Development of SCAR markers linked to the gene Or5 conferring resistance to broomrape (Orobanche cumana Wallr.) in sunflower

A consensus molecular linkage map of 61.9 cM containing the Or5 gene, which confers resistance to race E of broomrape orobanche cumana, five SCAR markers (three dominant, two codominant) and one RAPD marker were identified based on segregation data scored from two F₂ populations of susceptible×resistant sunflower line crosses. Bulked segregant analysis was carried out to generate the five SCAR markers, while the single RAPD marker in the group was identified from 61 segregating RAPD markers that were directly screened on one of the two F₂ populations. The five SCAR markers, RTS05, RTS28, RTS40, RTS29 and RTS41, were significantly (LOD≥4.0) linked to the Or5 gene and mapped separately at 5.6, 13.6, 14.1, 21.4 and 39.4 cM from the Or5 locus on one side, while the RAPD marker, UBC120_660, was found at 22.5 cM (LOD=1.4) on the opposite side. These markers should facilitate the efficient transfer of the resistance gene among sunflower breeding lines. As the first report on molecular markers linked to a broomrape resistance gene, the present work provides a starting point to study other genes and to examine the hypothesis of the clustering of broomrape resistance genes in sunflower. Received: 16 September 1998 / Accepted: 22 June 1999     

Development of SCAR markers linked to male sterility and very high linoleic acid content in safflower

Practically no molecular tools have been developed so far for safflower (Carthamus tinctorius L.) breeding. The objective of the present research was to develop molecular markers for the closely linked genes Li, controlling very high linoleic acid content, and Ms, controlling nuclear male sterility (NMS). A mapping population of 162 individuals was developed from the NMS line CL1 (64–79% linoleic acid) and the line CR-142 (84–90%), and phenotyped in the F₂ and F₃ generations. Bulked segregant analysis with random amplified polymorphic (RAPD) markers revealed linkage of five RAPD bands to the Li and Ms genes. RAPD fragments were converted into sequence-characterized amplified region (SCAR) markers. A linkage map including the five SCAR markers and the Li and Ms genes was constructed. SCAR markers flanked both loci at minimum distances of 15.7 cM from the Li locus and 3.7 cM from the Ms locus. These are the first molecular markers developed for trait selection in safflower.     

Identification and mapping on chromosome 9 of RAPD markers linked to Sw-5 in tomato by bulked segregant analysis

Bulked segregant analysis was used to identify random amplified polymorphic DNA (RAPD) markers linked to the Sw-5 gene for resistance to tomato spotted wilt virus (TSWV) in tomato. Using two pools of phenotyped individuals from one segregating population, we identified four RAPD markers linked to the gene of interest. Two of these appeared tightly linked to Sw-5, whereas another, linked in repulsion phase, enabled the identification of heterozygous and susceptible plants. After linkage analysis of an F₂ population, the RAPD markers were shown to be linked to Sw-5 within a distance of 10.5 cM. One of the RAPD markers close to Sw-5 was used to develop a SCAR (sequence characterized amplified region) marker. Another RAPD marker was stabilized into a pseudo-SCAR marker by enhancing the specificity of its primer sequence without cloning and sequencing. RAPD markers were mapped to chromosome 9 on the RFLP tomato map developed by Tanksley et al. (1992). The analysis of 13 F₃ families and eight BC₂ populations segregating for resistance to TSWV confirmed the linkage of the RAPD markers found. These markers are presently being used in marker-assisted plant breeding.     

Molecular markers for rust and pyricularia leaf spot disease resistance in pearl millet

