Linkage mapping of the Phg-1 and Co-1(4) genes for resistance to angular leaf spot and anthracnose in the common bean cultivar AND 277

The Andean common bean AND 277 has the Co-1 ⁴ and the Phg-1 alleles that confer resistance to 21 and eight races, respectively, of the anthracnose (ANT) and angular leaf spot (ALS) pathogens. Because of its broad resistance spectrum, Co-1 ⁴ is one of the main genes used in ANT resistance breeding. Additionally, Phg-1 is used for resistance to ALS. In this study, we elucidate the inheritance of the resistance of AND 277 to both pathogens using F₂ populations from the AND 277 × Rudá and AND 277 × Ouro Negro crosses and F_2:3 families from the AND 277 × Ouro Negro cross. Rudá and Ouro Negro are susceptible to all of the above races of both pathogens. Co-segregation analysis revealed that a single dominant gene in AND 277 confers resistance to races 65, 73, and 2047 of the ANT and to race 63-23 of the ALS pathogens. Co-1 ⁴ and Phg-1 are tightly linked (0.0 cM) on linkage group Pv01. Through synteny mapping between common bean and soybean we also identified two new molecular markers, CV542014⁴⁵⁰ and TGA1.1⁵⁷⁰, tagging the Co-1 ⁴ and Phg-1 loci. These markers are linked at 0.7 and 1.3 cM, respectively, from the Co-1 ⁴ /Phg-1 locus in coupling phase. The analysis of allele segregation in the BAT 93/Jalo EEP558 and California Dark Red Kidney/Yolano recombinant populations revealed that CV542014⁴⁵⁰ and TGA1.1⁵⁷⁰ segregated in the expected 1:1 ratio. Due to the physical linkage in cis configuration, Co-1 ⁴ and Phg-1 are inherited together and can be monitored indirectly with the CV542014⁴⁵⁰ and TGA1.1⁵⁷⁰ markers. These results illustrate the rapid discovery of new markers through synteny mapping. These markers will reduce the time and costs associated with the pyramiding of these two disease resistance genes.     

Co-segregation analysis and mapping of the anthracnose Co-10 and angular leaf spot Phg-ON disease-resistance genes in the common bean cultivar Ouro Negro

Anthracnose (ANT) and angular leaf spot (ALS) are devastating diseases of common bean (Phaseolus vulgaris L.). Ouro Negro is a highly productive common bean cultivar, which contains the Co-10 and Phg-ON genes for resistance to ANT and ALS, respectively. In this study, we performed a genetic co-segregation analysis of resistance to ANT and ALS using an F₂ population from the Rudá × Ouro Negro cross and the F_2:3 families from the AND 277 × Ouro Negro cross. Ouro Negro is resistant to races 7 and 73 of the ANT and race 63-39 of the ALS pathogens. Conversely, cultivars AND 277 and Rudá are susceptible to races 7 and 73 of ANT, respectively. Both cultivars are susceptible to race 63-39 of ALS. Co-segregation analysis revealed that Co-10 and Phg-ON were inherited together, conferring resistance to races 7 and 73 of ANT and race 63-39 of ALS. The Co-10 and Phg-ON genes were co-segregated and were tightly linked at a distance of 0.0 cM on chromosome Pv04. The molecular marker g2303 was linked to Co-10 and Phg-ON at a distance of 0.0 cM. Because of their physical linkage in a cis configuration, the Co-10 and Phg-ON resistance alleles are inherited together and can be monitored with great efficiency using g2303. The close linkage between the Co-10 and Phg-ON genes and prior evidence are consistent with the existence of a resistance gene cluster at one end of chromosome Pv04, which also contains the Co-3 locus and ANT resistance quantitative trait loci. These results will be very useful for breeding programs aimed at developing bean cultivars with ANT and ALS resistance using marker-assisted selection.     

