Development and characterization of a complete set of <Emphasis Type="Italic">Triticum aestivum</Emphasis>–<Emphasis Type="Italic">Roegneria ciliari</Emphasis>s disomic addition lines

Key message

A complete set wheat-R. ciliaris disomic addition lines (DALs) were characterized and the homoeologous groups and genome affinities of R. ciliaris chromosomes were determined.

Abstract

Wild relatives are rich gene resources for cultivated wheat. The development of alien addition chromosome lines not only greatly broadens the genetic diversity, but also provides genetic stocks for comparative genomics studies. Roegneria ciliaris (genome S^cS^cY^cY^c), a tetraploid wild relative of wheat, is tolerant or resistant to many abiotic and biotic stresses. To develop a complete set of wheat-R. ciliaris disomic addition lines (DALs), we undertook a euplasmic backcrossing program to overcome allocytoplasmic effects and preferential chromosome transmission. To improve the efficiency of identifying chromosomes from S^c and Y^c, we established techniques including sequential genomic in situ hybridization/fluorescence in situ hybridization (FISH) and molecular marker analysis. Fourteen DALs of wheat, each containing one pair of R. ciliaris chromosomes pairs, were characterized by FISH using four repetitive sequences [pTa794, pTa71, RcAfa and (GAA)₁₀] as probes. One hundred and sixty-two R. ciliaris-specific markers were developed. FISH and marker analysis enabled us to assign the homoeologous groups and genome affinities of R. ciliaris chromosomes. FHB resistance evaluation in successive five growth seasons showed that the amphiploid, DA2Y^c, DA5Y^c and DA6S^c had improved FHB resistance, indicating their potential value in wheat improvement. The 14 DALs are likely new gene resources and will be phenotyped for more agronomic performances traits.

     

Chromosomal Localization of Genes Conferring Desirable Agronomic Traits from Wheat-Agropyron cristatum Disomic Addition Line 5113

Creation of wheat-alien disomic addition lines and localization of desirable genes on alien chromosomes are important for utilization of these genes in genetic improvement of common wheat. In this study, wheat-Agropyron cristatum derivative line 5113 was characterized by genomic in situ hybridization (GISH) and specific-locus amplified fragment sequencing (SLAF-seq), and was demonstrated to be a novel wheat-A. cristatum disomic 6P addition line. Compared with its parent Fukuhokomugi (Fukuho), 5113 displayed multiple elite agronomic traits, including higher uppermost internode/plant height ratio, larger flag leaf, longer spike length, elevated grain number per spike and spikelet number per spike, more kernel number in the middle spikelet, more fertile tiller number per plant, and enhanced resistance to powdery mildew and leaf rust. Genes conferring these elite traits were localized on the A. cristatum 6P chromosome by using SLAF-seq markers and biparental populations (F₁, BC₁F₁ and BC₁F₂ populations) produced from the crosses between Fukuho and 5113. Taken together, chromosomal localization of these desirable genes will facilitate transferring of high-yield and high-resistance genes from A. cristatum into common wheat, and serve as the foundation for the utilization of 5113 in wheat breeding.     

Development of Triticum aestivum-Leymus racemosus translocation lines using gametocidal chromosomes

Specific chromosomes of certain Aegilops species introduced into wheat genome background may often facilitate chromosome breakage and refusion, and finally result in a variety of chromosome restructuring. Such a phenomenon is commonly called gametocidal effect of the chromosomes. The chromosome 2C of Ae. cylindrica is one of such chromosomes. In the present study, scab resistant wheat-L. racemosus addition lines involving chromosomes Lr.2 and Lr.7 were crossed to wheat-Ae. cylindrica disomic addition line Add2C. Then F₁ hybrids were subsequently backcrossed with wheat cv “Chinese Spring”. BC₁ plants with chromosome structural aberration were identified by C-banding. In the self-pollinated progenies of these plants, three translocation lines were developed and characterized by mitotic and meiotic analysis combined with C-banding and fluorescent in situ hybridization (FISH) using biotin-labeled genomic DNA of L. racemosus as probe. Some other putative translocation lines to be further characterized were also found. The practicability and efficiency of the translocation between wheat and alien chromosomes induced by gametocidal chromosomes, as well as the potential use of the developed alien translocation lines were also discussed.     