 Pearl millet [Pennisetum glaucum (L.) R.Br.] is a warm-season grass used for food, feed, fodder and forage, primarily in countries of Africa and India but grown around the world. The two most-destructive diseases to pearl millet in the United States are rust (caused by Puccinia substriata var. indica) and pyricularia leaf spot (caused by Pyricularia grisea). Genes for disease resistance to both pathogens have been transferred into agronomically acceptable forage and grain cultivars. A study was undertaken to identify molecular markers for three rust loci and one pyricularia resistance locus. Three segregating populations were screened for RAPDs using random decamer primers and for RFLPs using a core set of probes detecting single-copy markers on the pearl millet map. The rust resistance gene Rr ₁ from the pearl millet subspecies P. glaucum ssp. monodii was linked 8.5 cM from the RAPD OP-G8₃₅₀. The linkage of two RFLP markers, Xpsm108 (15.5 cM) and Xpsm174 (17.7 cM), placed the Rr ₁ gene on linkage-group 3 of the pearl millet map. Rust resistance genes from both Tift 89D₂ and ICMP 83506 were placed on linkage-group 4 by determining genetic linkage to the RFLP marker Xpsm716 (4.9 and 0.0 cM, respectively). Resistance in ICMP 83506 was also linked to the RFLP marker Xpsm306 (10.0 cM), while resistance in Tift 89D₂ was linked to RAPD markers OP-K19₃₅₀ (8.8 cM) and OP-O8₃₅₀ (19.6 cM). Fragments from OP-K19 and OP-O8 in the ICMP 83506 population, and Xpsm306 in the Tift 89D₂ population, were monomorphic. Only one RAPD marker (OP-D11₇₀₀, 5.6 cM) was linked to pyricularia leaf spot resistance. Attempts to detect polymorphisms with rice RFLP probes linked to rice blast resistance (Pyricularia oryzae; syn=P. grisea) were unsuccessful. Received: 19 May 1997 / Accepted: 21 October 1997     

Genetics of resistance to ascochyta blight (Ascochyta lentis) of lentil and the identification of closely linked RAPD markers

 Foliar resistance to Ascochyta lentis is controlled at a single major locus by a dominant gene (AbR ₁ ) in the lentil accession ILL5588 (cv ‘Northfield’). Flanking RAPD markers that are closely linked to the resistance locus in coupling phase were identified by bulked segregant analysis. Out of 261 decanucleotide primers screened 7 produced a polymorphic marker that segregated with the resistance locus, and all markers were found to exist within a single linkage group. Five of the seven RAPD markers were within 30 cM of the resistance locus. Log likelihood analysis for detecting QTL associated with the foliar resistance revealed that a single narrow peak accounted for almost 90% of the variance of resistance between the bulks. Preliminary mapping in an F₃ population revealed that the closest flanking markers were approximately 6 and 14 centiMorgans (cM) away from the resistance locus. These markers should be useful for the discrimination of resistant germplasm through marker-assisted selection in future breeding programmes and represent the first essential step towards the map-based cloning of this resistance gene. Received: 18 December 1997 / Accepted: 9 June 1998     

Identification of RAPD markers linked to a locus involved in quantitative resistance to TYLCV in tomato by bulked segregant analysis

 In tomato, Bulked Segregant Analysis was used to identify random amplified polymorphic DNA (RAPD) markers linked to a quantitative trait locus (QTL) involved in the resistance to the Tomato Yellow Leaf Curl Virus. F₄ lines were distributed into two pools, each consisting of the most resistant and of the most susceptible individuals, respectively. Both pools were screened using 600 random primers. Four RAPD markers were found to be linked to a QTL responsible for up to 27.7% of the resistance. These markers, localized in the same linkage group within a distance of 17.3 cM, were mapped to chromosome 6 on the tomato RFLP map. Received: 21 August 1996 / Accepted: 4 April 1997     

Development of markers linked to Diuraphisnoxia resistance in wheat using a novel PCR-RFLP approach

Through random amplified polymorphic DNA (RAPD) analysis we identified a putative marker linked to the Dn5 resistance gene. This marker was converted to a more reliable sequence-characterised-amplified regions (SCAR) marker. The initial SCAR marker amplified the correct amplification product but failed to discern between the susceptible and resistant individuals. Hence, it was utilised to sequence the internal fragment. All nested primers designed from the internal sequences were also unable to produce any polymorphism between the susceptible and resistant cultivars. Restriction digests were then performed on these fragments, and the restriction enzyme EcoRI was able to discern between the susceptible and resistant F₂ individuals of the Dn5 population. This granted one marker amplified with the internal SCAR primer set OPF14₁₀₈₃ the ability to differentiate between parental individuals carrying the Dn5 genes. This marker was tested in a segregating F₂ population carrying the Dn5 resistance gene and proved able to differentiate between the segregating individuals. This marker may prove useful in marker assisted selection (MAS), although performing restriction digests may hamper the throughput of a high number of samples. Received: 4 August 1999 / Accepted: 27 August 1999     

