Identification of SCAR markers linked to <Emphasis Type="Italic">or</Emphasis>, a gene inducing beta-carotene accumulation in Chinese cabbage

The or mutation in Chinese cabbage (Brassica rapa L. ssp. pekinensis) is a recessive, single-locus mutation that causes the head leaves of the plant to accumulate carotenoids and turn orange. In China, considerable attention has been focused in recent years on breeding the variety with orange head leaves. In this study, sequence-characterized amplified region (SCAR) markers linked to the or gene were identified based on random amplified polymorphic DNA (RAPD) and amplified fragment length polymorphism (AFLP) by performing a bulked segregant analysis (BSA) using a doubled haploid (DH) population derived from the F₁ cross between 91-112 (white head leaves) and T12-19 (orange head leaves) via microspore culture. Two RAPD markers—OPB01-845 and OPAX18-656—and 1 AFLP marker, namely, P67M54-172, were identified to be linked to the or gene, and they were successfully converted into the SCAR markers SCR-845, SCOR204, and SCOR127, respectively. In a linkage analysis, these 3 SCAR markers and 2 previously published simple sequence repeat markers, namely, BRMS-51 and Ni4D09 (located on R9 linkage group), were mapped to the same linkage group with the or gene at a LOD score of 6.0, indicating that the or gene should be located on the linkage group R9 of the A genome. In addition, accuracies of 92%, 90%, and 89.1% were obtained when 110 different inbred breeding lines of Chinese cabbage were used for investigation with these 3 SCAR markers, indicating that these makers could be used in marker-assisted selection in orange head leaf breeding programs for Chinese cabbage.     

Identification of AFLP and SCAR markers linked to the male fertility restorer gene of <Emphasis Type="Italic">pol</Emphasis> CMS (<Emphasis Type="Italic">Brassica napus</Emphasis> L.)

The pol cytoplasmic male-sterility system has been widely used as a component for utilization of heterosis in Brassica napus and offers an attractive system for study on nuclear–mitochondrial interactions in plants. Genetic analyses have indicated that one dominant gene, Rfp, was required to achieve complete fertility restoration. As a first step toward cloning of this restorer gene, we attempted molecular mapping of the Rfp locus using the amplified fragment length polymorphism (AFLP) technique combined with bulked segregant analysis (BSA) method. A BC₁ population segregating for Rfp gene was used for tagging. From the survey of 1,024 AFLP primer combinations, 13 linked AFLP markers were obtained and five of them were successfully converted into sequence characterized amplified region (SCAR) markers. A population of 193 plants was screened using these markers and the closest AFLP markers flanking Rfp were at the distances of 2.0 and 5.3 cM away, respectively. Further the AFLP or SCAR markers linked to the Rfp gene were integrated to one doubled-haploid (DH) population derived from the cross Quantum × No.2127-17 available in our laboratory, and Rfp gene was mapped on N18, which was the same as the previous report. These molecular markers will facilitate the marker-assisted selection (MAS) of pol CMS restorer lines.     

Bolting resistant breeding of Chinese cabbage. 1. Flower induction of late bolting variety without chilling treatment

Summary When a local slow bolting variety Osaka Shirona Bansei (Brassica rapa L. ssp. pekinensis, syn. B. campestris L. ssp. pekinensis) was grown in a phytotron (25°C, 16 hours day length without chilling treatment), one third of the plants bolted and flowered. In order to clarify the different flowering responses in the variety, a progeny line (FNC) of the flowering plants was chilled for 4 different periods (0, 22, 36 and 53 days) in a chamber of 2 7°C, then transplanted to three different conditions, i.e. PHY: 25–20°C day and night temperatures, 16 hours day length, GHL: 10 25°C, 16 hours day length with supplementary light and GHN: 10 25°C, natural day length (10 15 hours). In PHY, FNC bolted and flowered with almost the same leaf numbers in all 4 different chilling treatments. This means that FNC has very low sensitivity and no requirement to low temperature for its reproductive growth. In GHN (short day length), FNC bolted very slowly. Then the bolting and flowering of FNC were promoted by both long day length and high temperature. The newly found bolting characteristics of Osaka Shirona Bansei could be applied to breed unique slow bolting Chinese cabbage (B. rapa L. ssp. pekinensis) which might be non-sensitive to low temperature and its bolting and flowering would be induced with the combination of long day length and high temperature. Using the unique variety, it might be also possible to establish a new cropping type of Chinese cabbage (late autumn sowing, spring harvest).Abbreviations PHY Phytotron, long day and high temperature condition - GHL Greenhouse, long day and medium temperature condition - GHN Greenhouse, natural (short) day and medium temperature condition - FNC A progeny line of Osaka Shirona Bansei which flowered with no chilling treatment - FC A progeny line of Osaka Shirona Bansei which flowered with chilling treatment     

