (designated FpFp), used as a female parent, with the autotetraploid (2n = 4x = 28) Lolium multiflorum Lam. (designated LmLmLmLm), used as a male parent. The pattern of chromosome pairing calculated on the basis of the mean values of chromosome configurations identified in all 100 PMCs analysed, was: 0.71I Lm + 2.24I Fp + 2.18II Lm/Lm + 0.54II Lm/Fp + 4.18III Lm/Lm/Fp. A relatively high number of Lm/Lm bivalents and Fp univalents, and a low number of Lm/Fp bivalents and Lm univalents indicated that the pairing was preferential between L. multiflorum chromosomes. Other observations regarding chromosome pairing within the Lm/Lm/Fp trivalents also confirmed this preferential pairing in the analysed triploids, as the Fp chromosome was not randomly located in the chain- and frying-pan-shaped trivalents. The similarities and differences in chromosome pairing at metaphase I and the level of preferential pairing between Lolium chromosomes in the different triploid Lolium-Festuca hybrids are discussed.     

From Diploids to Allopolyploids: The Emergence of Efficient Pairing Control Genes in Plants

Polyploidy has played a major role in the evolution of higher plants. Precise control of chromosome pairing is vital for conferring meiotic regularity, and hence reproductive stability in allopolyploids. In this review, we examine whether strong evidence has accumulated for the presence and activity of pairing control genes in different allopolyploid species that are entirely bivalent forming and that display a strict disomic inheritance. We show that very good evidence has been adduced in Triticum species, Avena sativa, Festuca arundinacea, Brassica napus, Gossypium hirsutum, and G. barbadense, and in amphidiploids related to the diploid species Lolium perenne, L. multiflorum, and L. rigidum. More circumstantial evidence has been obtained for polyploids in the genera Aegilops, Hordeum, Nicotiana, and Coffea, which have received far less attention than the other species. Although these pairing regulators seem to control different processes operating throughout the premeiotic interphase and the meiotic prophase, little is known about their precise mode of action. We present three hypotheses that have been proposed to explain the origin and evolution of pairing control genes; none of them has been supported by direct evidence, and the origin of most pairing suppressors is still unknown. Accordingly, the study of pairing control genes is still an important task for understanding the stabilization and establishment of allopolyploid species.