Identification of molecular markers linked to the Yr15 stripe rust resistance gene of wheat originated in wild emmer wheat, Triticum dicoccoides

 The Yr15 gene of wheat confers resistance to the stripe rust pathogen Puccinia striiformis West., which is one of the most devastating diseases of wheat throughout the world. In the present study, molecular markers flanking the Yr15 gene of wheat have been identified using the near-isogenic-lines approach. RFLP screening of 76 probe-enzyme combinations revealed one polymorphic marker (Nor/TaqI) between the susceptible and the resistant lines. In addition, out of 340 RAPD primers tested, six produced polymorphic RAPD bands between the susceptible and the resistant lines. The genetic linkage of the polymorphic markers was tested on segregating F₂ population (123 plants) derived from crosses between stripe rust-susceptible Triticum durum wheat, cv D447, and a BC₃F₉ resistant line carrying Yr15 in a D447 background. A 2.8-kb fragment produced by the Nor RFLP probe and a 1420-bp PCR product generated by the RAPD primer OPB13 showed linkage, in coupling, with the Yr15 gene. Employing the standard maximum-likelihood technique it was found that the order OPB13 ₁₄₂₀ –Yr15–Nor1 on chromosome 1B appeared to be no less than 1000-times more probable than the closest alternative. The map distances between OPB13 ₁₄₂₀ –Yr15–Nor1 are 27.1 cM and 11.0 cM for the first and second intervals, respectively. The application of marker-assisted selection for the breeding of new wheat cultivars with the stripe rust resistance gene is discussed. Received: 27 February 1997/Accepted: 7 March 1997     

Molecular markers linked to the aluminium tolerance gene Alt1 in rye (Secale cereale L.)

 Rye has one of the most efficient group of genes for aluminium (Al) tolerance among cultivated species of Triticeae. This tolerance is controlled by at least two independent and dominant loci (Alt1 and Alt3) located on chromosomes 6RS and 4R. We used two pooled DNA samples, one of Al-tolerant individuals and another of Al-sensitive plants from one F₂ that segregated for the Alt1 locus. We also used two pooled DNA samples, one with genotypes 11 and another with genotypes 22 for the Lap1 locus (leucin aminopeptidase) from another F₂ progeny that segregated for this locus, located on the 6RS chromosome arm. We identified several RAPD markers associated with the pooled Al-tolerant plants and also with one of the bulks for the Lap1 locus. The RAPD fragments linked to Alt1 and Lap1 genes were transformed into SCAR markers to confirm their chromosomal location and linkage data. Two SCARs (ScR01 ₆₀₀ and ScB15 ₇₉₀₀ ) were closely linked to the Alt1 locus, ScR01 ₆₀₀ located 2.1 cM from Alt1 and ScB15 ₇₉₀ located 5.5 cM from Alt1, on the 6RS chromosome arm. These SCAR markers can aid in the transfer of Al tolerance genes into Al-sensitive germplasms. Received: 9 December 1997 / Accepted: 12 May 1998     

Construction of an RFLP linkage map for cultivated sunflower

 An RFLP linkage map was constructed for cultivated sunflower Helianthus annuus L., based on 271 loci detected by 232 cDNA probes. Ninety-three F₂ plants of a cross between inbred lines RHA 271 and HA 234 were used as the mapping population. These genetic markers plus a fertility restoration gene, Rf ₁, defined 20 linkage groups, covering 1164 cM of the sunflower genome. Of the 71 loci 202 had codominant genotypic segregation, with the rest showing dominant segregation. Thirty-two of the 232 probes gave multiple locus segregation. There were 39 clusters of tightly linked markers with 0 cM distance among loci. This map has an average marker-to-marker distance of 4.6 cM, with 11 markerless regions exceeding 20 cM. Received: 17 June 1997 / Accepted: 19 June 1997     

Identification and validation of molecular markers linked to the leaf rust resistance gene Lr19 in wheat

