Meiotic behaviour of Un,D and R genomes in the amphiploid Aegilops ventricosa -Secale cereale and the parental species

Summary Meiotic pairing frequencies of the Un and D genomes of Ae. ventricosa and the R of S. cereale could be easily established at metaphase I in Aegilops ventricosa — Secale cereale amphiploid plants as well as in its parental species by using the C-banding technique procedure. The results show a high diminution of chromosome pairing for all genomes in the amphiploid with respect to its parental species probably due to C-heterochromatin content and/or genotypic or cryptic interactions between the three genomes.     

Transfer of Ph I genes promoting homoeologous pairing from Triticum speltoides to common wheat

Diploid-like chromosome pairing in polyploid wheat is controlled by several Ph (pairing homoeologous) genes with major and minor effects. Homoeologous pairing occurs in either the absence of these genes or their inhibition by genes from other species (Ph ^I genes). We transferred Ph ^I genes from Triticum speltoides (syn Aegilops speltoides) to T. aestivum, and on the basis of further analysis it appears that two duplicate and independent Ph ^I genes were transferred. Since Ph ^I genes are epistatic to the Ph genes of wheat, homoeologous pairing between the wheat and alien chromosomes occurs in the F₁ hybrids. Using the Ph ^I gene stock, we could demonstrate homoeologous pairing between the wheat and Haynaldia villosa chromosomes. Since homoeologous pairing occurs in F₁ hybrids and no cytogenetic manipulation is needed, the Ph ^I gene stock may be a versatile tool for effecting rapid and efficient alien genetic transfers to wheat.Contribution no. 93-435-J from the Kansas Agricultural Experiment Station, Kansas State University, Manhattan, KS 66506-5502, USA     

Meiotic mutants of rye Secale cereale L. II. The nonhomologous synapsis in desynaptic mutants sy7 and sy10

We studied the expression and inheritance of two spontaneous mutations found in different populations of rye Secale cereale L. that cause high univalent frequency in meiosis and low fertility. Both mutations were inherited as monogenic recessives. For each of the mutations the corresponding gene symbols (sy7 and sy10) were suggested although their allelism has not been studied. These mutants differ in chiasma frequency and in the number of univalents per meiocyte. Electron microscopy of the wholemount surface-spread synaptonemal complexes (SCs) from microsporocytes of both mutants revealed that during meiotic prophase I random synapsis began and progressed that involved not only homologous but also nonhomologous chromosomes. SCs were formed with frequent changes of pairing partners (switches) and intrachromosomal foldbacks of unpaired axial elements. As a result, incompletely synapsed, non-homologous and multivalent SCs were formed in mutants by the stage analogous to pachytene in normal plants. In sy7 a maximum in the number of switches and foldbacks were observed at zygotene, whereas in sy10 this occurred at pachytene. We suggest that it is the process of recognition of homology that is impaired in both mutants. This leads to indiscriminate synapsis and prevents chiasma formation. Both mutants may be classified as desynaptic.     

Standard karyotypes ofAegilops uniaristata,Ae. mutica,Ae. comosa subspeciescomosa andheldreichii (Poaceae)

C-banding patterns and polymorphisms were analyzed in several accessions of the diploidAegilops speciesAe. uniaristata, Ae. mutica, andAe. comosa subsp.comosa and subsp.heldreichii, and standard karyotypes of these species were established. Variation in C-band size and location was observed between different accessions, but did not prevent chromosome identification. One accession ofAe. uniaristata was homozygous for whole-arm translocations involving chromosomes 1N and 5N. The homoeologous relationships of these chromosomes were established by comparison of chromosome morphologies and C-banding patterns to other diploidAegilops species with known chromosome homoeology. In addition, in situ hybridization analysis with a 5S rDNA probe was used to identify homoeologous groups 1 and 5 chromosomes. The present analysis permitted the assignment of allAe. mutica, comosa subsp.comosa, andAe. comosa subsp.heldreichii chromosomes, and three of the sevenAe. uniaristata chromosomes according to their homoeologous groups. The data presented will be useful analyzing genome differentiation in polyploidAegilops species.     