Development of T. aestivum L.-H. californicum Alien Chromosome Lines and Assignment of Homoeologous Groups of Hordeum californicum Chromosomes

Hordeum californicum （2n = 2x = 14, HH） is resistant to several wheat diseases and tolerant to lower nitrogen. In this study, a molecular karyotype of H. californicum chromosomes in the Triticum aestivum L. cv. Chinese Spring （CS）-H. californicum amphidiploid （2n = 6x = 56, AABBDDHH） was established. By genomic in situ hybridization （GISH） and multicolor fluorescent in situ hybridization （FISH） using repetitive DNA clones （pTa71, pTa794 and pSc119.2） as probes, the H. californicum chromosomes could be differentiated from each other and from the wheat chromosomes unequivocally. Based on molecular karyotype and marker analyses, 12 wheat--alien chromosome lines, including four disomic addition lines （DAH1, DAH3, DAH5 and DAH6）, five telosomic addition lines （MtH7L, MtHIS, MtH1L, DtH6S and DtH6L）, one multiple addition line involving H. californicum chromosome H2, one disomic substitution line （DSH4） and one translocation line （TH7S/1BL）, were identified from the progenies derived from the crosses of CS-H. californicum amphidiploid with common wheat varieties. A total of 482 EST （expressed sequence tag） or SSR （simple sequence repeat） markers specific for individual H. californicum chromosomes were identified, and 47, 50, 45, 49, 21, 51 and 40 markers were assigned to chromosomes H1, H2, H3, H4, H5, H6 and H7, respectively. According to the chromosome allocation of these markers, chromosomes H2, H3, H4, H5, and H7 of H. californicum have relationship with wheat homoeologous groups 5, 2, 6, 3, and 1, and hence could be designated as 5Hc, 2He, 6Hc, 3Hc and 1Hc, respectively. The chromosomes H1 and H6 were designated as 7Hc and 4Hc, respectively, by referring to SSR markers located on rye chromosomes.     

Development of <Emphasis Type="Italic">Triticum aestivum-Leymus racemosus</Emphasis> translocation lines using gametocidal chromosomes

Specific chromosomes of certain Aegilops species introduced into wheat genome background may often facilitate chromosome breakage and refusion, and finally result in a variety of chromosome restructuring. Such a phenomenon is commonly called gametocidal effect of the chromosomes. The chromosome 2C of Ae. cylindrica is one of such chromosomes. In the present study, scab resistant wheat-L. racemosus addition lines involving chromosomes Lr.2 and Lr.7 were crossed to wheat-Ae. cylindrica disomic addition line Add2C. Then F₁ hybrids were subsequently backcrossed with wheat cv “Chinese Spring”. BC₁ plants with chromosome structural aberration were identified by C-banding. In the self-pollinated progenies of these plants, three translocation lines were developed and characterized by mitotic and meiotic analysis combined with C-banding and fluorescent in situ hybridization (FISH) using biotin-labeled genomic DNA of L. racemosus as probe. Some other putative translocation lines to be further characterized were also found. The practicability and efficiency of the translocation between wheat and alien chromosomes induced by gametocidal chromosomes, as well as the potential use of the developed alien translocation lines were also discussed.     

