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.     

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.     

Wide hybridization in Brassica

Summary Crosses were made to obtain interspecific hybrids between B. fruticulosa (wild species , 2n = 16) × B. campestris (cultivar , 2n = 20). Although many pollen grains germinated and their tubes entered the style, only about 30% of the ovules received pollen tubes. Fertilized ovules aborted at various stages of development. A few hybrid seeds resulted from hand pollinations in the field, and they showed poor germination and seedling establishment. The in vitro culture of ovaries, ovules, and seeds increased the frequency of obtaining hybrid seeds and plants: the most effective method was ovary culture followed by ovule culture. The hybrid nature of the plants was confirmed through morphological, cytological, and electrophoretic studies. A meiotic analysis of F₁ hybrids (2n = 18) showed that they had 0–5 bivalents and were completely pollen sterile. Electrophoretic analysis of leaf esterases and acid phosphatases of F₁ hybrids revealed bands derived from each parent. Induced amphidiploids of F₁ hybrids contained mostly bivalents, and had about 50% fertile pollen.     

Inheritance of mucilage canals in Laminaria (section Simplices) in eastern Canada

Two experiments have been carried out to test the suitability of the occurrence of mucilage canals as a criterion for species or ecotype definition in the non-digitate section of the genus Laminaria. A matrix of crossability tests shows complete interfertility between all mucilage canal types, fertile F₁ hybrids being produced in all cases. Quantitative genetic analysis reveals a large environmental component in the phenotypic variance of degree of mucilage canal development. Only plants from Nova Scotia bred true with respect to mucilage canals. This characteristic is therefore considered generally unsuitable for taxonomic and biological species determination, though there may be evidence for intraspecific genotypic differentiation of Nova Scotian populations.     

Genetic interactions between wheat and rye genomes in triticale

Summary Six primary triticale lines were produced from two advanced breeding lines of Triticum durum and three inbred genotypes of Secale cereale. The wheat and rye parents and the triticale derivatives were crossed in all possible combinations within each species group. Chiasma and univalent frequency of parents and hybrids were determined. The primary triticale lines had more univalents and less chiasmata per pollen mother cell than the corresponding wheat and rye parents together. The parental wheat F₁ exhibited negative heterosis for chiasma frequency whereas all rye hybrids had much higher chiasma frequencies than their inbred parents. Triticale F₁s generally showed lower chiasma frequencies and more univalents than their parents, but the degree of pairing failure was dependent upon which of the parental species within the triticale, wheat or rye, was in the heterozygous state. F₁s with heterozygous wheat genome only showed the least reduction in chiasma number (presumably caused by gene actions within the wheat genome), while F₁s with heterozygous rye genome showed high reduction in chiasma frequency and an increase in pairing failure (induced by negative interactions between the heterozygous rye and the wheat genome in triticale). A high correlation was found between the frequency of undisturbed pollen mother cells and the frequency of aneuploids in the subsequent generation. A higher number of aneuploids occurred in those populations which were heterozygous for the rye genome.     

Reproduction and cytogenetic characterization of interspecific hybrids derived from crosses between Brassica carinata and B. rapa

The tri-genomic hybrid (ABC, 2n=27) between Brassica carinata (BBCC, 2n=34) and B. rapa (AA, 2n=20) is a unique material for studying genome relationships among Brassica species and a valuable bridge for transferring desirable characteristics from one species to the other within the genus Brassica. The crossability between B. carinata and B. rapa was varied with the cultivar of B. rapa. Hybrid pollen mother cells (PMCs), confirmed by morphological observation and molecular marker assay, could be grouped into 20 classes on the basis of chromosome pairing configurations. More than 30% of the PMCs had nine or more bivalents. Genomic in situ hybridization confirmed that two of the bivalents most likely belonged to the B genome. Nearly one-half of the PMCs had trivalents (0–2) and quadrivalents (0–2), which revealed partial homology among the A, B, and C genomes and suggested that there is a good possibility to transfer genes by means of recombination among the three genomes. The advantages of using the tri-genomic hybrids as bridge material for breeding new types of B. napus are discussed.     

