Disomic Chromosome Addition Lines Research Articles

Development of B. carinata with super-high erucic acid content through interspecific hybridization

Key messageDisomic alien chromosome addition Brassica carinata lines with super-high erucic acid content were developed through interspecific hybridization with B. juncea and characterized using molecular, cytological and biochemical techniques.Brassica carinata [A.] Braun (BBCC, 2n = 34) is a climate-resilient oilseed. Its seed oil is high in erucic acid (> 40%), rendering it well suited for the production of biofuel and other bio-based applications. To enhance the competitiveness of B. carinata with high erucic B. napus (HEAR), lines with super-high erucic acid content were developed through interspecific hybridization. To this end, a fad2B null allele from Brassica juncea (AABB, 2n = 36) was introgressed into B. carinata, resulting in a B. carinata fad2B mutant with erucic acid levels of over 50%. Subsequently, the FAE allele from B. rapa spp. yellow sarson (AA, 2n = 20) was transferred to the fad2B B. carinata line, yielding lines with erucic acid contents of up to 57.9%. Molecular analysis using the Brassica 90 K Illumina Infinium™ SNP genotyping array identified these lines as disomic alien chromosome addition lines, with two extra A08 chromosomes containing the BrFAE gene. The alien chromosomes from B. rapa were clearly distinguished by molecular cytogenetics in one of the addition lines. Analysis of microspore-derived offspring and hybrids from crosses with a CMS B. carinata line showed that the transfer rate of the A08 chromosome into male gametes was over 98%, resulting in almost completely stable transmission of an A08 chromosome copy into the progeny. The increase in erucic acid levels was accompanied by changes in the proportions of other fatty acids depending on the genetic changes that were introduced in the interspecific hybrids, providing valuable insights into erucic acid metabolism in Brassica.

Development of DNA Markers From Physically Mapped Loci in Aegilops comosa and Aegilops umbellulata Using Single-Gene FISH and Chromosome Sequences.

Breeding of agricultural crops adapted to climate change and resistant to diseases and pests is hindered by a limited gene pool because of domestication and thousands of years of human selection. One way to increase genetic variation is chromosome-mediated gene transfer from wild relatives by cross hybridization. In the case of wheat (Triticum aestivum), the species of genus Aegilops are a particularly attractive source of new genes and alleles. However, during the evolution of the Aegilops and Triticum genera, diversification of the D-genome lineage resulted in the formation of diploid C, M, and U genomes of Aegilops. The extent of structural genome alterations, which accompanied their evolution and speciation, and the shortage of molecular tools to detect Aegilops chromatin hamper gene transfer into wheat. To investigate the chromosome structure and help develop molecular markers with a known physical position that could improve the efficiency of the selection of desired introgressions, we developed single-gene fluorescence in situ hybridization (FISH) maps for M- and U-genome progenitors, Aegilops comosa and Aegilops umbellulata, respectively. Forty-three ortholog genes were located on 47 loci in Ae. comosa and on 52 loci in Ae. umbellulata using wheat cDNA probes. The results obtained showed that M-genome chromosomes preserved collinearity with those of wheat, excluding 2 and 6M containing an intrachromosomal rearrangement and paracentric inversion of 6ML, respectively. While Ae. umbellulata chromosomes 1, 3, and 5U maintained collinearity with wheat, structural reorganizations in 2, 4, 6, and 7U suggested a similarity with the C genome of Aegilops markgrafii. To develop molecular markers with exact physical positions on chromosomes of Aegilops, the single-gene FISH data were validated in silico using DNA sequence assemblies from flow-sorted M- and U-genome chromosomes. The sequence similarity search of cDNA sequences confirmed 44 out of the 47 single-gene loci in Ae. comosa and 40 of the 52 map positions in Ae. umbellulata. Polymorphic regions, thus, identified enabled the development of molecular markers, which were PCR validated using wheat-Aegilops disomic chromosome addition lines. The single-gene FISH-based approach allowed the development of PCR markers specific for cytogenetically mapped positions on Aegilops chromosomes, substituting as yet unavailable segregating map. The new knowledge and resources will support the efforts for the introgression of Aegilops genes into wheat and their cloning.

