Genetic analysis and gene mapping of a rice few-tillering mutant in early backcross populations ( Oryza sativa L.)

A rice mutant,G069, characteristic of few tiller numbers, was found in anther culture progeny from theF ₁ hybrid between anindica-japonica cross, Gui630×02428. The mutant has another two major features: delayed tillering development and yellowing apex and margin on the mature leaves. As a donor parent,G069 was further backcrossed with the recurrent parent,02428, for two turns to develop aBC ₂F₂ population. Genetic analysis in theBC ₂F₂ population showed that the traits of few-tillering and yellowing apex and margin on the mature leaves were controlled by one recessive gene. A pool of equally mixed genomic DNA, from few-tillering individual plants inBC ₂F₂, was constructed to screen polymorphism with simple sequence repeat (SSR) markers in comparison with the02428 genome. One SSR marker and three restriction fragment length polymorphism (RFLP) markers were found possibly linked with the recessive gene. By using these markers, the gene of few-tillering was mapped on chromosome 2 between RFLP marker C424 and S13984 with a genetic distance of 2.4 cM and 0.6 cM, respectively. The gene is designatedft1.     

Genetic analysis and gene mapping of a rice few-tillering mutant in early backcross populations (Oryza sativa L.)

A rice mutant, G069, characteristic of few tiller numbers, was found in anther culture progeny from the F1 hybrid between an indica-japonica cross, Gui630×02428. The mutant has another two major features: delayed tillering development and yellowing apex and margin on the mature leaves. As a donor parent, G069 was further backcrossed with the recurrent parent, 02428, for two turns to develop a BC2F2 population. Genetic analysis in the BC2F2 population showed that the traits of few-tillering and yellowing apex and margin on the mature leaves were controlled by one recessive gene. A pool of equally mixed genomic DNA, from few-tillering individual plants in BC2F2, was constructed to screen polymorphism with simple sequence repeat (SSR) markers in comparison with the 02428 genome. One SSR marker and three restriction fragment length polymorphism (RFLP) markers were found possibly linked with the recessive gene. By using these markers, the gene of few-tillering was mapped on chromosome 2 between RFLP marker C     

结合SSR标记和STS标记对家蚕无鳞毛翅基因的定位

家蚕突变表型无鳞毛翅(non-lepis wing, nlw)由隐性基因nlw控制。由于家蚕雌性不发生交换, 文章采用有鳞毛翅品系P50和无鳞毛翅品系U06两个品系组配F1代及BC₁回交群体, (U06×P50)×U06和U06×(U06×P50)分别记作BC₁F和BC₁M, 根据已经构建的家蚕SSR分子标记连锁图谱及已经发表的有关序列对nlw基因进行了连锁及定位分析。得到8个与nlw基因连锁的SSR(Simple sequence repeat)标记和1个STS(Sequence-tagged sites)标记。BC₁F群中的所有正常翅个体均表现出与(U06×P50)F₁相同的杂合带型; 而所有无鳞毛个体带型与亲本U06一致, 为纯合型。利用BC₁M群体构建了关于nlw基因的遗传连锁图, 连锁图的遗传距离为125.7 cM, 与nlw基因最近的引物为STS标记cash2p, 图距为11.4 cM。     

Molecular tagging and genetic mapping of the disease resistance gene<Emphasis Type="Italic"> RppQ</Emphasis> to southern corn rust

Southern corn rust (SCR), Puccinia polysora Underw, is a destructive disease in maize (Zea mays L.). Inbred line Qi319 is highly resistant to SCR. Results from the inoculation test and genetic analysis of SCR in five F₂ populations and five BC₁F₁ populations derived from resistant parent Qi319 clearly indicate that the resistance to SCR in Qi319 is controlled by a single dominant resistant gene, which was named RppQ. Simple sequence repeat (SSR) analysis was carried out in an F₂ population derived from the cross Qi319×340. Twenty SSR primer pairs evenly distributed on chromosome10 were screened at first. Out of them, two primer pairs, phi118 and phi 041, showed linkage with SCR resistance. Based on this result, eight new SSR primer pairs surrounding the region of primers phi118 and phi 041 were selected and further tested regarding their linkage relation with RppQ. Results indicated that SSR markers umc1,318 and umc 2,018 were linked to RppQ with a genetic distance of 4.76 and 14.59 cM, respectively. On the other side of RppQ, beyond SSR markers phi 041 and phi118, another SSR marker umc1,293 was linked to RppQ with a genetic distance of 3.78 cM. Because the five linkage SSR markers (phi118, phi 041, umc1,318, umc 2,018 and umc1,293) are all located on chromosome 10, the RppQ gene should also be located on chromosome 10. In order to fine map the RppQ gene, AFLP (amplified fragment length polymorphism) analysis was carried out. A total 54 AFLP primer combinations were analyzed; one AFLP marker, AF1, from the amplification products of primer combination E-AGC/M-CAA, showed linkage with the RppQ gene in a genetic distance of 3.34 cM. Finally the RppQ gene was mapped on the short arm of chromosome 10 between SSR markers phi 041 and AFLP marker AF1 with a genetic distance of 2.45 and 3.34 cM respectively.Communicated by H. F. Linskens     

