Karyotype reshufflings of <Emphasis Type="Italic">Festuca pratensis</Emphasis> × <Emphasis Type="Italic">Lolium perenne</Emphasis> hybrids

Many different processes have an impact on the shape of plant karyotype. Recently, cytogenetic examination of Lolium species has revealed the occurrence of spontaneous fragile sites (FSs) associated with 35S rDNA regions. The FSs are defined as the chromosomal regions that are sensitive to forming gaps or breaks on chromosomes. The shape of karyotype can also be determined by interstitial telomeric sequences (ITSs), what was recognized for the first time in this paper in chromosomes of Festuca pratensis × Lolium perenne hybrids. Both FSs and ITSs can contribute to genome instabilities and chromosome rearrangements. To evaluate whether these cytogenetic phenomena have an impact on karyotype reshuffling observed in Festuca × Lolium hybrids, we examined F₁ F. pratensis × L. perenne plants and generated F₂-F₉ progeny by fluorescent in situ hybridization (FISH) using rDNA sequences, telomere and centromere probes, as well as by genomic in situ hybridization (GISH). Analyses using a combination of FISH and GISH revealed that intergenomic rearrangements did not correspond to FSs but overlapped with ITSs for several analyzed genotypes. It suggests that internal telomeric repeats can affect the shape of F. pratensis × L. perenne karyotypes. However, other factors that are involved in rearrangements and have a more crucial impact could exist, but they are still unknown.     

Allelopathic Potential of <Emphasis Type="Italic">Koelreuteria bipinnata</Emphasis> var. <Emphasis Type="Italic">integrifoliola</Emphasis> on Germination of Three Turf Grasses

Allelopathy is very important for the scientific disposition of garden plants. To understand the allelopathic potential of Koelreuteria bipinnata Franch. var. integrifoliola, the germination of Agrostis tenuis Sibth., Festuca arundinacea Schreb. and Lolium perenne L. were determined under laboratory conditions. The results showed that root, stem and leaf aqueous extracts of K. bipinnata var. integrifoliola had allelopathic effects on all three turf grasses, and the allelopathic activity varied according to extract concentrations, test species, and extract sources. Lower extract concentrations did not affect or promoted the germination and initial seedling growth of turf grasses, but the highest concentrations almost had inhibitory effect. The order of allelopathic potentials of the three organs on germination of these receptors was root < stem < leaf. And at the highest concentration of leaf extract, the most strongly inhibition was found in A. tenuis, followed by F. arundinaces and then L. perenne. In addition, according to gas chromatography–mass spectrometry (GC–MS) analysis, the allelopathic potential compounds and their abundance in root, stem and leaf were obviously different. Therefore, the allelopathic compounds may responsible for allelopathy of K. bipinnata var. integrifoliola. These findings suggested that more attention should be paid to the leaf of K. bipinnata var. integrifoliola for the relative higher allelopathic effects.     

The quantitative analysis of chromosome pairing and chiasma formation based on the relative frequencies of M I configurations. II. Primary trisomics

On an earlier occasion the estimation of the “crossing-over potentials” of the two arms of a chromosome from the relative frequencies of the different types of bivalent was discussed. When in normal diploids the bivalents in M I can not be distinguished from each other, primary trisomics may be used to mark particular chromosomes. For the estimation of the “crossingover potentials” of the two arms the only type of configuration available (trivalent) is not sufficient. The required additional information may be obtained from the average probability (b) of the chromosome arms to be bound. Using the satellite chromosome trisomic ofSecale cereale it is shown that the use ofb introduces an excessive error, especially with highb values. Consequently, the primary trisomics can not be recommended for the estimation of the “crossing-over potentials” of the two arms of particular chromosomes. The telocentric trisomics permit the recognition of more configurations and are to be preferred. Partner exchange and nucleolus may both interfere with chiasma formation. The data suggest that the three homologous chromosomes may not be equal in respect to pairing and chiasma formations. There are indications that the initiation of pairing is localized in one locus on each arm.     

