Alien Gene Transfer Research Articles

Engineered Durum Wheat Germplasm with Multiple Alien Introgressions: Agronomic and Quality Performance

If genetic gains in wheat yield are to be achieved in today’s breeding, increasing the genetic variability of cultivated genotypes is an essential requisite to meet. To this aim, alien gene transfer through chromosome engineering (CE) is a validated and sound strategy. Attempts to incorporate more than one alien segment into cultivated wheat have been rare, particularly for tetraploid durum wheat. Here, we present the agronomic and quality performance of the first successful CE-mediated multiple introgression into the latter species. By assembling into 7AL, 3BS, and 1AS arms of a single genotype homoeologous segments of Thinopyrum ponticum 7el1L, Aegilops longissima 3SlS, and Triticum aestivum 1DS arms, respectively, we have stacked several valuable alien genes, comprising Lr19+Sr25+Yp (leaf and stem rust resistance and a gene increasing semolina yellowness), Pm13 (powdery mildew resistance), and Gli-D1/Glu-D3 (genes affecting gluten properties), respectively. Advanced progenies of single, double, and triple recombinants were field-tested across three years in a typical durum wheat growing area of central Italy. The results showed that not only all recombinants had normal phenotype and fertility, but also that one of the triple recombinants had the highest yield through all seasons compared with all other recombinants and control cultivars. Moreover, the multiple introgressions enhanced quality traits, including gluten characteristics and semolina yellow index. The presence of effective disease resistance genes confers additional breeding value to the novel and functional CE products, which can greatly contribute to crop security and safety.

Plasticity in Triticeae centromere DNA sequences: a wheat × tall wheatgrass (decaploid) model.

Centromeres mediate chromosome attachment to microtubules and maintain the integrity of chromosomes for proper segregation of the sister chromatids during cell division. Advances in the assembly of Triticeae genome sequences combined with the capacity to recover hybrid species derived from very distantly related species provides potential experimental systems for linking retrotransposon amplification and repositioning of centromeres via non-mendelian inheritance in partial amphiploid breeds. The decaploid tall wheatgrass (Thinopyrum ponticum) is one of the most successfully used perennial species in wheat breeding for generating translocation lines with valuable agronomic traits. We found that wheat centromere retrotransposons CRW and Quinta widely occur within the tall wheatgrass genome. In addition, one of the genome donors to Th. ponticum, Pseudoroegneria stipifolia (StSt), has been shown to have Abigail and a satellite repeat, CentSt. We also found two other centromeric retrotransposons, Abia and CL135 in Th. ponticum by ChIP-seq. Examination of partial amphiploid lines that were generated in the 1970s demonstrated extensive modification in centromere sequences using CentSt, Abigail and Abia as probes. We also detected that St-genome chromosomes were more enriched with Abigail and CentSt, whereas E-genome chromosomes were enriched with CRW and Quinta in tall wheatgrass and its closer relatives. It can be concluded that bursts of transposition of retrotransposons and repositioning of centromeres via non-mendelian segregation are common in partial amphiploids derived from interspecific hybrids. Practically speaking, our study reveals that the existence of homologous centromere functional sequences in both a donor and its receptor can substantially contribute to the successful transfer of alien genes into crop species. OPEN RESEARCH BADGES: This article has earned an Open Data Badge for making publicly available the digitally-shareable data necessary to reproduce the reported results. The data is available at https://www.ncbi.nlm.nih.gov/sra/SRR9089557; https://www.ncbi.nlm.nih.gov/sra/SRR9089558; https://www.ncbi.nlm.nih.gov/sra/SRR9089559; https://www.ncbi.nlm.nih.gov/sra/SRR9089560; https://www.ncbi.nlm.nih.gov/sra/SRR9089561; https://www.ncbi.nlm.nih.gov/sra/SRR9089562; https://www.ncbi.nlm.nih.gov/sra/SRR9089563; https://www.ncbi.nlm.nih.gov/sra/SRR9089564; https://www.ncbi.nlm.nih.gov/nuccore/MK999394; https://www.ncbi.nlm.nih.gov/nuccore/MK999395; https://www.ncbi.nlm.nih.gov/nuccore/MK999396.