Morphological and cytological evidence for polyphyletic allopolyploidy inArctostaphylos mewukka (Ericaceae)

The central Sierran tetraploidArctostaphylos mewukkaMerriam has been reported to be an allopolyploid originating from the diploid species,A. patulaGreene and eitherA. viscida subsp.viscidaParry orA. viscida subsp.mariposa (Dudley)P. V. Wells, although without conclusive evidence. Morphometrics and the verification and determination of chromosome numbers were used to substantiate the evolutionary relationships among these species. A closely related species,Arctostaphylos trueiKnight, was also examined using these methods to determine its separability fromA. mewukka. The morphometric analyses support a hypothesis for a polyphyletic origin ofA. mewukka from different races ofA. viscida andA. patula. The chromosomal data, although inclusive, also support this hypothesis. The data do not support the recognition ofA. truei as a taxonomic entity separate fromA. mewukka at the species level.     

Meiotic mutants of rye Secale cereale L.

Summary A mutant form of weedy rye characterized by male and female sterility and having a hereditary block in the chromosome synapsis has been found and described. Genetic analysis has shown the synapsis block to be determined by the recessive allele of a gene designated as sy-1. Electron microscopy of surface-spread microsporocyte nuclei revealed the complete absence of the synaptonemal complex over the whole meiotic prophase I, although the axial cores were perfectly formed by each chromosome. Only univalents were observed at metaphase I, their average number ranging from 13.1 to 14.0 per cell. A precocious distribution of univalents at the poles is observed at metaphase I. All of the later stages of meiosis were irregular and resulted in the formation of abnormal microspores. Thus, the mutant proves to be asynaptic because of the blocked initiation of synapses at prophase I.     

ph1b基因在普通小麦与Ae.crassa、Ae.crassassp杂种中的作用

通过对(中国春ph1b突变体×Ae. crassa)F_1、(中国春×Ae.crassa)F_1;(中国春ph1b突变体×Ae.crassassp)F_1、(中国春×Ae.crassassp)F_4花粉母细胞减数分裂中期Ⅰ染色体配对的研究。第一次证明了中国春ph1b突变体在诱导Ae.crassa、Ae.crassassp与普通小麦部分同源染色体配对方面有显著作用。可以利用ph1b基因通过诱导部分同源染色体配对交换的方法以染色体易位的方式把Ae.crassa和Ae.crassassp的有益基因导入普通小麦中。Ae.crassa和Ae.crassassp中不含有拟ph1基因。Ae.crassa和Ae.crassassp的D染色体组与普通小麦的D染色体组有明显区别。     

The inheritance of rye seed peroxidases

Summary Genetic analyses were conducted on peroxidase of the embryo and endosperm of seeds of one open pollinated and six inbred lines of cultivated rye (Secale cereale L.), and one line of Secale vavilovii Grossh. The analyses of the individual parts of the S. cereale seed yield a total of 14 peroxidase isozymes. Isozymes m, a, b, c, d, e, f and g (in order from faster to slower migration) were found in the embryo plus scutellum, while isozymes 1, 2, 3, 4, 5 and 6 (also from faster to slower migration) were peculiar of the endosperm. S. vavilovii has isozymes m, c₁, d, e, f and g in its embryo plus scutellum, and isozyme 2 in the endosperm. Segregation data indicated that at least 13 different loci would be controlling the peroxidase of S. cereale. Isozymes a and b are controlled by alleles of the same locus, all the other loci have one active and dominant allele coding for one isozyme, and other null and recessive allele. The estimation of linkage relationships shows that five endosperm loci are linked, and tentative maps are shown. A possible dosage effect and the existence of controlling gene(s) for endosperm isozyme 4 is reported. All these data and the high frequency of null alleles found are discussed in relation to recent reports.     

Assessment of genome relationships in the genus Oryza L. based on seed-protein profile analysis

Summary Cultivated and wild Oryza species belonging to different genomic groups were studied with regard to their soluble seed-protein profiles. There is an essential uniformity in the banding patterns within various genomes and the basic patterns are not species-specific but genome-specific. O. meridionalis contains a subgenome similar to the A genome of O. rufipogon. Certain specific bands present among A genome species have been found to be useful in tracing the phylogenetic affinity between the cultivated species and their presumed wild progenitors.     

B-chromosomes in inbred lines of rye (Secale cereale L.)

B chromosomes from an experimental population of the Japanese JNK strain of rye, isogenic for its Bs, have been backcrossed into twelve different inbred lines. The experiment is a way of studying the effects of the Bs against a range of different homozygous A chromosome backgrounds. This publication deals with pairing effects of both the As and the Bs, and their interactions, and with pollen mitosis. At meiosis there is a genotypic component to B effects, and they do not appear to act solely through a physical disturbance within the nucleus. In pollen the Bs are always present in more than 50% of the grains regardless of their pairing behaviour during meiosis; this result fits with a parasitic model of the activity of rye Bs.     

