Alien genes introgression and development of monosomic alien addition lines from Oryza latifolia Desv. to rice,Oryza sativa L.

Oryza latifolia, a tetraploid wild relative of cultivated rice is an important source of resistance to bacterial blight (BB), the brown planthopper (BPH) and the whitebacked planthopper (WBPH). Interspecific hybrids were obtained between an elite breeding line (IR31917-45-3-2) of Oryza sativa (2n=24 AA) and O. latifolia Acc. No. 100914 (2n=48 CCDD). The crossability in F1 was 7.58% and it ranged from 0.11 to 0.62 in backcross generations. The F1 hybrid showed 2-6 II, 0-2 III, 0-1 IV and 22-32 I; the mean being 3.92 II + 0.11 III + 0.02 IV + 27.30 I per cell at diakinesis. Monosomic alien addition lines (MAALs) having a 2n chromosome complement of O. sativa and one chromosome of O. latifolia were characterized based on morphology and isozyme banding pattern. The MAALs were designated as MAAL-1, MAAL-2, MAAL-4, MAAL-5, MAAL-6, MAAL-7, MAAL-8, MAAL-9, MAAL-10, MAAL-11 and MAAL-12. The female transmission rates of the alien chromosome varied from 4.4 to 35.5%, whereas 8 of the 11 MAALs transmitted the alien chromosome through the male gamete, the range being 1.7% (MAAL 10) to 11.9% (MAAL 12). Disomic progenies in BC3 and BC4 generations had complete resemblance to the O. sativa parent. Of the 2,295 disomic BC3F3 progenies, 309 showed introgression for resistance to BPH and 188 each for WBPH and BB resistance. Four plant progenies which were resistant to both BPH and WBPH were also resistant to BB race 2 of the Philippines. Nine of the 34 BC3F1 plants showed introgression for ten allozymes of O. latifolia, such as Est5, Amp1, Pgi1, Mdh3, Pgi2, Amp3, Pgd2, Est9, Amp2 and Sdh1, located on 8 of the 12 chromosomes. Alien introgression was also detected for morphological traits such as long awns, earliness, black hull, purple stigma and apiculus. Abnormal plants with many wild-species traits suddenly appeared in normal disomic progenies. These plants showing instability and abnormal segregation behaviour are being investigated for the activation of transposons.     

Precise Identification of the Introgressed Segments in Powdery Mildew-resistant Introgression Lines of Triticum aestivum-T.timopheevi

On the basis of the reported location of the Pm6 gene, 36 homoeologous group-2 specific probes were selected to detect polymorphism between wheat/Triticum timopheevi Zhuk. Pm6 introgression lines and their recurrent parent "Prins". Two Pm6 introgression lines IGV1-456, IGV1-458 were distinguished from the others. Nineteen long ann specific and six short ann specific probes detected the RFLPs between resistant IGV1456, IGV1-458 and susceptible control "Prins", indicated that the introgressed T. timopheevi 2G chromatin involve beth arms spanning across the centromere between markers Xcdo405 and Xbcd135. Only 6 of the nineteen long ann specific probes and two additional probes－BCD292, CDO678 showed RFLPs between chromosome 2B of "Prins" and IGV1-463. This means that the introgressed T. timopheevi segment in IGV1- 463 with breakpoints between markers Xbcd307 and Xcdo678 is smaller than those detected in IGV1-456 and IGV1-458. Two of the six long arm specific probes PSR934, BCD135 detected polymorphism between IGV1- 464 and "Pr ins", and only one clone BCD135 revealed RFLPs between IGV1-465 and "Pr ins", which indicated that the introgressed segments in these two lines are smaller than those in others. As the introgressed segments in all the introgression lines bear the Pm6 gene, after comparison of the overlaps of the introgressed segments, it might be reasonable to map the gene Pm6 in the region of marker Xbcd135-2BL flanked 2BL.     

Development of monosomic alien addition lines and introgression of genes from Oryza australiensis Domin. to cultivated rice O. sativa L.