Pathogenic Diversity in and Sources of Resistance to Uromyces appendiculatus in Southern Africa

The reaction of the first (1983) common bean international differential set and other germplasm to 248 single pustule isolates of the rust fungus Uromyces appendiculatus, collected from various southern African countries, was evaluated. Eleven of the most important isolates were re‐purified and re‐inoculated, this time also on the second (2002) revised and smaller international differential set. The 248 isolates could be grouped into 44 race‐groups. These were subjected to principal coordinates analysis (PCoA). A second PCoA was carried out using 25 of the most important of the 44, together with 34 African races reported by previous authors. Isolates were generally avirulent on accessions with the resistance genes Ur‐3+, ‐5 or ‐11, as well as Compuesto Negro Chimaltenango (CNC) and A 286, all small seeded, and the most useful sources were accessions carrying both Ur‐3 and Ur‐11, for instance BelMiNeb‐RMR‐7, BelDakMi‐RMR‐14 and ‐18. Isolates were generally virulent on large seeded accessions (with, among others Ur‐4, ‐6 or ‐9), reflecting the preference for large seeded beans in southern Africa and co‐evolution of host and pathogen. No large seeded accessions showed broad resistance. The least susceptible was Plant Introduction 260418, which rated resistant to moderately susceptible to the 11 races. These observations were confirmed by field ratings on the same accessions over multiple seasons. According to the PCoA, which proved useful for the identification of differentiating accessions, southern African isolates fell into three main clusters, for which Redlands Pioneer and the South Africa cultivar Teebus were the most discriminating differentials. Other accessions that showed particularly useful differentiating ability were Olathe and 51051. Of these, only Redlands Pioneer has been included in the 2002 differential set. The PCoA grouping of the African races was similar to that of the southern African race‐groups.     

Molecular markers linked to white rust resistance in mustard Brassica juncea

 White rust, caused by Albugo candida (Pers.) Kuntze, is an economically important disease of Brassica juncea (L.) Czern. and Coss mustard, particularly in India. The most efficient and cost-effective way of protecting mustard plants from white rust disease is through genetic resistance. The objective of this study was to identify RAPD markers for white rust resistance in an F₁-derived doubled-haploid (DH) population originating from a cross between white rust-susceptible and white rust-resistant breeding lines of B. juncea from the canola-quality B. juncea breeding project of the Agriculture and Agri-Food Canada-Saskatoon Research Centre. The DH population was used to screen for RAPD markers associated with white rust resistance/susceptibility using bulked segregant analysis. Two markers, WR2 and WR3, linked to white rust resistance, flanked the resistance locus Ac2 ₁ and were highly effective in identifying the presence or absence of the resistance gene in the DH population. These two markers were shown to be specific to the Russian source of white rust resistance utilized in this project. It is concluded that the availability of these RAPD markers will enhance the breeding for white rust resistance in B. juncea. Received: 17 December 1997 / Accepted: 7 April 1998     

Marker-assisted selection for two rust resistance genes in sunflower

In this study we report on the identification of molecular markers, OX20₆₀₀ and OO04₉₅₀, linked to the geneR _Adv in the proprietary inbred line P2. This gene confers resistance to most of the pathotypes of Puccinia helianthi identified in Australia. Analysis indicates these RAPD markers are linked to the resistance locus at 0.0 cM and 11 cM respectively. SCAR markers SCX20₆₀₀ and SCO04₉₅₀ derived from these two RAPD markers, and SCT06₉₅₀ derived from a previously reported RAPD marker linked at 4.5 cM from the R ₁ rust resistance gene were developed. SCX20₆₀₀ and SCO04₉₅₀ were linked at similar distances from their resistance locus as the RAPD markers. SCTO6₉₅₀ co-segregated completely with rust resistance. The robustness of the R ₁ SCAR marker was demonstrated through the amplification of the marker in a diverse range of sunflower germplasm considered to possess the R ₁ gene. The SCAR markers forR _Adv were not amplified in the sunflower rust differential set thereby supporting the contention that this is a novel resistance gene. They did amplify in a number of proprietary lines closely related to the line P2. This locus is under further investigation as it will be useful in our attempts to use molecular-assisted breeding to produce durable resistance in sunflower to P. helianthi.     