Identification of microsatellite markers linked to the blast resistance gene <Emphasis Type="Italic">Pi-1(t)</Emphasis> in rice

The present work was conducted to identify microsatellite markers linked to the rice blast resistance gene Pi-1(t) for a marker-assisted selection program. Twenty-four primer pairs corresponding to 19 microsatellite loci were selected from the Gramene database (www. gramene.org) considering their relative proximity to Pi-1(t) gene in the current rice genetic map. Progenitors and DNA bulks of resistant and susceptible families from F₃ segregating populations of a cross between the near-isogenic lines C101LAC (resistant) and C101A51 (susceptible) were used to identify polymorphic microsatellite markers associated to this gene through bulked segregant analysis. Putative molecular markers linked to the blast resistance gene Pi-1(t) were then used on the whole progeny for linkage analysis. Additionally, the diagnostic potential of the microsatellite markers associated to the resistance gene was also evaluated on 17 rice varieties planted in Latin America by amplification of the specific resistant alleles for the gene in each genotype. Comparing with greenhouse phenotypic evaluations for blast resistance, the usefulness of the highly linked microsatellite markers to identify resistant rice genotypes was evaluated. As expected, the phenotypic segregation in the F₃ generation agreed to the expected segregation ratio for a single gene model. Of the 24 microsatellite sequences tested, six resulted polymorphic and linked to the gene. Two markers (RM1233*I and RM224) mapped in the same position (0.0 cM) with the Pi-1(t) gene. Other three markers corresponding to the same genetic locus were located at 18.5 cM above the resistance gene, while another marker was positioned at 23.8 cM below the gene. Microsatellite analysis on elite rice varieties with different genetic background showed that all known sources of blast resistance included in this study carry the specific Pi-1(t) allele. Results are discussed considering the potential utility of the microsatellite markers found, for MAS in rice breeding programs aiming at developing rice varieties with durable blast resistance based on a combination of resistance genes. Centro Internactional de Agricultura Tropical (CIAT) institute where the research was carried out     

RAPD and SCAR markers for resistance to acochyta blight in lentil

Resistance to ascochyta blight of lentil (Lens culinaris Medikus),caused by the fungus Ascochyta lentis, is determined by a single recessive gene, ral ₂, in the lentil cultivar Indian head. Sixty F₂ individuals from a cross between Eston (susceptible) and Indian head (resistant) lentil were analyzed for the presence of random amplified polymorphic DNA (RAPD) markers linked to the ral ₂gene, using bulked segregant analysis (BSA). Out of 800 decanucleotide primers screened, two produced polymorphic markers that co-segregated with the resistance locus. These two RAPD markers, UBC227₁₂₉₀and OPD-10₈₇₀, flanked and were linked in repulsion phase to the gene ral ₂ at 12 cm and 16 cm, respectively. The RAPD fragments were converted to SCAR markers. The SCAR marker developed from UBC227₁₂₉₀ could not detect any polymorphism between the two parents or in the F₂. The SCAR marker developed from OPD-10₈₇₀ retained its polymorphism. The polymorphic RAPD marker UBC227₁₂₉₀ and the SCAR marker developed from OPD-10₈₇₀ can be used together in a marker assisted selection program for ascochyta blight resistance in lentil. This revised version was published online in July 2006 with corrections to the Cover Date.     

