Development of apple powdery mildew on sources of resistance to Podosphaera leucotricha, exposed to an inoculum virulent against the major resistance gene Pl-2

The major resistance gene Pl-2 in apple has recently been shown to be overcome by a virulent population of powdery mildew, Podosphaera leucotricha , in genotypes of the fourth generation after introgression of Pl-2 from crab apple, Malus zumi . Tests of pathogenicity in controlled conditions and observations in an orchard showed that the initial progenitor of Pl-2 , MAL 68/1, was overcome by a virulent inoculum. As a consequence, all selections derived from MAL 68/1 may lose their resistance to powdery mildew, if Pl-2 is used alone. Sources of resistance other than Pl-2 remained efficient to the virulent population: M. hupehensis , M. mandshurica , M. robusta , M. sargentii , M. sieboldii , D12, Mildew Immune Selection and 'White Angel'. The combination of Pl-2 with quantitative resistance genes resulted in a high level of resistance.     

Development of high-density interspecific genetic maps for the identification of QTLs conferring resistance to <Emphasis Type="Italic">Valsa ceratosperma</Emphasis> in apple

Valsa canker (Valsa ceratosperma (Tode ex Fr.) Maire) is one of the most destructive fungal diseases of apple, especially in Eastern Asia. In this study, the first high density genetic linkage map of Malus asiatica × Malus domestica was constructed by 640 simple sequence repeats (SSRs) and 490 single nucleotide polymorphisms (SNPs), which spanned 1497.5 cM with an average marker interval of 1.33 cM per marker. Quantitative trait loci (QTLs) for apple’s resistance to V. ceratosperma isolates 03-8 and xc56 were identified using the linkage map. Lesion lengths were used as the phenotypic data for the QTL analysis, which were measured on 1-year-old shoots inoculated with conidia of the two isolates. One QTL for resistance to isolate 03-8 was mapped on LG 16, and one QTL for resistance to isolate xc56 was detected on LG 9. Our research not only promoted the further understanding of the genetic basis of apple’s resistance to Valsa canker but also provided two molecular markers that might be used in future marker-assisted selection for resistance in apple breeding programs.     

EST-derived microsatellites as a rich source of molecular markers for oats

Polymerase chain reaction-based microsatellite markers are valuable tools for molecular breeding because of their co-dominant inheritance and their applicability for high-throughput analysis. Being still very limited for oats, their number has to be increased significantly to cover the entire genome. For these purposes, a set of 7031 recently published expressed sequence tags (ESTs) was screened for microsatellites with dinucleotide, trinucleotide and tetranucleotide repeat motifs. Subsequent in silico analysis resulted in the development of 216 primer pairs for Avena EST-derived microsatellite loci ( AME ). Using a sample set of 12 oat lines, 107 of 195 functional primers could be assayed as polymorphic. The marker variability averaged out at three alleles per locus and a polymorphic information content (PIC) value of 0.42. This variability documents their suitability for molecular oat-breeding purposes. Finally, 51 of the AME loci could be placed within the known reference map of 'Kanota' × 'Ogle' that previously contained only 12 microsatellite loci. Thus, a remarkable enhancing of the number of mapped oat microsatellite loci could be achieved.     

中品03-5373对大豆胞囊线虫3号生理小种免疫抗性的遗传解析

大豆胞囊线虫3号生理小种在我国已发现的8个小种中分布最为广泛,严重影响大豆生产。中品03-5373(ZP03-5373)是对3号小种免疫的优良抗源。本研究以中品03-5373为母本,与感病品种中黄13(ZH13)杂交建立包含254个家系的重组自交系群体,利用SSR、EST-SSR、In Del和SNP等506个分子标记对该分离群体进行基因型鉴定,构建全长为2651.90 c M的遗传图谱,标记间平均距离为5.24 c M。结合抗性鉴定数据,在中品03-5373中检测到3个控制大豆胞囊线虫3号生理小种的QTL区间,分别位于Gm07(SCN3-7)、Gm11(SCN3-11)和Gm18(SCN3-18)。其中SCN3-18可解释29.5%的抗性变异,为主效抗性位点;SCN3-7和SCN3-11分别控制6.2%和5.5%的抗性变异,为微效位点。SCN3-7与SCN3-18间存在显著的上位性互作。通过对中品03-5373祖先亲本2个QTL区间(SCN3-7和SCN3-11)侧翼标记的系谱追踪,进一步证明SCN3-7和SCN3-11与大豆胞囊线虫3号抗性相关。     