Development of RAPD and SCAR markers linked to the Russian wheat aphid resistance gene Dn2 in wheat

 RAPD (random amplified polymorphic DNA) analysis was used to identify molecular markers linked to the Dn2 gene conferring resistance to the Russian wheat aphid (Diuraphis noxia Mordvilko). A set of near-isogenic lines (NILs) was screened with 300 RAPD primers for polymorphisms linked to the Dn2 gene. A total of 2700 RAPD loci were screened for linkage to the resistance locus. Four polymorphic RAPD fragments, two in coupling phase and two in repulsion phase, were identified as putative RAPD markers for the Dn2 gene. Segregation analysis of these markers in an F₂ population segregating for the resistance gene revealed that all four markers were closely linked to the Dn2 locus. Linkage distances ranged from 3.3 cM to 4.4 cM. Southern analysis of the RAPD products using the cloned RAPD markers as probes confirmed the homology of the RAPD amplification products. The coupling-phase marker OPB10_880c and the repulsion-phase marker OPN1_400r were converted to sequence characterized amplified region (SCAR) markers. SCAR analysis of the F₂ population and other resistant and susceptible South African wheat cultivars corroborated the observed linkage of the RAPD markers to the Dn2 resistance locus. These markers will be useful for marker-assisted selection of the Dn2 gene for resistance breeding and gene pyramiding. Received: 1 July 1997 / Accepted: 20 October 1997     

An RGA – like marker detects all known Lr21 leaf rust resistance gene family members in Aegilops tauschii and wheat

Leaf rust is one of the most important diseases of wheat worldwide, particularly in the Great Plains region of the USA. One long-term strategy for the control of this disease may be through durable genetic resistance by gene pyramiding. An important step in this strategy is identifying molecular markers linked to different leaf rust-resistance genes. Here we report the molecular tagging of a leaf rust-resistance gene that may have the potential for durable resistance through further genetic manipulation and gene pyramiding. Lr39 was previously designated for a leaf rust-resistance gene introgressed from Aegilops tauschii accession TA1675 into the common wheat germplasm WGRC2. Lr40 was designated for a gene derived from Ae. tauschii accession TA1649 and is present in germplasm WGRC7. These genes are now believed to be allelic to Lr21, which was transferred to wheat from a different accession of Ae. tauschii. Molecular mapping of Lr39 and Lr40 indicates that both genes come from TA1649. WGRC2 and WRGC7 also have a similar infection type against rust culture PRTUS6. We suggest the designation of the gene in WGRC2 should be changed to Lr40. RFLP marker KSUD14 (locus Xksud14) was found 0.2-cM proximal to Lr40 in a WGRC2/Wichita F₂ population (218 individuals), and co-segregated with the gene in a WGRC7/ Wichita F₂ population (165 individuals). A PCR-based molecular marker developed from the sequence-tagged-site (STS) of Xksud14 was mapped to the same locus as the RFLP marker KSUD14 in both populations. KSUD14 has the structure of a resistance gene analog (RGA) including kinase2a and kinase3 domains similar to the Cre3 gene of wheat and the rust resistance gene Rp1-D of maize. When the PCR products amplified from KSU14 STS were cleaved with restriction enzyme MspI, an 885-bp fragment was found in WGRC2, WGRC7, the Lr21 near-isogenic line, and eight accessions of Ae. tauschii shown to have resistance gene alleles at the Lr21 locus. The KSUD14 PCR-based assay provides an excellent marker for Lr40 and Lr21 in diverse wheat breeding and wild Ae. tauschii populations. Received: 22 December 2000 / Accepted: 12 February 2001     

Development of wheat lines carrying stem rust resistance gene <Emphasis Type="Italic">Sr39</Emphasis> with reduced <Emphasis Type="Italic">Aegilops speltoides</Emphasis> chromatin and simple PCR markers for marker-assisted selection

The use of major resistance genes is a cost-effective strategy for preventing stem rust epidemics in wheat crops. The stem rust resistance gene Sr39 provides resistance to all currently known pathotypes of Puccinia graminis f. sp. tritici (Pgt) including Ug99 (TTKSK) and was introgressed together with leaf rust resistance gene Lr35 conferring adult plant resistance to P. triticina (Pt), into wheat from Aegilops speltoides. It has not been used extensively in wheat breeding because of the presumed but as yet undocumented negative agronomic effects associated with Ae. speltoides chromatin. This investigation reports the production of a set of recombinants with shortened Ae. speltoides segments through induction of homoeologous recombination between the wheat and the Ae. speltoides chromosome. Simple PCR-based DNA markers were developed for resistant and susceptible genotypes (Sr39#22r and Sr39#50s) and validated across a set of recombinant lines and wheat cultivars. These markers will facilitate the pyramiding of ameliorated sources of Sr39 with other stem rust resistance genes that are effective against the Pgt pathotype TTKSK and its variants.     

