Cytogenetic analysis of Lycopersicon esculentum (+) Solanum etuberosum somatic hybrids and their androgenetic regenerants

The aim of the study was to characterize genomic relationships among cultivated tomato (Lycopersicon esculentum Mill.) (2n=2x=24) and diploid (2n=2x=24) non-tuberous wild Solanum species (S. etuberosum Lindl.). Using genomic in situ hybridization (GISH) of mitotic and meiotic chromosomes, we analyzed intergeneric somatic hybrids between tomato and S. etuberosum. Of the five somatic hybrids, two plants were amphidiploids (2n=4x=48) mostly forming intragenomic bivalents in their microsporocytes, with a very low frequency of multivalents involving the chromosomes of tomato and S. etuberosum (less than 0.2 per meiocyte). Tomato chromosomes showed preferential elimination during subsequent meiotic divisions of the amphidiploids. Transmission of the parental chromosomes into microspores was also evaluated by GISH analysis of androgenic plants produced by direct embryogenesis from the amphidiploid somatic hybrids. Of the four androgenic regenerants, three were diploids (2n=2x=24 or 2n=2x+1=25) derived from reduced male gametes of the somatic hybrids, and one plant was a hypertetraploid (2n=4x+4=52). GISH revealed that each anther-derived plant had a unique chromosome composition. The prospects for introgression of desirable traits from S. etuberosum into the gene pool of cultivated tomato are discussed. Received: 2 August 2000 / Accepted: 4 December 2000     

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

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

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

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

Comparative linkage map of the Solanum lycopersicoides and S. sitiens genomes and their differentiation from tomato.

The wild nightshades Solanum lycopersicoides and Solanum sitiens are closely affiliated with the tomatoes (Lycopersicon spp.). Intergeneric hybridization with cultivated tomato (Lycopersicon esculentum) is impeded by strong reproductive barriers including hybrid sterility and suppressed recombination. Conservation of genome structure between these nightshades and tomato was studied by construction of a genetic map from F2 S. sitiens x S. lycopersicoides and comparison with existing maps of tomato. Owing to self-incompatibility of the F1, two hybrid plants were crossed to obtain a population of 82 F2 individuals. Using 166 previously mapped RFLP markers and 5 restriction enzymes, 101 loci polymorphic in the S. sitiens x S. lycopersicoides population were identified. Analysis of linkage between the markers resulted in a map with 12 linkage groups covering 1192 cM and one unlinked marker. Recombination rates were similar to those observed in tomato; however, significant segregation distortion was observed for markers on 7 out of the 12 chromosomes. All chromosomes were colinear with the tomato map, except for chromosome 10, where a paracentric inversion on the long arm was detected. In this region, S. sitiens and S. lycopersicoides share the same chromosomal configuration previously reported for potato (S. tuberosum) and pepper (Capsicum), suggesting that of tomato is derived. The 10L inversion explains the lack of recombination detected among homeologous chromosomes of intergeneric hybrids in this region. On this basis, we recognize two principle genomes, designated L for the Lycopersicon spp., and S for S. lycopersicoides and S. sitiens, the first examples of structural differentiation between tomato and its cross-compatible wild relatives.     

Production and meiotic analysis of autotriploid Triticum speltoides and T. bicorne

Summary Autotriploid Triticum speltoides and T. bicorne (2n=3x=21) were produced by pollinating autotetraploids with pollen from their respective diploids. The autotriploid plants were vigorous, male sterile, and morphologically resembled their diploid parents. At meiosis, T. speltoides (3x) averaged 2.52 univalents, 0.42 rod bivalents, 2.03 ring bivalents, 4.48 trivalents, and 0.03 chain quadrivalents per cell, and T. bicorne (3x) had 2.30 univalents, 0.20 rod bivalents, 2.10 ring bivalents, and 4.70 trivalents. Panhandle trivalents made up 27% of the total trivalents, and involved 18% of the total number of chromosomes observed in T. bicorne (3x), and 26% and 17% in T. speltoides (3x), respectively. The observed chromosome pairing in both triploids was predicted well from the expressions developed by Alonso and Kimber.Contribution from the Missouri Agricultural Experiment Station. Journal Series No. 10932     

A genetic map of tomato based on BC(1) Lycopersicon esculentum x Solanum lycopersicoides reveals overall synteny but suppressed recombination between these homeologous genomes