Characterization and mapping of <Emphasis Type="Italic">Rpi1</Emphasis>, a gene that confers dominant resistance to stalk rot in maize

The maize inbred lines 1145 (resistant) and Y331 (susceptible), and the F₁, F₂ and BC₁F₁ populations derived from them were inoculated with the pathogen Pythium inflatum Matthews, which causes stalk rot in Zea mays. Field data revealed that the ratio of resistant to susceptible plants was 3:1 in the F₂ population, and 1:1 in the BC₁F₁population, indicating that the resistance to P. inflatum Matthews was controlled by a single dominant gene in the 1145×Y331 cross. The gene that confers resistance to P. inflatum Matthews was designated Rpi1 for resistance to P. inflatum) according to the standard nomenclature for plant disease resistance genes. Fifty SSR markers from 10 chromosomes were first screened in the F₂ population to find markers linked to the Rpi1 gene. The results indicated that umc1702 and mmc0371 were both linked to Rpi1, placing the resistance gene on chromosome 4. RAPD (randomly amplified polymorphic DNA) markers were then tested in the F₂population using bulked segregant analysis (BSA). Four RAPD products were found to show linkage to the Rpi1 gene. Then 27 SSR markers and 8 RFLP markers in the region encompassing Rpi1 were used for fine-scale mapping of the resistance gene. Two SSR markers and four RFLP markers were linked to the Rpi1 gene. Finally, the Rpi1 gene was mapped between the SSR markers bnlg1937 and agrr286 on chromosome 4, 1.6 cM away from the former and 4.1 cM distant from the latter. This is the first time that a dominant gene for resistance to maize stalk rot caused by P. inflatum Matthews has been mapped with molecular marker techniques.     

Genetic analysis and molecular mapping of maize (<Emphasis Type="Italic">Zea mays</Emphasis> L.) stalk rot resistant gene<Emphasis Type="Italic"> Rfg</Emphasis>1

One single pathogen Fusarium graminearum Schw. was inoculated to maize inbred lines 1,145 (Resistant) and Y331 (Susceptive), and their progenies of F₁, F₂ and BC₁F₁ populations. Field statistical data revealed that all of the F₁ individuals were resistant to the disease and that the ratio of resistant plants to susceptive plants was 3:1 in the F₂ population, and 1:1 in the BC₁F₁ population. The results revealed that a single dominant gene controls the resistance to F. graminearum Schw.. The resistant gene to F. graminearum Schw. was denominated as Rfg1 according to the standard principle of the nomenclature of the plant disease resistant genes. RAPD (randomly amplified polymorphic DNA) combined with BSA (bulked segregant analysis) analysis was carried out in the developed F₂ and BC₁F₁ populations, respectively. Three RAPD products screened from the RAPD analysis with 820 Operon 10-mer primers showed the linkage relation with the resistant gene Rfg1. The three RAPD amplification products (OPD-20₁₀₀₀, OPA-04₁₁₀₀ and OPY-04₉₀₀) were cloned and their copy numbers were determined. The results indicated that only OPY-04₉₀₀ was a single-copy sequence. Then, OPY-04₉₀₀ was used as a probe to map the Rfg1 gene with a RIL F₇ mapping population provided by Henry Nguyen, which was developed from the cross S3×Mo17. Rfg1 was primarily mapped on chromosome 6 between the two linked markers OPY-04₉₀₀ and umc21 (Bin 6.04–6.05). In order to confirm the primary mapping result, 25 SSR (simple sequence repeat) markers and six RFLP (restriction fragment length polymorphism) markers in the Rfg1 gene-encompassing region were selected, and their linkage relation with Rfg1 was analyzed in our F₂ population. Results indicated that SSR marker mmc0241 and RFLP marker bnl3.03 are flanking the Rfg1 gene with a genetic distance of 3.0 cM and 2.0 cM, respectively. This is the first time to name and to map a single resistant gene of maize stalk rot through a single pathogen inoculation and molecular marker analysis.Communicated by H.F. Linskens     