Transmission of alien tomato chromosomes from BC1 to BC2 progenies derived from backcrossing potato (+) tomato fusion hybrids to potato: the selection of single additions for seven different tomato chromosomes

 By backcrossing three BC₁ genotypes of potato (+) tomato fusion hybrids to different tetraploid potato pollinators, BC₂ populations were produced. A combined total of 97 BC₂ plants from three BC₂ populations were analysed with chromosome-specific probes through restriction fragment length polymorphism (RFLP) for the presence of alien tomato chromosomes. The number of different alien tomato chromosomes transmitted through the female BC₁ parent ranged from 0 to 6, and the average number of different alien chromosomes transmitted per BC₂ plant varied between 1.7 and 3.4 in the different populations. This variation corresponded to the chromosome constitution of the individual BC₁ parents: parent 6739, which possessed 11 different alien chromosomes in a single condition, gave rise to progeny with a lower average number of alien chromosomes per plant than the BC₁ parent 2003 that possessed 2 of the 12 alien chromosomes in a disomic condition. In the latter case, the higher transmission rate was attributed to the more regular distribution of the two alien chromosomes in the disomic condition because of regular bivalent formation during meiosis as revealed by genomic in situ hybridisation (GISH) and fluorescent in situ hybridisation (FISH). The transmission frequencies of individual alien chromosomes were subjected to statistical analysis to test whether the maternal genotypes had an effect on alien-chromosome transmission. Among the BC₂ plants, a total of 27 single additions were detected for as many as seven different chromosomes (1, 2, 4, 6, 8, 10 and 12) out of the 12 possible types. Received: 4 March 1997 / Accepted: 28 August 1997     

Introgression of group 4 and 7 chromosomes of <Emphasis Type="Italic">Ae</Emphasis>. <Emphasis Type="Italic">peregrina</Emphasis> in wheat enhances grain iron and zinc density

Dietary deficiency of iron and zinc micronutrients affects more than two billion people worldwide. Breeding for micronutrient-dense crops is the most sustainable and cost-effective approach for alleviation of micronutrient malnutrition. Three accessions of Aegilops peregrina (Hack.) Maire & Weill (2n = 28, U^PU^PS^PS^P), selected for high grain iron and zinc concentration were crossed with Triticum aestivum L. cv. Chinese Spring (Ph ^I ). The sterile F₁ hybrids were backcrossed with elite wheat cultivars to get fertile BC₂F₂ derivatives. Some of the fertile BC₂F₂ derivatives showed nearly 100% increase in grain iron and more than 200% increase in grain zinc concentration compared to the recipient wheat cultivars. The development of derivatives with significantly higher grain micronutrients, high thousand-grain weight and harvest index suggests that the enhanced micronutrient concentration is due to the distinct genetic system of Ae. peregrina and not to the concentration effect. Genomic in situ hybridization, comparison of introgressed chromosomes with the standard karyotype of Ae. peregrina and simple sequence repeat marker analysis revealed the introgression of 7S^P chromosomes in five selected derivatives, 7U^P in four, group 4 and 4S^P in three and a translocated 5U^P of Ae. peregrina in one of the selected derivatives. Molecular marker analysis using the introgressed chromosome markers indicated that two of the BC₂F₃ progenies were stabilized as disomic addition lines. It could, therefore, be concluded that the group 4 and 7 chromosomes of Ae. peregrina carry the genes for high grain iron and zinc concentration.     

Development and Molecular Cytogenetic Identification of a Novel Wheat–Leymus mollis Lm#7Ns (7D) Disomic Substitution Line with Stripe Rust Resistance