A leaf rust resistance gene Lr19 on the chromosome 7DL of wheat derived from Agropyron elongatum was tagged with random amplified polymorphic DNA (RAPD) and microsatellite markers. The F₂ population of 340 plants derived from a cross between the leaf rust resistant near-isogenic line (NIL) of Thatcher (Tc + Lr19) and leaf rust susceptible line Agra Local that segregated for dominant monogenic leaf rust resistance was utilized for generating the mapping population. The molecular markers were mapped in the F₂ derived F₃ homozygous population of 140 seedlings. Sixteen RAPD markers were identified as linked to the alien gene Lr19 among which eight were in a coupling phase linkage. Twelve RAPD markers co-segregated with Lr19 locus. Nine microsatellite markers located on the long arm of chromosome 7D were also mapped as linked to the gene Lr19, including 7 markers which co-segregated with Lr19 locus, thus generating a saturated region carrying 25 molecular markers linked to the gene Lr19 within 10.2 ± 0.062 cM on either side of the locus. Two RAPD markers S265₅₁₂ and S253₇₃₇ which flanked the locus Lr19 were converted to sequence characterized amplified region markers SCS265₅₁₂ and SCS253₇₃₆, respectively. The marker SCS265₅₁₂ was linked with Lr19 in a coupling phase and the marker SCS253₇₃₆ was linked in a repulsion phase, which when used together mimicked one co-dominant marker capable of distinguishing the heterozygous resistant seedlings from the homozygous resistant. The molecular markers were validated on NILs mostly in Thatcher background isogenic for 44 different Lr genes belonging to both native and alien origin. The validation for polymorphism in common leaf rust susceptible cultivars also confirmed the utility of these tightly linked markers to the gene Lr19 in marker-assisted selection.     

Genetic mapping in pea. 2. Identification of RAPD and SCAR markers linked to genes affecting plant architecture

 Random amplified polymorphic DNA (RAPD) markers linked to two morphological markers ( fa and det), three ramosus genes (rms2, rms3 and rms4) and two genes conferring flowering response to photoperiod in pea (sn, dne) were selected by bulk segregant analysis on F₂ populations. Two RAPD fragments were cloned and sequenced to generate the two SCAR markers V20 and S2 which are linked to rms3 and dne, respectively. All these genes, except rms2, were previously located on the pea classical linkage map. Rms2 mapped to linkage group IB which contains the afila gene. Precise genetic maps of the regions containing the genes were obtained and compared to the RAPD map generated from the recombinant inbred-lines population of the cross Térèse×K586. This cross was chosen because several mutants were obtained from cultivars Térèse and Torsdag (K586 was derived from Torsdag). This collection of isogenic lines was used for the construction of F₂ mapping populations in which polymorphic RAPD markers were already known and mapped. Moreover, the well-known problem in pea of variability in the linkage associations between crosses was avoided. This work contributes to the precise integration between the classical map and the molecular maps existing in pea. Received: 13 March 1998 / Accepted: 29 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.     

Characterization and fine mapping of <Emphasis Type="Italic">RppQ</Emphasis>, a resistance gene to southern corn rust in maize

Southern corn rust (SCR) is a fungal disease caused by Puccinia polysora Underw, which can infect maize and may result in substantial yield losses in maize production. The maize inbred line Qi319 carries the SCR resistance gene RppQ. In order to identify molecular markers linked to the RppQ gene, several techniques were utilized including random amplified polymorphic DNA (RAPD), simple sequence repeat (SSR), and amplified fragment length polymorphism (AFLP). In addition, sequence characterized amplified region (SCAR) techniques combined with bulked segregant analysis (BSA) were used. Seven RAPD markers, eight SSR markers, and sixty-three AFLP primer combinations amplified polymorphisms between two parents and two bulk populations. A large F₂ population was used for genetic analysis and for fine mapping of the RppQ gene region. One AFLP polymorphic band, M-CAA/E-AGC₃₂₄, was converted to a SCAR marker, MA7, which was mapped to a position 0.46 cM from RppQ. Finally, the RppQ gene was mapped between the SCAR marker MA7 and the AFLP marker M-CCG/E-AGA₁₅₇ with distances of 0.46 and 1.71 cM, respectively.     