НАСЛЕДОВАНИЕ ЭФФЕКТИВНОЙ ЮВЕНИЛЬНОЙ УСТОЙЧИВОСТИ ШЕСТИ ОБРАЗЦОВ AEGILOPS SPELTOIDES TAUSCH К ЛИСТОВОЙ РЖАВЧИНЕ

Background. Leaf rust (causal agent: Puccinia triticina Erikss.) is a serious disease of bread wheat in all crop-growing regions. An environmentally safe and economically profitable method to protect plants is cultivation of resistant varieties. Their development requires searching for the forms carrying new genes of resistance. Despite the fact that more than 70 Lr genes have been described, only two (Lr39(41) and Lr47) are effective in the seedling stage over all the territory of the Russian Federation. Thus, expanding the set of effective leaf rust resistance genes is a high-priority task. An important source of such genes are wild relatives of Triticum aestivum L., including Aegilops L. species. Knowing genetic control of resistance in newly identified forms will help to avoid the transfer of the same alien resistance genes onto bread wheat. Materials and methods. Inheritance of effective juvenile leaf rust resistance was studied in 6 accessions of Ae. speltoides Tausch from the VIR collection. Crossings were carried out in the field of Pushkin and Pavlovsk Laboratories of VIR (St. Petersburg). Genetic control of resistance to the disease was analyzed in the following accessions of Ae. speltoides: k-1000 (Turkey), k-1015 (Afghanistan), k-1593 (Iraq), k-2279 (Iran), k-2753 and k-2819 (unknown origin). Results and conclusions. The analysis of segregation for seedling resistance to leaf rust in F 2 и F 3 from the crosses between the 6 studied accessions and the susceptible Ae. speltoides accession k-1596 showed that each of them possessed one dominant resistance gene. The absence of susceptible plants in hybrid populations from the crosses between resistant accessions testified to a tight linkage or, more likely, the identity of their genes associated with resistance. The identified resistance gene cannot be identical to Lr28, Lr35, Lr36 and Lr51, earlier introgressed into the T. aestivum genome from Ae. speltoides. Before the introgression of the newly identified gene, it is necessary to study its identity to Lr47 using the phytopathological test; the use of molecular markers for this purpose is little informative.

Development and characterization of wheat-sea wheatgrass (Thinopyrum junceiforme) amphiploids for biotic stress resistance and abiotic stress tolerance.

Development of a complete wheat-Thinopyrum junceiforme amphiploid facilitated identification of resistance to multiple pests and abiotic stress derived from the wild species and shed new light on its genome composition. Wheat production is facing numerous challenges from biotic and abiotic stresses. Alien gene transfer has been an effective approach for wheat germplasm enhancement. Thinopyrum junceiforme, also known as sea wheatgrass (SWG), is a distant relative of wheat and a relatively untapped source for wheat improvement. In the present study, we developed a complete amphiploid, 13G819, between emmer wheat and SWG for the first time. Analysis of the chromosome constitution of the wheat-SWG amphiploid by multiple-color genomic in situ hybridization indicated that SWG is an allotetraploid with its J1 genome closely related to Th. bessarabicum and Th. elongatum, and its J2 genome was derived from an unknown source. Two SWG-derived perennial wheat lines, 14F3516 and 14F3536, are partial amphiploids and carry 13 SWG chromosomes of mixed J1 and J2 genome composition, suggesting cytological instability. We challenged the amphiploid 13G819 with various abiotic and biotic stress treatments together with its emmer wheat parent. Compared to its emmer wheat parent, the amphiploid showed high tolerance to waterlogging, manganese toxicity and salinity, low nitrogen and possibly to heat as well. The amphiploid 13G819 is also highly resistant to the wheat streak mosaic virus (temperature insensitive) and Fusarium head blight. All three amphiploids had solid stems, which confer resistance to wheat stem sawflies. All these traits make SWG an excellent source for improving wheat resistance to diseases and insects and tolerance to abiotic stress.

In vitro propagation of Cajanus cajan × C. cajanifolius hybrid and its characterization using cyto-morphological and SSR markers

