Biochemical markers associated with two Mv chromosomes from Aegilops ventricosa in wheat-Aegilops addition lines

Summary The distribution of three biochemical markers, U-1, CM-4 and Aph_v-a, -b, among wheat-Aegilops addition lines carrying M^v chromosomes from Aegilops ventricosa (genomes D^vM^v) has been investigated. Addition lines which had been previously grouped together on the basis of common non-biochemical characters carried marker U-1, a protein component from the 2M urea extract. The added chromosome, in the appropriate genetic background, seems to confer a high level of resistance to the eyespot disease, caused by the fungus Cercosporella herpotrichoides. The other two markers were concomitantly associated with another similarly formed group of addition lines. Both CM-4, a protein component from the chloroform:methanol extract, and Aph_v-a, -b, alkaline phosphate isozymes, have been previously shown to be associated with homoeologous chromosome group 4, which suggests that the added chromosome in the second group of addition lines is 4M^v.     

Control of Endosperm Proteins in TRITICUM AESTIVUM (Var. Chinese Spring) and AEGILOPS UMBELLULATA by Homoeologous Group 1 Chromosomes

The genetic control of major wheat endosperm proteins by homoeologous group 1 chromosomes has been studied by two-dimensional polyacrylamide gel electrophoresis. The control of at least 15 distinct protein subunits or groups of protein subunits has been allocated to chromosomes 1A, 1B and 1D of Chinese Spring wheat from the analysis of grains of aneuploid genotypes. In addition, six protein subunits have been shown to be controlled by chromosome 1C^u of the related species, Aegilops umbellulata, from studies of wheat lines carrying disomic substitutions of 1C^u chromosomes. On the basis of protein subunit patterns, chromosome 1C^u is more closely related to chromosome 1D of wheat than to chromosomes 1A or 1B.     

Effects of different base populations on selection response in Drosophila

Oregon‐R, +3, and crossbred strains of Drosophila melanogaster were tested for their response to selection for abdominal bristle number. Various subsidiary tests, consisting of heritability estimations, testing for lethal second and third chromosomes, and chromosome assays were conducted on the selection replicates, which had undergone 14 generations of selection. Evidence showed that a plateau which occurred very early in the +3 high selection replicates was due to fixation of a few additive genes with large effects, thus accounting for the low phenotypic and additive genetic variance, the slight regression in abdominal bristle number on relaxation of selection, the absence of directional dominance, and the low frequency of recessive lethals.

High frequencies of second and third chromosome lethals were found in the Oregon‐R high and low replicates and in the +3 low replicates. That these lethals were not selected for heterozygote superiority for extreme bristle effect was indicated by the slight regression of these replicates on relaxation of selection, and by the absence of high, fluctuating phenotypic variances.

From chromosome assays it appears that the two parental strains had different arrays of genes affecting high bristle number, with these genes located mostly in chromosome II in the Oregon‐R high line but in chromosome III in the +3 high line. In the Crossbred high line, high bristle factors were located in both the second and third chromosomes. The low bristle factors were located mainly in the second chromosome in all three low selection lines.

It appears that the original cross had combined different genes favouring high bristle number, thus allowing greater response in the Crossbred high selection line. The same did not occur for low selection; the response from the Crossbred low line was similar to that of the parental low lines, suggesting that the gene arrays affecting low bristle number in the two original populations were comparable.     

Chromosome Interactions in DROSOPHILA MELANOGASTER. II. Total Fitness

In a large experiment, using nearly 200 population cages, we have measured the fitness of Drosophila melanogaster homozygous (1) for the second chromosome, (2) for the third chromosome, and (3) for both chromosomes. Twentyfour second chromosomes and 24 third chromosomes sampled from a natural population were tested. The mean fitness of the homozygous flies is 0.081 ± 0.014 for the second chromosome, 0.080 ± 0.017 for the third chromosome, and 0.079 ± 0.024 for both chromosomes simultaneously. Assuming that fitnesses are multiplicative (the additive fitness model makes no sense in the present case because of the large selection coefficients involved), the expected mean fitness of the homozygotes for both chromosomes is 0.0066; their observed fitness is more than ten times greater. Thus, it appears that synergistic interactions between loci are considerable; and that, consequently, the fitness function substantially departs from linearity. Two models are tentatively suggested for the fitness function: a "threshold" model and a "synergistic" model.—The experiments reported here confirm previous results showing that the concealed genetic load present in natural populations of Drosophila is sufficient to account for the selective maintenance of numerous polymorphisms (of the order of 1000).     