Chromosomal location of genes for resistance to powdery mildew in Agropyron cristatum and mapping of conserved orthologous set molecular markers

Agropyron cristatum exhibits resistance to Blumeria graminis f. sp. tritici. Disomic and ditelosomic chromosome addition lines of A. cristatum in ‘Chinese Spring’ wheat were utilized to determine which A. cristatum chromosomes carry resistance gene(s). Resistance is conferred by gene(s) on chromosome arms 2PL and 6PL. The availability of molecular markers capable of detecting these chromosome arms in a wheat background would be very useful for marker-assisted introgression of 2PL and 6PL chromatin into common wheat. With this aim, 170 wheat conserved orthologous set (COS) markers (92 and 78 from wheat homoeologous groups 2 and 6 respectively) were assessed for their utility in A. cristatum. A total of 116 (68.2%) COS markers successfully amplified product in A. cristatum and 46 (40.0%) of these markers were polymorphic between A. cristatum and common wheat. From marker loci mapping on wheat homoeologous group 2 chromosomes, 23 markers (34.9%) were polymorphic between A. cristatum and common wheat and from them 13 markers were assigned to chromosome arm 2PL and six markers were mapped to chromosome 4P of A. cristatum showing that this chromosome is related to wheat homoeologous group 2. From marker loci mapping on wheat homoeologous group 6 chromosomes, 23 (46.0%) markers were polymorphic between A. cristatum and common wheat and from them 17 markers were located on chromosome 6P, six of them were mapped to chromosome arm 6PS and five to chromosome arm 6PL, respectively. The specific COS markers allocated on the long arms of chromosomes 2P and 6P may have a role in marker-assisted screening in wheat breeding for powdery mildew disease resistance.

Evaluation of root porosity and radial oxygen loss of disomic addition lines of Hordeum marinum in wheat.

Hordeum marinum Huds. is a waterlogging-tolerant wild relative of wheat (Triticum aestivum L.). Greater root porosity (gas volume per root volume) and formation of a barrier to reduce root radial O2 loss (ROL) contribute to the waterlogging tolerance of H. marinum and these traits are evident in some H. marinum-wheat amphiploids. We evaluated root porosity, ROL patterns and tolerance to hypoxic stagnant conditions for 10 various H. marinum (two accessions) disomic chromosome addition (DA) lines in wheat (two varieties), produced from two H. marinum-wheat amphiploids and their recurrent wheat parents. None of the DA lines had a barrier to ROL or higher root porosity than the wheat parents. Lack of a root ROL barrier in the six DA lines for H. marinum accession H21 in Chinese Spring (CS) wheat indicates that the gene(s) for this trait do not reside on one of these six chromosomes; unfortunately, chromosome 3 of H. marinum has not been isolated in CS. Unlike the H21-CS amphiploid, which formed a partial ROL barrier in roots, the H90-Westonia amphiploid and the four derived DA lines available did not. The unaltered root aeration traits in the available DA lines challenge the strategy of using H. marinum as a donor of these traits to wheat.

Chromosomal assignment of oil radish resistance to Meloidogyne incognita and M. javanica using a set of disomic rapeseed-radish chromosome addition lines

Root-knot nematodes cause severe damage to a great number of crops worldwide. The use of nematicides is restricted due to environmental and toxicological risks and control of the pest by crop rotation is difficult because root-knot nematodes have a very wide range of host plants. To verify the strategy of converting rapeseed from a tolerant host for Meloidogyne incognita and M. javanica to a resistant catch crop, a complete set of nine disomic rapeseed-radish chromosome addition lines (lines A to I) was tested for resistance against these Meloidogyne species. Thirty plants of each addition line and the rapeseed and radish parents as control were infected with 2500 second-stage juveniles per plant. The presence of the alien radish chromosome was confirmed by chromosome-specific microsatellite markers. After cultivation of the inoculated plants for 10 weeks in a climatic chamber the root systems were washed. The egg masses were stained with Cochenille Red and counted. The radish parent A24 was found to be resistant to M. incognita (2.4 egg masses (g root)−1) and M. javanica (0.4 egg masses (g root)−1) compared to 53.3 and 33.1 egg masses (g root)−1 for the susceptible rapeseed parent cv. Madora. The radish chromosome e was shown to be the carrier of radish root-knot nematode resistance with an average number of <1 egg mass (g root)−1 for M. incognita and M. javanica. The disomic addition lines B, C, D, G, H and I and the parental radish line A107 were classified as highly susceptible, whereas the addition lines A and F showed significantly reduced susceptibility for M. incognita but not for M. javanica. To our knowledge this is the first study on resistance effects of individual radish chromosomes in a rapeseed background against these root-knot nematodes.