Cajanus cajanifolius, the putative progenitor species of pigeonpea (C. cajan), has many agro-economic traits that deserve attention for introgression into pigeonpea cultivars. However, unidirectional compatibility creates barriers for interspecific hybridization and alien gene transfer between these two species. In the present study, very low percentage of pod setting and F1 seed germination were observed. Thus, attempts were made for the propagation of interspecific F1 hybrids in vitro, and an efficient in vitro propagation protocol has been optimized. Excised cotyledonary explants of F1 hybrids were cultured on both MS and Blaydes’ medium supplemented with NAA, BAP and GA3 at various combinations and concentrations. MS medium with BAP (25 μM) was most suitable for multiple shoot induction. MS medium was found to be superior for both multiple shoot and root induction from cotyledonary explants. Cyto-morphological and SSR marker based analysis confirmed the hybridity of the micro-propagated F1 plantlets. Meiocytes of the regenerated F1 hybrids experienced chromosome heteromorphism during diakinesis leading to laggard and bridge formation at anaphase-I. The present study evidenced the scope of interspecific hybridization between C. cajan and C. cajanifolius aiming at transmission of stress tolerant genes from C. cajanifolius to the cultivated gene pool of pigeonpea for broadening its genetic base.

Molecular Cytogenetic Mapping of Satellite DNA Sequences in Aegilops geniculata and Wheat

Fluorescence in situ hybridization (FISH) provides an efficient system for cytogenetic analysis of wild relatives of wheat for individual chromosome identification, elucidation of homoeologous relationships, and for monitoring alien gene transfers into wheat. This study is aimed at developing cytogenetic markers for chromosome identification of wheat and Aegilops geniculata (2n = 4x = 28, U^gU^gM^gM^g) using satellite DNAs obtained from flow-sorted chromosome 5M^g. FISH was performed to localize the satellite DNAs on chromosomes of wheat and selected Aegilops species. The FISH signals for satellite DNAs on chromosome 5M^g were generally associated with constitutive heterochromatin regions corresponding to C-band-positive chromatin including telomeric, pericentromeric, centromeric, and interstitial regions of all the 14 chromosome pairs of Ae. geniculata. Most satellite DNAs also generated FISH signals on wheat chromosomes and provided diagnostic chromosome arm-specific cytogenetic markers that significantly improved chromosome identification in wheat. The newly identified satellite DNA CL36 produced localized M^g genome chromosome-specific FISH signals in Ae. geniculata and in the M genome of the putative diploid donor species Ae. comosa subsp. subventricosa but not in Ae. comosa subsp. comosa, suggesting that the M^g genome of Ae. geniculata was probably derived from subsp. subventricosa.

Current status of tissue culture and genetic transformation research in cotton (Gossypium spp.)

Cotton (Gossypium spp.) is an economically very important fiber yielding crop, which is grown almost in sixty-five countries throughout the world. Like other crops, cotton also suffers from major biotic and abiotic stresses. In fact, the losses due to insect pests in cotton are enormous compared to other crops, thereby reducing the actual economic potential. It is a well-known fact that more than half of the total pesticide consumption across the world is utilized on controlling insect pests in this crop. Though conventional breeding and integrated pest management practices have resulted in improving/developing fiber quality, heat tolerance, CMS lines and yield, much success has not been reported with respect to biotic and abiotic stresses, especially insect pests due to the non-availability of genes conferring resistance within a crossable gene pool. Thus, genetic engineering has become an inevitable tool in finding solutions to these problems and transfer of alien genes into commercially important cotton varieties in the last two decades. In fact ~81 % of cotton grown throughout the world is genetically modified. Despite these achievements, several limitations still exist in achieving cotton transformation. In this review, we discuss the status of different regeneration and transformation methods in cotton along with the major factors that exert influence in developing cotton transgenics, besides the chronological progress made in tissue culture and cotton transformation technology.

Wheat–barley hybridization: the last 40 years

AbstractSeveral useful alien gene transfers have been reported from related species into wheat (Triticum aestivum), but very few publications have dealt with the development of wheat/barley (Hordeum vulgare) introgression lines. An overview is given here of wheat × barley hybridization over the last forty years, including the development of wheat × barley hybrids, and of addition and translocation lines with various barley cultivars. A short summary is also given of the wheat × barley hybrids produced with other Hordeum species. The meiotic pairing behaviour of wheat × barley hybrids is presented, with special regard to the detection of wheat–barley homoeologous pairing using the molecular cytogenetic technique GISH. The effect of in vitro multiplication on the genome composition of intergeneric hybrids is discussed, and the production and characterization of the latest wheat/barley translocation lines are presented. An overview of the agronomical traits (β-glucan content, earliness, salt tolerance, sprouting resistance, etc.) of the newly developed introgression lines is given. The exploitation and possible use of wheat/barley introgression lines for the most up-to-date molecular genetic studies (transcriptome analysis, sequencing of flow-sorted chromosomes) are also discussed.

