摘要:

The flax L locus exists as a single gene with at least 13 alleles with different rust-resistance specificities. With regards to resistance to North American races of flax rust the L2, L6, and L11alleles are of major importance. Molecular markers have been developed by screening primer sets, whose sequences were based on the nucleotide sequence of L6, for their ability to amplify segments of the L gene. One primer combination was found to amplify only the L6or L11alleles and another primer set was found to amplify the 3'end of all important L alleles. The latter primer set yielded a 1.3 kb fragment which upon digestion with the endonucleaseMboI generated RFLP patterns unique to L2, L6, L9, and L11. The application of PCR markers to a set of 22 cultivars, comprised of deregistered, recent, and yet to be released cultivars verifies genetic studies done by previous workers and demonstrates the usefulness of the markers for following segregation of L alleles in crosses amongst wide or narrow selections of cultivars. Overall, the results confirmed that L6is present in many Canadian flax cultivars. However, in several recently-released flax cultivars that have rust resistance conditioned by genes at other loci, the L9allele was detected. These molecular markers will be useful in marker-assisted selection and the introduction of new genes for rust resistance in the flax breeding programs.Key words: flax rust, PCR/RFLP marker, marker-assisted selection.

ISSN:0831-2796    

DOI:10.1139/g98-101

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

Short runs of mononucleotide repeats are present in chloroplast genomes of higher plants. In soybean, rice, and pine, PCR (polymerase chain reaction) with flanking primers has shown that the numbers of A or T residues in such repeats are variable among closely related taxa. Here we describe a set of primers for studying mononucleotide repeat variation in chloroplast DNA of angiosperms where database information is limited. A total of 39 (A)nand (T)nrepeats (n10) were identified in the tobacco chloroplast genome, and DNA sequences encompassing these 39 regions were aligned with orthologous DNA sequences in the databases. Consensus primer pairs were constructed and used to amplify total genomic DNA from a hierarchical set of angiosperms. All 10 primer pairs generated PCR products from members of the Solanaceae, and 8 of the 10 were also functional in most other angiosperm species. Levels of interspecific polymorphism within the generaNicotiana,Lycopersicon(both Solanaceae), andActinidia(Actinidiaceae) proved to be high, while intraspecific variation inNicotiana tabacum,Lycopersicon esculentum, andActinidia chinensiswas limited. Sequence analysis of PCR products from three primer pairs revealed variable numbers of A, G, and T residues in mononucleotide arrays as the major cause of polymorphism inActinidia. Our results suggest that universal primers targeted to mononucleotide repeats may serve as general tools to study chloroplast variation in angiosperms.Key words: genetic markers, chloroplast genome, microsatellites, consensus primers, angiosperms.

ISSN:0831-2796    

DOI:10.1139/g98-104

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

Maize streak, incited by maize streak geminivirus (MSV), is a major disease limiting maize (Zea maysL.) production over widespread areas of Africa. To understand the genetic basis of tolerance to MSV, recombinant inbred lines (RILs) derived from the cross of the MSV tolerant inbred Tzi4 with the MSV susceptible inbred Hi34, were evaluated for MSV tolerance. Experiments were conducted using controlled leafhopper (Cicadulinaspp.) infestation in one glasshouse experiment at Namulonge, Uganda, and two field experiments at Centro Internacional de Mejoramiento de Maiz y Trigo, Harare, Zimbabwe. Eighty-seven RILs were genotyped at 82 loci by restriction fragment length polymorphism (RFLP) analysis. The association between genotype at RFLP marker loci and MSV tolerance was determined using single-factor analysis of variance (SFAOV), multiple regression, and interval mapping procedures. There was a significant association of MSV tolerance with RFLP markers on the short arm of chromosome 1. By SFAOV, the portion of the phenotypic variance explained by genotype class (R2) for the association betweennpi262and the area under disease progress curve (AUDPC) measure of MSV tolerance was as high as 76% in field experiments. Interval mapping analyses (Knapp and Bridges 1990; Nelson 1997) identified the chromosome region bracketed bybnl12.06aandnpi262as explaining the largest proportion of the variation in MSV tolerance. After classification of symptom responses from the final field ratings into resistant and susceptible classes, qualitative analysis of data fit a chi-square test to a 1:1 Mendelian ratio, further indicating presence of a single major gene. Multipoint linkage analysis placed this gene, designatedmsv1, at a genetic distance of 3 cM distal tonpi262. Identification of the tightly linked molecular marker locusnpi262should greatly aid ongoing conversion of susceptible African varieties to maize streak resistance.Key words:Zea maysL.,Cicadulinaspp., host resistance, gene mapping, molecular markers.