Construction of a linkage map and identification of DNA markers linked to Fom-1, a gene conferring resistance to Fusarium oxysporum f.sp. melonis race 2 in melon

Resistance to Fusarium oxysporum f.sp. melonis race 2 is conferred by a single dominant gene, Fom-1 in melon. Here, we identified DNA markers tightly linked to Fom-1 that could be used for marker assisted selection in breeding programs. First, we developed 125 F₂ plants derived from the cross between melon lines P11 (fom-1fom-1) and MR-1 (Fom-1Fom-1). Using the F₂ population, we constructed a linkage map including 14 SSR markers which had not been mapped previously. Fom-1 was confirmed to be allocated to linkage group 7. Then, we identified four AFLP markers using bulked segregant analysis. The AFLP marker TAG/GCC-470 was completely linked to Fom-1 and other three markers were mapped near Fom-1. TAG/GCC-470 and TCG/GGT-400 were respectively converted to STS and CAPS markers. Usefulness of DNA markers was confirmed in the analysis with several melon cultivars and lines.     

Tagging the juvenile locus in soybean [Glycine max (L.) Merr.] with molecular markers

Soybean cultivars carrying the `long juvenile trait' show a delayed flowering response under short day conditions. The incorporation of this character into genotypes of agronomic interest may allow a broader range of sowing dates and latitudes for a single cultivar adaptation. The objective of this work was to identify molecular markers linked to the juvenile locus in soybean. Experiments were carried out using two pairs of near isogenic lines(NILs) differing in the presence of the long juvenile trait, and RAPD markers. Four hundred primers were first screened to find polymorphism associated with the trait. Additional differences between NILs were sought by digesting the genomic DNA with five restriction enzymes. Polymorphic fragments detected between NILs were tested for linkage to the juvenile locus in the corresponding F₂ segregating populations. Marker bc357-HaeIII was linked (χ²L = 46.316) to the juvenile locus with an estimated recombination frequency of 0.13 ± 0.03in one of the genetic backgrounds studied. The fragment was cloned, sequenced and converted into a SCAR marker. Moreover,bc357-HaeIII was used as RFLP probe. Both, SCAR and RFLP generated markers linked to the juvenile locus in the two genetic backgrounds analysed. Results presented in this work can be utilised for both, the localisation of the gene associated with the character and for tagging the juvenile trait in soybean breeding programs. This revised version was published online in August 2006 with corrections to the Cover Date.     

Development of AFLP and derived CAPS markers for root-knot nematode resistance in cotton

Resistance to root-knot nematode (Meloidogyne incognita) is determined by a single major gene rkn1 in Gossypium hirsutum Acala NemX cotton. Bulked segregant analysis (BSA) combined with amplified fragment length polymorphism (AFLP) was used to identify molecular markers linked to rkn1. DNA pools from homozygous susceptible (S) and resistant (R) bulks of an F_2:3 originating from the intraspecific cross NemX × SJ-2 were screened with 128 EcoR1/Mse1 primer combinations. Putative AFLP markers were then screened with 60 F_2:7 RIL plants and four AFLP markers were found linked to rkn1. The linkage of AFLP markers to rkn1 was also confirmed in a F₂ population. The closest AFLP marker was converted to a cleaved amplified polymorphic sequence (CAPS) marker (designated GHACC1) by aligning the sequences from both susceptible and resistant parents. GHACC1 linkage to rkn1 was confirmed in the F₂ (1R:3S), F_2:7 RIL (1R:1S) and the backcross population SJ-2 × F₁ (NemX × SJ-2) (1 heterozygous: 1 homozygous). The four AFLP markers, GHACC1 plus two SSR markers (CIR316 and BNL1231) linked to rkn1 from previous work were mapped to intervals of 2.6–14.2 cM from the rkn1 locus, and the genomic region around rkn1 was spanned to about 28.2 cM in the F_2:7 population. The PCR-based GHACC1 and CIR316 markers were tested on 21 nematode resistant and susceptible cotton breeding lines and cultivars. GHACC1 was suitable for nematode resistance screening within G.␣hirsutum, but not G. barbadense, whereas CIR316 was useful in both species, indicating their␣potential for utilization in marker-assisted selection.     