CHROMOSOMAL ASSIGNMENT OF RADISH LINKAGE GROUPS USING A COMPLETE SET OF DISOMIC RAPESEED-RADISH CHROMOSOME ADDITION LINES

Radish, Raphanus sativus L., is a vegetable with high economic importance, especially in Asia. A genetic map with 322 markers and a total length of 673 cM was anchored to chromosomes using a complete set of disomic rapeseed-radish chromosome addition lines. Eighteen SSRs and one CAPS marker, at least two for each linkage group, were assigned to the individual radish chromosomes. Three of the radish chromosomes (C, D and H) were characterized cytogenetically by fluorescence in situ hybridization (FISH). The anchored linkage map can be used for QTL analysis of morphological characters and other traits.

Identification of disomic alien chromosome addition lines and a substitution line from monosomic alien addition lines of Chinese kale – flowering Chinese cabbage

SummaryGeneration of disomic alien chromosome addition lines and alien chromosome substitution lines is important for genetic research and chromosome engineering. After determining the transmission rates for alien chromosomes, we created five Chinese kale–flowering Chinese cabbage disomic alien addition lines and one substitution line. Transmission rates ranged from 11.46 – 38.18% via the female gametes, and from 4.88 – 12.90% through the male gametes. The disomic addition lines (CC+2A2, CC+2A3, CC+2A6, CC+2A8, and CC+2A9) were produced from selfed progenies of their corresponding monosomic addition lines. The substitution line C1/A9 was also obtained from the selfed progeny of monosomic line CC+A9, following cytological identification and simple sequence repeat DNA marker analysis.

Development and Application of EST-Based Markers Specific for Chromosome Arms of Rye (Secale cereale L.)

To develop a set of molecular markers specific for the chromosome arms of rye, a total of 1,098 and 93 primer pairs derived from the expressed sequence tag (EST) sequences distributed on all 21 wheat chromosomes and 7 rye chromosomes, respectively, were initially screened on common wheat ‘Chinese Spring’ and rye cultivar ‘Imperial’. Four hundred and fourteen EST-based markers were specific for the rye genome. Seven disomic chromosome addition lines, 10 telosomic addition lines and 1 translocation line of ‘Chinese Spring-Imperial’ were confirmed by genomic in situ hybridization and fluorescencein situ hybridization, and used to screen the rye-specific markers. Thirty-one of the 414 markers produced stable specific amplicons in ‘Imperial’, as well as individual addition lines and were assigned to 13 chromosome arms of rye except for 6RS. Six rye cultivars, wheat cultivar ‘Xiaoyan 6’ and accessions of 4 wheat relatives were then used to test the specificity of the 31 EST-based markers. To confirm the specificity, 4 wheat-rye derivatives of ‘Xiaoyan 6 × German White’, with chromosomes 1RS, 2R and 4R, were amplified by some of the EST-based markers. The results indicated that they can effectively be used to detect corresponding rye chromosomes or chromosome arms introgressed into a wheat background, and hence to accelerate the utilization of rye genes in wheat breeding.

Molecular cloning and mapping of casein kinase 2 alpha and beta subunit genes in barley

Casein kinase 2 (CK2) is a ubiquitous, highly pleiotropic, constitutively active, and messenger-independent Ser/Thr protein kinase. It is found in two different forms: the heterotetrameric CK2, composed of two alpha catalytic subunits and two beta regulatory subunits, and the monomeric CK2 alpha, consisting of the alpha catalytic subunit. In the present study, we isolated barley cDNA clones of the CK2 alpha and beta subunit genes, designated HvCK2A and HvCK2B, respectively. Chromosome assignment, using a set of wheat-barley disomic chromosome addition lines, and RFLP mapping, using two doubled haploid populations, showed that HvCK2A was duplicated on the short arm of chromosome 2H and the long arm of chromosome 5H (designated HvCK2a-2H and HvCK2a-5H, respectively), and a single copy of HvCK2B was located on the long arm of chromosome 1H (designated HvCK2b). A PCR-Southern hybridization experiment demonstrated that the HvCK2A sequence originated from the HvCK2a-5H locus, showing that at least HvCK2a-5H was expressed. The present cDNA sequences and genomic organization of the two subunits will facilitate further functional analysis of CK2 in barley.