Dual-color FISH karyotype analyses using rDNAs in three Cucurbitaceae species

Dual-color fluorescence in situ hybridization (FISH) analysis of three Cucurbitaceae species from different genera was conducted using 5S and 45S rDNA probes. In Benincasa hispida (Thunb.) Cogn. (2n=24), the 45S rDNA probe hybridized on two chromosomes, one in the short arm of a medium-sized metacentric chromosome and another at the satellite of a chromosome. The 5S rDNA hybridized at a site proximal to the centromere of the same short arm of the 45S rRNA gene locus that occupied almost the entire short arm. For Citrullus lanatus (Thunb.) Matsum & Nakai (2n=22), the 45S rDNA probe hybridized at sites in the short arms of two chromosomes and the 5S rDNA probe was co-localized with the 45S rRNA locus at the region proximal to the centromere in one chromosome. The 45S rRNA loci occupied almost all of the short arms in both chromosomes. In Cucurbita moschata Duch. (2n=40), the 45S rDNA probe hybridized in five chromosomes in which the 45S rRNA genes occupied almost two-thirds of the chromosomes in two large chromosomes and the entire short arm of a medium-sized chromosome. Two other loci were present in two medium-sized chromosomes, one in the proximal region in the short arm of a chromosome and another at the tip of the long arm of a chromosome. Chromosomes of B. hispida were relatively larger than those of the other two species. The karyotype of B. hispida is composed of two metacentrics and 10 submetacentrics, while that of C. lanatus is composed of seven metacentrics and four submetacentrics and that of C. moschata is composed of 18 metacentrics and two submetacentrics. Comparative chromosome evolution among the three Cucurbitaceae species was attempted using the karyotypes and the chromosomal distribution patterns of the 5S and 45S rDNAs. The results presented herein will be useful in elucidating the phylogenetic relationships among Cucurbitaceae species, and will provide basic data for their breeding programs.     

Host range of wheat striate virus

Na sání p?irozeně infikovaného p?ena?e?e viru prou?kovitosti p?enice (VPP) k?ísaCalligypona pellucida F. reagovaly charakteristickými p?íznaky v poměrně zna?ném rozsahuBromus arvensis L.,B. mollis L.,Avena fatua L.,A. nuda L. (HOEJ.),Triticum aestivum L. s. s.,T. compactum HOST.,T. dicoccum SCHRANK aHordeum murinum L., v men?ím podílu pakLolium multiflorum LAM.,L. perenne L.,Bromus tectorum L.,Poa annua L., Avena strigosa SCHREB., A. sterilis L.,Triticum spelta L.,T. durum DESF.,T. turgidum L. aT. polonicum L. Dal?ích 42 rostlinných druh? ze 6 ?eledí v této testaci neonemocnělo. Negativně vyzněl i pokus o umělé naka?eníPhleum pratense L.,tîeba?e u tohoto rostlinného druhu jsme v p?írodě pozorovali typické p?íznaky VPP. Máme za to, ?e některé negativní výsledky byly asi v p?í?inné spojitosti se ?na?ně kolísající p? ena?e?skou ú?inností vektora, známou ji? z d?ívěj?ích prací. V kulturách pícnin prvního u?itkového roku v místech s nadměrně hojným výskytem larevCalligypona pellucida bylo p?i terénních pozorováních zaznamenáno v některých lokalitách na ?eskomoravské vyso?ině silněj?í napadení VPP uLolium multiflorum. Charakteristické p?íznaky VPP jsme p?i tom zjistili i naPhleum pratense, Lolium perenne a Bromus mollis.     

Intraspecific divergence in wheats of the Emmer group using in situ hybridization with the Spelt-1 family of tandem repeats