ISSN:0831-2796    

DOI:10.1139/g98-099

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

Microsatellites or simple sequence repeats (SSRs) have been demonstrated to be abundant and hypervariable in some eukaryotic genomes. Although the presence of microsatellites is very well documented in many plant species, no information on microsatellites in beans (PhaseolusandVigna) is available. To assess the abundance and usefulness of bean microsatellites as genetic markers, 326 DNA sequences from the GenBank databases were searched. Sixty-one simple repetitive DNA sequences with 23 different types of repetitive DNA motifs were identified as potential microsatellites. Among these were 49 microsatellites from common bean (Phaseolus vulgaris)entries and 12 microsatellites from the genusVigna. The most abundant type of microsatellite found in this search was that with di-nucleotide repeats of AT/TA.Microsatellites with tri- and tetra-nucleotide motifs were also identified. PCR analysis of 12 of the microsatellite-containing loci revealed that 11 of the 12 primer pairs could produce easily-scorable fragments, or groups of fragments. Allelic variation of the 11 loci was surveyed in 12 common bean inbred lines representing a diversity of germplasms. Seven of the 11 microsatellite loci were polymorphic and yielded 2-10 alleles. Analyses of the polymorphic loci in a common bean F6recombinant inbred population showed that each segregated in a Mendelian fashion.Key words: microsatellite, simple sequence repeat, molecular marker, bean.

ISSN:0831-2796    

DOI:10.1139/g98-100

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

Cytological investigation revealed desynapsis in microsporogenesis of a wild diploid clone ofVaccinium darrowi.Expression of desynapsis appears variable among the pollen mother cells (PMCs). In the PMCs expressing desynapsis, all or most chromosomes appeared to be completely desynapsed before anaphase I (AI) since bivalents were rare at this stage. In some PMCs complete separation of chromatids was also observed before AI. Consequently, one or both meiotic divisions were lacking, which in turn suggests either a lack of spindle formation or function. Lack of spindle function was hypothesized from the observation that in PMCs with only separated chromatids (daughter chromosomes) before AI or anaphase II (AII), their subsequent movement to anaphase poles was not observed. Thus, spindle formation or function appears to be dependent on paired homologues (bivalents) or minimally joined sister chromatids (univalents) being present. Omission of meiosis II could lead to formation of fertile 2npollen (~5%), since a balanced chromosome complement would be expected with an equational division of the entire chromosome complement at AI. The genetic constitution of the 2ngamete would be equivalent to first division restitution (FDR) origin. If chiasmata are lacking then recombination would be absent, and 100% transmission of parental heterozygosity would be expected with FDR 2ngametes. Because desynapsis may arise from the lack of effective chiasmata between the paired homologues, a high level of parental heterozygosity is expected to be retained in the 2ngametes. The potential usage of the 2ngametes in blueberry breeding was discussed.Key words: desynapsis, spindle abnormality, 2npollen, blueberry.

ISSN:0831-2796    

DOI:10.1139/g98-098

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

Primers based on a conserved nucleotide binding site (NBS) found in several cloned plant disease resistance genes were used to amplify DNA fragments from the genome of common bean (Phaseolus vulgaris). Cloning and sequence analysis of these fragments uncovered eight unique classes of disease-resistance related sequences. All eight classes contained the conserved kinase 2 motif, and five classes contained the kinase 3a motif. Gene expression was noted for five of the eight classes of sequences. A clone from the SB3 class mapped 17.8 cM from theUr-6gene that confers resistance to several races of the bean rust pathogenUromyces appendiculatus. Linkage mapping identified microclusters of disease-resistance related sequence in common bean, and sequences mapped to four linkage groups in one population. Comparison with similar sequences from soybean (Glycine max) revealed that any one class of common bean disease-resistance related sequences was more identical to a soybean NBS-containing sequence than to the sequence of another common bean class.Key words: nucleotide binding sites, disease-resistance related sequences,Phaseolus vulgaris,Glycine max.