Leymus mollis (2n = 4x = 28, NsNsXmXm) possesses novel and important genes for resistance against multi-fungal diseases. The development of new wheat—L. mollis introgression lines is of great significance for wheat disease resistance breeding. M11003-3-1-15-8, a novel disomic substitution line of common wheat cv. 7182 –L. mollis, developed and selected from the BC₁F₅ progeny between wheat cv. 7182 and octoploid Tritileymus M47 (2n = 8x = 56, AABBDDNsNs), was characterized by morphological and cytogenetic identification, analysis of functional molecular markers, genomic in situ hybridization (GISH), sequential fluorescence in situ hybridization (FISH)—genomic in situ hybridization (GISH) and disease resistance evaluation. Cytological observations suggested that M11003-3-1-15-8 contained 42 chromosomes and formed 21 bivalents at meiotic metaphase I. The GISH investigations showed that line contained 40 wheat chromosomes and a pair of L. mollis chromosomes. EST-STS multiple loci markers and PLUG (PCR-based Landmark Unique Gene) markers confirmed that the introduced L. mollis chromosomes belonged to homoeologous group 7, it was designated as Lm#7Ns. While nulli-tetrasomic and sequential FISH-GISH analysis using the oligonucleotide Oligo-pSc119.2 and Oligo-pTa535 as probes revealed that the wheat 7D chromosomes were absent in M11003-3-1-15-8. Therefore, it was deduced that M11003-3-1-15-8 was a wheat–L. mollis Lm#7Ns (7D) disomic substitution line. Field disease resistance demonstrated that the introduced L. mollis chromosomes Lm#7Ns were responsible for the stripe rust resistance at the adult stage. Moreover, M11003-3-1-15-8 had a superior numbers of florets. The novel disomic substitution line M11003-3-1-15-8, could be exploited as an important genetic material in wheat resistance breeding programs and genetic resources.     

Identification and development of diagnostic markers for a powdery mildew resistance gene on chromosome 2R of Chinese rye cultivar Jingzhouheimai

Chinese rye cultivar Jingzhouheimai (Secale cereale L.) shows a high level of resistance to powdery mildew. Identification, location, and mapping of the resistance gene would be helpful for developing a highly resistant germplasm or cultivar in wheat. Using sequential C-banding, GISH, and marker analysis, an addition chromosome with powdery mildew resistance was identified in a line derived from a cross between Chinese wheat landrace Huixianhong and rye cultivar Jingzhouheimai. The line, designated H-J DA2RDS1R(1D), had 44 chromosomes including two pairs of rye chromosomes, 1R and 2R, and lacked a pair of wheat chromosomes 1D, that is, it is a double disomic addition disomic substitution line. According to its reaction to different isolates of the powdery mildew pathogen, the resistance gene in H-J DA2RDS1R(1D) differed from the Pm8 and Pm7 genes located earlier on rye chromosomes 1R and 2R, respectively. In order to determine the location of the resistance gene, line H-J DA2RDS1R(1D) was crossed with wheat landrace Huixianhong and the F2 population and corresponding F2:3 families were tested for disease reaction and assessed with molecular markers. The results showed that a resistance gene, designated PmJZHM2RL, is located in rye chromosome arm 2RL.     

Molecular cytogenetic identification of a wheat–<Emphasis Type="Italic">Aegilops geniculata</Emphasis> Roth 7M<Superscript>g</Superscript> disomic addition line with powdery mildew resistance

Aegilops geniculata Roth is an important germplasm resource for the transfer of beneficial genes into common wheat (Triticum aestivum L.). A new disomic addition line NA0973-5-4-1-2-9-1 was developed from the BC₁F₆ progeny of the cross wheat cv. Chinese Spring (CS)/Ae. geniculata SY159//CS. We characterized this new line by morphological and cytogenetic identification, analysis of functional molecular markers, genomic in situ hybridization (GISH), fluorescence in situ hybridization (FISH), and disease resistance evaluation. Cytological observations suggested that NA0973-5-4-1-2-9-1 contained 44 chromosomes and formed 22 bivalents at meiotic metaphase I. The GISH investigations showed that the line contained 42 wheat chromosomes and a pair of Ae. geniculata chromosomes. EST-STS multiple loci markers and PLUG (PCR-based landmark unique gene) markers confirmed that the introduced Ae. geniculata chromosomes belonged to homoeologous group 7. FISH identification suggested that NA0973-5-4-1-2-9-1 possessed an additional pair of 7M^g chromosomes, and at the same time, there were structural differences in a pair of 6D chromosomes between NA0973-5-4-1-2-9-1 and TA7661 (CS-AEGEN DA 7M^g). After inoculation with powdery mildew (Blumeria graminis f. sp. tritici, Bgt) isolates E09, NA0973-5-4-1-2-9-1 exhibited a powdery mildew resistance infection type different from that of TA7661, and we conclude that the powdery mildew resistance of NA0973-5-4-1-2-9-1 originated from its parent Ae. geniculata SY159. Therefore, NA0973-5-4-1-2-9-1 can be used as a donor source for introducing novel disease resistance genes into wheat during breeding programs with the assistance of molecular and cytogenetic markers.     