Fluorescence in situ hybridization (FISH) was used to study the distribution of Spelt-1 repetitive DNA sequences on chromosomes of 37 accessions representing eight polyploidy wheat species of the Emmer evolutionary lineage: Triticum dicoccoides Körn, T. dicoccum (Schrank) Schuebel, T. durum Desf., T. polonicum L., T. carthlicum Nevski, T. aethiopicum Jakubz., T. aestivum L., and T. spelta L. Substantial polymorphism in the number, distribution, and the sizes of the Spelt-1 loci was revealed. On the chromosomes of the accessions examined, Spelt-1 tandem repeats were found in seven different positions (per haploid chromosome set). These were “potential hybridization sites”, including the subtelomeric regions of either short or long arms of chromosomes 2A and 6B, the short arm of chromosome 1B, and the long arms of chromosomes 2B and 3B. However, in individual genotypes, only from one to three Spelt-1 loci were revealed. Furthermore, no hybridization with Spelt-1 probe was detected on chromosomes from 12 accessions. Thus, the total number of Spelt-1 sites in karyotypes varied from zero to three, with the average number of 1.16. This was substantially lower than in the species of the Timopheevi section and diploid Aegilops speltoides Tausch, a putative donor of the B genome. The decrease of the content of Spelt-1 sequences in the genomes of the Emmer group wheats in comparison with the species of the Timopheevii group and diploid Ae. speltoides was assumed to result from the repetitive sequences reorganization during polyploidization and the repeat elimination during wheat evolution.     

Cytogenetic characterization of <Emphasis Type="Italic">Solanum lycopersicoides</Emphasis> Dun. Alien chromosome additions in cultured tomato

Cytogenetic analysis of five Solanum lycopersicoides monosomic alien addition lines of tomato was carried out. Meiotic analysis showed that additional chromosomes caused serious abnormalities. It was demonstrated that different chromosomes of S. lycopersicoides had different effects on chromosome pairing. For instance, associations formed between chromosomes II and IV of S. lycopersicoides and chromosomes of cultured tomato were trivalents, while chromosome XI in all cells was present as a univalent. Pachytene analysis showed that chromosomes of homeologous group II paired at their long arms, and their nucleolus organizer regions were of different sizes. The use of molecular markers provided accelerated identification of the introgression of S. lycopersicoides genetic material.     

Molecular and cytogenic analysis of pericentromeric heterochromatin in ovarian nurse cells of <Emphasis Type="Italic">Drosophila melanogaster</Emphasis> subgroup species

Evolutionary rearrangements of pericentromeric heterochromatin among Drosophila melanogaster subgroup species have been investigated. A region-specific DNA library from Drosophila orena ovarian nurse cell chromocenter was obtained by the microdissection of polythene chromosomes. The probe has been localized on chromosomes of ovarian nurse cells of Drosophila melanogaster subgroup species using fluorescent hybridization in situ. Sequences homologous to the sequences of the DNA probe were detected in the chromocenter and pericentromeric regions of D. orena polythene chromosomes, in all pericentromeric regions of other species with several exceptions. There was no labeling on one of the arms of the D. simulans chromosome 2; however, these sequences were present on the telomere of D. erecta chromosome 3 and in regions adjacent to the brightly DAPI-stained heterochromatin blocks of D. yakuba, D. santomea and D. teissieri chromosomes 2 and 3. At the S₆ stage (secondary reticulate nucleus), labeled chromatin can be found mostly within a restricted territory in D. orena nucleus; no such chromatin can be detected throughout the rest of the nucleus. On the contrary, at this stage, in nuclei of other species, labeled DNA is spread diffusely.     

FISH-aimed karyotype analysis in <Emphasis Type="Italic">Aconitum</Emphasis> subgen. <Emphasis Type="Italic">Aconitum</Emphasis> reveals excessive rDNA sites in tetraploid taxa

The location of 5S and 35S rDNA sequences in chromosomes of four Aconitum subsp. Aconitum species was analyzed after fluorescence in situ hybridization (FISH). Both in diploids (2n?=?2x?=?16; Aconitum variegatum, A. degenii) and tetraploids (2n?=?4×?=?32; A. firmum, A. plicatum), rDNA repeats were localized exclusively on the shorter arms of chromosomes, in subterminal or pericentromeric sites. All analyzed species showed similar basal genome size (Cx?=?5.31–5.71 pg). The most striking features of tetraploid karyotypes were the conservation of diploid rDNA loci and emergence of many additional 5S rDNA clusters. Chromosomal distribution of excessive ribosomal sites suggests their role in the secondary diploidization of tetraploid karyotypes.     