Genetic analyses and mapping of a new thermo-sensitive genic male sterile gene in maize

The present study describes a novel thermo-sensitive genic male sterile (TGMS) line, Qiong68ms. To analyse the mode of fertility inheritance and tag the TGMS gene, a set of F₂, BC₁ and F_2:3 populations derived from a cross between Qiong68ms and K12 were evaluated for a period of 2 years. Classical genetic analyses and QTL mapping using the mean restoration percentage of the F_2:3 populations revealed that the fertility of Qiong68ms was likely to be governed by a single recessive gene, which was named tms3; the tms3 gene was mapped to a location between SSR markers umc2129 and umc1041, at a distance of 3.7 cM form umc2129 and 1.5 cM form umc1041. The molecular markers tightly linked with tms3 gene will aid in the transfer of the TGMS gene to various background inbred lines using the MAS method.     

Molecular tagging and mapping of the erect panicle gene in rice

Erect panicle (EP) is one of the more important traits of the proposed ideotype of high-yielding rice. Several rice cultivars with the EP phenotype, which has been reported to be controlled by a dominant gene, have been successfully developed and released for commercial production in North China. To analyze the inheritance of the EP trait, we generated segregating F₂ and BC₁F₁ populations by crossing an EP-type variety, Liaojing 5, and a curved-panicle-type variety, Fengjin. Our results confirmed that a dominant gene controls the EP trait. Simple-sequence repeat (SSR) and bulked segregant analyses of the F₂ population revealed that the EP gene is located on chromosome 9, between two newly developed SSR markers, RM5833-11 and RM5686-23, at a genetic distance of 1.5 and 0.9 cM, respectively. Markers closer to the EP gene were developed by amplified fragment length polymorphism (AFLP) analysis with 128 AFLP primer combinations. Three AFLP markers were found to be linked to the EP gene, and the nearest marker, E-TA/M-CTC₂₀₀, was mapped to the same location as SSR marker RM5686-23, 1.5 cM from the EP gene. A local map around the EP gene comprising nine SSR and one AFLP marker was constructed. These markers will be useful for marker-assisted selection (MAS) for the EP trait in rice breeding programs.     

Genetic Analysis and Physical Mapping of Lk-4(t), a Major Gene Controlling Grain Length in Rice, with a BC2F2 Population

Grain size and shape are important factors affecting grain quality and yield in rice. Mapping, tagging and identification of their related genes can lead us to understand their expression pattern and mechanism network, which is to their control. In this study we mapped a grain length controlling gene named Lk-4(t) with SSR and CAPs markers by screening 800 recessive plants in a BC₂F₂ population derived from a cross of Shuhui527xXiaoli and backcrossed with Xiaoli as the donor parent. The distribution of grain shape parameters and thousand grain weight in F₂ and BC₂F₂ population showed that backcross can diminish most unnecessary variations to identify the target gene more clearly. There were only two grain length phenotypes found among the 3 209 BC₂F₂ plants, long and short, indicating it is a qualitative trait. The frequency distribution for the grain length showed a typical segregation ratio of 3 : 1, suggesting that only one allele was responsible for the variation. By screening the recessive long grain plants with three CAPs markers, P1-EcoR V, P2-Sac I and P3-Mbo I, we tagged the locus on the arm of chromosome 3 near the centromere. Lk-4(t) was located between P1-EcoRV and P2-Sac I, with genetic distance of 0.90 cM and 0.50 cM from the two markers respectively. Mapping of the gene is a foundation for its final identification and function analysis.     