Syntenic relationships between the U and M genomes of Aegilops, wheat and the model species Brachypodium and rice as revealed by COS markers.

Diploid Aegilops umbellulata and Ae. comosa and their natural allotetraploid hybrids Ae. biuncialis and Ae. geniculata are important wild gene sources for wheat. With the aim of assisting in alien gene transfer, this study provides gene-based conserved orthologous set (COS) markers for the U and M genome chromosomes. Out of the 140 markers tested on a series of wheat-Aegilops chromosome introgression lines and flow-sorted subgenomic chromosome fractions, 100 were assigned to Aegilops chromosomes and six and seven duplications were identified in the U and M genomes, respectively. The marker-specific EST sequences were BLAST-ed to Brachypodium and rice genomic sequences to investigate macrosyntenic relationships between the U and M genomes of Aegilops, wheat and the model species. Five syntenic regions of Brachypodium identified genome rearrangements differentiating the U genome from the M genome and from the D genome of wheat. All of them seem to have evolved at the diploid level and to have been modified differentially in the polyploid species Ae. biuncialis and Ae. geniculata. A certain level of wheat–Aegilops homology was detected for group 1, 2, 3 and 5 chromosomes, while a clearly rearranged structure was showed for the group 4, 6 and 7 Aegilops chromosomes relative to wheat. The conserved orthologous set markers assigned to Aegilops chromosomes promise to accelerate gene introgression by facilitating the identification of alien chromatin. The syntenic relationships between the Aegilops species, wheat and model species will facilitate the targeted development of new markers specific for U and M genomic regions and will contribute to the understanding of molecular processes related to allopolyploidization.

An Effective Procedure for In Vitro Culture ofEleusine coracana(L.) and Its Application

Efficient protocols for callus production, plantlet regeneration, protoplast isolation, and micronucleation of finger millet (Eleusine coracana(L.) Gaertn.) were developed. White nodulated calli were formed on medium with N6macrosalts, MS microsalts, 2.4-dichlorophenoxyacetic acid (2 mg L−1), kinetin (0.4 mg L−1), 1-naphthalene acetic acid (2 mg L−1), and certain additives. It was found that appropriate supplementation leads to formation of numerous shoots. Healthy rooted plantlets formed on hormone-free media. Although different tested additives had no significant effect on percentage of callus formation, it affected callus quality that further dictated plant-forming capacities. Seedlings were better source tissues for protoplasts isolation compared to callus cultures. About protoplasts were isolated from one gram of seedling coleoptyles. Microcolonies were visible after 20–25 days' incubation on KM8p medium supplemented with glutamine (100 mg L−1) and proline (500 mg L−1). Here we also present a procedure of an efficient induction of micronuclei after chlorpropham (10 μM) and cytochalasin-B (20 μM) seedlings treatment with subsequent microprotoplasts isolation. This technique is discussed for the transfer of alien chromosomes and genes from finger millet by microprotoplast-mediated chromosome transfer.

Introgression and characterization of a goatgrass gene for a high level of resistance to ug99 stem rust in tetraploid wheat.

The transfer of alien genes to crop plants using chromosome engineering has been attempted infrequently in tetraploid durum wheat (Triticum turgidum L. subsp. durum). Here, we report a highly efficient approach for the transfer of two genes conferring resistance to stem rust race Pgt-TTKSK (Ug99) from goatgrass (Aegilops speltoides) to tetraploid wheat. The durum line DAS15, carrying the stem rust resistance gene Sr47 derived from Ae. speltoides, was crossed, and backcrossed, to durum 5D(5B) aneuploids to induce homeologous pairing. After a final cross to ‘Rusty’ durum, allosyndetic recombinants were recovered. The Ae. speltoides chromosomal segment carrying Sr47 was found to have two stem rust resistance genes. One gene conditioning an infection type (IT) 2 was located in the same chromosomal region of 2BS as Sr39 and was assigned the temporary gene symbol SrAes7t. Based on ITs observed on a diverse set of rust races, SrAes7t may be the same as Sr39. The second gene conditioned an IT 0; and was located on chromosome arm 2BL. This gene retained the symbol Sr47 because it had a different IT and map location from other stem rust resistance genes derived from Ae. speltoides. Allosyndetic recombinant lines carrying each gene on minimal alien chromosomal segments were identified as were molecular markers distinguishing each alien segment. This study demonstrated that chromosome engineering of Ae. speltoides segments is feasible in tetraploid wheat. The Sr47 gene confers high-level and broad spectrum resistance to stem rust and should be very useful in efforts to control TTKSK.