Incipient Genome Differentiation in Gossypium. I. Chromosomes 14, 15, 16, 19 and 20 Assessed in G. HIRSUTUM, G. RAIMONDII and G. LOBATUM by Means of Seven a-D Translocations

The genus Gossypium is favorable for study of genome divergence at several levels. Early stages of divergence have been studied among four D genomes by comparing chiasma frequencies (reciprocal exchanges) between pairs of genomes and between individual counterpart chromosomes marked by heterozygous translocations. D₅ (G. raimondii) shows barely detectable differentiation from from D_h (G. hirsutum), whereas D₇ (G. lobatum) is considerably less closely related to D_h than is D₅. Fragmentary data suggest that D_2–2 (G. harknessii) falls between D₅ and D₇ in its relationship to D_h. Since chiasma frequencies in individual chromosomes and marked regions exhibit the same order of relationships as their corresponding whole genomes, it is concluded that the genome differentiation is generalized (i.e., nucleus-wide) rather than localized in specific chromosomes or chromosome regions. Estimates of relationships based on reciprocal exchange frequencies agree with those based upon preferential synapsis in allohexaploids reported previously. Since preferential synapsis and reciprocal exchange frequencies reveal the same order of relationships, it is concluded that to some extent they reflect common underlying changes in chromosome properties, despite recent evidence that synapsis and crossing over are under independent genetic control.     

Genetic variation for preadult viability in Drosophila melanogaster

The extent of genetic variation in fitness and its components and genetic variation's dependence on environmental conditions remain key issues in evolutionary biology. We present measurements of genetic variation in preadult viability in a laboratory-adapted population of Drosophila melanogaster, made at four different densities. By crossing flies heterozygous for a wild-type chromosome and one of two different balancers (TM1, TM2), we measure both heterozygous (TM1/+, TM2/+) and homozygous (+/+) viability relative to a standard genotype (TM1/TM2). Forty wild-type chromosomes were tested, of which 10 were chosen to be homozygous viable. The mean numbers produced varied significantly between chromosome lines, with an estimated between-line variance in log(e) numbers of 0.013. Relative viabilities also varied significantly across chromosome lines, with a variance in log(e) homozygous viability of 1.76 and of log(e) heterozygous viability of 0.165. The between-line variance for numbers emerging increased with density, from 0.009 at lowest density to 0.079 at highest. The genetic variance in relative viability increases with density, but not significantly. Overall, the effects of different chromosomes on relative viability were remarkably consistent across densities and across the two heterozygous genotypes (TM1, TM2). The 10 lines that carried homozygous viable wild-type chromosomes produced significantly more adults than the 30 lethal lines at low density and significantly fewer adults at the highest density. Similarly, there was a positive correlation between heterozygous viability and mean numbers at low density, but a negative correlation at high density.     

Isolation and identification of Triticum aestivum L. em. Thell. cv Chinese Spring-T. peregrinum Hackel disomic chromosome addition lines

Analyses of RFLPs, isozymes, morphological markers and chromosome pairing were used to isolate 12 Triticum aestivum cv Chinese Spring (genomes A, B, and D)-T. peregrinum (genomes S^v and U^v) disomic chromosome addition lines. The evidence obtained indicates that each of the 12 lines contains an intact pair of T. peregrinum chromosomes. One monosomic addition line, believed to contain an intact 6S^v chromosome, was also isolated. A CS-7U^v chromosome addition line was not obtained. Syntenic relationships in common with the standard Triticeae arrangement were found for five of the seven S^v genome chromosomes. The exceptions were 4S^v and 7S^v. A reciprocal translocation exists between 4S¹ and 7S¹ in T. longissimum and evidence was obtained that the same translocation exists in T. peregrinum. In contrast, evidence for syntenic relationships in common with the standard Triticeae arrangements were found for only one U^v chromosome of T. peregrinum.; namely, chromosome 2U^v. All other U^v genome chromosomes are involved in at least one translocation, and the same translocations were found in the U genome of T. umbellulatum. Evidence was also obtained indicating that the centromeric regions of 4U and 4U^v are homoeologous to the centromeric regions of Triticeae homoeologous group-6 chromosomes, that the centromeric regions of 6U and 6U^v are homoeologous to the centromeric regions of group-4 chromosomes, and that 4U and 4U^v are more closely related overall to Triticeae homoeologous group-6 chromosomes than they are to group-4 chromosomes.     