Genetic Analysis and Molecular Mapping of a Novel Gene Conferring Resistance to Rice Stripe Virus

Rice stripe virus (RSV) is one of the most damaging diseases affecting rice in East Asia. Rice variety 502 is highly resistant to RSV, while variety 5112 is extremely susceptible. Field statistical data revealed that all “502 × 5112” F₁ individuals were resistant to RSV and the ratio of resistant to susceptible plants was 3:1 in the F₂ population and 1:1 in the BC₁F₁ population. These results indicated that a dominant gene, designated RSV1, controlled the resistance. Simple sequence repeat (SSR) analysis was subsequently carried out in an F₂ population. Sixty SSR markers evenly distributed on the 12 rice chromosomes were screened and tested. Two markers, RM229 and RM206, showed linkage with RSV1. Based on this result, six SSR markers flanking RM229 and RM206 were further selected and tested. Results indicated that SSR markers RM457 and RM473E were linked to RSV1 with a genetic distance of 4.5 and 5.0 cM, respectively. All of the four SSR markers (RM229, RM473E, RM457 and RM206) linked to RSV1 were all located on chromosome 11, therefore RSV1 should be located on chromosome 11 also. In order to find some new markers more closely linked to the RSV1 gene, sequence-related amplified polymorphism (SRAP) analysis was performed. A total of 30 SRAP primer-pairs were analyzed, and one marker SR1 showed linkage with RSV1 at a genetic distance of 2.9 cM. Finally, RSV1 gene was mapped on chromosome 11 between SSR markers RM457 and SRAP marker SR1 with a genetic distance of 4.5 cM and 2.9 cM, respectively.     

Genetic basis of low-temperature-sensitive sterility in indica-japonica hybrids of rice as determined by RFLP analysis

 Low-temperature-sensitive sterility (LTSS) has become one of the major obstacles in indica-japonica hybrid rice breeding. In this study, we determined, using RFLP markers, the genetic basis of LTSS in two populations derived from crosses between indica and japonica parents, the BC₁F₁ of 3037/02428//3037 and the F₂ of 3037/02428. The fertility segregation in the two populations under low-temperature conditions was used as a measurement of the temperature sensitivity of the various genotypes in the populations. A RFLP survey of bulked extremes from the BC₁F₁ population identified three genomic regions, two on chromosome 1 and one on chromosome 12, that were likely to contain genes for LTSS (or Ste loci). One-way ANOVA and QTL analysis using a total of 19 markers from these three genomic regions resolved three Ste loci in the BC₁F₁ population and two Ste loci in the F₂ population. On the basis of chromosomal location these loci were distinct from those governing wide-compatibility identified in previous studies. Two- and three-way ANOVA showed that these loci acted essentially independent of each other in conditioning LTSS. The main mode of gene action was an interaction between the indica and the japonica alleles within each locus. For each respective locus this resulted in a drastic fertility reduction in the heterozygote state relative to the homozygote state. The results have significant implications in indica-japonica hybrid rice breeding programs. Received : 10 April 1996 / Accepted: 2 June 1997     

SSR based linkage and mapping analysis of C,a yellow cocoon gene in the silkworm,Bombyx mori

The yellow color of the cocoon of the silkworm Bombyx mori is controlled by three genes, Y (Yellow haemolymph), I (Yellow inhibitor) and C (Outer‐layer yellow cocoon), which are located on linkage groups 2, 9 and 12, respectively. Taking advantage of a lack of crossing over in females, reciprocal backcrossed F₁ (BC₁) progeny were used for linkage analysis and mapping of the C gene using silkworm strains C108 and KY, which spin white and yellow cocoons, respectively. DNA was extracted from individual pupae and analyzed for simple sequence repeat (SSR) markers. The C gene was found to be linked to seven SSR markers. All the yellow cocoon individuals from a female heterozygous backcross (BC₁ F) showed a heterozygous profile for SSR markers on linkage group 12, whereas individuals with light yellow cocoons showed the homozygous profile of the strain C108. Using a reciprocal heterozygous male backcross (BC₁ M), we constructed a linkage map of 36.4 cM with the C gene located at the distal end, and the closest SSR marker at a distance of 13.9 cM.     