Oryza australiensis, a diploid wild relative of cultivated rice, is an important source of resistance to brown planthopper (BPH) and bacterial blight (BB). Interspecific hybrids between three breeding lines of O. sativa (2n=24, AA) and four accessions of O. australiensis (2n=24, EE) were obtained through embryo rescue. The crossability ranged from 0.25% to 0.90%. The mean frequency of bivalents at diakinesis/metaphase I in F₁ hybrids (AE) was 2.29 to 4.85 with a range of 0–8 bivalents. F₁ hybrids were completely male sterile. We did not obtain any BC₁ progenies even after pollinating 20,234 spikelets of AE hybrids with O. sativa pollen. We crossed the artificially induced autotetraploid of an elite breeding line (IR31917-45-3-2) with O. australiensis (Acc. 100882) and, following embryo rescue, produced six F₁ hybrid plants (AAE). These triploid hybrids were backcrossed to O. sativa. The chromosome number of 16 BC₁ plants varied from 28 to 31, and all were male sterile. BC₂ plants had 24–28 chromosomes. Eight monosomic alien addition lines (MAALs) having a 2n chromosome complement of O. sativa and one chromosome of O. australiensis were selected from the BC₂ F₂ progenies. The MAALs resembled the primary trisomies of O. sativa in morphology, and on the basis of this morphological similarity the MAALs were designated as MAAL-1, -4, -5, -7, -9, -10, -11, and -12. The identity of the alien chromosome was verified at the pachytene stage of meiosis. The alien chromosomes paired with the homoeologous pairs to form trivalents at a frequency of 13.2% to 24.0% at diakinesis and 7.5% to 18.5% at metaphase I. The female transmission rates of alien chromosomes varied from 4.2% to 37.2%, whereas three of the eight MAALs transmitted the alien chromosome through the male gametes. BC₂ progenies consisting of disomic and aneuploid plants were examined for the presence of O. australiensis traits. Alien introgression was detected for morphological traits, such as long awns, earliness, and Amp-3 and Est-2 allozymes. Of the 600 BC₂ F₄ progenies 4 were resistant to BPH and 1 to race 6 of BB. F₃ segregation data suggest that earliness is a recessive trait and that BPH resistance is monogenic recessive in two of the four lines but controlled by a dominant gene in the other two lines.     

Alien introgression in rice

Rice (Oryza sativa L.) productivity is affected by several biotic and abiotic stresses. The genetic variability for some of these stresses is limited in the cultivated rice germplasm. Moreover, changes in insect biotypes and disease races are a continuing threat to increased rice production. There is thus an urgent need to broaden the rice gene pool by introgressing genes for such traits from diverse sources. The wild species of Oryza representing AA, BB, CC, BBCC, CCDD, EE, FF, GG and HHJJ genomes are an important reservoir of useful genes. However, low crossability and limited recombination between chromosomes of cultivated and wild species limit the transfer of such genes. At IRRI, a series of hybrids and monosomic alien addition lines have been produced through embryo rescue following hybridization between rice and several distantly related species. Cytoplasmic male sterility and genes for resistance to grassy stunt virus and bacterial blight have been transferred from A genome wild species into rice. Similarly, genes for resistance to brown planthopper, bacterial blight and blast have also been introgressed across crossability barriers from distanly related species into rice. Some of the introgressed genes have been mapped via linkage to molecular markers. One of the genes Xa-21 introgressed from O. longistaminata has been cloned and physically mapped on chromosome 11 of rice using BAC library and flourescence in-situ hybridization. RFLP analysis revealed introgression from 11 of the 12 chromosomes of C genome species into rice. Introgression has also been obtained from other distant genomes (EE, FF, GG) into rice and in majority of the cases one or two RFLP markers were introgressed. Reciprocal replacement of RFLP alleles of wild species with the alleles of O. sativa indicates alien gene transfer through crossing over. The rapid recovery of recurrent phenotypes in BC₂ and BC₃ generations from wide crosses is an indication of limited recombination. Further cytogenetic and molecular investigations are required to determine precisely the mechanism of introgression of small chromosome segments from distant genomes in the face of limited homoeologous chromosome pairing. Future research should focus on enhancing recombination between homoeologous chromosomes. Introgression of QTL from wild species should be attempted to increase the yield potential of rice.     