F(1) hybrids between the cultivated tomato (Lycopersicon esculentum) and the wild nightshade Solanum lycopersicoides are male sterile and unilaterally incompatible, breeding barriers that impede further crosses to tomato. Meiosis is disrupted in 2x hybrids, with reduced chiasma formation and frequent univalents, but is normal in allotetraploid hybrids, indicating the genomes are homeologous. In this study, a partially male-fertile F(1) was backcrossed to tomato, producing the first BC(1) population suitable for genetic mapping from this cross. BC(1) plants were genotyped at marker loci to study the transmission of wild alleles and to measure rates of homeologous recombination. The pattern of segregation distortion, in favor of homozygotes on chromosomes 2 and 5 and heterozygotes on chromosomes 6 and 9, suggested linkage to a small number of loci under selection on each chromosome. Genome ratios nonetheless fit Mendelian expectations. Resulting genetic maps were essentially colinear with existing tomato maps but showed an overall reduction in recombination of approximately 27%. Recombination suppression was observed for all chromosomes except 9 and 12, affected both proximal and distal regions, and was most severe on chromosome 10 (70% reduction). Recombination between markers on the long arm of this chromosome was completely eliminated, suggesting a lack of colinearity between S. lycopersicoides and L. esculentum homeologues in this region. Results are discussed with respect to phylogenetic relationships between the species and their potential use for studies of homeologous pairing and recombination in a diploid plant genome.     

Origin of an alien disomic addition with an aberrant homologue of chromosome-10 of tomato and its meiotic behaviour in a potato background revealed through GISH

 While characterising potato (Solanum tuberosum, 2n=4x=48) clones with alien tomato (Lycopersicon esculentum) chromosome additions, a single addition for chromosome-10 of tomato was identified through restriction fragment length polymorphism (RFLP) analysis. This plant, 2101–1, was a BC₂ derivative from a cross between a potato (+) tomato fusion hybrid backcrossed to potato. Cytological analysis of its somatic chromosomes through genomic in situ hybridisation (GISH) indicated the presence of four genomes of potato with two alien tomato chromosomes, of which one was much smaller than the other. Analysis of chromosome pairing at the pachytene and metaphase-I stages of microsporogenesis indicated that the large and small chromosomes were homologues. Thus, it was a disomic addition for chromosome-10 of tomato. The size difference was found to be due to a deletion. Fluorescent in situ hybridisation (FISH) experiments, using the telomeric repeat pAtT4 from Arabidopsis thaliana and the sub-telomeric repeat TGRI, showed intact telomeres and sub-telomeres for both alien chromosomes. Thus, the deletion that the smaller of the homologues suffered was interstitial and most probably occurred in the centromeric heterochromatic region of the long arm. The pattern of distribution of large and small chromosomes to telophase-II nuclei during microsporogenesis indicated that the deletion did not affect the meiotic behaviour of the smaller chromosome. In contrast, the frequencies of transmission of the large and the small chromosomes through the female parent, estimated in 96 BC₃ progeny of plants by RFLP and GISH analyses, appeared to be very different, 69.2% and 3.8% respectively. This study also provides evidence that two different chromatids of a pair of homologues, rather than two chromatids of a single chromosome, are most likely to be involved in the origin of a disomic. The aberrant chromosome can be used for the physical mapping of chromosome-10. Received: 9 June 1998 / Accepted: 28 October 1998     

萝卜与甘蓝属间杂种基因组原位杂交分析

用基因组原位杂交方法（Genomic in situ hybridization, 简称GISH）研究了萝卜( Raphanus sativus,2n=18,RR)和甘蓝（Brassica oleracea , 2n=18, CC）属间杂种F1减数分裂过程。结果表明杂种体细胞染色体组成为RC,2n=18,但花粉母细胞有三种不同类型：1. RC,2n=18, 终变期染色体平均配对构型为14.87Ⅰ+1.20Ⅱ+0.04Ⅲ+0.06Ⅳ, 染色体配对主要发生在萝卜和甘蓝染色体之间, 后期Ⅰ9条萝卜染色体主要以5/4和6/3的分离比移向两极, 所形成配子的染色体数目和组成均不平衡,配子败育; 2. RRCC,4n=36, 终变期染色体形成18个二价体,后期Ⅰ染色体均衡分离,形成RC不减数配子;3. RRCC缺体,4n=30－34, 少数萝卜染色体丢失,形成的配子具有全套的甘蓝染色体和部分萝卜染色体。     