Repetitive, genome-specific probes in wheat (Triticum aestivum L. em Thell) amplified with minisatellite core sequences

The detection and analysis of DNA polymorphisms in crops is an essential component of marker-assisted selection and cultivar identification in plant breeding. We have explored the direct amplification of minisatellite DNA by PCR (DAMD-PCR) as a means for generating DNA probes that are useful for detecting DNA polymorphisms and DNA fingerprinting in wheat. This technique was facilitated by high-stringency PCR with known plant and animal minisatellite core sequences as primers on wheat genomic DNA. The products of DAMD-PCR from Triticum aestivum, T. durum, T. monococcum, T. speltoides and T. tauschii showed a high degree of polymorphism and the various genomes could be identified. Cloning of the DAMD-PCR products and subsequent Southern hybridization frequently revealed polymorphic probes showing a good degree of genome specificity. In addition, polymorphic, single locus, and moderately dispersed PCR products were cloned that may have a potential for DNA fingerprinting. Our experiments were limited primarily to diploid wheats and the results indicated that DAMD-PCR may isolate genome-specific probes from wild diploid wheat species that could be used to monitor genome introgression into hexaploid wheat.This paper reports the results of research only. Mention of a proprietary product does not constitute an endorsement or a recommendation for its use by the USDA or the University of Missouri. Contribution from the University of Missouri, the Agricultural Experimental Station and U.S. Department of Agriculture-Agricultural Research Service, Plant Genetics Research Unit, journal series No. 12523     

Non-reductional meiosis in aTriticum turgidum ×Aegilops longissima hybrid and in backcrosses of its amphidiploid withT. turgidum (Poaceae)

Meiosis was studied in aT. turgidum ×Ae. longissima hybrid (ABS¹, 2n = 21) and in backcrosses of its amphidiploid toT. turgidum. Analysis of PMCs of the hybrid showed that non-reductional meiosis led to the production of a large number of non-reduced male gametes. The hybrid showed high seed set. All progeny had 2n = 42. The BC₁ plants (2n = 35, AABBS¹) showed the expected meiotic pairing of 14^II + 7^I. At anaphase I, univalents behaved in a non-reductional way. The possible role of meiotic non-reduction is discussed in terms of the evolution of theTriticum-Aegilops complex.     

D genome doners for Aegilops cylindrica (CCDD) and Triticum aestivum (AABBDD) deduced from esterase isozyme analysis

Summary Putative D genome donors for Aegilops cylindrica (2n = 28, CCDD) and Triticum aestivum (2n = 42, AABBDD) were studied with the isoelectric focusing patterns of esterase isozymes. 103 strains of Ae. cylindrica were uniform in their isozyme pattern. 30 strains of the putative parent, Ae. caudata, showed no zymogram variation, whereas the other parent, Ae. squarrosa, comprised 3 phenotypes. Natural Ae. cylindrica had an isozyme pattern which corresponded to a mixture of esterases from Ae. caudata and type 3 Ae. squarrosa. Therefore, it is concluded that the D genome donor of Ae. cylindrica is derived from type 3 Ae. squarrosa. These results suggest that Ae. cylindrica originated with a single amphiploidy event, and the C and D genomes have remained remarkably constant regarding esterase isozyme composition.On the other hand, T. aestivum comprised three zymogram phenotypes. These phenotypes contain bands which can be ascribed to the D genome of type 2 Ae. squarrosa. These results suggest that the D genome of Ae. cylindrica differs from that of T. aestivum. Evolution of the AB and D genomes of T. aestivum is indicated by the zymogram polymorphism. The origin of Ae. cylindrica is possibly more recent than that of T. aestivum.Contribution No. 433 of the Laboratory of Genetics, Faculty of Agriculture, Kyoto University     

Colchicine-induced polyploidization depends on tubulin polymerization in c-metaphase cells