RFLP analysis of rice (Oryza sativa L.) introgression lines

Summary Fifty-two introgression lines (BC₂F₈) from crosses between two Oryza sativa parents and five accessions of O. officinalis were analyzed for the introgression of O. officinalis chromosome segments. DNA from the parents and introgression lines was analyzed with 177 RFLP markers located at approximately 10-cM intervals over the rice chromosomes. Most probe/enzyme combinations detected RFLPs between the parents. Of the 174 informative markers, 28 identified putative O. officinalis introgressed chromosome segments in 1 or more of the introgression lines. Introgressed segments were found on 11 of the 12 rice chromosomes. In most cases of introgression, O. sativa RFLP alleles were replaced by O. officinalis alleles. Introgressed segments were very small in size and similar in plants derived from early and later generations. Some nonconventional recombination mechanism may be involved in the transfer of such small chromosomal segments from O. officinalis chromosomes to those of O. sativa. Some of the introgressed segments show association with genes for brown planthopper (BPH) resistance in some introgressed lines, but not in others. Thus, none of the RFLP markers could be unambiguously associated with BPH resistance.     

Recombination is suppressed in an alien introgression in peanut harboring Rma, a dominant root-knot nematode resistance gene

Rma, a dominant root-knot nematode resistance gene introduced into tetraploid peanut (Arachis hypogaea) from a synthetic allotetraploid donor (TxAG-6), has been widely deployed in modern cultivars. The genomic location and borders of the alien chromosome segment introgressed from TxAG-6 into NemaTAM (a BC₇-derived introgression line) and other modern cultivars carrying Rma have not been genetically mapped, and resistance gene candidates (RGCs) have not been identified for Rma. Our study focused on densely populating the alien introgression with codominant DNA markers, identifying and mapping the borders of the alien introgression carried by NemaTAM, and identifying RGCs for Rma. Altogether, 2,847 simple sequence repeat (SSR) and 380 single strand conformational polymorphism (SSCP) markers were screened for linkage to Rma-247 of the SSCP markers targeted 202 nucleotide binding site (NBS) leucine-rich repeat (LRR) and other resistance (R) gene homologs (75 were identified by mining a peanut EST database). SSR, NBS-LRR, and Ser/Thr receptor-like protein loci within the alien introgression co-segregated with Rma in an F₄ population (Gregory × Tifguard) and were tightly linked and spanned 3.4 cM in an F₅ population (NemaTAM × GP-NC-WS-14). By comparative mapping in the A-genome progenitor of peanut (A. duranensis), Rma was discovered to have been introduced on an interstitial alien chromosome segment spanning one-third to one-half of chromosome 9A. Numerous codominant DNA markers were identified for finer mapping of Rma, shortening the alien introgression harboring Rma by marker-assisted selection, and introducing novel root-knot nematode R-genes into peanut by targeting syntenic segments on chromosomes 9A and 9B in wild diploid donors.     

Characterization of euploid backcross progenies derived from interspecific hybrids between Oryza sativa and O. eichingeri by restriction fragment length polymorphism (RFLP) analysis and genomic in situ hybridization (GISH).

Restriction fragment length polymorphism (RFLP) analysis and GISH (genomic in situ hybridization) were performed on euploid plants derived from crosses between Oryza sativa (2n = 24, AA) and two brown planthopper-resistant accessions of O. eichingeri (2n = 24, CC). After screening with 164 RFLP markers, 60 of the 67 euploid plants were identified as introgression lines, each carrying 1-6 small O. eichingeri segments integrated on chromosomes 1, 2, 6, or 10. In the somatic chromosome preparations of F1 hybrid, O. eichingeri chromosomes, fluorescing greenish-yellow in the sequential GISH, appeared to be longer and to contain more heterochromatin than O. sativa ones, and this karyotypic polymorphism can be used to detect some introgressed O. eichingeri segments in euploid plants. In addition, GISH identification presented direct evidence for the transfer of small segments from O. eichingeri to O. sativa chromosome(s) which were subsequently recognized according to their condensation pattern, arm ratio, and chromosome length. The present results would contribute to the molecular mapping and selection of O. eichingeri--derived brown planthopper-resistant gene and positive yield QTLs.     