Identification of RAPD markers linked to the rust (<Emphasis Type="Italic">Uromyces fabae</Emphasis>) resistance gene in pea (<Emphasis Type="Italic">Pisum sativum</Emphasis>)

Summary Two RAPD markers linked to gene for resistance (assayed as pustule number cm⁻² leaf area) to rust [Uromyces fabae (Pers.) de Bary] in pea (Pisum sativum L.) were identified using a mapping population of 31 BC₁F₁ [HUVP 1 (HUVP 1 × FC 1] plants, FC 1 being the resistant parent. The analysis of genetics of rust resistance was based on the parents, F₁, F₂, BC₁F₁ and BC₁F₂ generations. Rust resistance in pea is of non-hypersensitive type; it appeared to be governed by a single partially dominant gene for which symbol Ruf is proposed. Further, this trait seems to be affected by some polygenes in addition to the proposed oligogene Ruf. A total of 614 decamer primers were used to survey the parental polymorphism with regard to DNA amplification by polymerase chain reaction. The primers that amplified polymorphic bands present in the resistant parent (FC 1) were used for bulked segregant analysis. Those markers that amplified consistently and differentially in the resistant and susceptible bulks were separately tested with the 31 BC₁F₁ individuals. Two RAPD makers, viz., SC10-82₃₆₀ (primer, GCCGTGAAGT), and SCRI-71₁₀₀₀ (primer, GTGGCGTAGT), flanking the rust resistance gene (Ruf) with a distance of 10.8 cM (0.097 rF and LOD of 5.05) and 24.5 cM (0.194 rF and a LOD of 2.72), respectively, were identified. These RAPD markers were not close enough to Ruf to allow a dependable maker-assisted selection for rust resistance. However, if the two makers flanking Ruf were used together, the effectiveness of MAS would be improved considerably.     

RFLP/AFLP mapping of a brown planthopper (Nilaparvata lugens Stål) resistance gene Bph1 in rice

We have constructed a linkage map of the rice brown planthopper (BPH)resistance gene, Bph1. RFLP and AFLP markers were selected by thebulked segregant analysis and used in the mapping study of 262 F₂sthat were derived from a cross of `Tsukushibare', a susceptible japonica cultivar, and `Norin-PL3', an authentic japonicaBph1-introgression line. Twenty markers were mapped within a 28.9-cMregion containing the Bph1 locus on the long arm of rice chromosome12. Combining the result of segregation analysis of BPH resistance by themass seedling test and that of the markers, the Bph1 locus wasmapped within a 5.8-cM region between two flanking markers. The closestAFLP markers, em5814N and em2802N, was at 2.7 cM proximal to theBph1 locus. Together with the previously constructed high-resolutionmap of bph2 locating the locus at ca. 10 cM proximal to the Bph1 locus, this improved version of the linkage map would facilitatepyramiding these two important BPH resistance genes.     

Identification of RAPD and SCAR markers linked to northern leaf blight resistance in waxy corn (Zea mays var. ceratina)

Exserohilum turcicum causes northern corn leaf blight (NCLB), an important disease occurring in maize producing areas throughout the world. Currently, the development of cultivars resistant to E. turcicum seems to be the most efficient method to control NCLB damage. Marker-assisted selection (MAS) enables breeders to improve selection efficiency. The objective of this work was to identify random amplified polymorphic DNA (RAPD) and sequence characterized amplified region (SCAR) markers associated with NCLB resistance. Bulked segregant analysis (BSA) was used to search for RAPD markers linked to NCLB resistance genes, using F₂ segregating population obtained by crossing a susceptible inbred ‘209W’ line with a resistant inbred ‘241W’ line. Two hundred and twenty-two decamer primers were screened to identify four RAPD markers: OPA07₅₂₁, OPA16₄₅₇, OPB09₅₂₀, and OPE20₅₃₆ linked to NCLB resistance phenotype. These markers were converted into dominant SCAR markers: SCA07₄₉₆, SCA16₄₂₀, SCB09₄₆₄, and SCE20₄₂₉, respectively. The RAPD and SCAR markers were developed successfully to identify NCLB resistant genotypes in segregating progenies carrying NCLB resistant traits. Thus, the markers identified in this study should be applicable for MAS for the NCLB resistance in waxy corn breeding programs.     

Molecular mapping of a gene conferring resistance to Aphanomyces root rot (black root) in sugar beet (<Emphasis Type="Italic">Beta vulgaris</Emphasis> L.)