Molecular characterization of durum and common wheat recombinant lines carrying leaf rust resistance (Lr19) and yellow pigment (Y) genes from Lophopyrum ponticum

Chromosome 7E from Lophopyrum ponticum carries a valuable leaf rust resistant gene designated Lr19. This gene has not been widely used in common wheat breeding because of linkage with the yellow pigment gene Y. This gene tints flour yellow, reducing its appeal in bread making. However, a high level of yellow pigment is desirable in durum wheat breeding. We produced 97 recombinant chromosomes between L. ponticum transfer 7D.7E#1 and its wheat homoeologues, using the ph1b mutation that promotes homoeologous pairing. We characterized a subset of 37 of these lines with 11 molecular markers and evaluated their resistance to leaf rust and the abundance of yellow pigment. The Lr19 gene was mapped between loci Xwg420 and Xmwg2062, whereas Y was mapped distal to Xpsr687, the most distal marker on the long arm of chromosome 7. A short terminal 7EL segment translocated to 7A, including Lr19 and Y (line 1-23), has been transferred to durum wheat by backcrossing. The presence of this alien segment significantly increased the abundance of yellow pigment. The Lr19 also conferred resistance to a new durum leaf rust race from California and Mexico that is virulent on most durum wheat cultivars. The new durum lines with the recombinant 7E segment will be useful parents to increase yellow pigment and leaf rust resistance in durum wheat breeding programs. For the common wheat breeding programs, we selected the recombinant line 1-96, which has an interstitial 7E segment carrying Lr19 but not Y. This recombinant line can be used to improve leaf rust resistance without affecting flour color. The 7EL/7DL 1-96 recombinant chromosome did not show the meiotic self-elimination previously reported for a 7EL/7BL translocation.     

Molecular tagging of a novel rust resistance gene R 12 in sunflower (Helianthus annuus L.)

Sunflower production in North America has recently suffered economic losses in yield and seed quality from sunflower rust (Puccinia helianthi Schwein.) because of the increasing incidence and lack of resistance to new rust races. RHA 464, a newly released sunflower male fertility restorer line, is resistant to both of the most predominant and most virulent rust races identified in the Northern Great Plains of the USA. The gene conditioning rust resistance in RHA 464 originated from wild Helianthus annuus L., but has not been molecularly marked or determined to be independent from other rust loci. The objectives of this study are to identify molecular markers linked to the rust resistance gene and to investigate the allelism of this gene with the unmapped rust resistance genes present in HA-R6, HA-R8 and RHA 397. Virulence phenotypes of seedlings for the F₂ population and F_2:3 families suggested that a single dominant gene confers rust resistance in RHA 464, and this gene was designated as R ₁₂ . Bulked segregant analysis identified ten markers polymorphic between resistant and susceptible bulks. In subsequent genetic mapping, the ten markers covered 33.4 cM of genetic distance on linkage group 11 of sunflower. A co-dominant marker CRT275-11 is the closest marker distal to R ₁₂ with a genetic distance of 1.0 cM, while ZVG53, a dominant marker linked in the repulsion phase, is proximal to R ₁₂ with a genetic distance of 9.6 cM. The allelism test demonstrated that R ₁₂ is not allelic to the rust resistance genes in HA-R6, HA-R8 and RHA 397, and it is also not linked to any previously mapped rust resistance genes. Discovery of the R ₁₂ novel rust resistance locus in sunflower and associated markers will potentially support the molecular marker-assisted introgression and pyramiding of R ₁₂ into sunflower breeding lines.     

SCAR markers linked to the common bean rust resistance gene Ur-13

Rust in common bean (Phaseolus vulgaris L.) is caused by Uromyces appendiculatus Pers.:Pers. (Unger) which exhibits a high level of pathogenic diversity. Resistance to this disease is conditioned by a considerable number of genes. Pyramiding resistance genes is desirable and could be simplified by the use of molecular markers closely linked to the genes. The resistance gene Ur-13, present in the South African large seeded cultivar Kranskop, has been used extensively in the local breeding program. The purpose of this study was the development of a molecular marker linked to Ur-13. An F₂ population derived from a cross between Kranskop and a susceptible (South African) cultivar Bonus was used in combination with bulked segregant analysis utilizing the amplified fragment length polymorphism (AFLP) technique. Seven AFLP fragments linked significantly to the rust resistance and five were successfully converted to sequence characterized amplified region (SCAR) markers. The co-dominant SCAR markers derived from a 405 bp EAACMACC fragment, KB126, was located 1.6 cM from the gene. Two additional SCAR markers and one cleaved amplified polymorphic sequence marker were located further from the gene. The gene was mapped to linkage group B8 on the BAT 93/Jalo EEP 558 core map (chromosome 3).     