小麦族鹅观草属三种植物的生物系统学研究

本文研究了禾本科小麦族鹅观草属的3个种:缘毛鹅观草(Roegneria pendulina Neuski 2n=4x=28),纤毛鹅观草(R. ciliaris (Trin.) Nevski 2n=4x=28)和鹅观草(R. kamoji Ohwi 2n=6x=42)及其种间杂种的形态变异和染色体配对行为。各杂种F_1的减数分裂染色体配对数较高,但杂种高度不育。在杂种减数分裂中还观察到一定频率的多价体形成。以上结果充分表明该3种植物享有两个共同的基本染色体组,在S和Y染色体组之间发生过染色体相互易位,缘毛鹅观草的染色体组可拟定为S~PY~P。     

DNA content of heterochromatin and euchromatin in tomato (Lycopersicon esculentum) pachytene chromosomes.

Lycopersicon esculentum (tomato) has a small genome (2C = 1.90 pg of DNA) packaged in 2n = 2x = 24 small acrocentric to metacentric chromosomes. Like the chromosomes of other members of the family Solanaceae, tomato chromosomes have pericentromeric heterochromatin. To determine the fraction of the tomato genome found in euchromatin versus heterochromatin, we stained pachytene chromosomes from primary microsporocytes with Feulgen and analyzed them by densitometry and image analysis. In association with previously published synaptonemal complex karyotype data for tomato, our results indicate that 77% of the tomato microsporocyte genome is located in heterochromatin and 23% is found in euchromatin. If heterochromatin is assumed to contain few active genes, then the functional genes of the tomato must be concentrated in an effective genome of only 0.22 pg of DNA (1C = 0.95 pg x 0.23 = 0.22 pg). The physical segregation of euchromatin and heterochromatin in tomato chromosomes coupled with the small effective genome size suggests that tomato may be a more useful subject for chromosome walking and gene mapping studies than would be predicted based on its genome size alone. Key words : tomato, Lycopersicon esculentum, genome size, heterochromatin, euchromatin, pachytene chromosomes, synaptonemal complex.     

Chromosome relationships between Lolium and Festuca (Gramineae)

With a view to eclucidating chromosome relationships between Lolium perenne (Lp), L. multiflorum (Lm) and Festuca pratensis (Fp), chromosome pairing in different diploid (2n=14), auto-allotriploid (2n=3x=21), trispecific (2n=3x=21), amphidiploid (2n=4x=28) and auto-allohexaploid (2n=6x=42) hybrids between them was analysed. At all these levels of ploidy there was very good chiasmate pairing between the chromosomes of the three species and, on the whole, there was little evidence of preferential pairing of the chromosomes of a particular species in the triploid, tetraploid and hexaploid hybrids. A critical test for this also came from the synaptic ability of the chromosomes of the single genome with those of the duplicated genome in the auto-allotriploids which formed predominantly trivalents with 2, 3 or even 4 chiasmata. Moreover, the homology between the Lp and Lm chromosomes seems strong enough to pass the discrimination limits of the B-chromosomes which do not suppress homoeologous pairing in the Lp LmLm triploid and LpLm diploid hybrids. — The triploids having two genomes of a Lolium species and one of F. pratensis had some male and female fertility which suggested genetic compatibility of the parental chromosomes resulting, presumably, in compensation at the gametic level. Also, the occurrence of comparable chiasma frequencies in the auto-allotriploids and trispecific hybrids showed that they were not markedly affected whether two doses of one genome and one of the other or all the three different genomes from the three species were present. From the trend of chromosome pairing in all these hybrids it is concluded that there is little structural differentiation between the chromosomes of the three species, no effective isolation barrier to gene-flow between them, and that they are closely related phylogenetically, having possibly evolved from a common progenitor. Taxonomic revision of the two Lolium species is suggested.     