Caused by Aphanomyces cochlioides Drechsler, Aphanomyces root rot is a serious disease of sugar beet (Beta vulgaris L.), for which sources of resistance are scarce. To identify the segregation pattern of the rare resistance trait found in Japanese sugar beet line ‘NK-310mm-O’, F₁ and BC₁F₂ seedings, drawn from a cross between ‘NK-310mm-O’ and susceptible line ‘NK-184mm-O’, were inoculated with zoospores and their survival evaluated in the greenhouse. Resistance segregation followed was that of a single dominant gene, which was designated Acr1 (Aphanomyces cochlioides resistance 1). Molecular markers tightly linked to Acr1 were identified by bulked segregant analysis of two BC₁F₂ populations. Fourteen AFLP markers linked to Acr1 were identified, the closest located within ±3.3 cM. Three F₅ lines and two BC₂F₁ lines, selected on the basis of their Acr1-AFLP markers, were tested for their resistance to Aphanomyces root rot in a highly infested field. Results indicated that Acr1 conferred significant resistance to Aphanomyces root rot at the field level. Based on its linkage with CAPS marker tk, a representative marker for chromosome III, Acr1 was located on this chromosome. The clear linkage between tk and Rhizomania resistance trait Rz1, suggests the clustering of major disease resistance genes on chromosome III.     

Determination of the genetic variation in the effect of temperature and daylength on bolting of Brassica campestris L.

Summary Effects of temperature and daylength on the bolting of a number of B. campestris accessions were investigated both in the open and in the IVT phytotron. From the results it was concluded that low temperature and genotype are the predominant factors with respect to bolting. Daylength has rather limited influence. One cultivar bolted more than 12 weeks earlier at 10 and 14°C than at 18°C. On the other hand some cultivars did not require vernalization at all.At 14°C and short daylength, depending on genotype, the period of time between sowing and 50% bolting ranged from 8 to 30 weeks. At this temperature the stimulating effect of long day (24 h), depending again on the genotype, ranged from 0 to 4 weeks. The genotypes most resistant to bolting appeared to be the stubble turnips (B. campestris ssp. rapa).In terms of seed(ling) vernalization at 5°C the cold requirement ranged from 0 to more than 3 weeks, depending on the genotype. The required vernalization periods at 5°C can be used as a criterion in screening for resistance to bolting.     

Development of molecular markers linked to the <Emphasis Type="Italic">Fom-1</Emphasis> locus for resistance to Fusarium race 2 in melon

Fusarium wilt, caused by Fusarium oxysporum f. sp. melonis (F.o.m), is a worldwide soil-borne disease of melon (Cucumis melo L.). The most effective control measure available is the use of resistant varieties. Resistance to races 0 and 2 of this fungal pathogen is conditioned by the dominant gene Fom-1. An F₂ population derived from the ‘Charentais-Fom1’ × ‘TRG-1551’ cross was used in combination with bulked segregant analysis utilizing the random amplified polymorphic DNA (RAPD) markers, in order to develop molecular markers linked to the locus Fom-1. Four hundred decamer primers were screened to identify three RAPD markers (B17₆₄₉, V01₅₇₈, and V06₁₀₉₂) linked to Fom-1 locus. Fragments amplified by primers B17₆₄₉ and V01₅₇₈ were linked in coupling phase to Fom1, at 3.5 and 4 cM respectively, whereas V06₁₀₉₂ marker was linked in repulsion to the same dominant resistant allele at 15.1 cM from the Fom-1 locus. These RAPDs were cloned and sequenced in order to design primers that would amplify only the target fragment. The derived sequence characterized amplified region (SCAR) markers SB17₆₄₅ and SV01₅₇₄ (645 and 574 bp, respectively) were present only in the resistant parent. The SV06₁₀₉₂ marker amplified a band of 1092 bp only in the susceptible parent. These markers are more universal than the CAPS markers developed by Brotman et al. (Theor Appl Genet 10:337–345, 2005). The analysis of 24 melon accessions, representing several melon types, with these markers revealed that different melon types behaved differently with the developed markers supporting the theory of multiple, independent origins of resistance to races 0 and 2 of F.o.m.     