Interaction between contrasting rice genotypes and soil physical conditions induced by hydraulic stresses typical of alternate wetting and drying irrigation of soil

Background and aims

Drought events, agricultural practices and plant communities influence microbial and soil abiotic parameters which can feedback to fodder production. This study aimed to determine which soil legacies influence plant biomass production and nutritional quality, and its resistance and recovery to extreme weather events.

Methods

In a greenhouse experiment, soil legacy effects on Lolium perenne were examined, first under optimal conditions, and subsequently during and after drought. We used subalpine grassland soils previously cultivated for two years with grass communities of distinct functional composition, and subjected to combinations of climatic stress and simulated management.

Results

The soil legacy of climatic stress increased biomass production of Lolium perenne and its resistance and recovery to a new drought. This beneficial effect resulted from higher nutrient availability in soils previously exposed to climatic stresses due to lower competitive abilities and resistance of microbial communities to a new drought. This negative effect on microbial communities was strongest in soils from previously cut and fertilized grasslands or dominated by conservative grasses.

Conclusion

In subalpine grasslands more frequent climatic stresses could benefit fodder production in the short term, but threaten ecosystem functioning and the maintenance of traditional agricultural practices in the long term.

     

The karyotype of the great sculpin, <Emphasis Type="Italic">Myoxocephalus polyacanthocephalus</Emphasis> (Pallas, 1814) (Pisces: Cottidae), from the Russian part of the species range

The karyotype of the great sculpin, Myoxocephalus polyacanthocephalus (Pallas, 1814) (Pisces: Cottidae) from the Sea of Okhotsk and the Sea of Japan has been studied for the first time. The karyotype is stable; it consists of 40 chromosomes (4 metacentric, 2 submeta-subtelocentric, 20 subtelocentric, and 14 acrocentric chromosomes); the number of chromosomal arms is 44 + 2. Nucleolar organizer regions (NOR) are found in the telomeric region of the arm in one homologue of a pair of small metacentric chromosomes, using the Ag-NOR banding technique. A comparative analysis of the karyotype of M. polyacanthocephalus and the karyotypes of other Myoxocephalus species (M. stelleri, M. brandtii, M. jaok, M. ochotensis, and M. scorpius) has been carried out based on the main karyotype characters, as well as on the number and localization of NORs. The identified differences make it possible to differentiate the studied species, whereas the general traits indicate their taxonomic proximity.     

Quinacrine Fluorescence Patterns and Terminal DNA Labelling of Human <Emphasis Type="Italic">C</Emphasis> Group Chromosomes

THE human C group chromosomes have been difficult to study because they have rather similar morphology. Application of the quinacrine fluorescent staining technique developed by Caspersson et al.¹ now allows the identification of individual chromosomes and of the chromosome segments involved in translocations because the fluorescent patterns are not altered by the translocation^2–4. We have reported the value of this technique in analysing abnormalities of the D⁴ and G³ groups. We report here a variety of structural changes of C group chromosomes which have been characterized in this way, as well as the terminal DNA replication pattern of the C group chromosomes.     

Strategic timing of nitrogen fertilization to increase root biomass and nitrogen-use efficiency of <Emphasis Type="Italic">Lolium perenne</Emphasis> L.

Aims

During the first days after harvest of Lolium perenne L., N remobilized from roots and stubble forms the main N source for regrowth. Low N uptake from the soil during this period may lead to N loss if N fertilizer is applied too soon. Furthermore, temporary N deprivation has been found to stimulate root growth. We therefore hypothesized that a strategic delay in N application after harvest may improve N-use efficiency of L. perenne grassland by increasing root biomass and reducing N loss.

Methods

In a laboratory and field experiment with L. perenne, we delayed N fertilizer application after harvest for 0, 3, 6, 9 and 12 days, repeated this for up to six harvest cycles, and determined effects on herbage yield, herbage N uptake and root biomass.

Results

In both experiments, delaying N application for up to 12 days had no significant effect on root biomass or total herbage N uptake, but it significantly reduced total herbage yield in the laboratory experiment. Total yield tended to be highest when N application was delayed for 3 days. Two growth periods in the field experiment showed significantly higher N uptake when N application was delayed, possibly due to rainfall-induced N losses in the treatments with shorter delay.