Inheritance of acylsugar contents in tomatoes derived from an interspecific cross with the wild tomato Lycopersicon pennellii and their effect on spider mite repellence

Acylsugars present in Lycopersicon pennellii are responsible for the high levels of pest resistance often found in this wild tomato taxon. We investigated the inheritance of acylsugar contents in segregating populations of the interspecific tomato cross L. esculentum x L. pennellii and estimated correlations between leaflet acylsugar contents and the levels of mite repellence. Acylsugar contents were quantified with the Sommogy-Nelson colorimetric method in the acessions L. esculentum 'TOM-584' (P(1), low acylsugars), L. pennellii 'LA-716' (P(2), high acylsugars), in the interspecific F(1) (P(1) x P(2)) and in the F(2 )(P(1) x P(2)) generations. Mite resistance was assessed by a repellence test. Broad-sense heritability of acylsugar contents was moderately high (h(2)(b) = 0.476). Frequency distributions in the P(1), P(2), F(1) and F(2) can be explained by the action of a single major locus, with near-complete dominance of the L. esculentum allele for low-acylsugar content over the L. pennellii allele for high content. Indirect selection for high levels of acylsugars in leaflets led to correlated increases in the levels of mite repellency, indicating that acylsugars may be the main factor involved in mite resistance.     

A molecular linkage map of tomato displaying chromosomal locations of resistance gene analogs based on a Lycopersicon esculentum x Lycopersicon hirsutum cross.

A molecular linkage map of tomato was constructed based on a BC1 population (N = 145) of a cross between Lycopersicon esculentum Mill. line NC84173 (maternal and recurrent parent) and Lycopersicon hirsutum Humb. and Bonpl. accession PI126445. NC84173 is an advanced breeding line that is resistant to several tomato diseases, not including early blight (EB) and late blight (LB). PI126445 is a self-incompatible accession that is resistant to many tomato diseases, including EB and LB. The map included 142 restriction fragment length polymorphism (RFLP) markers and 29 resistance gene analogs (RGAs). RGA loci were identified by PCR amplification of genomic DNA from the BC1 population, using ten pairs of degenerate oligonucleotide primers designed based on conserved leucine-rich repeat (LRR), nucleotide binding site (NBS), and serine (threonine) protein kinase (PtoKin) domains of known resistance genes (R genes). The PCR-amplified DNAs were separated by denaturing polyacrylamide gel electrophoresis (PAGE), which allowed separation of heterogeneous products and identification and mapping of individual RGA loci. The map spanned 1469 cM of the 12 tomato chromosomes with an average marker distance of 8.6 cM. The RGA loci were mapped to 9 of the 12 tomato chromosomes. Locations of some RGAs coincided with locations of several known tomato R genes or quantitative resistance loci (QRLs), including Cf-1, Cf-4, Cf-9, Cf-ECP2, rx-1, and Cm1.1 (chromosome 1); Tm-1 (chromosome 2); Asc (chrromosme 3); Pto, Fen, and Prf (chromosome 5); 01-1, Mi, Ty-1, Cm6.1, Cf-2, CF-5, Bw-5, and Bw-1 (chromosome 6); I-1, 1-3, and Ph-1 (chromosome 7); Tm-2a and Fr1 (chromosome 9); and Lv (chromosome 12). These co-localizations indicate that the RGA loci were either linked to or part of the known R genes. Furthermore, similar to that for many R gene families, several RGA loci were found in clusters, suggesting their potential evolutionary relationship with R genes. Comparisons of the present map with other molecular linkage maps of tomato, including the high density L. esculentum x Lycopersicon pennellii map, indicated that the lengths of the maps and linear order of RFLP markers were in good agreement, though certain chromosomal regions were less consistent than others in terms of the frequency of recombination. The present map provides a basis for identification and mapping of genes and QTLs for disease resistance and other desirable traits in PI126445 and other L. hirsutum accessions, and will be useful for marker-assisted selection and map-based gene cloning in tomato.     

Homeologous recombination in Solanum lycopersicoides introgression lines of cultivated tomato

A library of "introgression lines" containing Solanum lycopersicoides chromosome segments in the genetic background of cultivated tomato (Lycopersicon esculentum) was used to study factors affecting homeologous recombination. Recombination rates were estimated in progeny of 43 heterozygous introgressions and whole-chromosome substitution lines, together representing 11 of the 12 tomato chromosomes. Recombination within homeologous segments was reduced to as little as 0-10% of expected frequencies. Relative recombination rates were positively correlated with the length of introgressed segments on the tomato map. The highest recombination (up to 40-50% of normal) was observed in long introgressions or substitution lines. Double-introgression lines containing two homeologous segments on opposite chromosome arms were synthesized to increase their combined length. Recombination was higher in the double than in the single segment lines, despite a preference for crossovers in the region of homology between segments. A greater increase in homeologous recombination was obtained by crossing the S. lycopersicoides introgression lines to L. pennellii--a phylogenetically intermediate species--or to L. esculentum lines containing single L. pennellii segments on the same chromosome. Recombination rates were highest in regions of overlap between S. lycopersicoides and L. pennellii segments. The potential application of these results to breeding with introgression lines is discussed.     