Molecular marker-based detection of Ph1b mutation to increase homoeologous pairing in wheat (Triticum aestivum)

Despite the close relationship between three genomes of wheat, meiosis in wheat is characterized by formation of bivalents only. The homologous pairing of polyploidy wheat is controlled by Ph1 (pairing homologous) locus located on long arm of chromosome 5B which suppresses pairing and recombination between homoeologous chromosomes. However, similar genes have also been identified in T. turgidum and T. timopheevii with lesser impact. Cytogenetic manipulations for suppressing the Ph1 pairing regulation would be necessary to bring about the desired chromosome pairing and hence alien gene transfers into cultivated wheat. In the present study, PCR based marker was used to transfer the recessive mutation in Ph1 locus (Ph1b) from bread wheat cultivar Chinese Spring to Indian bread and durum wheat cultivars. The availability of Ph1b locus in Indian wheat genetic background will help in transfer of alien genes of economic and agronomic importance.

Chromosome isolation by flow sorting in Aegilops umbellulata and Ae. comosa and their allotetraploid hybrids Ae. biuncialis and Ae. geniculata.

This study evaluates the potential of flow cytometry for chromosome sorting in two wild diploid wheats Aegilops umbellulata and Ae. comosa and their natural allotetraploid hybrids Ae. biuncialis and Ae. geniculata. Flow karyotypes obtained after the analysis of DAPI-stained chromosomes were characterized and content of chromosome peaks was determined. Peaks of chromosome 1U could be discriminated in flow karyotypes of Ae. umbellulata and Ae. biuncialis and the chromosome could be sorted with purities exceeding 95%. The remaining chromosomes formed composite peaks and could be sorted in groups of two to four. Twenty four wheat SSR markers were tested for their position on chromosomes of Ae. umbellulata and Ae. comosa using PCR on DNA amplified from flow-sorted chromosomes and genomic DNA of wheat-Ae. geniculata addition lines, respectively. Six SSR markers were located on particular Aegilops chromosomes using sorted chromosomes, thus confirming the usefulness of this approach for physical mapping. The SSR markers are suitable for marker assisted selection of wheat-Aegilops introgression lines. The results obtained in this work provide new opportunities for dissecting genomes of wild relatives of wheat with the aim to assist in alien gene transfer and discovery of novel genes for wheat improvement.

Synthesis and cytological analyses of hybrids between hexaploid wheat, with and without Ph1, and diploid wheatgrass

The usefulness of wide hybridization in genetic enhancement of crop plants like wheat, Triticum aestivum L. (2n = 6x = 42; AABBDD genomes), is well documented. Diploid wheatgrass, Lophopyrum elongatum (Host) A. Love (2n = 2x = 14; EE genome), is a source of several desirable traits including Fusarium head blight resistance. The objective of this study was to report on the synthesis and cytological analyses of wheat × wheatgrass hybrids and highlight homoeologous pairing involving the wheat and wheatgrass chromosomes. We hybridized wheatgrass with two important, crossable cultivars, ‘Chinese Spring,’ and ‘Fukohokomugi,’ of bread wheat and produced 11 tetraploid (2n = 4x = 28; ABDE) and two pentaploid (2n = 5x = 28; ABDEE) hybrids. To help promote homoeologous pairing and hence genetic recombination between the wheat and grass chromosomes, we also used the Chinese Spring mutant ph1bph1b. Using molecular markers, we readily detected intergeneric hybrids without Ph1. The hybrids without Ph1 showed multivalent formation involving wheat and grass chromosomes. However, the lack of Ph1 produced a much higher homoeologous pairing in the haploid chromosome complement in the CS ph1bph1b × wheatgrass hybrids than in the disomic complement of CS ph1bph1b. The pentaploid hybrids resulted from the fusion of a normal 21-chromsome gamete of the wheat parent with an unreduced, 14-chromsome gamete of diploid wheatgrass. These hybrids showed a remarkable degree of Ph1-enforced preferential pairing among the homologous wheatgrass chromosomes. Varying degrees of homoeologous pairing in various hybrids were detected that could facilitate alien gene transfer into wheat.

Targeted introgression of a wheat stem rust resistance gene by DNA marker-assisted chromosome engineering.