Conclusions

Our results do not provide evidence that delaying N application improves N-use efficiency of L. perenne grassland by increasing root biomass. However, strategic timing of N fertilizer application based on rainfall forecasts could contribute to improve N-use efficiency by reducing N losses from leaching and denitrification.

     

The <Emphasis Type="Italic">Drosophila bipectinata</Emphasis> species complex: phylogenetic relationship among different members based on chromosomal variations

Making interspecific hybridizations, where possible remains an unparalleled option for studying the intricacies of speciation. In the Drosophila bipectinata species complex comprising of four species, namely D. bipectinata, D. parabipectinata, D. malerkotliana and D. pseudoananassae, interspecific hybrids can be obtained in the laboratory, thus bequeathing an ideal opportunity for studying speciation and phylogeny. With the view of investigating the degree of divergence between each species pair, we planned to study the polytene chromosomes of the F ₁ hybrids, as it would mirror the level of compatibility between the genomes of the parental species. Two sets of crosses were made, one involving homozygous strains of all four species from India and the other including homozygous strains from different places across the globe. Polytene chromosomes of F ₁ larvae from both sets of crosses had similar configurations. In F ₁ larvae from crosses involving D. bipectinata, D. parabipectinata and D. malerkotliana, complex configurations (depicting overlapping inversions) could be detected in different arms. However, they were fairly synapsed, indicating that the differences are only at the level of gene arrangements. The polytene chromosomes of larvae obtained by crossing D. pseudoananassae with the other three species were very thin with gross asynapsis in all the arms, demonstrating that the genome of D. pseudoananassae is widely diverged from rest of the species. The overlapping inversions (reflected in complex configuration), are inferred in the light of earlier chromosomal studies performed in this complex.     

Cytogenetic analyses of eight species in the genus <Emphasis Type="Italic">Leptodactylus</Emphasis> Fitzinger, 1843 (Amphibia,Anura, Leptodactylidae), including a new diploid number and a karyotype with multiple translocations

Background

The karyotypes of Leptodactylus species usually consist of 22 bi-armed chromosomes, but morphological variations in some chromosomes and even differences in the 2n have been reported. To better understand the mechanisms responsible for these differences, eight species were analysed using classical and molecular cytogenetic techniques, including replication banding with BrdU incorporation.

Results

Distinct chromosome numbers were found: 2n = 22 in Leptodactylus chaquensis, L. labyrinthicus, L. pentadactylus, L. petersii, L. podicipinus, and L. rhodomystax; 2n = 20 in Leptodactylus sp. (aff. podicipinus); and 2n = 24 in L. marmoratus. Among the species with 2n = 22, only three had the same basic karyotype. Leptodactylus pentadactylus presented multiple translocations, L. petersii displayed chromosome morphological discrepancy, and L. podicipinus had four pairs of telocentric chromosomes. Replication banding was crucial for characterising this variability and for explaining the reduced 2n in Leptodactylus sp. (aff. podicipinus). Leptodactylus marmoratus had few chromosomes with a similar banding patterns to the 2n = 22 karyotypes. The majority of the species presented a single NOR-bearing pair, which was confirmed using Ag-impregnation and FISH with an rDNA probe. In general, the NOR-bearing chromosomes corresponded to chromosome 8, but NORs were found on chromosome 3 or 4 in some species. Leptodactylus marmoratus had NORs on chromosome pairs 6 and 8. The data from C-banding, fluorochrome staining, and FISH using the telomeric probe helped in characterising the repetitive sequences. Even though hybridisation did occur on the chromosome ends, telomere-like repetitive sequences outside of the telomere region were identified. Metaphase I cells from L. pentadactylus confirmed its complex karyotype constitution because 12 chromosomes appeared as ring-shaped chain in addition to five bivalents.

Conclusions

Species of Leptodactylus exhibited both major and minor karyotypic differences which were identified by classical and molecular cytogenetic techniques. Replication banding, which is a unique procedure that has been used to obtain longitudinal multiple band patterns in amphibian chromosomes, allowed us to outline the general mechanisms responsible for these karyotype differences. The findings also suggested that L. marmoratus, which was formerly included in the genus Adenomera, may have undergone great chromosomal repatterning.