Synthesis, morphology and cytogenetics of Raphanofortii (TTRR, 2n = 38): a new amphidiploid of hybrid Brassica tournefortii (TT, 2n = 20) ×Raphanus caudatus (RR, 2n=18)

Amphidiploid Raphanofortii was synthesized by colchicinization of the F₁ hybrid Brassica tournefortii (TT, 2n = 20)×Raphanus caudatus (RR, 2n = 18). The crossability between these two species, and the cytomorphology of the F₁ plants and the amphidiploids were investigated. Intergeneric hybrids between the species were obtained only when B. tournefortii was involved as female parent. The hybrid plants were intermediate for most of the morphological attributes and showed very low pollen fertility compared to the parents. Although a majority of the pollen mother cells of the dihaploid hybrid (TR, 2n = 19) harboured univalents, a maximum of six bivalents were also observed. Of the 37 colchicine-treated F₁ plants analyzed cytologically, 21 were found to be true amphidiploids (2n = 38), whereas seven were mixoploids. Meiosis in the amphidiploids was characterized by the occurrence of 19 bivalents, though multivalents and univalents were also observed in a few cells. Most of the amphidiploid plants exhibited a fairly high pollen and seed fertility, which was further enhanced with the advancement of generations. Out of 69 plants investigated in the A₂ generation, 64 were euploids while the remaining five were aneuploids (2n = 36, 37, 39, 40 and 42). The newly synthesized Raphanofortii has great potential as a new commercial crop, as well as a bridge species for the transfer of economically important attributes of both the species to other Brassicas. Received: 2 November 1999 / Accepted: 26 March 2000     

SUPERNUMERARY CHROMOSOMES IN TRADESCANTIA II. EFFECT OF COLCHICINE ON MEIOTIC ISOCHROMOSOME CONFIGURATIONS

The effect of colchicine on meiotic pairing and configuration frequencies of three homologous isosupernumerary chromosomes was investigated. In the absence of colchicine, the three isochromosomes displayed a high degree of interchromosomal pairing and chiasma formation. As a consequence, a high frequency of bivalents and trivalents were observed at diakinesis-metaphase I. The unique structure of isochromosomes enables them to pair intrachromosomally (i.e., foldback pairing) yet the preferential occurrence of interchromosomal pairing suggests that all six arms of the three isosupernumerary chromosomes were in close association prior to or upon initiation of synapsis. Supernumerary chromosomes in microsporocytes treated during presynapsis or early synapsis with colchicine exhibited a significant reduction (P < 0.001) in the number of bivalents and trivalents at diakinesis. However, there was no reduction in overall chiasma frequency among supernumeraries due to the induction of increased intrachromosomal pairing and chiasma formation. A colchicine-sensitive association or alignment of homologues preceding effective pairing has been demonstrated in standard chromosomes of a number of plant species. This study provides the first evidence to indicate that at least certain supernumerary chromosomes may display presynaptic association as well. The results also support the strongly held contention that colchicine is not directly preventing or inhibiting the actual formation of chiasmata, since no reduction in chiasma frequency was observed in the isochromosomes.     

Comparative chiasma analysis using a computerised optical digitiser

A new computerised technique has been devised for measuring the distribution of chiasmata along diplotene bivalents. The method involves the introduction into the field of view of the microscope, of a fine light spot which can be accurately manipulated along the chromosomes of each bivalent. The data recorded include (a) the positions of the chiasmata along the bivalent in terms of their relative distances from the centromere and (b) the individual bivalent and cellular chiasma frequencies. — The method has been applied to the analysis of chiasma distribution patterns in the two known species of the genus Caledia, C. species nova 1 and C. captiva and in two chromosomal races of the latter. Statistical tests indicate that within bivalents at least 40% of the comparative distribution patterns of chiasmata between races and species are significantly different. Similar comparisons between populations within races reveal only 18% significant differences. — The observed distribution patterns of chiasmata in this genus suggest that chiasma formation is sequential from centromere to telomere. — The variation in the frequency and distribution of chiasmata between races and species suggests that the interference distances between successive chiasmata are, at least partially, independent of chiasma frequency and position. — The interracial and interspecific differences in chromosome structure are correlated with changes in chiasma pattern.     