Identification of molecular markers for resistance to Septoria nodorum blotch in durum wheat

The development of Septoria nodorum blotch-resistant cultivars has become a high priority objective for durum wheat breeding programs. Marker-assisted selection enables breeders to improve selection efficiency. In order to develop markers for resistance to Septoria nodorum blotch, a set of F₅ recombinant inbred lines, derived from the crosses Sceptre/3–6, Sceptre/S9–10 and Sceptre/S12–1, was developed based on the F₂-derived family method. Two RAPD markers, designated UBC521₆₅₀ and RC37₅₁₀, were detected by bulked segregant analysis and located approximately 15 and 13.1 centiMorgans (cM) from the resistance gene snbTM, respectively. A SCAR marker was also successfully developed for marker-assisted selection in breeding programs based on the sequence of the RAPD marker UBC521₆₅₀. This is the first report of DNA-based markers linked to resistance for Septoria nodorum blotch in durum wheat. Received: 8 March 2000 / Accepted: 25 June 2000     

Molecular mapping of <Emphasis Type="Italic">Stb1</Emphasis>, a potentially durable gene for resistance to septoria tritici blotch in wheat

Septoria tritici blotch (STB), caused by the ascomycete Mycosphaerella graminicola (anamorph Septoria tritici), was the most destructive disease of wheat in Indiana and adjacent states before deployment of the resistance gene Stb1 during the early 1970s. Since then, Stb1 has provided durable protection against STB in widely grown wheat cultivars. However, its chromosomal location and allelic relationships to most other STB genes are not known, so the molecular mapping of Stb1 is of great interest. Genetic analyses and molecular mapping were performed for two mapping populations. A total of 148 F₁ plants (mapping population I) were derived from a three-way cross between the resistant line P881072-75-1 and the susceptible lines P881072-75-2 and Monon, and 106 F₆ recombinant-inbred lines (mapping population II) were developed from a cross between the resistant line 72626E2-12-9-1 and the susceptible cultivar Arthur. Bulked-segregant analysis with random amplified polymorphic DNA (RAPD), amplified fragment length polymorphism (AFLP), and microsatellite or simple-sequence repeat (SSR) markers was conducted to identify those that were putatively linked to the Stb1 gene. Segregation analyses confirmed that a single dominant gene controls the resistance to M. graminicola in each mapping population. Two RAPD markers, G7₁₂₀₀ and H19₅₂₀, were tightly linked to Stb1 in wheat line P881072-75-1 at distances of less than 0.68 cM and 1.4 cM, respectively. In mapping population II, the most closely linked marker was SSR Xbarc74, which was 2.8 cM proximal to Stb1 on chromosome 5BL. Microsatellite loci Xgwm335 and Xgwm213 also were proximal to Stb1 at distances of 7.4 cM and 8.3 cM, respectively. The flanking AFLP marker, EcoRI-AGC/MseI-CTA-1, was 8.4 cM distal to Stb1. The two RAPD markers, G7₁₂₀₀ and H19₅₂₀, and AFLP EcoRI-AGC/MseI-CTA-1, were cloned and sequenced for conversion into sequence-characterized amplified region (SCAR) markers. Only RAPD allele H19₅₂₀ could be converted successfully, and none of the SCAR markers was diagnostic for the Stb1 locus. Analysis of SSR and the original RAPD primers on several 5BL deletion stocks positioned the Stb1 locus in the region delineated by chromosome breakpoints at fraction lengths 0.59 and 0.75. The molecular markers tightly linked to Stb1 could be useful for marker-assisted selection and for pyramiding of Stb1 with other genes for resistance to M. graminicola in wheat.     