Chromosome engineering is a useful strategy for transfer of alien genes from wild relatives into modern crops. However, this strategy has not been extensively used for alien gene introgression in most crops due to low efficiency of conventional cytogenetic techniques. Here, we report an improved scheme of chromosome engineering for efficient elimination of a large amount of goatgrass (Aegilops speltoides) chromatin surrounding Sr39, a gene that provides resistance to multiple stem rust races, including Ug99 (TTKSK) in wheat. The wheat ph1b mutation, which promotes meiotic pairing between homoeologous chromosomes, was employed to induce recombination between wheat chromosome 2B and goatgrass 2S chromatin using a backcross scheme favorable for inducing and detecting the homoeologous recombinants with small goatgrass chromosome segments. Forty recombinants with Sr39 with reduced surrounding goatgrass chromatin were quickly identified from 1048 backcross progenies through disease screening and molecular marker analysis. Four of the recombinants carrying Sr39 with a minimal amount of goatgrass chromatin (2.87-9.15% of the translocated chromosomes) were verified using genomic in situ hybridization. Approximately 97% of the goatgrass chromatin was eliminated in one of the recombinants, in which a tiny goatgrass chromosome segment containing Sr39 was retained in the wheat genome. Localization of the goatgrass chromatin in the recombinants led to rapid development of three molecular markers tightly linked to Sr39. The new wheat lines and markers provide useful resources for the ongoing global effort to combat Ug99. This study has demonstrated great potential of chromosome engineering in genome manipulation for plant improvement.

Genetic control of chromosome behaviour: Implications in evolution, crop improvement, and human biology

Chromosomes and chromosome pairing are pivotal to all biological sciences. The study of chromosomes helps unravel several aspects of an organism. Although the foundation of genetics occurred with the formulation of the laws of heredity in 1865, long before the discovery of chromosomes, their subsequent discovery put genetics on a sound footing. With the elucidation of parallelism between chromosome behaviour during meiosis and genes during the course of breeding, the laws of genetics, viz., the law of segregation and the law of independent assortment, could be explained. The interdependence of the disciplines of cytology and genetics led to their alliance resulting in the birth of the hybrid discipline of cytogenetics, during the first decade of the twentieth century. The fast, heterotic growth exhibited by cytogenetics has no parallel in the history of science. Research on chromosome pairing helped elucidate evolutionary phenomena that led to the production of allopolyploid crop plants. Chromosome research enriched the disciplines of genetics, plant breeding, biology, and medicine, which, in turn, have contributed to human welfare. The advances in genetics and cytogenetics accelerated the process of crop improvement as well, and resulted in the development of improved cereal cultivars that launched the famous Green Revolution. Cytogenetic manipulation of chromosome pairing facilitated alien gene transfers and genomic reconstruction of crop species. Alien chromosome additions also contributed to genomic repatterning and crop improvement. The discovery of chromosome number in humans helped unravel the effects of chromosomal imbalance on physical and mental abnormalities, miscarriage in pregnant women, and incidence of several forms of cancer in humans. The study of various aspects of chromosomes has positively impacted human welfare. How chromosome research has influenced basic genetics, plant breeding, and human biology and medicine is briefly described in this paper.

Development of consistently crossable wheat genotypes for alien wheat gene transfer through fine-mapping of the Kr1 locus

Breeders can force sexual hybridisation between wheat and related grass species to produce interspecific hybrids containing a dihaploid set of wheat and related chromosomes. This facilitates the introgression of desirable genes into wheat from the secondary gene pool. However, most elite European wheat varieties carry genes that suppress crossability, making the transfer of novel traits from exotic germplasm into elite wheat varieties difficult or impossible. Previous studies have identified at least five crossability loci in wheat. Here, the crossability locus with the largest effect, Kr1 on chromosome arm 5BL, was fine-mapped by developing a series of recombinant substitution lines in which the genome of the normally non-crossable wheat variety 'Hobbit sib' carries a recombinant 5BL chromosome arm containing segments from the crossable variety 'Chinese Spring'. These recombinant lines were scored for their ability to cross with rye over four seasons. Analysis revealed at least two regions on 5BL affecting crossability, including the Kr1 locus. However, the ability to set seed is highly dependent on prevailing environmental conditions. Typically, even crossable wheat lines exhibit little or no seed set when crossed with rye in winter, but show up to 90% seed set from similar crosses made in summer. By recombining different combinations of the two regions affecting crossability, wheat lines that consistently exhibit up to 50% seed set, whether crossed in the UK winter or summer conditions, were generated, thus creating a very important tool for increasing the efficiency of alien wheat transfer programmes.