Fine mapping of the uniform immature fruit color gene u in cucumber (Cucumis sativus L.)

Mottled/uniform color at the flower end of immature fruit is a highly important external quality trait that affects the market value of cucumber. Genetic analysis of different F₂ and backcross populations revealed that one single recessive gene, u (uniform immature fruit color), determines the uniform immature fruit color trait in cucumber. Based on earlier studies, the u locus is located on chromosome 5 (Chr. 5). By combining bulked segregant analysis using 60 published molecular markers on Chr. 5, we found that eight markers are polymorphic and are linked to the u locus. In addition, we developed five new relevant polymorphic simple sequence repeat (SSR) markers between markers SSR16203 and SSR15818. Subsequently, the F₂ population (477 individuals) from the cross of S06 (uniform fruit color line) × S94 (mottled fruit color line) was used for fine mapping of the u gene. The u gene was mapped to a 313.2-kb region between markers SSR10 and SSR27, at a genetic distance of 0.8 and 0.5 cM, respectively. Moreover, validity analysis of the codominant markers SSR10 and SSR27 was performed using 50 lines with mottled/uniform fruit color, demonstrating that these two SSR markers can be used for marker-assisted selection of the mottled/uniform fruit color trait in cucumber breeding. The results of this study will facilitate the cloning of the u gene.     

Identification and characterization of RAPD and SCAR markers linked to anthracnose resistance gene in sorghum [Sorghum bicolor (L.) Moench]

Anthracnose, one of the destructive foliar diseases of sorghum growing in warm humid regions, is incited by the fungus Colletotrichum graminicola.The inheritance of anthracnose resistance was studied using the parental cultivars of Sorghum bicolor (L.) Moench, HC 136 (susceptible to anthracnose) and G 73 (anthracnose resistant). The F₁ and F₂ plants were inoculated with the local isolates of C. graminicola cultures. The F₂ plants showed a segregation ratio of 3 (susceptible): 1(resistant) indicating that the locus for resistance to anthracnose in sorghum accession G 73 segregates as a recessive trait in a cross to susceptible cultivar HC 136. RAPD (random amplified polymorphic DNA) marker OPJ 01₁₄₃₇ was identified as marker closely linked to anthracnose resistance gene in sorghum by bulked segregant analysis of HC 136 × G73 derived recombinant inbred lines (RILs) of sorghum. A total of 84 random decamer primers were used to screen polymorphism among the parental genotypes. Among these, only 24 primers were polymorphic. On bulked segregant analysis, primer OPJ 01 amplified a 1437 bp fragment only in resistant parent G 73 and resistant bulk. The marker OPJ 01₁₄₃₇ was cloned and sequenced. The sequence of RAPD marker OPJ 01₁₄₃₇ was used to generate specific markers called sequence characterized amplified regions (SCARs). A pair of SCAR markers SCJ 01-1 and SCJ 01-2 was developed using Mac Vector program. SCAR amplification of resistant and susceptible parents along with their respective bulks and RILs confirmed that SCAR marker SCJ 01 is at the same loci as that of RAPD marker OPJ 01₁₄₃₇ and hence, is linked to anthracnose resistance gene. Resistant parent G 73 and resistant bulk amplified single specific band on PCR amplification using SCAR primer pairs. The RAPD marker OPJ 01₁₄₃₇ was mapped at a distance of 3.26 cM apart from the locus governing anthracnose resistance on the sorghum genetic map by the segregation analysis of the RILs. Using BLAST program, it was found that the marker showed 100 per cent alignment with the contig{_}3966 located on the longer arm of chromosome 8 of sorghum genome. Therefore, these identified RAPD and SCAR markers can be used in the resistance-breeding program of sorghum anthracnose by marker-assisted selection.An erratum to this article can be found at     

Fusarium vascular wilt in lentil: Inheritance and identification of DNA markers for resistance

The inheritance of resistance to lentil (Lens culinaris Medik.) vascular wilt caused by Fusarium oxysporum f.sp. lentis was investigated in a cross between resistant (ILL5588) and susceptible (L692–16-l(s)) lines. F_2:4 progenies and F_6:8, F_6:9 recombinant inbred line (RIL) populations were assessed for their wilt reaction for three seasons in a well-established wilt-sick plot. Resistance to wilt was conditioned by a single dominant gene in the populations studied. The map location of the Fw locus was identified for the first time through linkage to a random amplified polymorphic DNA (RAPD) marker (OPK-15₉₀₀) at 10.8 cM. Two other RAPD markers (OP-BH₈₀₀ and OP-DI5₅₀₀) identified by bulked segregant analysis were associated in the coupling phase with the resistance trait, and another marker (OP-C04₆₅₀) was associated with repulsion. The DNA markers reported here will provide a starting point in marker-assisted selection for vascular wilt resistance in lentil.     