Chromosome synteny of the a genome of two evolutionary wheat lines

In order to estimate synteny between A^t and A polyploid wheat genomes belonging to different evolutionary lines (Timopheevi and Emmer), saturation of chromosome maps of Triticum timopheevii A^t genome by molecular markers has been conducted. Totally, 179 EST-SSR and 48 genomic SSR-markers have been used with the following integration of 13 and 7 markers correspondingly into chromosome maps of A^t genome. ESTSSR showed higher transferability and lower polymorphism than genomic SSR markers. The chromosome maps designed were compared to maps of homoeologous chromosome group of the T. aestivum A genome. No disturbances of colinearity, i.e., of the order of markers within the chromosome segments on which they had been previously mapped, were observed. According to the quantity assessment of markers amplifying in homoeologous chromosomes, the maximum divergence was detected in two groups (4A^t/4A and 3A^t/3A) among the seven chromosomes examined in the A ^t and A genomes. Comparison of molecular genetic mapping results with the published results of studying meiosis of F₁ hybrids and the frequency of chromosomes substitution in introgressive T. aestivum × T. timopheevii lines suggest that individual chromosomes of the A^t and A genomes evolve differently. Translocations were shown to introduce the major impact on the divergence of 4A^t/4A and 6A^t/6A chromosomes, while mutations of the primary DNA structure, on the divergence of homoeologous group 3 chromosomes. The level of reorganization of other chromosomes during the evolution in the A^t and A genomes was significantly lower.     

Cytogenetic Analysis of Hybrids Resistant to Yellow Rust and Powdery Mildew Obtained by Crossing Common Wheat (Triticum aestivum L., AABBDD) with Wheats of the Timopheevi Group (AtAtGG)

The karyotypes of 47 hybrid lines obtained from crosses of common wheat Triticum aestivum L. (cv. Rodina and line 353) with Triticum timopheevii(Zhuk.) Zhuk. (A ^t A ^t GG) and related species T. militinae Zhuk. et Migusch. (A ^t A ^t GG) and T. kiharae Dorof. et Migusch. (A ^t A ^t GGD ^sq D ^sq) were analyzed by C-banding. Most lines were resistant to yellow rust and powdery mildew. The introgression of alien genetic material to the common wheat genome was realized via substitutions of complete A ⁺-,G-, and D-genome chromosomes, chromosome arms, or their fragments. The pattern of chromosome substitutions in resistant lines differed from that in introgressive hybrids selected for other traits. Substitutions of chromosomes 6G, 2A^t, 2G, and 5G were revealed in 31, 23, 18, and 13 lines, respectively. Substitutions of chromosomes 4G, 4A^t, and 6A^t were not observed. In 15 lines, a 5BS.5BL-5GL translocation was identified. High frequency of substitutions of chromosomes 2A^t, 2G, 5G, and 6G indicate that they may carry the resistance genes and that they are closely related to the respective homoeologous chromosomes of common wheat that determines their high compensation ability.     

Genetic Variance for Body Size in a Natural Population of Drosophila Buzzatii

Previous work has shown thorax length to be under directional selection in the Drosophila buzzatii population of Carboneras. In order to predict the genetic consequences of natural selection, genetic variation for this trait was investigated in two ways. First, narrow sense heritability was estimated in the laboratory F2 generation of a sample of wild flies by means of the offspring-parent regression. A relatively high value, 0.59, was obtained. Because the phenotypic variance of wild flies was 7-9 times that of the flies raised in the laboratory, "natural" heritability may be estimated as one-seventh to one-ninth that value. Second, the contribution of the second and fourth chromosomes, which are polymorphic for paracentric inversions, to the genetic variance of thorax length was estimated in the field and in the laboratory. This was done with the assistance of a simple genetic model which shows that the variance among chromosome arrangements and the variance among karyotypes provide minimum estimates of the chromosome's contribution to the additive and genetic variances of the trait, respectively. In males raised under optimal conditions in the laboratory, the variance among second-chromosome karyotypes accounted for 11.43% of the total phenotypic variance and most of this variance was additive; by contrast, the contribution of the fourth chromosome was nonsignificant. The variance among second-chromosome karyotypes accounted for 1.56-1.78% of the total phenotypic variance in wild males and was nonsignificant in wild females. The variance among fourth chromosome karyotypes accounted for 0.14-3.48% of the total phenotypic variance in wild flies. At both chromosomes, the proportion of additive variance was higher in mating flies than in nonmating flies.     