The microtubule cytoskeleton plays a crucial role in the cell cycle and in mitosis. Colchicine is a microtubule-depolymerizing agent that has long been used to induce chromosome individualization in cells arrested at metaphase and also in the induction of polyploid plants. Although attempts have been made to explain the processes and mechanisms underlying polyploidy induction, the role of the cytoskeleton still remains largely unknown. Through immunodetection of alpha-tubulin, different concentrations (0.5 or 5 mM) of colchicine were found to produce opposite effects in the organization of the cytoskeleton in rye (Secale cereale L.). A low concentration (0.5 mM) induced depolymerization of the microtubular cytoskeleton in all phases of the cell cycle. In contrast, a high concentration (5 mM) was found to induce the polymerization of new tubulin-containing structures in c-metaphase cells. Furthermore, both treatments also showed contrasting effects in the induction of polyploid cells. Flow cytometric analysis and quantitative assessments of nucleolus-organizing regions revealed that only the high-concentration colchicine treatment was effective in the formation of polyploid cells. Our studies indicate that spindle disruption alone is insufficient for the induction of polyploid cells. The absence of any tubulin structures in plants treated with colchicine at the low concentration induced cell anomalies, such as the occurrence of nuclei with irregular shape and/or (additional) micronuclei, 12 h after recovery, pointing to a direct effect on cell viability. In contrast, the almost insignificant level of cell anomalies in the high-concentration treatment suggests that the presence of new tubulin-containing structures allows the reconstitution of 4C nuclei and their progression into the cell cycle.     

Phylogeny of tall fescue and related species using RFLPs

The wild species of tall fescue (Festuca arundinacea var.genuina Schreb.) represent a wide range of genetic variation and constitute potential germplasm for tall fescue improvement. Our objective was to evaluate genome specificity of the previously-identified DNA probes and to examine the phylogenetic relationship of tall fescue with six related species by using RFLP data. A total of 29 DNA probes from aPstI-genomic library of tall fescue were hybridized toEcoRI-orHindIII-digested DNA of 32 plants from sixFestuca species and fromLolium perenne L. Fifteen probes hybridized to all seven species. The remaining 14 probes showed differential hybridization patterns (i.e., ±), especially at the diploid and tetraploid levels. This hybridization pattern reflected genome divergence in these species. The DNA probes will be useful markers in breeding programs involving interspecific and intergeneric hybridization. Cluster analyses were performed using the average genetic distances calculated with the RFLP data from 53 probe-enzyme combinations. Generally, genotypes from the same species were grouped in the same cluster. These data indicated that tall fescue has a close relationship withF. pratensis Huds. (diploid),F. arundinacea var.glaucescens Boiss. (tetraploid), andL. perenne L. (diploid) and thatFestuca pratensis andL. perenne had the closest degree of relationship.This paper is a contribution of the Missouri Agricultural Experimental Station, Journal Series no. 11,798     

RFLP-based maps of the homoeologous group-6 chromosomes of wheat and their application in the tagging of Pm12, a powdery mildew resistance gene transferred from Aegilops speltoides to wheat

Genetic maps of the homoeologous group-6 chromosomes of bread wheat, Triticum aestivum, have been constructed spanning 103 cM on 6A, 90 cM on 6B and 124 cM on 6D. These maps were transferred to a Chinese Spring (CS) x line #31 cross to locate a dominant powdery mildew resistance gene, Pm12, introgressed into line #31 from Aegilops speltoides. Pm12 was shown to lie on the short arm of translocation chromosome 6BS-6SS.6SL in line #31, but could not be mapped more precisely due to the lack of recombination between the 6S Ae. speltoides segment and chromosome 6B. Possible strategies to reduce the size of the alien segment, which probably encompasses the complete long arm and more than 82% of the short arm of chromosome 6B, are discussed.     

Chromosomal location of genes controlling seed proteins in species related to wheat

Summary The seed proteins of Chinese Spring wheat stocks which possess single chromosomes from other plant species related to wheat have been separated by gel electrophoresis in the presence of sodium dodecyl sulphate. Marker protein bands have been detected for both arms of barley chromosome 5, chromosome E (= 1R) and B (= 2R) of rye, chromosomes A,B (= 1C^u) and C (= 5C^u) of Aegilops umbellulata and chromosomes I and III of Agropyron elongatum. These studies, and previous findings, indicate that chromosome 5 of barley, chromosome 1R of rye, chromosome I of Ag. elongatum and possibly chromosome 1C^u of Ae. umbellulata are similar to chromosomes 1A, 1B and 1D in hexaploid wheat in that they carry genes controlling prolamins on their short arms and genes controlling high-molecular-weight (apparent molecular weight greater than 86,000) seed protein species on their long arms. These findings support the idea that all these chromosomes are derived from a common ancestral chromosome and that they have maintained their integrity since their derivation from that ancestral chromosome.