Genetic localization of a bruchid resistance gene and its relationship to insecticidal cyclopeptide alkaloids, the vignatic acids, in mungbean ( Vigna radiata L. Wilczek)

Bruchid resistance, controlled by a single dominant gene (Br) in a wild mungbean accession (TC1966), has been incorporated into cultivated mungbean (Vigna radiata). The resistance gene simultaneously confers inhibitory activity against the bean bug, Riptortus clavatus Thunberg (Hemiptera: Alydidae). The resultant isogenic line (BC₂₀ generation) was characterized by the presence of a group of novel cyclopeptide alkaloids, called vignatic acids. A linkage map was constructed for Br and the vignatic acid gene (Va) using restriction fragment length polymorphism (RFLP) markers and a segregating BC₂₀F₂ population. By screening resistant and susceptible parental lines with 479 primers, eight randomly amplified polymorphic DNA (RAPD) markers linked to Br were identified and cloned for use as RFLP probes. All eight RAPD-based markers, one mungbean, and four common bean genomic clones were effectively integrated around Br within a 3.7-cM interval. Br was mapped to a 0.7-cM segment between a cluster consisting of six markers and a common bean RFLP marker, Bng110. The six markers are closest to the bruchid resistance gene, approximately 0.2 cM away. The vignatic acid gene, Va, cosegregated with bruchid resistance. However, one individual was identified in the BC₂₀F₂ population that retained vignatic acids in spite of its bruchid susceptibility. Consequently, Va was mapped to a single locus at the same position as the cluster of markers and 0.2 cM away from Br. These results suggest that the vignatic acids are not the principal factors responsible for bruchid resistance in V. radiata but will facilitate the use of map-based cloning strategies to isolate the Br gene. Received: 20 November 1997 / Accepted: 6 January 1998     

Identification of RAPD markers linked to a major blast resistance gene in rice

Rice blast, caused byPyricularia grisea, is a major production constraint in many parts of the world. The Korean rice variety Tongil showed high levels of resistance for about six years when widely planted under highly disease-conducive conditions, before becoming susceptible. Tongil was found to carry a single dominant gene, designatedPi-10t, conferring resistance to isolate 106 of the blast pathogen from the Philippines. We report here the use of bulked segregant RAPD analysis for rapid identification of DNA markers linked toPi-10t. Pooled DNA extracts from five homozygous blast-resistant (RR) and five susceptible (rr) BC₃F₂ plants, derived from a CO39 × Tongil cross, were analyzed by RFLP using 83 polymorphic probes and by RAPD using 468 random oligomers. We identified two RAPD markers linked to thePi-10t locus: RRF6 (3.8 ± 1.2 cM) and RRH18 (2.9 ± 0.9 cM). Linkage of these markers withPi-10t was verified using an F2 population segregating forPi-10t. The two linked RAPD markers mapped 7 cM apart on chromosome 5. Chromosomal regions surrounding thePi-10t gene were examined with additional RFLP markers to define the segment introgressed from the donor genome.Pi-10t is likely to be a new blast-resistance locus, because no other known resistance gene has been mapped on chromosome 5. These tightly linked RAPD markers could facilitate early selection of thePi-10t locus in rice breeding programmes.     

Identification and mapping of pm2026: a recessive powdery mildew resistance gene in an einkorn (Triticum monococcum L.) accession

Triticum monococcum accession TA2026 showed resistance to wheat powdery mildew. To identify the resistance gene and transfer it to common wheat, genetic analysis and molecular mapping were conducted using an F₂ population and derived F₃ families from the cross of TA2026 × M389. The results indicated that TA2026 possessed a recessive powdery mildew resistance gene. This gene was mapped to the terminal portion of chromosome 5A^mL and flanked by SSR marker loci Xcfd39 and Xgwm126. Eight RFLP markers previously mapped to the terminal chromosome 5A^mL were converted into STS markers. Three loci, detected by MAG1491, MAG1493 and MAG1494, the STS markers derived from RFLP probes CDO1312, PSR164 and PSR1201, respectively, were linked to this resistance gene with Xmag1493 only 0.9 cM apart from it. In addition, the STS marker MAG2170 developed from the tentative consensus wheat cDNA encoding the Mlo-like protein identified a locus co-segregating with Xmag1493. This is the first recessive powdery mildew resistance gene identified on chromosome 5A^m, and is temporarily designated pm2026. We have successfully transferred it to a tetraploid background, and this resistance stock will now be used as the bridge parent for its transfer to common wheat.     