Cytogenetics of double cross hybrids between Pennisetum americanum — P. purpureum amphiploids and P. americanum x Pennisetum squamulatum interspecific hybrids

Summary Pearl millet, Pennisetum americanum L. Leeke-napiergrass, Pennisetum purpureum Schum. amphiploids (2n=42) were crossed with pearl millet X Pennisetum squamulatum Fresen. interspecific hybrids (2n=41) to study the potential of germplasm transfer from wild Pennisetum species to pearl millet. These two interspecific hybrids were highly cross-compatible and more than two thousand trispecific progenies were produced from 17 double crosses. All doublecross hybrids were perennial and showed a wide range of morphological variations intermediate to both parents in vegetative and inflorescence characteristics. Some crosses resulted in sublethal progenies. Chromosomes paired mainly as bivalents (¯x15.88) or remained as univalents. At metaphase I, trivalents, quadrivalents, an occasional hexavalent and a high frequency of bivalents indicated some homeology among the genomes of the three species. Delayed separation of bivalents, unequal segregation of multivalents, lagging chromosomes, and chromatin bridges were observed at anaphase I. Although approximately 93% of the double-cross hybrids were male-sterile, pollen stainability in male-fertile plants ranged up to 94%. Seed set ranged from 0 to 37 seed per inflorescence in 71 plants under open-pollinated conditions. Apomictic embryo sac development was observed in double-cross progenies when crosses involved a pearl millet x P. squamulatum apomictic hybrid as pollen parent. These new double-cross hybrids may serve as bridging hybrids to transfer genes controlling apomixis and other plant characteristics from the wild Pennisetum species to pearl millet.     

The influence of B-chromosomes on chiasma frequencies in Black Mexican Sweet Corn

The mean chiasma frequency at first metaphase of meiosis in pollen mother cells of a maize variety, Black Mexican Sweet Corn, increases with increasing number ofB-chromosomes. The increased chiasma frequency is also reflected by a decrease in the number of rod bivalents at first metaphase. There is some indication that theB-chromosomes also influence the distribution of chiasmata between pollen mother cells. The increase in chiasma frequency due toBs is closely analogous to the increase in crossing-over carlier attributed toBs between marker genes located on chromosome III. Together the evidence confirm the role ofBs in controlling genetic recombination at meiosis.     

Chromosome evolution in the Gibasis linearis alliance (Commelinaceae)

Two related species of Gibasis, G. venustula (x = 6) and G. speciosa (x = 5) have been shown to be differentiated by a Robertsonian fusion. Meiotic analysis of the F₁ hybrids has revealed further chromosome differentiation of the parent species, involving several interchanges and inversions. These rearrangements tend to be concentrated in the Robertsonian group, and give rise to unusual meiotic configurations. The sets of the two species are nonetheless highly homologous as shown by high chiasma frequency and as much as 65% stainable pollen in the F₁. Models are proposed suggesting the possible evolutionary pathways of this karyotypic differentiation. The results are discussed in terms of chromosome evolution and its consequences for these species.     

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.     