Specific Features of the Nuclear Genome Recombination in Backcross Progenies of Barley–Wheat Hybrids Hordeum vulgare L. (2n = 14) × Triticum aestivum L. (2n = 42)

The backcross progenies of the barley–wheat hybrids Hordeum vulgare L. (2n = 14) × Triticum aestivum L. (2n= 42) and two alloplasmic lines derived from them were studied using microsatellite markers of barley and wheat. The F₁ hybrids and first backcross plants BC₁ contained the genetic material of both cultivated barley and the cultivars of common wheat involved in developing of these hybrid genotypes. The genomes of BC₃, BC₄, and alloplasmic lines contained no microsatellite markers of the cultivated barley, whereas chromosomes of each homeologous group of common wheat were identified. In chromosomes of backcross progenies BC₃, BC₄, and alloplasmic lines yielded by backcrosses of hybrids and various common wheat cultivars, microsatellite markers of the parental wheat cultivars were shown to undergo recombination.     

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

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

Production of alloplasmic and euplasmic wheat-barley ditelosomic substitution lines 7H<Superscript>1</Superscript>L<Superscript>mar</Superscript>(7D) and analysis of the 18S/5S mitochondrial repeat in these lines

Alloplasmic lines of common wheat with disomic substitution of chromosome 7D for telocentric chromosome 7H¹L^mar of barley H. marinum subsp. gussoneanum Hudson were isolated from the plants of generation BC₃, produced as a result of backcrossing of barley-wheat hybrids H. marinum subsp. gussoneanum (2n = 28) × T. aestivum (2n = 42), Pyrotrix, cultivar, with 28 common wheat cultivars Pyrotrix 28 and Novosibirskaya 67. Chromosome substitution pattern was determined using SSR analysis and C-banding. In preliminary genomic in situ hybridization experiments, telocentric chromosomes were assigned to wild barley was established. In the BC₃F₈ generations of three alloplasmic lines with the 7H¹L^mar(7D) substitution type the differences in fertility manifestation were observed: most of the L-32(1) plants were sterile, in line L-32(2) only sporadic plants were sterile, and line L-32(3) was fertile. Simultaneously with these experiments, using selfpollinated progeny of the hybrids obtained in crosses of common wheat cultivar Saratovskaya 29 (2n = 41), monosomic for chromosome 7D, with common wheat cultivar Pyrotrix 28 with addition of pair of telocentric chromosomes 7H¹L^mar (7D) of barley H. marinum subsp. gussoneanum, euplasmic wheat-barley ditelosomic substitution 7H¹L^mar (7D) lines were isolated. The lines obtained had normal fertility. PCR analysis of the 18S/5S mitochondrial repeat (hereafter, mtDNA sequence) in alloplasmic and euplasmic ditelosomic substitution lines 7H¹L^mar(7D) was performed. In the plants from alloplasmic sterile line L-32(1), the sequences only of the barley (maternal) type were revealed, while the plants from alloplasmic fertile lines L-32(2) and L-32(3) demonstrated heteroplasmy (the presence of barley- and wheat-like sequences within one individual). In euplasmic ditelosomic substitution lines the presence of only wheat-like 18S/5S mitochondrial repeat sequences was observed. The results indicate that the presence of barley-like mtDNA sequences in alloplasmic substitution lines was not associated with the presence of barley chromosomes in their nuclear genomes.     