Molecular mapping of the Oregon Wolfe Barleys: a phenotypically polymorphic doubled-haploid population

A phenotypically polymorphic barley (Hordeum vulgare L.) mapping population was developed using morphological marker stocks as parents. Ninety-four doubled-haploid lines were derived for genetic mapping from an F₁ using the Hordeum bulbosum system. A linkage map was constructed using 12 morphological markers, 87 restriction fragment length polymorphism (RFLP), five random amplified polymorphic DNA (RAPD), one sequence-tagged site (STS), one intron fragment length polymorphism (IFLP), 33 simple sequence repeat (SSR), and 586 amplified fragment length polymorphism (AFLP) markers. The genetic map spanned 1,387 cM with an average density of one marker every 1.9 cM. AFLP markers tended to cluster on centromeric regions and were more abundant on chromosome 1 (7H). RAPD markers showed a high level of segregation distortion, 54% compared with the 26% observed for AFLP markers, 27% for SSR markers, and 18% for RFLP markers. Three major regions of segregation distortion, based on RFLP and morphological markers, were located on chromosomes 2 (2H), 3 (3H), and 7 (5H). Segregation distortion may indicate that preferential gametic selection occurred during the development of the doubled-haploid lines. This may be due to the extreme phenotypes determined by alleles at morphological trait loci of the dominant and recessive parental stocks. Several molecular markers were found to be closely linked to morphological loci. The linkage map reported herein will be useful in integrating data on quantitative traits with morphological variants and should aid in map-based cloning of genes controlling morphological traits. Received: 23 August 2000 / Accepted: 15 December 2000     

Introgression into tomato (Lycopersicon esculentum) of the L. chmielewskii sucrose accumulator gene (sucr) controlling fruit sugar composition

High sucrose concentration in fruit of Lycopersicon chmielewskii is governed by the recessive sucrose accumulator gene (sucr) that is situated in the pericentromeric region of chromosome 3. The sucr gene was introgressed into the genetic background of the hexose-accumulating cultivated tomato (L. esculentum cv Hunt 100) by marker-assisted selection using tightly linked RFLP markers and a tomato acid invertase cDNA as probes for sucr. RFLP mapping indicated that the segment containing sucr comprised over 43.2 cM in the BC₁F₂ generation, representing over one-third of the total length of chromosome 3. By selecting for crossovers between sucr and the flanking visual marker r (yellow fruit flesh) and RFLP marker TG288, we were able to reduce the size of the sucr introgression fragment to 0.8–7.1 cM by the BC₅ generation. Smaller recombinant fragments were not obtained despite screening a large BC₆F₂ population. The smallest sucr introgression reduced recombination between the flanking visual markers sy (sunny) and bls (baby lea syndrome) by 38%. To facilitate future introgression and recombination experiments, a PCR-based test for the sucr gene was developed using primers specific to the tomato invertase gene. This assay takes advantage of a small deletion that maps to the second intron of the L. chmielewskii nvertase gene. The assay detected significant allelic variation both within and between hexose- and sucrose-accumulating Lycopersicon spp.     

Molecular mapping of the reverse thermo-sensitive genic male-sterile gene (rtms1) in rice

TGMS (thermo-sensitive genic male-sterile) rice is widely used in hybrid rice production. Because of a specific temperature requirement, it can be used only in a narrow rice-growing zone in Asia. A newly discovered reverse thermo-sensitive genic male-sterile line, J207S, has an opposite phynotype compared to the normal TGMS lines. J207S is completely sterile when the temperature is lower than 31°C. Thus, it can be widely used in a larger area. Genetic analysis indicated that the sterility of J207S was controlled by a single recessive gene which was first named as rtms1. An F₂ population from the cross between J207S and E921 was developed and used for molecular mapping of the rtms1 gene. The AFLP (amplified fragment length polymorphism) technique, combined with BSA (bulked segregant analysis), was used to screen markers linked to the target gene, and eight polymorphic AFLP loci were identified. Co-segregating analysis using the F₂ population showed that two of them, Rev1 and Rev7, were closely linked to the target gene with a recombinant rate of 3.8% and 7.7%, respectively. Both Rev1 and Rev7 were found to be single-copy sequences through Southern analysis. Rev1 was subsequently mapped on chromosome 10 with a doubled-haploid mapping populations derived from the cross CT9993 × IR62266 available at Texas Tech University. RM222 and RG257 were linked to Rev1 at a distance of 11.8 cM and 4.6 cM, respectively. Additional SSR markers from the rice map of Cornell University, RFLP markers from the map of RGP in Japan and the map of Texas Tech University were selected from the region surrounding Rev1 on chromosome 10 to conduct the fine-mapping of the rtms1 gene. Presently, rtms1 was mapped between RM239 and RG257 with genetic distance of 3.6 cM and 4.0 cM, respectively. The most-closely linked AFLP marker, Rev1, 4.2 cM from the rtms1 gene, was sequenced and converted into a SCAR (sequence characterized amplified region) marker which could facilitate marker-assisted selection of the rtms1 gene. Received: 2 November 2000 / Accepted: 21 November 2000     