An analysis of interspecific hybrids and phylogenetic implications inCucumis (Cucurbitaceae)

Investigations on interspecific crossability in 8Cucumis species (2n = 24) and chromosome pairing and pollen fertility of their hybrids from 15 combinations have been utilized for tracing the phylogenetic relationships among these taxa and factors responsible for their differentiation. A collective evaluation of data suggests that there are three broad groups of species, one of the spiny fruited interfertile species, whose hybrids show varying degree of chromosome associations and low to high pollen fertility; the second of species with non-spiny fruits, which are completely incompatible with the former but weakly compatible with the cultivated species,C. melo L. to produce partly developed seeds, and the third group ofC. metuliferus E. Mey. exSchrad. andC. melo and its different botanical varieties. The species with spiny fruits can be further divided based on karyomorphological similarities and/or on relative genomic affinity, indicated by chromosome pairing and hybrid pollen fertility.Cytogenetics inCucumis III.     

The control of chiasma distribution in the locust,Schistocerca gregaria (Forskål)

Chiasma distribution at diplotene in Schistocerca gregaria males can be taken to indicate the positions at which crossing over occurred prior to diplotene since chiasma terminalisation is entirely absent. Analysis of chiasma frequency and position leads to a model for the mechanism controlling distribution which has three main components. — i) The bivalents vary in length between cells due to unknown factors and increase in bivalent length leads to an increase in chiasma frequency. — ii) Within bivalents chiasma initiation is sequential from telomere to centromere with the first chiasma usually forming close to the telomere. — iii) Interference operates with the same polarity and determines a distance within which crossing over is precluded.     

A CYTOGENETIC ANALYSIS OF CERTAIN POLYPLOIDS IN GRINDELIA (COMPOSITAE)

Two diploid taxa, Grindelia procera and G. camporum, and 3 tetraploid ones, G. camporum, G. hirsutula, and G. stricta, have been studied to ascertain their interrelationships. Meiosis in diploid parental strains was regular, the common chromosome configuration being 5 rod bivalents and 1 ring bivalent. The average chiasmata frequency per chromosome was 0.60. Pollen fertility was about 90% in all strains examined. Diploid interspecific hybrids had normal meiosis with an average chiasmata frequency of 0.56 per chromosome. No heterozygosity for inversions or interchanges was detected, and pollen fertility was above 85%. Meiosis in parental tetraploid strains was characterized by the presence of quadrivalents in addition to a complementary number of bivalents. The average chiasmata frequency per chromosome was 0.59 and pollen fertility was generally about 80%. Tetraploid interspecific hybrids also had quadrivalents, normal meiosis, and high pollen fertility. Close genetic relationships between the diploids and between the tetraploids are indicated, and geographical, ecological, and seasonal barriers to gene exchange exist. Attempts to obtain hybrids between diploids and tetraploids were successful in a few cases. The hybrids were tetraploid and had normal meiosis and fertility similar to parental and F₁ tetraploids. Their origin was by the union of unreduced gametes of the diploid female parent and normal pollen from the tetraploid parent. On the basis of chromosome homology, normal meiosis, plus high fertility exhibited in the diploid, tetraploid, and diploid X tetraploid interspecific hybrids, these species of Grindelia are considered to be a part of an autopolyploid complex. Gene exchange between diploids and diploids, tetraploids and tetraploids, and diploids and tetraploids is possible. Tetraploid G. camporum may have originated by hybridization between G. procera and diploid G. camporum with subsequent doubling of chromosomes and selection for the combined characteristics of the diploids.     

Behavior of meiotic chromosomes in Pinus wallichiana, P. strobus and their hybrid and nrDNA localization in pollen mother cells of the hybrid by using FISH

The complete process of meiosis was investigated in Pinus wallichiana, P. strobus and their artificial hybrid （F1） using microsporocytes. It is revealed that there were slightly lower chiasma frequency, lower ring bivalent frequency, lower meiotic index and distinctly higher frequency of aberrance （chromosomal bridges, fragments or micronuclei） in pollen mother cells （PMCs） of the hybrid （F1） than those of the parental species, which showed a certain degree of differentiation between homologous chromosomes of the two parents. However, relatively higher frequency of ring bivalents and higher meiotic index in all the three entities indicate the great stability of genomes of parental species, and the differentiation of genomes between the two parents must have been slight. Total nineteen signal loci of 18S rDNA were observed in nine bivalents of the hybrid （F1）, among which one bivalent bears two loci, while the others have only one. It is suggested that distinct differentiation at genetic level existed in homologous chromosomes of the two parental species, whereas only slight differentiation at karyotypic and genomic levels take place between the parent species.     