Production and molecular and cytogenetic analyses of euploid (2n = 42) and telocentric addition (2n = 42 + 2t) alloplasmic lines (Hordeum marinum subsp. gussoneanum)-Triticum aestivum

Individual plants from the BC₁F₆ and BC₁F₈ backcross progenies of barley-wheat [H. marinum subsp. gussoneanum Hudson (=H. geniculatum All.) (2n = 28) × T. aestivum L. (2n = 42)] and the BC₁F₆ progeny of their amphiploids were used to obtain alloplasmic euploid (2n = 42) lines L-28, L-29, and L-49 and alloplasmic telocentric addition (2n = 42 + 2t) lines L-37, L-38, and L-50. The lines were examined by genomic in situ hybridization (GISH), microsatellite analysis, chromosome C-banding, and PCR analysis of the mitochondrial 18S/5S repeat. Lines L-29 and L-49 were characterized by substitution of wild barley chromosome 7H¹ for common wheat chromosome 7D. In line L-49, common wheat chromosomes 1B, 5D, and 7D were substituted with homeologous barley chromosomes. Lines L-37, L-38, and L-50 each contained a pair of telocentric chromosomes, which corresponded to barley chromosome arm 7H¹L. All lines displayed heteroplasmy for the mitochondrial 18S/5S locus; i.e., both barley and wheat sequences were found. Original Russian Text ? N.V. Trubacheeva, E.D. Badaeva, I.G. Adonina, L.I. Belova, E.P. Devyatkina, L.A. Pershina, 2008, published in Genetika, 2008, Vol. 44, No. 1, pp. 81–89.     

Features of alloplasmic wheat-barley substitution and addition lines (<Emphasis Type="Italic">Hordeum marinum</Emphasis> subsp. <Emphasis Type="Italic">gussoneanum</Emphasis>)-<Emphasis Type="Italic">Triticum aestivum</Emphasis>

Two alloplasmic wheat-barley substitution lines were studied: a line replaced at three pairs of chromosomes 1H ^mar (1B), 5H ^mar (5D), and 7H ^mar (7D), and the disomic-substituted line 7H ^mar (7D). The lines were constructed on the basis of individual plants from BC₁F₈ and BC₂F₆ progeny of barley-wheat hybrids (H. marinum subsp. gussoneanum Hudson (= H. geniculatum All.) (2n = 28) × T. aestivum L.) (2n = 42) (Pyrotrix 28), respectively. Moreover, the alloplasmic wheat-barley ditelosomic addition line 7HL ^mar isolated among plants from the BC₁F₆ progeny of a barley-wheat amphiploid was studied, which in this work corresponds to BC₂F₁₀ and BC₂F₁₁ progeny. It was ascertained that when grown in the field, these alloplasmic lines manifest stable self-fertility. Plants of the given lines are characterized by low height, shortened ears, the fewer number of stems and ears, and of spikelets in the ear, by decreased grain productivity and weight of 1000 grains, in comparison with the common wheat cultivar Pyrotrix 28. The inhibition of trait expression in alloplasmic wheat-barley substitution and addition lines may be connected not only with the influence of wild barley chromosomes functioning in the genotypic environment of common wheat, but also with the effect of the barley cytoplasm. The alloplasmic line with substitution of chromosomes 1H ^mar (1B), 5H ^mar (5D), and 7H ^mar (7D) or the alloplasmic line 5HL ^mar with ditelosomic addition have, in comparison with the common wheat cultivar Pyrotrix 28, an increased grain protein content, which is explained by the effect of wild barley H. marinum subsp. gussoneanum chromosomes.     

Homoeologous recombination-based transfer and molecular cytogenetic mapping of powdery mildew-resistant gene <Emphasis Type="Italic">Pm57</Emphasis> from <Emphasis Type="Italic">Aegilops searsii</Emphasis> into wheat

Key message

Pm57, a novel resistant gene against powdery mildew, was transferred into common wheat from Ae. searsi and further mapped to 2S ^s #1L at an interval of FL0.75 to FL0.87.