四倍体鲫鲤、三倍体湘云鲫染色体减数分裂观察

用精巢细胞直接制片法观察了异源四倍体鲫鲤、三倍体湘云鲫和二倍体红鲫、湘江野鲤精母细胞染色体第一次减数分裂中期配对情况 ;作为对照 ,观察了上述四种鱼肾细胞的有丝分裂中期染色体。在精母细胞第一次减数分裂中 ,异源四倍体鲫鲤同源染色体两两配对 ,形成 10 0个二价体 ,没有观察到单价体、三价体和四价体 ;三倍体湘云鲫精母细胞形成 5 0个二价体和 5 0个单价体 ;红鲫和湘江野鲤精母细胞分别形成 5 0个二价体。肾细胞检测表明异源四倍体的染色体数目为 4n =2 0 0 ;湘云鲫为 3n =15 0 ;红鲫和湘江野鲤分别为 2n =10 0。减数分裂时染色体分布情况与肾细胞染色体检测结果相吻合。具有四套染色体的异源四倍体鲫鲤在减数分裂中只形成 10 0个二价体 ,而不形成 2 5个四价体或其它形式 ,为产生稳定一致的二倍体配子提供了重要的遗传保障 ,也为人工培育的异源四倍体鲫鲤群体能够世世代代自身繁衍下去提供了重要的遗传学证据。三倍体湘云鲫在减数分裂过程中出现二价体、单价体共存 ,同源染色体在配对和分离中出现紊乱 ,导致非整倍体生殖细胞的产生 ,为湘云鲫的不育性提供了染色体水平上的证据     

RFLP Maps Based on a Common Set of Clones Reveal Modes of Chromosomal Evolution in Potato and Tomato

Potato (Solanum tuberosum L.) and tomato (Lycopersicon esculentum) are members of the Solanaceae (nightshade family) and have the same basic chromosome number (x = 12). However, they cannot be cross-hybridized and, until now, it was unknown how conserved the gene order might be between these two species. We report herein the construction of a genetic linkage map of potato chromosomes based on genomic and cDNA clones from tomato. The potato map was drawn from segregation data derived from the interspecific cross S. phureja X (S. tuberosum X S. chacoense) (2n = 2x = 24), and consists of 135 markers defining 12 distinct linkage groups. Nearly all of the tomato probes tested hybridized to potato DNA, and in most cases, the copy number of the employed clones was the same in both species. Furthermore, all clones mapped to the same linkage group in both species. For nine chromosomes, the order of loci appears to be identical in the two species, while for the other three, intrachromosomal rearrangements are apparent, all of which appear to be paracentric inversions with one breakpoint at or near the centromere. These results are consistent with cytogenetic theory, previously untested in plants, which predicts that paracentric inversions will have the least negative effect on fitness and thus be the most likely form of chromosomal rearrangements to survive through evolutionary time. Linkage maps based on a common set of restriction fragment length polymorphism markers provide a basis for uniting the previously separate disciplines of tomato and potato genetics. Using these maps, it may now be possible to test theories about homologies or orthologies of other genes, including those coding for disease resistance and stress tolerances.     

Cytological studies of triploids and their progeny from male-sterile (ms1) soybean

Summary Triploids (2n=3X=60) were obtained from genetic male-sterile (ms1 ms1) soybean [Glycine max (L.) Merr.] plants. Meiosis, pollen fertility, and chromosome number of their progeny were studied. Studies of meiosis in fertile and sterile triploids revealed no distinguishable differences in chromosome associations. Male-sterile plants formed coenocytic microspores characteristic of the ms1 mutant. Restitution of some dyad and tetrad nuclei were observed in male-sterile plants. Chromosomes of the triploids tended to occur in trivalents during diakinesis and metaphase I (MI), but multivalents, bivalents, and univalents also were observed. Average types and frequencies of chromosome associations per cell in diakinesis and MI from 542 pollen mother cells were 0.004 IX + 0.06 VI + 0.002 V + 0.005 IV + 16.99 III + 1.79 II + 5.03 I. Some secondary associations, nonhomologous pairing, and aberrant nucleolar distributions occasionally were observed. Such behavior support the hypothesis of duplicated genomes and the polyploid origin of soybean. Pollen fertility in male-fertile triploid plants (Ms1 ms1 ms1) varied from 57% to 82%, with an average of about 71%. Chromosome numbers of progenies obtained from these fertile triploids varied from 2n=40 to 2n=71, and exhibited a near-random distribution, with the majority (about 60%) being between 56 and 65. Progenies of the fertile triploids gave segregation ratios for the ms1 allele, which confirmed the Ms1 ms1 ms1 genotype.Joint contribution: Agricultural Research Service, U.S. Department of Agriculture, and Journal Paper No. J-11672 of the Iowa Agriculture and Home Economics Experiment Station, Ames, IA 50011, USA, Project 2471     