Marker-assisted pyramiding of brown planthopper (Nilaparvata lugens Stål) resistance genes Bph1 and Bph2 on rice chromosome 12

Brown planthopper (BPH) (Nilaparvata lugens St?l) is a significant insect pest of rice (Oryza sativa L.). We constructed a gene-pyramided japonica line, in which two BPH resistance genes Bph1 and Bph2 on the long arm of chromosome 12 independently derived from two indica resistance lines were combined through the recombinant selection. The gene-pyramiding was achieved based on the previously constructed high-resolution linkage maps of the two genes. Two co-dominant and four dominant PCR-based markers flanking the loci were used to select for a homozygous recombinant line in a segregating population that was derived from a cross between the parental homozygous single-gene introgression lines. BPH bioassay showed that the resistance level of the pyramided line was equivalent to that of the Bph1-single introgression line, which showed a higher level of resistance than the Bph2-single introgression line. The pyramid line should provide a useful experimental means for studying the fine structure of the chromosomal region covering these two major BPH resistance genes.     

Identification of QTLs for some agronomic traits in rice using an introgression line from Oryza minuta

Wild progenitor species provide potential gene sources for complex traits such as yield and multiple resistances to biotic and abiotic stresses, and thus are expected to contribute to sustainable food supplies. An introgression line 'IR71033-121-15' was derived from a wild species Oryza minuta (2n = 48, BBCC, Acc No. 101141) at IRRI. Introgression analysis using 530 SSR and STS markers revealed that at least 14 chromosomal segments distributed over 12 chromosomes had been introgressed from O. minuta. An F2:3 population from the cross between IR71033 and Junambyeo (a Korean japonica cultivar) consisting of 146 lines was used for quantitative trait loci (QTL) analysis of 16 agronomic traits. A total of 36 single-locus QTLs (S-QTLs) and 45 digenic epistasis (E-QTLs) were identified. In spite of it's inferiority of O. minuta for most of the traits studied, its alleles contributed positively to 57% of the QTLs. The other QTLs originated from either parent, IR71033 or Junambyeo. QTLs for phenotypically correlated traits were mostly detected on introgressed segments. Fourteen QTLs corresponded to QTLs reported earlier, indicating that these QTLs are stable across genetic backgrounds. Twenty-two QTLs controlling yield and its components had not been detected in previous QTL studies. Of these, thirteen consisted of potentially novel alleles from O. minuta. QTLs from O. minuta introgression could be new sources of natural variation for the genetic improvement of rice.     

RFLP-based maps of the homoeologous group-6 chromosomes of wheat and their application in the tagging of Pm12, a powdery mildew resistance gene transferred from Aegilops speltoides to wheat

Genetic maps of the homoeologous group-6 chromosomes of bread wheat, Triticum aestivum, have been constructed spanning 103 cM on 6A, 90 cM on 6B and 124 cM on 6D. These maps were transferred to a Chinese Spring (CS) x line #31 cross to locate a dominant powdery mildew resistance gene, Pm12, introgressed into line #31 from Aegilops speltoides. Pm12 was shown to lie on the short arm of translocation chromosome 6BS-6SS.6SL in line #31, but could not be mapped more precisely due to the lack of recombination between the 6S Ae. speltoides segment and chromosome 6B. Possible strategies to reduce the size of the alien segment, which probably encompasses the complete long arm and more than 82% of the short arm of chromosome 6B, are discussed.     

Structural organization of an alien Thinopyrum intermedium group 7 chromosome in U.S. soft red winter wheat (Triticum aestivum L.).

Barley yellow dwarf virus (BYDV) resistance in soft red winter wheat (SRWW) cultivars has been achieved by substituting a group 7 chromosome from Thinopyrum intermedium for chromosome 7D. To localize BYDV resistance, a detailed molecular genetic analysis was done on the alien group 7 Th. intermedium chromosome to determine its structural organization. Triticeae group 7 RFLP markers and rye specific repetitive sequences used in the analysis showed that the alien chromosome in the P29 substitution line has distinguishing features. The 350-480 bp rye telomeric sequence family was present on the long arm as determined by Southern and fluorescence in situ hybridization. However, further analysis using a rye dispersed repetitive sequence indicated that this alien chromosome does not contain introgressed segments from the rye genome. The alien chromosome is homoeologous to wheat chromosomes 7A and 7D as determined by RFLP analysis. Presence of the waxy gene on chromosomes 7A, 7B, and 7D but its absence on the alien chromosome in P29 suggests some internal structural differences on the short arm between Th. intermedium and wheat group 7 chromosomes. The identification of rye telomeric sequences on the alien Thinopyrum chromosome and the homoeology to wheat chromosomes 7A and 7D provide the necessary information and tools to analyze smaller segments of the Thinopyrum chromosome and to localize BYDV resistance in SRWW cultivars.     