Validation and identification of molecular markers linked to the leaf rust resistance gene <Emphasis Type="Italic">Lr</Emphasis>28 in wheat

Leaf rust resistance gene Lr28 controls one of the important resistances in the Indian subcontinent against the most prevalent Puccinia triticina pathotype 77-5. Pyramiding Lr28 with other resistance genes would therefore, provide durable resistance against rust, a process that can be facilitated by DNA markers. A microsatellite marker wmc313 linked to Lr28 at a distance of 5.0 cM was identified in the population HD2329 × HW2037. The marker was validated in another population developed from WL711× CS + Lr28: 2D/2M 3/8 (acc. 2956) as well as in a few near- isogenic lines (NILs) carrying gene Lr28. Compared to the previously reported marker TPSCAR SCS421₅₇₀, wmc313 is more closely linked to Lr28. Both these markers flanking the gene should be useful in the deployment of Lr28 into the breeding program using marker-assisted selection allowing pyramiding with other effective genes to confer durable resistance.     

Inheritance and Mechanism of Resistance to Rice Stripe Disease in cv. Zhendao 88, a Chinese Rice Cultivar

Mechanisms of resistance to rice stripe disease in a Chinese rice cultivar (Oryza sativa L., cv. Zhendao 88) were determined, and molecular markers for the resistance gene were identified. Single tillers at the seedling stage were inoculated with Rice stripe virus (RSV) and its vector, the small brown planthopper (SBPH) Laodelphax striatellus Fallen, to test for non‐preference and antibiosis. The inheritance of resistance in the F₂ and F_{2 : 3} lines from the cross cvs Zhendao 88× Wuyujing No. 3 was also examined by single‐tiller inoculation. Cv. Zhendao 88 was highly resistant to RSV and weakly resistant to SBPH. The resistance gene was mapped by SSR and RAPD analyses to rice chromosome 11 within 4.7 cm of a SSR marker RM229 and a RAPD marker OPO11. Data and inheritance analysis indicated that rice stripe disease resistance in cv. Zhendao 88 was derived principally from resistance to RSV and controlled by a single dominant gene. Breeding for rice stripe resistance could be accelerated by using cv. Zhendao 88 as a resistant parent if the linked marker for virus resistance were used in a marker‐assisted progeny selection programme.     

Identification and validation of SSR markers linked to the stem rust resistance gene Sr6 on the short arm of chromosome 2D in wheat

The wheat stem rust resistance gene Sr6, present in several wheat cultivars, confers a high level of resistance against a wide range of races of Puccinia graminis f. sp. tritici. Resistance conferred by Sr6 is influenced by temperature, light intensity, and genetic background of the recipient genotype. Here, we report the identification and validation of molecular markers linked to Sr6 that can be used for the detection of this gene in wheat breeding programs. A mapping population of 136 F₂ plants and their F_2:3 families derived from a cross between near-isogenic lines, ‘Chinese Spring’ and ISr6-Ra, were screened for stem rust reaction in the seedling stage. Bulked segregant analysis (BSA) based on seedling tests was used to screen 418 SSR markers that covered the entire genome of wheat. Four markers, Xwmc453, Xcfd43, Xcfd77, and Xgwm484, were mapped within a chromosome region that spanned 9.7 cM from Sr6. The closest markers, Xwmc453 and Xcfd43, were linked to Sr6 at a distance of 1.1 and 1.5 cM, respectively. The markers Xwmc453 and Xcfd43 amplified Sr6-specific marker alleles that were diagnostic for Sr6 in a diverse set of 46 wheat accessions and breeding lines developed and/or collected in Australia, Canada, China, Egypt, Ethiopia, Kenya, Mexico, South Africa, and USA. These markers can now be used for marker-assisted selection of Sr6 and for pyramiding it with other stem rust resistance genes.     