A novel intergeneric hybrid in the Triticeae: Triticum aestivum x Psathyrost achys juncea

Summary Two hybrid embryos of intergeneric origin between Triticum aestivum cv Fukuho (2n=6x=42, AABBDD) and Psathyrostachys juncea (2n=2x=14, NN) were successfully rescued. One hybrid plant had the expected chromosome number of 28 (ABDN), whereas the second plant had 35 chromosomes. The average meiotic chromosome pairing in the 35-chromosome hybrid was 21.87 univalents + 6.38 bivalents + 0.11 trivalents + 0.009 quadrivalents, which indicates that two copies of the N genome were present. Chromosome pairing in the 28-chromosome hybrid was low (1.35 bivalents), and pointed out the lack of homology between the wheat genomes and the P. juncea genome. These new hybrids showed some necrosis and chlorosis, which caused severe floral abortion in the plant that had 35 chromosomes. These problems became gradually less severe after 18 months.Contrib. no. 372     

Evolutionary implications of permanent odd polyploidy in the stable sexual, pentaploid of Rosa canina L

In Rosa canina (2n = 5x = 35), the pollen and ovular parents contribute, respectively, seven and 28 chromosomes to the zygote. At meiosis I, 14 chromosomes form seven bivalents and 21 chromosomes remain as univalents. Fluorescent in situ hybridization to mitotic and pollen mother cells (PMC) of R. canina showed that 10 chromosomes (two per genome) carry ribosomal DNA (rDNA) loci. Five chromosomes carry terminal 18S-5.8S-26S rDNA loci; three of these also carry paracentric 5S rDNA loci and were designated as marker chromosomes 1. Five chromosomes carry only 5S rDNA loci and three of these were designated as marker chromosomes 2. The remaining four of the 10 chromosomes with rDNA loci were individually identifiable by the type and relative sizes of their rDNA loci and were numbered separately. At PMC meiosis, two marker chromosomes 1 and two marker chromosomes 2 formed bivalents, whereas the others were unpaired. In a gynogenetic haploid of R. canina (n = 4x = 28), obtained after pollination with gamma-irradiated pollen, chromosomes at meiosis I in PMC remained predominantly unpaired. The data indicate only one pair of truly homologous genomes in R. canina. The 21 unpaired chromosomes probably remain as univalents through multiple generations and do not recombine. The long-term evolutionary consequence for the univalents is likely to be genetic degradation through accumulated mutational change as in the mammalian Y chromosome and chromosomes of asexual species. But there is no indication that univalents carry degenerate 5S rDNA families. This may point to a recent evolution of the R. canina meiotic system.     

Use of introgression lines and zonal mapping to identify RAPD markers linked to QTL

RAPD primers were identified as giving parent-specific bands when screened with a set of introgression lines containing introgressed regions of Lycopersicon pennellii that encompass 5 quantitative trait loci affiliated with the production and composition of acylsugars, compounds associated with insect resistance. Primers giving L. pennellii introgression specific bands were zonally mapped to identify bands affiliated with the quantitative trait target and flanking regions using subsets of 7 to 16 F2 individuals which contained small overlapping segments (zones) of the L. pennellii genome spanning those regions. Seventeen RAPD primers, agt-related primers, and an agt clone were then used in mapping the complete F2 population of 144 individuals. This work resulted in the identification of RAPD markers for three of the 5 quantitative trait loci and the construction of an integrated RAPD/RFLP genomic map for tomato (Lycopersicon esculentum x L. pennellii LA716) of 111 RAPD and 8 acylglucose transferase related markers added to a framework map of 150 RFLP markers.