ISSN:0831-2796    

DOI:10.1139/g98-097

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

Digoxigenin-labeled total genomic DNA fromOryza eichingeriwas hybridized in situ to somatic chromosome preparations of F1, F2, backcross progenies, and a pollen-derived tetraploid plant (E24) fromO. sativa(2n= 24, genome AA) ×O. eichingeri(2n= 24, genome CC), which allowed a definitive discrimination between A- and C-genome chromosomes. Twelve chromosomes in F1, F2, BC1, and twenty-four chromosomes in plant E24were clearly revealed to be ofO. eichingeriorigin, thus confirming that both BC1and F2were allotriploids (2n= 36, AAC) while plant E24was an amphiploid (2n= 48, AACC). In addition, the presence ofO. eichingerichromosomes in four alien addition lines was characterized. The results suggest that FISH/GISH may be a powerful tool for monitoring theO. sativa-alien chromosome in the progenies of rice interspecific hybridization.Key words: fluorescent in situ hybridization,Oryza sativa,Oryza eichingeri, amphiploid, alien addition lines

ISSN:0831-2796    

DOI:10.1139/g98-096

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

In order to obtain new information on the genome organization ofArachisribosomal DNA, more particularly amongA. hypogaeaand its close relatives, the distribution of the 18S-5.8S-26S and 5S ribosomal RNA gene families on the chromosomes of 21 diploid and tetraploidArachisspecies, selected from six of nine taxonomic sections, was analyzed by in situ hybridization with pTa71 (18S-5.8S-26S rDNA) and pTa794 (5S rDNA) clones. Two major 18S-5.8S-26S rDNA loci with intense signals were found in the nucleolus organizer regions (NOR) of each of the diploid and tetraploid species. In addition to extended signals at major NORs, two to six medium and (or) minute-sized signals were also observed. Variability in the number, size, and location of 18S-5.8S-26S sites could generally distinguish species within the same genome as well as between species with different genomes. The use of double fluorescence in situ hybridization enabled us to locate the positions of 5S rRNA genes in relation to the chromosomal location of 18S-5.8S-26S rRNA genes inArachischromosomes which were difficult to karyotype. Two or four 5S rDNA loci and 18S-5.8S-26S rDNA loci were generally located on different chromosomes. The tandemly repeated 5S rDNA sites were diagnostic for T and C genomes. In one species, each of B and Am genomes, the two ribosomal gene families were observed to occur at the same locus. BarringA. ipaensisandA. valida, all the diploid species had characteristic centromeric bands in all the 20 chromosomes. In tetraploid speciesA. hypogaeaandA. monticolaonly 20 out of 40 chromosomes showed centromeric bands. Comparative studies of distribution of the two ribosomal gene families, and occurrence of centromeric bands in only 20 chromosomes of the tetraploid species suggests thatA. villosaandA. ipaensisare the diploid progenitors ofA. hypogaeaandA. monticola. This study excludesA. batizocoias the B genome donor species forA. hypogaeaandA. monticola.Key words:Arachisspecies, 5S rRNA, 18S-5.8S-26S rRNA, in situ hybridization, evolution.

ISSN:0831-2796    

DOI:10.1139/g98-092

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

The molecular organization of the 18S, 5.8S, and 28S ribosomal RNA gene repeat units, located at the single nucleolus organizer region (NOR) locus in the chicken, was investigated in genetically distinct populations of research and commercial chickens. Substantial gene repeat variation within and among NORs was documented. Intact ribosomal gene repeat size ranged from 11 kb to over 50 kb. Unique combinations of ribosomal genes, of different size, were specific to particular populations. It was determined that the basis for the ribosomal gene repeat size variation was intergenic spacer (IGS) length heterogeneity. Interestingly, in different populations, the location of the variation that contributes to length heterogeneity was specific to particular IGS subregions. In addition to IGS variation, an inbred line of Red Jungle Fowl exhibited coding region variation. Ribosomal gene copy number variation was also studied, and line averages ranged from 279 to 368. Average rDNA array size (a function of copy number and gene repeat length) was calculated for each of the populations and found to vary over a range of two megabases, from 5 to 7 Mb.Key words: rDNA, NOR, IGS, genetic variation, chicken.

ISSN:0831-2796    

DOI:10.1139/g98-110

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

We describe a PCR-based method (DT-PCR) that integrates both DNA amplification and directed chain termination into a single-step process. This method exploits unbalanced nucleotide concentrations to induce the polymerase chain reaction to terminate at specific nucleotide sites, leading to the generation of two sets of nested termination fragments from genomic DNA. The kinetic mechanism underlying the termination process is outlined and the application of this method to the detection and characterization of mutations in fragments as long as 1 kb is described. The method is effective for the analysis of both haploid and diploid genomes, and not only allows the recognition of both indels (insertions and deletions) and nucleotide substitutions, but also enables the determination of their position in a single-step fashion.Key words: DT-PCR, unbalanced dNTPs, chain termination, mutation detection.

ISSN:0831-2796    

DOI:10.1139/g98-107

出版商:NRC Research Press    

年代:1999

数据来源: NRC