Identification and potential use of RAPD markers linked to Yam mosaic virus resistance in white yam (Dioscorea rotundatd)

Resistance to Yam mosaic virus (YMV) in tetraploid white yam (Dioscorea rotundatd) is inherited differentially as a dominant and recessive character. Elite D. rotundata breeding lines with durable resistance to YMV can be developed by pyramiding major dominant and recessive genes using marker‐assisted selection (MAS). The tetraploid breeding line, TDr 89/01444, is a source of dominant genetic resistance to yam mosaic disease. Bulked segregant analysis was used to search for random amplified polymorphic DNA (RAPD) markers linked to YMV resistance in F₁ progeny derived from a cross between TDr 89/01444 and the susceptible female parent, TDr 87/00571. The F₁ progeny segregated 1:1 (resistantsusceptible) when inoculated with a Nigerian isolate of YMV, confirming that resistance to YMV in TDr 89/01444 was dominantly inherited. A single locus that contributes to YMV resistance in TDr 89/01444 was identified and tentatively named Ymv‐1. Two RAPD markers closely linked in coupling phase with Ymv‐1 were identified, both of which were mapped on the same linkage group: OPW18₈₅₀ (3.0 centiMorgans [cM]) and OPX15₈₅₀ (2.0 cM). Both markers successfully identified Ymv‐1 in resistant genotypes among 12 D. rotundata varieties and in resistant F1 individuals from the cross TDr 93–1 × TDr 877 00211, indicating their potential for use in marker‐assisted selection. OPW18₈₅₀ and OPX15₈₅₀ are the first DNA markers for YMV resistance and represent a starting point in the use of molecular markers to assist breeding for resistance to YMV.     

Identification of RAPD markers for 11 Hessian fly resistance genes in wheat

 The pyramiding of genes that confer race- or biotype-specific resistance has become increasingly attractive as a breeding strategy now that DNA-based marker-assisted selection is feasible. Our objective here was to identify DNA markers closely linked to genes in wheat (Triticum aestivum L.) that condition resistance to Hessian fly [Mayetiola destructor (Say)]. We used a set of near-isogenic wheat lines, each carrying a resistance gene at 1 of 11 loci (H3, H5, H6, H9, H10, H11, H12, H13, H14, H16 or H17) and developed by backcrossing to the Hessian fly-susceptible wheat cultivar ‘Newton’. Using genomic DNA of these 11 lines and ‘Newton’, we have identified 18 randomly amplified polymorphic DNA (RAPD) markers linked to the 11 resistance genes. Seven of these markers were identified by denaturing gradient gel electrophoresis and the others by agarose gel electrophoresis. We confirmed linkage to the Hessian fly resistance loci by cosegregation analysis in F₂ populations of 50–120 plants for each different gene. Several of the DNA markers were used to determine the presence/absence of specific Hessian fly resistance genes in resistant wheat lines that have 1 or possibly multiple genes for resistance. The use of RAPD markers presents a valuable strategy for selection of single and combined Hessian fly resistance genes in wheat improvement. Received: 20 March 1996 / Accepted: 6 September 1996     

Molecular mapping of the rust resistance gene <Emphasis Type="Italic">R</Emphasis><Subscript><Emphasis Type="Italic">4</Emphasis></Subscript> to a large NBS-LRR cluster on linkage group 13 of sunflower

Rust is a serious fungal disease in the sunflower growing areas worldwide with increasing importance in North America in recent years. Several genes conferring resistance to rust have been identified in sunflower, but few of them have been genetically mapped and linked to molecular markers. The rust resistance gene R ₄ in the germplasm line HA-R3 was derived from an Argentinean open-pollinated variety and is still one of most effective genes. The objectives of this study were to determine the chromosome location of the R ₄ gene and the allelic relationship of R ₄ with the R _adv rust resistance gene. A total of 63 DNA markers previously mapped to linkage group (LG) 13 were used to screen for polymorphisms between two parental lines HA 89 and HA-R3. A genetic map of LG 13 was constructed with 21 markers, resulting in a total map length of 93.8 cM and an average distance of 4.5 cM between markers. Two markers, ZVG61 and ORS581, flanked the R ₄ gene at 2.1 and 0.8 cM, respectively, and were located on the lower end of LG 13 within a large NBS-LRR cluster identified previously. The PCR pattern generated by primer pair ZVG61 was unique in the HA-R3 line, compared to lines HA-R1, HA-R4, and HA-R5, which carry other R ₄ alleles. A SCAR marker linked to the rust resistance gene R _adv mapped to LG 13 at 13.9 cM from the R ₄ locus, indicating that R _adv is not an allele of the R ₄ locus. The markers tightly linked to the R ₄ gene will facilitate gene pyramiding for rust resistance breeding of sunflower.     