     

Karyotype of the sculpin <Emphasis Type="Italic">Myoxocephalus jaok</Emphasis> (Pisces: Cottidae) from Peter the Great Bay,Sea of Japan

The karyotype of the sculpin Myoxocephalus jaok from the Ussuriisky, Amursky, and Vostok Bays was studied. It was found that 2n = 24, among the chromosomes there were 16 metacentric, 4 submetacentric, and 4 acrocentric, NF = 44. There was no variation in the number of chromosomes, and no differences between male and female karyotypes were revealed. A comparison of Myoxocephalus jaok, M. brandti and M. stelleri karyotypes was performed. The pronounced distinction of Myoxocephalus jaok karyotype resulting from chromosomal rearrangements was shown.     

Molecular and cytogenetic analyses provide evidence of the introgression of chromosomal segments from the wild <Emphasis Type="Italic">Cucumis hystrix</Emphasis> into the cultivated cucumber through the bridge of a synthetic allotetraploid

Cucumis × hytivus (2n = 4× = 38) is a synthetic allotetraploid obtained from interspecific hybridization between the cucumber (2n = 2× = 14) and its wild relative C. hystrix (2n = 2× = 24). The synthesis of this species built a bridge for cucumber improvement through gene introgression. Allotriploid and introgression lines (ILs) have previously been produced and characterized with respect to morphology, cytology, and molecular markers. However, no clear evidence of how the chromosomal segments of C. hystrix were introgressed and inherited was found owing to the small size of chromosomes. In the present study, cucumber-C. hystrix introgression lines were developed by backcrossing the allotriploid to North China cucumber breeding line “P01” followed by self-pollination. The introgressed segments of C. hystrix in the ILs were revealed by meiotic pachytene chromosome analysis. Fluorescence in situ hybridization (FISH) was performed on pachytene chromosomes using fosmid clones from cucumber, which confirmed that introgression occurred in the long arm of chromosome 7. Molecular analysis using a set of 53 simple sequence repeats (SSRs) indicated that the chromosomal segments of C. hystrix were introduced into 4 cucumber chromosomes, the short arms of chromosomes 2 and 6, and long arms of chromosomes 3 and 7. The inheritance of alien sequences in the long arm of chromosome 7 was investigated with 21 SSRs in self-pollinated progenies. C. hystrix-specific bands of several SSRs were still present in some individuals, indicating that the introgressed segment was partially preserved. The first unambiguous identification of alien chromosome segments in cucumber ILs using combined molecular cytogenetics could facilitate the determination of effects of wild alleles and promote cucumber improvement.     

Fine mapping a self-fertility locus in perennial ryegrass

Key message

A self-fertility locus was fine mapped to a 1.6 cM region on linkage group 5 in a perennial ryegrass population. This locus was the main determinant of pollen self-compatibility.

Abstract

In grasses, self-incompatibility (SI) is characterized by a two-loci gametophytic (S and Z) mechanism acting together in the recognition and inhibition of self-pollen. Mutations affecting the expression of SI have been reported in a few grass species. In perennial ryegrass (Lolium perenne L.), a mutation independent from S and Z, and mapping on linkage group 5 (LG 5), was previously reported to produce self-fertile plants. Here, we describe fine mapping of the self-fertility (SF) gene in a perennial ryegrass population and determine whether there is any effect of other genomic regions on the pollen compatibility. The phenotypic segregation of SF showed a bimodal distribution with one mean at 49% pollen compatibility and the other at 91%. Marker-trait association analysis showed that only markers on LG 5 were significantly associated with the trait. A single gene model explained 82% of the observed variability and no effects of the other regions were detected. Using segregation and linkage analysis, the SF locus was located to a 1.6 cM region on LG 5. The flanking marker sequences were aligned to rice and Brachypodium distachyon reference genomes to estimate the physical distance. We provide markers tightly linked to SF that can be used for introgression of this trait into advanced breeding germplasm. Moreover, our results represent a further step towards the identification of the SF gene in LG 5.