Abstract

Powdery mildew, caused by the fungus Blumeria graminis f. sp. tritici, is one of the most severe foliar diseases of wheat causing reduction in grain yield and quality. Host plant resistance is the most effective and environmentally safe approach to control this disease. Tests of a set of Chinese Spring–Ae. searsii (S^sS^s, 2n?=?2x?=?14) Feldman & Kislev ex K. Hammer disomic addition lines with a mixed isolate of the powdery mildew fungus identified a novel resistance gene(s), designed as Pm57, which was located on chromosome 2S^s#1. Here, we report the development of ten wheat–Ae. searsii recombinants. The wheat chromosomes involved in five of these recombinants were identified by FISH and SSR marker analysis and three of them were resistant to powdery mildew. Pm57 was further mapped to the long arm of chromosome 2S^s#1 at a fraction length interval of FL 0.75 to FL 0.87. The recombinant stocks T2BS.2BL-2S^s#1L 89-346 (TA5108) with distal 2S^s#1L segments of 28% and 89(5)69 (TA5109) with 33% may be useful in wheat improvement. The PCR marker X2L4g9p4/HaeIII was validated to specifically identify the Ae. searsii 2S^s#1L segment harboring Pm57 in T2BS.2BL-2S^s#1L against 16 wheat varieties and advanced breeding lines, and the development of more user-friendly KASP markers is underway.

     

Standard karyotype of Triticum searsii and its relationship with other S-genome species and common wheat

C-banding polymorphism was analyzed in 14 accessions of Triticum searsii from Israel, and a generalized idiogram of the species was established. One accession was homozygous for whole arm translocations T1S^sS·4S^sS and T1S^sL·4S^sL. C-banding analysis was also used to identify 7 T. aestivum cv Chinese Spring-T. searsii disomic chromosome addition lines, 14 ditelosomic chromosome addition lines, 21 disomic whole chromosome, and 31 ditelosomic chromosome substitution lines. The identity of these lines was further confirmed by meiotic pairing analysis. Sporophytic and gametophytic compensation tests were used to determine the homoeologous relationships of the T. searsii chromosomes. The results show that the T. searsii chromosomes do not compensate well for their wheat homoeologues. The C-banding patterns of T. searsii chromosomes are distinct from those of other S-genome species and from the B-genome chromosomes of wheat, indicating that T. searsii is not a direct B-genome donor species of T. turgidum and T. aestivum.Contribution No. 95-72-J from the Kansas Agricultural Experiment Station, Kansas State University, Manhattan, Kansas, USA     

The mechanism of sex determination in Rumex acetosella

Summary Cytogenetic studies were made with particular emphasis on the sex-determining mechanism in Rumex acetosella (6 x = 42) and its hybrids (F ₁, F ₂, BC ₁ and BC ₂) with R. hastatulus (synthetic 4 x = 16 = 4 A +4 X = and 4 x = 18 = 4 A + 2 (X Y ₁ Y ₂) = ). Rumex acetosella was almost strictly dioecious with 5050 male and female. Breeding tests revealed that the males were heterogametic. The longest chromosomes (S), usually two, are the sex chromosomes of this hexaploid species. The S chromosomes are homomorphic in both male and female. The sex chromosome: autosome ratios, and the strong epistatic male effect of the S ^M chromosome in the polyploid dioecious species and in the hybrids, are evidence of an X/Y Melandrium type sex-determining mechanism controlled by a single pair of homomorphic sex chromosomes. Thus, the sex chromosome formula of the males was S ^F S ^M and that of females was S ^F S ^F. The present approach is a new method for resolving the sex-determining mechanism in a dioecious species.     