Delineation of interspecific epistasis on fiber quality traits in Gossypium hirsutum by ADAA analysis of intermated G. barbadense chromosome substitution lines

Genetic diversity is the foundation of any crop improvement program, but the most cultivated Upland cotton [Gossypium hirsutum L., 2n?=?52, genomic formula?2(AD)₁] has a very narrow gene pool resulting from its evolutionary origin and domestication history. Cultivars of this cotton species (G. hirsutum L.) are prized for their combination of exceptional yield, other agronomic traits, and good fiber properties, whereas the other cultivated 52-chromosome species, G. barbadense L. [2n?=?52, genomic formula?2(AD)₂], is widely regarded as having the opposite attributes. It has exceptionally good fiber qualities, but generally lower yield and less desirable agronomic traits. Breeders have long aspired to combine the best attributes of G. hirsutum and G. barbadense, but have had limited success. F₁ hybrids are readily created and largely fertile, so the limited success may be due to cryptic biological and technical challenges associated with the conventional methods of interspecific introgression. We have developed a complementary alternative approach for introgression based on chromosome substitution line, followed by increasingly sophisticated genetic analyses of chromosome-derived families to describe the inheritance and breeding values of the chromosome substitution lines. Here, we analyze fiber quality traits of progeny families from a partial diallel crossing scheme among selected chromosome substitution lines (CS-B lines). The results provide a more detailed and precise QTL dissection of fiber traits, and an opportunity to examine allelic interaction effects between two substituted chromosomes versus one substituted chromosome. This approach creates new germplasm based on pair wise combinations of quasi-isogenic chromosome substitutions. The relative genetic simplicity of two-chromosome interactions departs significantly from complex or RIL-based populations, in which huge numbers of loci are segregating in all 26 chromosome pairs. Data were analyzed according to the ADAA genetic model, which revealed significant additive, dominance, and additive-by-additive epistasis effects on all of the fiber quality traits associated with the substituted chromosome or chromosome arm of CS-B lines. Fiber of line 3-79, the donor parent for the substituted chromosomes, had the highest Upper Half Mean length (UHM), uniformity ratio, strength, elongation, and lowest micronaire among all parents and hybrids. CS-B16 and CS-B25 had significant additive effects for all fiber traits. Assuming a uniform genetic background of the CS-B lines, the comparative analysis of the double-heterozygous hybrid combinations (CS-B?×?CS-B) versus their respective single heterozygous combinations (CS-B?×?TM-1) demonstrated that interspecific epistatic effects between the genes in the chromosomes played a major role in most of the fiber quality traits. Results showed that fiber of several hybrids including CS-B16?×?CS-B22Lo, CS-B16?×?CS-B25 and CS-B16?×?TM-1 had significantly greater dominance effects for elongation and hybrid CS-B16?×?CS-B17 had higher fiber strength than their parental lines. Multiple antagonistic genetic effects were also present for fiber quality traits associated with most of the substituted chromosomes and chromosome arms. Results from this study highlight the vital importance of epistasis in fiber quality traits and detected novel effects of some cryptic beneficial alleles affecting fiber quality on the 3-79 chromosomes, whose effects were not detected in the 3-79 parental lines.     