Molecular mapping of stripe rust resistance gene YrH921 in a wheat introgression line H921-11-1

Several novel stripe rust pathogen races emerging in the wheat-planting regions of China in recent years were virulent to a majority of the designated wheat seedling resistance genes. Therefore, it is of great significance to continuously select more new and valuable materials for enriching resistant sources diversity, pyramiding different excellent resistance genes and achieving durable resistance. In this study, a resistance gene, temporarily designated as YrH921, was identified from wheat–Psathyrostachys huashanica introgression line H921-11-1. Two hybrid populations, 160 F₂ plants and corresponding derived F_2:3 families, of the two parents about Mingxian169 as female and H921-11-1 as male, were used to evaluate stripe rust resistance in seedling stage and as a mapping population. At last, a genetic map which comprises of four simple sequence repeat (SSR) markers and six expressed sequence tag (EST) markers was constructed. YrH921 was located on the long arm of chromosome 5A. Two closely linked EST-STS markers (BF483937 and BF484913) were screened, and the genetic distance linked to YrH921 was 3.0 and 4.3 cM, respectively. There was great value in research and production if the two closest markers were effectively used for marker-assisted selection of YrH921 in breeding.     

A family of LRR sequences in the vicinity of the Co-2 locus for anthracnose resistance in Phaseolus vulgaris and its potential use in marker-assisted selection

 Molecular markers offer new opportunities for breeding for disease resistance. Resistance gene pyramiding in a single cultivar, as a strategy for durable resistance, can be facilitated by marker-assisted selection (MAS). A RAPD marker, ROH20⁴⁵⁰, linked to the Mesoamerican Co-2 anthracnose resistance gene, was previously transformed into a SCAR marker, SCH20. In the present paper we have further characterized the relevance of the SCH20 SCAR marker in different genetic backgrounds. Since this SCAR marker was found to be useful mainly in the Andean gene pool, we identified a new PCR-based marker (SCAreoli) for indirect scoring of the presence of the Co-2 gene. The SCAreoli SCAR marker is polymorphic in the Mesoamerican as well as in the Andean gene pool and should be useful in MAS. We also report that PvH20, the cloned sequence corresponding to the 450-bp RAPD marker ROH20⁴⁵⁰, contains six imperfect leucine-rich repeats, and reveals a family of related sequences in the vicinity of the Co-2 locus. These results are discussed in the context of the recent cloning of some plant resistance genes. Received: 26 June 1997 / Accepted: 13 October 1997     

Genetic and Molecular Mapping of Stripe Rust Resistance Genes in Wheat Cultivar Zhongliang 12

Stripe rust, caused by Puccinia striiformis f.sp. tritici (Pst), is one of the most widespread and destructive diseases of wheat worldwide. Resistance breeding is constantly pursued for decades to tackle the variations of prevalent Pst races. Zhongliang 12 has strong resistance to abiotic stresses, wide adaptability, higher resistance to stripe rust and excellent biological characteristics. To identify the resistance gene(s) against stripe rust, Zhongliang 12 was crossed with stripe rust susceptible genotype Mingxian 169, and F₁, F₂, F_2 : 3 and BC₁ progenies were tested with Chinese Pst race CYR30 and CYR31 in seedling stage in greenhouse. Zhongliang 12 possessed different dominant genes for resistance to each race. Linkage maps were constructed with four simple sequence repeats (SSRs) markers, Xwmc695, Xcfd20, Xbarc121 and Xbarc49, for the gene on wheat chromosome 7AL conferring resistance to CYR30 (temporarily designated as Yrzhong12‐1) with genetic distance ranging from 3.1 to 10.8 cM and four SSR markers, Xpsp3003, Xcfd2129, Xwmc673 and Xwmc51, for the gene on wheat chromosome 1AL conferring resistance to CYR31 (temporarily designated as Yrzhong12‐2) with genetic distance ranging from 3.9 cM to 9.3 cM. The molecular markers closely linked to each gene should be useful in marker‐assisted selection in breeding programmes for against stripe rust.