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

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

RFLP analysis of the size of chromosomal segments retained around the Tm-2 locus of tomato during backcross breeding

Summary Genes introduced into cultivated plants by backcross breeding programs are flanked by introgressed segments of DNA derived from the donor parent. This phenomenon is known as linkage drag and is frequently thought to affect traits other than the one originally targeted. The Tm-2 gene of Lycopersicon peruvianum, which confers resistance to tobacco mosaic virus, was introduced into several different tomato cultivars (L. esculentum) by repeated backcrossing. We have measured the sizes of the introgressed segments flanking the Tm-2 locus in several of these cultivars using a high density map of restriction fragment length polymorphic (RFLP) markers. The smallest introgressed segment is estimated to be 4 cM in length, while the longest is over 51 cM in length and contains the entire short arm of chromosome 9. Additionally, RFLP analysis was performed on remnant seed from different intermediate generations corresponding to two different backcross breeding programs for TMV resistance. The results reveal that plants containing desirable recombination near the resistance gene were rarely selected during backcrossing and, as a result, the backcross breeding method was largely ineffective in reducing the size of linked DNA around the resistance gene. We propose that, by monitoring recombination around genes of interest with linked RFLP markers, one can quickly and efficiently reduce the amount of linkage drag associated with introgression. Using such a procedure, it is estimated that an introgressed segment can be obtained in two generations that is as small as that which would otherwise require 100 backcross generations without RFLP selection.     

紫米基因与RFLP标记的连锁分析

选用种皮呈紫黑色的水稻体细胞无性系变异体黑珍米和其种皮呈无色的原始亲本Ｂａｓｍａｔｉ３７０配制组合,同时应用１２１个ＤＮＡ探针检测了黑珍米与Ｂａｓｍａｔｉ３７０之间的ＲＦＬＰ。应用Ｆ２和Ｆ３群体研究了紫色种皮的遗传控制。结果表明,有一个显性主效基因控制着黑珍米和Ｂａｓｍａｔｉ３７０在种皮颜色上的差异。通过多态性ＤＮＡ探针与种皮颜色的共分离分析,发现该基因与水稻第四染色体上的ＤＮＡ标记ＲＧ３２９和ＲＧ２１４连锁,与ＲＧ３２９和ＲＧ２１４的遗传图距分别为１８．９ｃＭ和２６．３ｃＭ。     

RFLP analysis of the progeny from Oryza alta Swallen x Oryza sativa L.

RFLP analyses were carried out in the progeny from a cross of two phylogenetically distant rice species, wild rice Oryza alta Swallen (CCDD, 2n = 48) and cultivated rice O. sativa L. (AA, 2n = 24). The sterile plants gave heterozygous RFLP patterns at most of the loci detected. They looked more like their wild rice parent, with 36 chromosomes in their root-tip cells and pollen mother cells. In two partially fertile plants, however, most of the markers that were used showed RFLP patterns similar to the cultivated parent, O. sativa. By cytological study, it was found that nearly one-third of the chromosomes had been eliminated in the partially fertile plants. Their seeds have short awns, which is a characteristic of their wild parent, O. alta. An introgression occurred in one of the partially fertile plants, which led to the discussion about a nonconventional mechanism in wide hybridization for transference of wild rice chromosome segments to cultivated rice chromosomes.     

江西东乡野生稻苗期抗旱基因定位

普通野生稻是栽培稻的祖先种,其遗传多样性远远大于栽培稻,蕴涵着栽培品种中难以找到的重要性状.以江西东乡普通野生稻为供体、以桂朝2号为遗传背景的野生稻基因渗入系（BC4F5、BC4F6）为材料,利用30%的PEG人工模拟干旱环境,对渗入系二叶一心苗期进行抗旱鉴定,共定位了12个与抗旱有关的QTL,其中在第2、6和12染色体上发现了4个QTL的加性效应值为正,来自东乡野生稻的等位基因能使渗入系的抗旱性增强,特别是位于第12染色体RM17附近的qSDT12-2在多次重复中均被检测到,在PEG处理后1-8 d能稳定表达.通过对抗旱性QTL的动态分析,发现不同QTL表达时间不同.     