RAPD markers linked to a clubroot-resistance locus in Brassica rapa L.

Linkage of random amplified polymorphic DNA (RAPD) markers with resistance genes to clubroot (Plasmodiophora brassicae Wor.) in Brassica rapa L. was studied in a doubled haploid (DH population obtained by microspore culture. Thirty-six DH lines were obtained from F₁ plants from a cross between susceptible ‘Homei P09’ and resistant ‘Siloga S2’ plants. ‘Homei P09’ was a DH line obtained by microspore culture of the Chinese cabbage variety ‘Homei’, which is highly responsive in microspore culture. The resistant line ‘Siloga S2’ was obtained by two rounds of selfing of the fodder turnip ‘Siloga’. Three RAPD markers, RA12-75A, WE22B and WE49B, were found to be linked to a clubroot-resistance locus. These three markers were linked in the DH lines and an F₂ population and should be useful for marker-assisted selection in breeding programs. This revised version was published online in July 2006 with corrections to the Cover Date.     

四倍体小麦地方品种矮蓝麦矮秆性状的遗传分析

四倍体圆锥小麦(Triticum turgidum L.ssp.turgidum)地方品种矮蓝麦是我国重要的小麦矮秆基因资源,经鉴定其矮秆特性对外源赤霉酸敏感。2012年配制矮蓝麦与2个高秆圆锥小麦的正反交组合,2012—2013年在四川绵阳分别种植F1、F2代和F2:3家系,对株高的遗传分析表明,矮蓝麦的矮秆性状受1对隐性基因控制。利用BSA法构建高秆和矮秆池筛选多态性SSR标记,并对矮蓝麦/青稞麦F2分离群体进行连锁分析,将目标基因定位于7AS染色体上,与标记GWM471的遗传距离为2.5 c M。矮蓝麦与矮秆番麦正反交的F1和F2群体表现非常相似的株高变异特征,初步推测矮蓝麦的矮秆基因是Rht22;进一步用高通量SNP和DAr T标记对两品种进行全基因组扫描,发现二者的遗传相似性高达98.7%~99.3%。因此认为,历史上矮蓝麦和矮秆番麦可能是同一品种,是通过人为交流而传播到不同地方。矮蓝麦携带的矮秆基因在人工合成六倍体小麦遗传背景中降低株高能力中等或较弱,在育种中需要聚合其他矮秆基因而被利用。     

Identification of Resistance Genes Against Powdery Mildew in Four Accessions of Hordeum Vulgare SSP. Spontaneum

Summary Four newly detected accessions of wild barley (Hordeum vulgare ssp. spontaneum) resistant to powdery mildew caused by Blumeria graminis f. sp. hordei were studied with the aim of finding the number of genes/loci conferring the resistance of individual accessions, the type of inheritance of the genes and their relationships to the Mla locus. F₂ populations after crosses between the winter variety ‘Tiffany’ and four wild barley accessions and use of microsatellite DNA markers were focused on the identification of individual resistance genes/loci by means of their chromosomal locations. In PI466495, one locus conferring powdery mildew resistance was identified in highly significant linkage with the marker Bmac0213. This location is consistent with the known locus Mla on chromosome 1HS. In the other three accessions the resistance was determined by two independent loci. In PI466197, PI466297 and PI466461, one locus was identified on chromosome 1HS and three new loci were revealed on chromosomes 2HS (highly significant linkage with Bmac0134), 7HS (highly significant linkage with Bmag0021) and 7HL (significant linkage with EBmac0755). Our prospective aim is identification of further linked DNA markers and the exact location of the resistance genes on the barley chromosomes.