Mapping barley genes to chromosome arms by transcript profiling of wheat–barley ditelosomic chromosome addition lines

Wheat-barley disomic and ditelosomic chromosome addition lines have been used as genetic tools for a range of applications since their development in the 1980s. In the present study, we used the Affymetrix Barley1 GeneChip for comparative transcript analysis of the barley cultivar Betzes, the wheat cultivar Chinese Spring, and Chinese Spring - Betzes ditelosomic chromosome addition lines to physically map barley genes to their respective chromosome arm locations. We mapped 1257 barley genes to chromosome arms 1HS, 2HS, 2HL, 3HS, 3HL, 4HS, 4HL, 5HS, 5HL, 7HS, and 7HL based on their transcript levels in the ditelosomic addition lines. The number of genes assigned to individual chromosome arms ranged from 24 to 197. We validated the physical locations of the genes through comparison with our previous chromosome-based physical mapping, comparative in silico mapping with rice and wheat, and single feature polymorphism (SFP) analysis. We found our physical mapping of barley genes to chromosome arms to be consistent with our previous physical mapping to whole chromosomes. In silico comparative mapping of barley genes assigned to chromosome arms revealed that the average genomic synteny to wheat and rice chromosome arms was 63.2% and 65.5%, respectively. In the 1257 mapped genes, we identified SFPs in 924 genes between the appropriate ditelosomic line and Chinese Spring that supported physical map placements. We also identified a single small rearrangement event between rice chromosome 9 and barley chromosome 4H that accounts for the loss of synteny for several genes.

Characterization of chromosome-specific S-SAP markers and their use in studying genetic diversity in Aegilops species

The short interspersed nuclear element (SINE), Au, was used to develop sequence-specific amplified polymorphism (S-SAP) markers for U- and M-genome chromosomes. The markers were localized using Triticum aestivum (wheat)-- Aegilops geniculata and wheat-- Aegilops biuncialis disomic chromosome addition lines. Thirty-seven markers distributed over 6 U and 6 M chromosomes were produced. A genetic diversity study carried out on 37 accessions from Ae. biuncialis, Ae. comosa, Ae. geniculata, and Ae. umbellulata suggested that Ae. biuncialis have arisen from its diploid ancestors more recently than Ae. geniculata. Several earlier studies indicated that the M genomes in polyploid Aegilops species had accumulated substantial rearrangements, whereas the U genomes remained essentially unmodified. However, this cannot be attributed to the preferential insertion of retroelements into the M genome chromosomes. Fourteen markers from a total of 8 chromosomes were sequenced; 3 markers were similar to known plant genes, 1 was derived from a long terminal repeat (LTR) retrotransposon, and 10 markers did not match to any known DNA sequences, suggesting that they were located in the highly variable intergenic regions.

Use of wild relatives to improve salt tolerance in wheat

There is considerable variability in salt tolerance amongst members of the Triticeae, with the tribe even containing a number of halophytes. This is a review of what is known of the differences in salt tolerance of selected species in this tribe of grasses, and the potential to use wild species to improve salt tolerance in wheat. Most investigators have concentrated on differences in ion accumulation in leaves, describing a desirable phenotype with low leaf Na+ concentration and a high K+/Na+ ratio. Little information is available on other traits (such as "tissue tolerance" of accumulated Na+ and Cl-) that might also contribute to salt tolerance. The sources of Na+ "exclusion" amongst the various genomes that make up tetraploid (AABB) durum wheat (Triticum turgidum L. ssp. durum), hexaploid (AABBDD) bread wheat (Triticum aestivum L. ssp. aestivum), and wild relatives (e.g. Aegilops spp., Thinopyrum spp., Elytrigia elongata syn. Lophopyrum elongatum, Hordeum spp.) are described. The halophytes display a capacity for Na+ "exclusion", and in some cases Cl- "exclusion", even at relatively high salinity. Significantly, it is possible to hybridize several wild species in the Triticeae with durum and bread wheat. Progenitors have been used to make synthetic hexaploids. Halophytic relatives, such as tall wheatgrass spp., have been used to produce amphiploids, disomic chromosome addition and substitution lines, and recombinant lines in wheat. Examples of improved Na+ "exclusion" and enhanced salt tolerance in various derivatives from these various hybridization programmes are given. As several sources of improved Na+ "exclusion" are now known to reside on different chromosomes in various genomes of species in the Triticeae, further work to identify the underlying mechanisms and then to pyramid the controlling genes for the various traits, that could act additively or even synergistically, might enable substantial gains in salt tolerance to be achieved.