Genomic in situ hybridization (GISH) analyses of Thinopyrum intermedium, its partial amphiploid Zhong 5, and disease-resistant derivatives in wheat

Genomic in situhybridization (GISH) to root-tip cells at mitotic metaphase, using genomic DNA probes from Thinopyrum intermedium and Pseudoroegneria strigosa, was used to examine the genomic constitution of Th. intermedium, the 56-chromosome partial amphiploid to wheat called Zhong 5 and disease-resistant derivatives of Zhong 5, in a wheat background. Evidence from GISH indicated that Th. intermedium contained seven pairs of St, seven J^S and 21 J chromosomes; three pairs of Th. intermedium chromosomes with satellites in their short arms belonging to the St, J, J genomes and homoeologous groups 1, 1, and 5 respectively. GISH results using different materials and different probes showed that seven pairs of added Th. intermedium chromosomes in Zhong 5 included three pairs of St chromosomes, two pairs of J^S chromosomes and two pairs of St-J^S reciprocal tanslocation chromosomes. A pair of chromosomes, which substituted a pair of wheat chromosomes in Yi 4212 and in HG 295 and was added to 21 pairs of wheat chromosomes in the disomic additions Z1, Z2 and Z6, conferred BYDV-resistance and was identical to a pair of St-J^S tanslocation chromosomes (StJ^S) in Zhong 5. The StJ^S chromosome had a special GISH signal pattern and could be easily distinguished from other added chromosomes in Zhong 5; it has not yet been possible to locate the BYDV-resistant gene(s) of this translocated chromosome either in the St chromosome portion belonging to homoeologous group 2 or in the J^S chromosome portion whose homoeologous group relationship is still uncertain. Among 22 chromosome pairs in disomic addition line Z3, the added chromosome pair had satellites and belonged to the St genome and homoeologous group 1. Disomic addition line Z4 carried a pair of added chromosomes which was composed of a group-7 J^S chromosome translocated with a wheat chromosome; this chromosome was different to 7 Ai-1, but was identical to 7 Ai-2. The leaf rust and stem rust resistance genes were located in the distal region of the long arm, whereas the stripe rust resistance gene(s) was located in the short arm or in the proximal region of the long arm of 7 Ai-2. A pair of J^S-wheat translocation chromosomes, which originated from the WJ^S chromosomes in Z4, was added to the disomic addition line Z5; the added chromosomes of Z5 carried leaf and stem rust resistance but not stripe rust resistance; Z5 is a potentially useful source for rust resistance genes in wheat breeding and for cloning these novel rust-resistant genes. GISH analysis using the St genome as a probe has proved advantageous in identifying alien Th. intermedium in wheat. Received: 17 May 1999 / Accepted: 22 June 1999     

Molecular cytogenetic analysis of Leymus racemosus chromosomes added to wheat

Five disomic, two double-disomic, and two ditelosomic addition lines and one disomic substitution line derived from the crosses of Triticum aestivum (2n=6x=42, AABBDD)×Leymus racemosus (2n= 4x=28, JJNN) were identified by C-banding analysis. The homoeology of the added Leymus chromosomes was determined by RFLP analysis. Four of five disomic addition lines belonged to group 2, 5, 6 and 7 chromosomes of L. racemosus; these were designated as 2Lr?1(NAU516), 5Lr?1(NAU504, NAU514), 6Lr?1 (NAU512), and 7Lr?1(NAU501). Two additional chromosomes, 1Lr?1 and 3Lr?1, were present in double-disomic addition lines 1Lr?1+5Lr?1 (NAU525) and 3Lr?1+7Lr?1(NAU524), respec-tively. In the disomic substitution line wheat chromosome 2B was replaced by L. racemosus chromosome 2Lr?1 (NAU551). Two telocentric chromosomes, 2Lr?2S (NAU509) and 7Lr?1S (NAU511), were isolated as ditelosomic addition lines. The study presented here provides the first evidence of homoeology of the added L. racemosus chromosomes with wheat chromosomes using DNA markers. Our data provide the basis for further directed chromosome engineering aimed at producing compensating wheat-L. racemosus translocation lines.