Genome differentiation in Aegilops. 3. Evolution of the D-genome cluster

 Six polyploid Aegilops species containing the D genome were studied by C-banding and fluorescence in situ hybridization (FISH) using clones pTa71 (18S-5.8S-26S rDNA), pTa794 (5S rDNA), and pAs1 (non-coding repetitive DNA sequence) as probes. The C-banding and pAs1-FISH patterns of Ae. cylindrica chromosomes were identical to those of the parental species. However, inactivation of the NOR on chromosome 5D with a simultaneous decrease in the size of the pTa71-FISH site was observed. The N^v and D^v genomes of Ae. ventricosa were somewhat modified as compared with the N genome of Ae. uniaristata and the D genome of Ae. tauschii. Modifications included minor changes in the C-banding and pAs1-FISH patterns, complete deletion of the NOR on chromosome 5D^v, and the loss of several minor 18S-5.8S-26S rDNA loci on N^v genome chromosomes. According to C-banding and FISH analyses, the D^cr1 genome of Ae. crassa is more similar to the D^v genome of Ae. ventricosa than to the D genome of Ae. tauschii. Mapping of the 18S-5.8S-26S rDNA and 5S rDNA loci by multicolor FISH suggests that the second (X^cr) genome of tetraploid Ae. crassa is a derivative of the S genome (section Emarginata of the Sitopsis group). Both genomes of Ae. crassa were significantly modified as the result of chromosomal rearrangements and redistribution of highly repetitive DNA sequences. Hexaploid Ae. crassa and Ae. vavilovii arose from the hybridization of chromosomal type N of tetraploid Ae. crassa with Ae. tauschii and Ae. searsii, respectively. Chromosomal type T1 of tetraploid Ae. crassa and Ae. umbellulata were the ancestral forms of Ae. juvenalis. The high level of genome modification in Ae. juvenalis indicates that it is the oldest hexaploid species in this group. The occurrence of hexaploid Ae. crassa was accompanied by a species-specific translocation between chromosomes 4D^cr1 and 7X^cr. No chromosome changes relative to the parental species were detected in Ae. vavilovii, however, its intraspecific diversity was accompanied by a translocation between chromosomes 3X^cr and 3D^cr1. Received July 24, 2001 Accepted October 1, 2001     

Flow sorting of C-genome chromosomes from wild relatives of wheat Aegilops markgrafii,Ae. triuncialis and Ae. cylindrica,and their molecular organization

Background and Aims Aegilops markgrafii (CC) and its natural hybrids Ae. triuncialis (U^tU^tC^tC^t) and Ae. cylindrica (D^cD^cC^cC^c) represent a rich reservoir of useful genes for improvement of bread wheat (Triticum aestivum), but the limited information available on their genome structure and the shortage of molecular (cyto-) genetic tools hamper the utilization of the extant genetic diversity. This study provides the complete karyotypes in the three species obtained after fluorescent in situ hybridization (FISH) with repetitive DNA probes, and evaluates the potential of flow cytometric chromosome sorting.Methods The flow karyotypes obtained after the analysis of 4'',6-diamidino-2-phenylindole (DAPI)-stained chromosomes were characterized and the chromosome content of the peaks on the flow karyotypes was determined by FISH. Twenty-nine conserved orthologous set (COS) markers covering all seven wheat homoeologous chromosome groups were used for PCR with DNA amplified from flow-sorted chromosomes and genomic DNA.Key Results FISH with repetitive DNA probes revealed that chromosomes 4C, 5C, 7C^t, T6U^tS.6U^tL-5C^tL, 1C^c and 5D^c could be sorted with purities ranging from 66 to 91 %, while the remaining chromosomes could be sorted in groups of 2–5. This identified a partial wheat–C-genome homology for group 4 and 5 chromosomes. In addition, 1C chromosomes were homologous with group 1 of wheat; a small segment from group 2 indicated 1C–2C rearrangement. An extensively rearranged structure of chromosome 7C relative to wheat was also detected.Conclusions The possibility of purifying Aegilops chromosomes provides an attractive opportunity to investigate the structure and evolution of the Aegilops C genome and to develop molecular tools to facilitate the identification of alien chromatin and support alien introgression breeding in bread wheat.     

Development of chromosome-specific markers with high polymorphism for allotetraploid cotton based on genome-wide characterization of simple sequence repeats in diploid cottons (Gossypium arboreum L. and Gossypium raimondii Ulbrich)

Background

Tetraploid cotton contains two sets of homologous chromosomes, the At- and Dt-subgenomes. Consequently, many markers in cotton were mapped to multiple positions during linkage genetic map construction, posing a challenge to anchoring linkage groups and mapping economically-important genes to particular chromosomes. Chromosome-specific markers could solve this problem. Recently, the genomes of two diploid species were sequenced whose progenitors were putative contributors of the At- and Dt-subgenomes to tetraploid cotton. These sequences provide a powerful tool for developing chromosome-specific markers given the high level of synteny among tetraploid and diploid cotton genomes. In this study, simple sequence repeats (SSRs) on each chromosome in the two diploid genomes were characterized. Chromosome-specific SSRs were developed by comparative analysis and proved to distinguish chromosomes.