Genetics and molecular mapping of genes for high-temperature resistance to stripe rust in wheat cultivar Xiaoyan 54

Stripe rust, caused by Puccinia striiformis f. sp. tritici, is one of the most widespread and destructive wheat diseases worldwide. Growing resistant cultivars is the preferred means of control of the disease. The winter wheat cultivar Xiaoyan 54 has high-temperature resistance to stripe rust. To identify genes for stripe rust resistance, Xiaoyan 54 was crossed with Mingxian 169, a winter wheat genotype susceptible to all Chinese races of the pathogen. Seedlings and adult plants of the parents and F₁, F₂, F₃ and F₄ progeny were tested with Chinese race CYR32 under controlled greenhouse conditions and in the field. Xiaoyan 54 has two recessive resistance genes, designated as Yrxy1 and Yrxy2, conferring high-temperature resistance. Simple sequence repeat (SSR) primers were used to identify molecular markers flanking Yrxy2 using 181 plants from one segregating F₃ line. A total of nine markers, two of which flanked the locus at genetic distances of 4.0 and 6.4 cM on the long arm of chromosome 2A were identified. Resistance gene analog polymorphism (RGAP) and SSR techniques were used to identify molecular markers linked to Yrxy1. A linkage group of nine RGAP and two SSR markers was constructed for Yrxy1 using 177 plants of another segregating F₃ line. Two RGAP markers were closely linked to the locus with genetic distances of 2.3 and 3.5 cM. Amplification of a set of nulli-tetrasomic Chinese Spring lines with RGAP markers M8 and M9 and the two SSR markers located Yrxy1 on the short arm of chromosome 7A. The SSR markers Xbarc49 and Xwmc422 were 15.8 and 26.1 cM, respectively, from the gene. The closely linked molecular markers should be useful for incorporating the resistance genes into commercial cultivars and combining them with other genes for stripe rust resistance.     

Development of SRAP, SRAP-RGA, RAPD and SCAR markers linked with a Fusarium wilt resistance gene in eggplant

Fusarium wilt (Fusarium oxysporum Schlecht. f. sp. melongenae) is a vascular disease of eggplant (Solanum melongena L.). The objectives of this work were (1) to confirm the monogenic inheritance of fusarium wilt resistance in eggplant, (2) to identify molecular markers linked to this resistance, and (3) to develop SCAR markers from most informative markers. We report the tagging of the gene for resistance to fusarium wilt (FOM) in eggplant using SRAP, RGA, SRAP-RGA and RAPD markers. Analysis of segregation data confirmed the monogenic inheritance of resistance. DNA from F₂ and BC₁ populations of eggplant segregating for fusarium wilt resistance was screened with 2,316 primer combinations to detect polymorphism. Three markers were linked within 2.6 cM of the gene. The codominant SRAP marker Me8/Em5 and dominant SRAP-RGA marker Em12/GLPL2 were tightly linked to each other and mapped 1.2 cM from the resistance gene, whereas RAPD marker H12 mapped 2.6 cM from the gene and on the same side as the other two markers. The SRAP marker was converted into two dominant SCAR markers that were confirmed to be linked to the resistance gene in the F_2, BC₁ and F₂ of BC₃ generations of the same cross. These markers provide a starting point for mapping the eggplant FOM resistance gene in eggplant and for exploring the synteny between solanaceous crops for fusarium wilt resistance genes. The SCAR markers will be useful for identifying fusarium wilt-resistant genotypes in marker-assisted selection breeding programs using segregating progenies of the resistant eggplant progenitor used in this study.