The effect of supernumerary chromosomes on meiosis in Puschkinia libanotica (Liliaceae)

The presence of the partly heterochromatic supernumerary chromosomes in pollen mother cells of Puschkinia libanotica raises the chiasma frequency in the A chromosome bivalents. The pattern of chiasma distribution along each of the five A bivalents was related to the DNA labelling pattern of mitotic chromosomes. Regions that showed heavy labelling at the end of the DNA synthetic phase had fewer chiasmata than lightly labelled regions. As this relation is the opposite to that found by Rees and Evans in another species we regard any correlation between labelling pattern and chiasma distribution as fortuitous.     

Development of monosomic alien addition lines and introgression of genes from Oryza australiensis Domin. to cultivated rice O. sativa L.

Oryza australiensis, a diploid wild relative of cultivated rice, is an important source of resistance to brown planthopper (BPH) and bacterial blight (BB). Interspecific hybrids between three breeding lines of O. sativa (2n=24, AA) and four accessions of O. australiensis (2n=24, EE) were obtained through embryo rescue. The crossability ranged from 0.25% to 0.90%. The mean frequency of bivalents at diakinesis/metaphase I in F₁ hybrids (AE) was 2.29 to 4.85 with a range of 0–8 bivalents. F₁ hybrids were completely male sterile. We did not obtain any BC₁ progenies even after pollinating 20,234 spikelets of AE hybrids with O. sativa pollen. We crossed the artificially induced autotetraploid of an elite breeding line (IR31917-45-3-2) with O. australiensis (Acc. 100882) and, following embryo rescue, produced six F₁ hybrid plants (AAE). These triploid hybrids were backcrossed to O. sativa. The chromosome number of 16 BC₁ plants varied from 28 to 31, and all were male sterile. BC₂ plants had 24–28 chromosomes. Eight monosomic alien addition lines (MAALs) having a 2n chromosome complement of O. sativa and one chromosome of O. australiensis were selected from the BC₂ F₂ progenies. The MAALs resembled the primary trisomies of O. sativa in morphology, and on the basis of this morphological similarity the MAALs were designated as MAAL-1, -4, -5, -7, -9, -10, -11, and -12. The identity of the alien chromosome was verified at the pachytene stage of meiosis. The alien chromosomes paired with the homoeologous pairs to form trivalents at a frequency of 13.2% to 24.0% at diakinesis and 7.5% to 18.5% at metaphase I. The female transmission rates of alien chromosomes varied from 4.2% to 37.2%, whereas three of the eight MAALs transmitted the alien chromosome through the male gametes. BC₂ progenies consisting of disomic and aneuploid plants were examined for the presence of O. australiensis traits. Alien introgression was detected for morphological traits, such as long awns, earliness, and Amp-3 and Est-2 allozymes. Of the 600 BC₂ F₄ progenies 4 were resistant to BPH and 1 to race 6 of BB. F₃ segregation data suggest that earliness is a recessive trait and that BPH resistance is monogenic recessive in two of the four lines but controlled by a dominant gene in the other two lines.     

Chromosome pairing in tetraploid hybrids between Lolium perenne and L. multiflorum

Summary Chromosome association at first meiotic metaphase in tetraploid hybrids between Lolium perenne and L. multiflorum was compared with that in autotetraploid L. perenne. The hybrids were found to have significantly higher levels of bivalent frequency, and lower levels of multivalent and chiasma frequency. A significant increase in multivalent frequency with increasing chiasma formation was found in both groups, but the increase was much less in the hybrids. These differences in chromosome associations between the two groups must therefore reflect differences in chiasma distribution and it is suggested that the results indicate a significant degree of preferential bivalent pairing in the hybrids.