A consensus map for <Emphasis Type="Italic">Cucurbita pepo</Emphasis>

Using random amplified polymorphic DNA (RAPD), amplified fragment length polymorphism (AFLP), simple sequence repeats (SSR), and morphological traits, the first genetic maps for Cucurbita pepo (2n=2x=40) were constructed and compared. The two mapping populations consisted of 92 F₂ individuals each. One map was developed from a cross between an oil-seed pumpkin breeding line and a zucchini accession, into which genes for resistance to Zucchini Yellow Mosaic Virus (ZYMV) from a related species, C. moschata, had been introgressed. The other map was developed from a cross between an oil-seed pumpkin and a crookneck variety. A total of 332 and 323 markers were mapped in the two populations. Markers were distributed in each map over 21 linkage groups and covered an average of 2,200 cM of the C. pepo genome. The two maps had 62 loci in common, which enabled identification of 14 homologous linkage groups. Polyacrylamide gel analyses allowed detection of a high number of markers suitable for mapping, 10% of which were co-dominant RAPD loci. In the Pumpkin-Zucchini population, bulked segregant analysis (BSA) identified seven markers less than 7 cM distant from the locus n, affecting lignification of the seed coat. One of these markers, linked to the recessive hull-less allele (AW11-420), was also found in the Pumpkin-Crookneck population, 4 cM from n. In the Pumpkin-Zucchini population, 24 RAPD markers, previously introduced into C. pepo from C. moschata, were mapped in two linkage groups (13 and 11 markers in LGpz1 and LGpz2, respectively), together with two sequence characterized amplified region (SCAR) markers linked to genes for resistance to ZYMV.     

RAPD and SCAR markers linked to the Ma1 root-knot nematode resistance gene in Myrobalan plum (Prunus cerasifera Ehr.)

 The Myrobalan plum (Prunus cerasifera) is a self-incompatible species in which the clones P.2175, P.1079 and P.2980 are highly resistant to all root-knot nematodes (RKN), Meloidogyne spp. Each clone bears a single major dominant gene, designated Ma1, Ma2 and Ma3 respectively, that controls a high and wide-spectrum resistance. Bulked segregant analysis (BSA) and random amplified polymorphic DNA (RAPD) analysis were both performed to detect markers linked to the Ma1 gene using three segregating progenies from P.2175 (Ma1 ma1) crossed by three host parents (ma1 ma1). Four dominant coupling-phase markers were identified from a total of 660 10-base primers tested. The resulting linkage map spans 14.7 cM and comprises three markers located on the same side of Ma1 and one marker located on the other side. The nearest markers (OPAL19₇₂₀ and OPA16₁₄₀₀) are located at 3.7 and 6.7 cM, respectively, on each side of the gene. Among the three markers that could be successfully converted into sequence characterized amplified region (SCAR) markers, two of them (SCAL19₆₉₀ and SCAN12₆₂₀) were scored as dominant markers whereas the third (SCAO19₇₇₀) failed to produce any polymorphism. SCAL19, and to a lesser extent SCAN12, can be used reliably in the marker-assisted selection of Prunus rootstocks. These markers are adequate to identify the Ma1 RKN resistance gene in intraspecific segregating progenies and will be suitable for the creation of interspecific rootstocks involving Myrobalan plum. Some of the RAPD and SCAR markers for Ma1 were also recovered in clones P.1079 and P.2980, but not in additional host clones, suggesting that Ma1, Ma2 and Ma3 are either allelic or at least closely linked. Received: 22 September 1998 / Accepted: 19 December 1998     

A genetic linkage map of cowpea (Vigna unguiculata) developed from a cross between two inbred, domesticated lines

 We have constructed a genetic linkage map within the cultivated gene pool of cowpea (2n=2x=22) from an F₈ recombinant inbred population (94 individuals) derived from a cross between the inbreds IT84S-2049 and 524B. These breeding lines, developed in Nigeria and California, show contrasting reactions against several pests and diseases and differ in several morphological traits. Parental lines were screened with 332 random RAPD decamers, 74 RFLP probes (bean, cowpea and mung bean genomic DNA clones), and 17 AFLP primer combinations. RAPD primers were twice as efficient as AFLP primers and RFLP probes in detecting polymorphisms in this cross. The map consists of 181 loci, comprising 133 RAPDs, 19 RFLPs, 25 AFLPs, three morphological/classical markers, and a biochemical marker (dehydrin). These markers identified 12 linkage groups spanning 972 cM with an average distance of 6.4 cM between markers. Linkage groups ranged from 3 to 257 cM in length and included from 2 to 41 markers, respectively. A gene for earliness was mapped on linkage group 2. Seed weight showed a significant association with a RAPD marker on linkage group 5. This map should facilitate the identification of markers that “tag” genes for pest and disease resistance and other traits in the cultivated gene pool of cowpea. Received: 16 September 1996 / Accepted: 25 April 1997     

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.