Transcriptome Analysis and Physical Mapping of Barley Genes in Wheat–Barley Chromosome Addition Lines

Wheat-barley chromosome addition lines are useful genetic resources for a variety of studies. In this study, transcript accumulation patterns in Betzes barley, Chinese Spring wheat, and Chinese Spring-Betzes chromosome addition lines were examined with the Barley1 Affymetrix GeneChip probe array. Of the 4014 transcripts detected in Betzes but not in Chinese Spring, 365, 271, 265, 323, 194, and 369 were detected in wheat-barley disomic chromosome addition lines 2(2H), 3(3H), 4(4H), 7(5H), 6(6H), and 1(7H), respectively. Thus, 1787 barley transcripts were detected in a wheat genetic background and, by virtue of the addition line in which they were detected, were physically mapped to barley chromosomes. We validated and extended our approach to physically map barley genes to the long and short arms of chromosome 6(6H). Our physical map data exhibited a high level of synteny with homologous sequences on the wheat and/or rice syntenous chromosomes, indicating that our barley physical maps are robust. Our results show that barley transcript detection in wheat-barley chromosome addition lines is an efficient approach for large-scale physical mapping of genes.

GISH analysis of disomic Brassica napus-Crambe abyssinica chromosome addition lines produced by microspore culture from monosomic addition lines

Two Brassica napus-Crambe abyssinica monosomic addition lines (2n=39, AACC plus a single chromosome from C. abyssinca) were obtained from the F(2) progeny of the asymmetric somatic hybrid. The alien chromosome from C. abyssinca in the addition line was clearly distinguished by genomic in situ hybridization (GISH). Twenty-seven microspore-derived plants from the addition lines were obtained. Fourteen seedlings were determined to be diploid plants (2n=38) arising from spontaneous chromosome doubling, while 13 seedlings were confirmed as haploid plants. Doubled haploid plants produced after treatment with colchicine and two disomic chromosome addition lines (2n=40, AACC plus a single pair of homologous chromosomes from C. abyssinca) could again be identified by GISH analysis. The lines are potentially useful for molecular genetic analysis of novel C. abyssinica genes or alleles contributing to traits relevant for oilseed rape (B. napus) breeding.

Identification of intergenomic translocations involving wheat, Hordeum vulgare and Hordeum chilense chromosomes by FISH.

Intergenomic translocations between wheat, Hordeum chilense and Hordeum vulgare have been obtained in tritordeum background. Advanced lines from the crosses between three disomic chromosome addition lines for chromosome 2Hv, 3Hv, and 4Hv of barley (Hordeum vulgare) in Triticum aestivum cv. Chinese Spring (CS) and hexaploid tritordeum (2n = 6x = 42, AABBHchHch) were analyzed. Multicolor FISH using both genomic DNA from H. chilense and H. vulgare were used to establish the presence and numbers of H. vulgare introgressions into tritordeum. Interspecific H. vulgare/H. chilense and intergeneric wheat/H. vulgare and wheat/H. chilense translocations were identified. Frequencies of plants containing different kinds of intergenomic translocations between chromosome arms are presented. These lines can be useful for introgressing into tritordeum characters of interest from H. vulgare.