RFLP Analysis of Progeny from Hybrid of Oryza alta×O.sativa

Oryza alta Swallen is a species of allotetraploid wild rice (CCDD, 2n = 48) with high biomass production and resistant to several insects and diseases. The high polymorphism (RFLP) between O. alta and O. sativa L. (average 90%) reveals the long phylogenical distance between these two species which may impede the crossing. The chromosome constitutions of several progeny from O. alta × O. sativa were analyzed with 22 mapped rice RFLP markers. The results showed that almost all triploid sterile plants which had 36 chromosomes were, as expected, composed of the chromosomes from two parents. But the two partial fertile regenerated plants from 02428 (O. sativa) × WHS601-2 (O. alta) which had only 24 and 25 chromosomes respectively, in most cases, had RFLP patterns similiar to their O. sativa parent. Therefore the chromosomes constituted their genomes were mainly from O. sativa or have high homology with the chromosomes of O. sativa. It seems evident that chromosome elimination had occurred during the wide hybridization as O. alta RFLP patterns could be found in them. Furthermore, that the introgression of O. alta chromosome fragment into that of O. sativa in an F2 plant was indicative that some kind of recombination also occurred. Regarding the rare chromosome pairing in PMCs, the probability of the existence of a nonconventional mechanism for the wild rice chromosomes (chromosome fragments ) to introgressing into cultivated rice genomes in a relatively short time was discussed.     

Mapping of stripe rust resistance gene in an <Emphasis Type="Italic">Aegilops caudata</Emphasis> introgression line in wheat and its genetic association with leaf rust resistance

A pair of stripe rust and leaf rust resistance genes was introgressed from Aegilops caudata, a nonprogenitor diploid species with the CC genome, to cultivated wheat. Inheritance and genetic mapping of stripe rust resistance gene in backcross-recombinant inbred line (BC-RIL) population derived from the cross of a wheat–Ae. caudata introgression line (IL) T291-2(pau16060) with wheat cv. PBW343 is reported here. Segregation of BC-RILs for stripe rust resistance depicted a single major gene conditioning adult plant resistance (APR) with stripe rust reaction varying from TR-20MS in resistant RILs signifying the presence of some minor genes as well. Genetic association with leaf rust resistance revealed that two genes are located at a recombination distance of 13%. IL T291-2 had earlier been reported to carry introgressions on wheat chromosomes 2D, 3D, 4D, 5D, 6D and 7D. Genetic mapping indicated the introgression of stripe rust resistance gene on wheat chromosome 5DS in the region carrying leaf rust resistance gene LrAc, but as an independent introgression. Simple sequence repeat (SSR) and sequence-tagged site (STS) markers designed from the survey sequence data of 5DS enriched the target region harbouring stripe and leaf rust resistance genes. Stripe rust resistance locus, temporarily designated as YrAc, mapped at the distal most end of 5DS linked with a group of four colocated SSRs and two resistance gene analogue (RGA)-STS markers at a distance of 5.3 cM. LrAc mapped at a distance of 9.0 cM from the YrAc and at 2.8 cM from RGA-STS marker Ta5DS_2737450, YrAc and LrAc appear to be the candidate genes for marker-assisted enrichment of the wheat gene pool for rust resistance.     

Restriction fragment length polymorphisms linked to genes for resistance to crown rust (Puccinia coronata) in near-isogenic lines of hexaploid oat (Avena sativa).

Crown rust, perhaps the most important fungal disease of oat, is caused by Puccinia coronata. An examination of near-isogenic lines (NILs) of hexaploid oat (Avena sativa) was conducted to identify markers linked to genes for resistance to crown rust. These lines were created such that a unique resistance gene is present in each of the two recurrent parent backgrounds. The six NILs of the current study, X434-II, X466-I, and Y345 (recurrent parent C237-89) and D486, D494, and D526 (recurrent parent Lang), thus provide a pair of lines to study each of three resistance genes. Restriction fragment length polymorphisms and resistance loci were mapped using BC1F2 populations. Three markers were found linked to a locus for resistance to crown rust race 203, the closest at 1.9 cM in line D494 and 3.8 cM in line X466-I. In lines D526 and Y345 a marker was placed 1.0 and 1.9 cM, respectively, from the locus conferring resistance to crown rust race 345, and in D486 and X434-II a marker mapped at 8.0 and 10.2 cM from the locus for resistance to rust race 264B.