Results

A total of 200,744 and 142,409 SSRs were detected on the 13 chromosomes of Gossypium arboreum L. and Gossypium raimondii Ulbrich, respectively. Chromosome-specific SSRs were obtained by comparing SSR flanking sequences from each chromosome with those from the other 25 chromosomes. The average was 7,996 per chromosome. To confirm their chromosome specificity, these SSRs were used to distinguish two homologous chromosomes in tetraploid cotton through linkage group construction. The chromosome-specific SSRs and previously-reported chromosome markers were grouped together, and no marker mapped to another homologous chromosome, proving that the chromosome-specific SSRs were unique and could distinguish homologous chromosomes in tetraploid cotton. Because longer dinucleotide AT-rich repeats were the most polymorphic in previous reports, the SSRs on each chromosome were sorted by motif type and repeat length for convenient selection. The primer sequences of all chromosome-specific SSRs were also made publicly available.

Conclusion

Chromosome-specific SSRs are efficient tools for chromosome identification by anchoring linkage groups to particular chromosomes during genetic mapping and are especially useful in mapping of qualitative-trait genes or quantitative trait loci with just a few markers. The SSRs reported here will facilitate a number of genetic and genomic studies in cotton, including construction of high-density genetic maps, positional gene cloning, fingerprinting, and genetic diversity and comparative evolutionary analyses among Gossypium species.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-015-1265-2) contains supplementary material, which is available to authorized users.     

Incipient Genome Differentiation in Gossypium. III. Comparison of Chromosomes of G. HIRSUTUM and Asiatic Diploids Using Heterozygous Translocations

Hybrids between upland cotton (G. hirsutum, genome constitution 2A_hD_h) and either A-genome or D-genome diploid species exhibit 26 paired and 13 unpaired chromosomes at metaphase I. The A_h and D_h genomes are therefore considered homoeologous with those of the respective diploids. Previous studies, nevertheless, revealed a low level of ("incipient") differentiation between D_h and various diploid D genomes. The diploid A genomes have been regarded as more closely homologous to A_h on the basis of low preferential pairing and autotetraploid segregation ratios in allohexaploids.—The present study addressed the following questions: Are the diploid A genomes differentiated from A_h in meiotic homology? If so, is the differentiation manifested equally by all 13 chromosomes or is it localized in certain chromosomes?—Three diploid A-genome lines representing G. herbaceum and G. arboreum were hybridized by in ovulo culture of embryos (1) with a standard line of G. hirsutum, which differs from G. herbaceum by two and from G. arboreum by three naturally occurring reciprocal translocations involving chromosomes 1–5, and (2) with six lines homozygous for experimental translocations involving chromosomes 6, 7, 10, 11, 12 and 13. Chiasma frequencies in hybrids were compared with those in appropriate G. hirsutum controls. In every comparison overall chiasma frequencies were slightly lower in the hybrids. Therefore A_h appears to be differentiated from the diploid A genomes. No localized differentiation was detected in chromosomes marked by experimental translocations. The differentiation may be localized mainly in chromosomes 4 and 5.     

Limits to environmental masking of genetic quality in sexual signals

There is considerable debate over the value of male sexual ornaments as signals of genetic quality. Studies alternately report that environmental variation enhances or diminishes the genetic signal, or leads to crossover where genotypes perform well in one environment but poorly in another. A unified understanding is lacking. We conduct a novel experimental test examining the dual effects of distinct categories of genetic (inbred vs. crossed parental lines) and environmental quality (low, through high to extreme larval food stress) on a condition‐dependent male ornament. We find that differences in genetic quality signalled by the ornament (male eyespan in Diasemopsis meigenii stalk‐eyed flies) become visible and are amplified under high stress but are overwhelmed in extreme‐stress environments. Variance among independent genetic lines increases with environmental stress in both genetic quality classes, but at a slower rate in high quality outcrossed flies. Individual genetic lines generally maintain their ranks across environments, except among high quality lines under low environmental stress, where low genetic variance among lines precludes differentiation between ranks. Our results provide a conceptual advance, demonstrating a unified pattern for how genetic and environmental quality interact. They show when environmental conditions lead to the amplification of differences in signals of genetic quality and thereby enhance the potential indirect genetic benefits gained by female mate choice.     