Evaluation of Lophopyrum elongatum as a source of genetic diversity to increase the waterlogging tolerance of hexaploid wheat (Triticum aestivum)

• Waterlogging tolerance and its physiological basis were evaluated in Lophopyrum elongatum (a species from a salt marsh habitat), Triticum aestivum (cv. Chinese Spring), their amphiploid, and disomic chromosome addition lines. • Growth in drained or waterlogged soil and aerated or deoxygenated stagnant nutrient solution were evaluated. Porosity, aerenchyma, rates of O2 consumption, radial O2 loss, and ethanolic fermentation in adventitious roots of selected genotypes were also measured. • L. elongatum was more tolerant of deoxygenated stagnant nutrient solution or waterlogged soil (0–48% reductions in growth, respectively) than ‘Chinese Spring’ (63–84% reductions), the amphiploid (49–81% reductions), or the addition lines (56–92% reductions). Roots of L. elongatum had a higher constitutive porosity than ‘Chinese Spring’, resulting in greater internal O2 movement in these roots when intact plants were first transferred to an O2-free root medium. This trait, as well as the slower growth and development of L. elongatum, might have contributed to its greater waterlogging tolerance. • Despite the differences between L. elongatum and ‘Chinese Spring’ in some traits, none of the Lophopyrum × wheat lines showed substantial improvement in waterlogging tolerance.

Isolation, identification and characterization of disomic and translocated barley chromosome addition lines of common wheat

Two disomic barley chromosome addition lines and five translocated chromosome addition lines of common wheat cultivar Shinchunaga were isolated. They were derived from a hybrid plant between Shinchunaga and cultivated barley Nyugoruden (New Golden) by backcrossing with wheat and self pollination. Barley chromosomes added to chromosome arms involved in the translocated chromosomes were identified by C-banding method and by crossing these lines with Chinese Spring/Betzes addition lines. Two disomic addition lines were identified to have chromosome 6 and 7 of barley, respectively. Two of the five translocated chromosome addition lines were clarified to have same chromosome constitution, 42 wheat chromosomes and a pair of translocated chromosomes constituted with a long arm of chromosome 5B of wheat and a short arm of chromosome 7 of barley. The other three lines could not be identified due to chromosome rearrangement. Performances of these seven lines on agronomic characters were examined. Addition of barley chromosome 7 induced early heading, and chromosome 6 showed lated heading. Almost all of the lines except that of chromosome 6 showed short culm length and all showed reduced number of tillers, spikelets and grains per ear, and low seed fertility. These lines would be useful for genetic analyses in wheat and barley and for induction of useful genes of barley into wheat.

Transfer of Wheat Streak Mosaic Virus Resistance from Agropyron intermedium into Wheat

Wheat streak mosaic is a damaging disease of cultivated bread wheat, Triticum aestivum L. em Thell., in many parts of the world. No wheat cultivar has a high level of resistance to WSMV or its vector, the wheat curl mite, Eriophyes tulipae Keifer. Genes conferring resistance to wheat curl mite colonization have been transferred from Aegilops tauschii Coss., Cmc1, and from Agropyron elongatum (Host) Beauv., Cmc2. A gene conditioning resistance to WSMV, Wsm1, was transferred from Agropyron intermedium (Host) Beauv. into common wheat. To broaden the genetic base of wheat, new sources of WSMV resistance are continuously sought. This study reports a new source of WSMV resistance derived from A. intermedium and its transfer into hexaploid wheat. C‐banding analysis was used to cytogenetically identify the A. intermedium chromosomes and chromosome arms in three WSMV resistant wheat‐A. intermedium derivatives, designated as 6957,6961, and 6962. All lines were identified as disomic chromosome addition lines with an A. intermedium chromosome arm in common. Restriction fragment length polymorphism analysis was used to establish homoeology of the A. intermedium chromosome arm carrying the gene or gene complex conditioning resistance to WSMV. The arm belonged to the long arm of the wheat Group 4 chromosomes, and was designated as 4Ai#3L. The added A. intermedium chromosomes present in Lines 6957 and 6961 probably originated from centricfusion. The WSMV resistance of these lines is different from that conditioned by Wsm1 and may have significance in breeding WSMV resistant wheat cultivars.