Ancestral Genetic Resources Provide an Alternative to GMO Crops

Concern about the effects of pesticides on human health and the environment, has been a major rationale for pro-moting  transgenic crops, often  referred  to as genetically modified organisms (GMOs), or as genetically  enhanced (GE) crops.   Companies  that sell genetically engineered crop plants claim that biotechnology offers a safe alterna-tive to agricultural chemicals and is  necessary to feed the world’s expanding human population. However, there are still many unknowns about the safety of GMOs for human health and the  environment, and virtually nothing is known about  how  the  genomes  of  organisms may  be  affected by horizontal transfer of alien genes into plants, animals, and even humans. An alternative approach  to  transgen-ic  technology  is  the exploitation of beneficial genes  from wild  relatives of crop plants using conventional breeding methods. This paper describes how genetic engineering  differs  from conventional plant breeding,  then compares and  contrasts benefits  from  transgenic engineering with traditional methods of crop  improvement. An example of how the ancestral genes model has been employed to im-part an insect resistance trait to corn based on native re-sistance  from  a wild  relative  is  compared  to  transgenic corn with  resistance  to  the same  insect engineered with  a transgene from a bacterium. Using the ancestral genes approach, harmful chemicals used to control the worst in-sect pest of corn can be eliminated with no  consequenc-es to human health or the environment; whereas with the transgenic approach,  there are many safety concerns  in both arenas.

Attempts to induce homoeologous pairing between wheat and Agropyron cristatum genomes

Agropyron cristatum (2n = 4x = 28, PPPP) possesses potentially valuable traits that could be used in wheat (Triticum aestivum) improvement through interspecific hybridization. Homoeologous pairing between wheat chromosomes and P chromosomes added to wheat in a set of wheat - A. cristatum addition lines was assessed. First, the Ph-suppressing effect of P chromosomes (except 7P) was analyzed. It was concluded that this system is polygenic with no major gene, and consequently, has no prospect in the transfer of alien genes from wild relatives. In a second step, the potential of the deletion ph1b of the Ph1 gene for inducing P-ABD pairing was evaluated. Allosyndetic associations between P and ABD genomes are very rare. This very low level of pairing is likely due to divergence in the repeated sequences between Agropyron and wheat genomes. Development of translocation lines using ionizing radiation seems to be a more suitable technique than homoeologous recombination to exploit the A. cristatum genome in wheat improvement.

Transfer of resistance to potato virus�Y (PVY) from Nicotiana africana to Nicotiana tabacum: possible influence of tissue culture on the rate of introgression

A disomic chromosome addition line of tobacco, Nicotiana tabacum L., was established previously that possesses a single chromosome pair from N. africana [Merxm. and Buttler]. This addition chromosome carries a gene that confers increased resistance to severe strains of potato virus Y (PVY). Methods to increase the probability of gene transfer from alien chromosomes to tobacco (2n=48) are desired. In the research described here, the PVY resistance gene was transferred to a tobacco chromosome from the N. africana addition chromosome in seven independent cases. One introgression event was obtained using conventional backcrossing of the disomic addition line to N. tabacum cv. Petite Havana, while the remaining six events were obtained using a scheme that involved exposure of explants of the addition line to tissue culture. Twenty-six derived 2n=48 individuals heterozygous for PVY resistance were found to exhibit 24 bivalents or 23 bivalents + 2 univalents at metaphase I. Ovular transmission rates for the PVY resistance factor ranged from 25% to 52%, while pollen transmission rates were much lower, ranging from 0 to 39%. Fifty-one random amplified polymorphic DNA (RAPD) markers specific for the intact addition chromosome were identified and used to characterize derived 2n=48/PVY-resistant genotypes. Variability was observed among these plants with respect to the total number of N. africana RAPD markers that were present, which is an indication that crossing over was occurring within each of the seven introgressed chromosome segments. A limited molecular marker-assisted backcrossing experiment allowed for selection of a 2n=48/PVY-resistant individual that possessed only 6 of the 51 original N. africana RAPD markers. In vitro culture is potentially a valuable system for increasing the rate of alien gene transfer in tobacco, and the successful transfer of PVY resistance from N. africana may allow for an increased level and range of resistance to this virus in tobacco.