Comparative genetic analysis of the Aegilops longissima and Ae. sharonensis genomes with common wheat

Aegilops longissima Schw. et Musch. (2n= 2x=14, S^lS^l) and Aegilops sharonensis Eig. (2n=2x=14, S^lS^l) are diploid species belonging to the section Sitopsis in the tribe Triticeae and potential donors of useful genes for wheat breeding. A comparative genetic map was constructed of the Ae. longissima genome, using RFLP probes with known location in wheat. A high degree of conserved colinearity was observed between the wild diploid and basic wheat genome, represented by the D genome of cultivated wheat. Chromosomes 1S^l, 2S^l, 3S^l, 5S^l and 6S^l are colinear with wheat chromosomes 1D, 2D, 3D, 5D and 6D, respectively. The analysis confirmed that chromosomes 4S^l and 7S^l are translocated relative to wheat. The short arms and major part of the long arms are homoeologous to most of wheat chromosomes 4D and 7D respectively, but the region corresponding to the distal segment of 7D was translocated from 7S^lL to the distal region of 4S^lL. The map and RFLP markers were then used to analyse the genomes and added chromosomes in a set of ’Chinese Spring’ (CS)/Ae. longissima chromosome additions. The study confirmed the availability of disomic CS/Ae. longissima addition lines for chromosomes 1S^l, 2S^l, 3S^l, 4S^l and 5S^l. An as yet unpublished set of Ae. sharonensis chromosome addition lines were also available for analysis. Due to the gametocidal nature of Ae. sharonensis chromosomes 2S^l and 4S^l, additions 1S^l, 3S^l, 5S^l, 6S^l and 7S^l were produced in a (4D)4S^l background, and 2S^l and 4S^l in a euploid wheat background. The analysis also confirmed that the 4/7 translocation found in Ae. longissima was not present in Ae. sharonensis although the two wild relatives of wheat are considered to be closely related. The phenotypes of the Ae. sharonensis addition lines are described in an Appendix. Received: 28 September 2000 / Accepted: 19 January 2001     

DNA content of wheat monosomics at interphase estimated by flow cytometry

 Two complete, independently maintained sets of 21 monosomic wheat lines derived from cv. ‘Chinese Spring’ were analyzed for their DNA content at the G1 stage with flow cytometry. The DNA content of individual chromosomes was estimated by subtracting the value of a monosomic line from that of euploid wheat. Our data show that the estimated 2C DNA of individual wheat chromosomes in 21 monosomics at the G1 stage ranges from about 0.58 pg in chromosome 1D to approximately 1.12 pg in chromosome 3A. The A genome (2C=6.15 pg) seems to contain more DNA than the B (2C=6.09 pg) and D (2C=5.05 pg) genomes. Analysis of variance showed significant differences (α=0.01) in DNA content both among homoeologous groups and among genomes. Our estimates of interphase DNA content of wheat chromosomes from monosomic lines were poorly correlated to the chromosome sizes at metaphase (r=0.622, P≤0.01). This poor correlation might be due to differential coiling among chromosomes during cell division, possible bias of fluorochrome binding to heterochromatin, or heterogeneity among monosomic lines. Finally, flow cytometry may aid but cannot replace cytological checks in aneuploid maintenance. Received: 21 January 1997 / Accepted: 23 June 1997     

Genetic transfer of resistance to powdery mildew and of an associated biochemical marker from Aegilops ventricosa to hexaploid wheat

Summary Resistance to powdery mildew, caused by the fungus Erysiphe graminis f.sp. tritici, has been transferred from Aegilops ventricosa (genomes D^vM^v) to hexaploid wheat (Triticum aestivum, ABD). In two transfer lines, H-93-8 and H-93-35, the resistance gene was linked to a gene encoding protein U-1, whereas one line, H-93-33, was resistant but lacked the molecular marker, and another line, H-93-1, was susceptible but carried the gene for U-1, indicating that the original M^v chromosome from Ae. ventricosa, carrying the two genes, had undergone recombination with a wheat chromosome in the last two lines.