Cytological and molecular characterization of oat x maize partial hybrids

In cereals, interspecific and intergeneric hybridizations (wide crosses) which yield karyotypically stable hybrid plants have been used as starting points to widen the genetic base of a crop and to construct stocks for genetic analysis. Also, uniparental genome elimination in karyotypically unstable hybrids has been utilized for cereal haploid production. We have crossed hexaploid oat (2n=6x=42, Avena sativa L.) and maize (2n=2x=20, Zea mays L.) and recovered 90 progenies through embryo rescue. Fifty-two plants (58%) produced from oatxmaize hybridization were oat haploids (2n=3x=21) following maize chromosome elimination. Twenty-eight plants (31%) were found to be stable partial hybrids with 1-4 maize chromosomes in addition to a haploid set of 21 oat chromosomes (2n=21+1 to 2n=21+4). Ten of the ninety plants produced were found to be apparent chromosomal chimeras, where some tissues in a given plant contained maize chromosomes while other tissues did not, or else different tissues contained a different number of maize chromosomes. DNA restriction fragment length polymorphisms (RFLPs) were used to identify the maize chromosome(s) present in the various oat-maize progenies. Maize chromosomes 2, 3, 4, 5, 6, 7, 8, and 9 were detected in partial hybrids and chromosomal chimeras. Maize chromosomes 1 and 10 were not detected in the plants analyzed to-date. Furthermore, partial self-fertility, which is common in oat haploids, was also observed in some oat-maize hybrids. Upon selfing, partial hybrids with one or two maize chromosomes showed nearly complete transmission of the maize chromosome to give self-fertile maize-chromosome-addition oat plants. Fertile lines were recovered that contained an added maize chromosome or chromosome pair representing six of the ten maize chromosomes. Four independently derived disomic maize chromosome addition lines contained chromosome 4, one line carried chromosome 7, two lines had chromosome 9, one had chromosome 2, and one had chromosome 3. One maize chromosome-8 monosomic addition line was also identified. We also identified a double disomic addition line containing both maize chromosomes 4 and 7. This constitutes the first report of the production of karyotypically stable partial hybrids involving highly unrelated species from two subfamilies of the Gramineae (Pooideae - oat, and Panicoideae - maize) and the subsequent recovery of fertile oat-maize chromosome addition lines. These represent novel material for gene/ marker mapping, maize chromosome manipulation, the study of maize gene expression in oat, and the transfer of maize DNA, genes, or active transposons to oat.

Cytological and molecular characterization of oat�maize partial hybrids

In cereals, interspecific and intergeneric hybridizations (wide crosses) which yield karyotypically stable hybrid plants have been used as starting points to widen the genetic base of a crop and to construct stocks for genetic analysis. Also, uniparental genome elimination in karyotypically unstable hybrids has been utilized for cereal haploid production. We have crossed hexaploid oat (2n=6x=42, Avena sativa L.) and maize (2n=2x=20, Zea mays L.) and recovered 90 progenies through embryo rescue. Fifty-two plants (58%) produced from oat x maize hybridization were oat haploids (2n=3x=21) iollowing maize chromosome elimination. Twenty-eight plants (31%) were found to be stable partial hybrids with 1-4 maize chromosomes in addition to a haploid set of 21 oat chromosomes (2n=21+1 to 2n=21+4). Ten of the ninety plants produced were found to be apparent chromosomal chimeras, where some tissues in a given plant contained maize chromosomes while other tissues did not, or else different tissues contained a different number of maize chromosomes. DNA restriction fragment length polymorphisms (RFLPs) were used to identify the maize chromosome(s) present in the various oat-maize progenies. Maize chromosomes 2, 3, 4, 5, 6, 7, 8, and 9 were detected in partial hybrids and chromosomal chimeras. Maize chromosomes 1 and 10 were not detected in the plants analyzed to-date. Furthermore, partial self-fertility, which is common in oat haploids, was also observed in some oat-maize hybrids. Upon selfing, partial hybrids with one or two maize chromosomes showed nearly complete transmission of the maize chromosome to give self-fertile maize-chromosome-addition oat plants. Fertile lines were recovered that contained an added maize chromosome or chromosome pair representing six of the ten maize chromosomes. Four independently derived disomic maize chromosome addition lines contained chromosome 4, one line carried chromosome 7, two lines had chromosome 9, one had chromosome 2, and one had chromosome 3. One maize chromosome-8 monosomic addition line was also identified. We also identified a double disomic addition line containing both maize chromosomes 4 and 7. This constitutes the first report of the production of karyotypically stable partial hybrids involving highly unrelated species from two subfamilies of the Gramineae (Pooideae - oat, and Panicoideae - maize) and the subsequent recovery of fertile oat-maize chromosome addition lines. These represent novel material for gene/marker mapping, maize chromosome manipulation, the study of maize gene expression in oat, and the transfer of maize DNA, genes, or active transposons to oat.