NaCl胁迫对八棱海棠幼苗生长及其生理指标的影响

为明确八棱海棠的耐盐特性,为其在盐碱地区的园林绿化应用提供科学依据,采用砂基培养法,研究八棱海棠幼苗在不同浓度NaCl胁迫下的生长量和部分生理指标的变化过程。结果表明：随着NaCl浓度的升高,八棱海棠的株高、茎粗、叶片含水量、叶绿素含量呈减少趋势;MDA含量和可溶性糖含量呈上升趋势;脯氨酸呈先下降后上升趋势,变化平缓。通过对外观形态的观测以及生理指标的综合分析,推断出八棱海棠的耐盐阈值、存活阈值为0.6%。     

Resistance sources to Valsa canker (Valsa ceratosperma) in a germplasm collection of diverse Malus species

Although Valsa canker caused by Valsa ceratosperma (Tode ex Fr.) Maire is one of the most destructive diseases in apple ( Malus  ×  domestica Borkh.) especially in eastern Asia, information available to help with breeding against Valsa canker in apples is limited. In this work, 53 accessions of diverse Malus species and their interspecific hybrids were tested for resistance to V. ceratosperma , using an excised shoot assay. Dormant shoots and succulent growing shoots from each accession were inoculated with a virulent isolate AVC-12 of V. ceratosperma , and the length of necrosis was measured at 10 days post-inoculation for the dormant shoots and at 7 days post-inoculation for the growing shoots. The lesion length relative to the susceptible control 'Fuji' in dormant shoots (RL_D) and to that in growing shoots (RL_G) were simple but useful parameters to differentiate between resistant and susceptible accessions. Fourteen accessions from M. baccata , M. florentina , M. halliana , M. micromalus , M. pratii , M. sieboldii , M. yunnanensis , M.  ×  floribunda and M.  ×  platycarpa gave low RL_D and RL_G values of less than 0.6 and were evaluated as resistant regardless of the difference in the stage of growth. The highest level of resistance was found in M. sieboldii . This high level of resistance in M. sieboldii was effective against different isolates of V. ceratosperma .     

Using a linkage mapping approach to identify QTL for day-neutrality in the octoploid strawberry

A linkage mapping approach was used to identify quantitative trait loci (QTL) associated with day-neutrality in the commercial strawberry, Fragaria  ×  ananassa (Duch ex Rozier). Amplified Fragment Length Polymorphism (AFLP) markers were used to build a genetic map with a population of 127 lines developed by crossing the day-neutral (DN) 'Tribute' with the short-day (SD) 'Honeoye'. The population was genotyped with AFLP markers and 429 single dose restriction fragments (SDRF) were placed on a consensus map of 1541 cM with 43 linkage groups. Individuals from the mapping population were observed for their flowering habit throughout the growing season in Michigan (MI), Minnesota (MN), Maryland (MD), Oregon (OR) and California (CA). Eight QTL were found that were either location specific or shared among locations. None of these QTL explained >36% of the phenotypic variation, indicating that the inheritance of day-neutrality is likely a polygenic trait.     

Development of PCR-based markers for a major locus conferring powdery mildew resistance in mungbean (Vigna radiata)

Powdery mildew (PM) can cause significant yield loss in mungbean and several loci conferring resistance to this disease have been identified. A restriction fragment length polymorphism (RFLP) marker (VrCS65) linked closely to one of these loci was used to screen a mungbean bacterial artificial chromosome (BAC) library and positive BAC clones identified were used to develop simple sequence repeat (SSR or microsatellite) and sequence tagged site (STS) markers. Four of the new PCR markers (including two SSRs and two STSs) co-segregated with the original RFLP marker VrCS65, and another SSR marker (VrCS SSR2) was located 0.5 cM away from it. These PCR-based and locus-specific markers could be useful in breeding cultivars with enhanced resistance to PM and in the further characterization of the locus including the isolation of gene(s) responsible for the resistance.     

Use of SSR markers to assess sexual vs. apomictic origin and ploidy level of breeding progeny derived from crosses of apple proliferation-resistant Malus sieboldii and its hybrids with Malus × domestica cultivars

To obtain apple rootstocks resistant to apple proliferation and suitable to modern fruit growing, 24 cross-combinations were performed over a 5-year period using Malus sieboldii and its hybrids as donors of the resistance trait and standard apple rootstock Malus  ×  domestica genotypes as donors of agronomic value. Breeding with these genotypes was achieved despite different degrees of apomixis and polyploidy. Sets of five to six locus-specific microsatellite markers were identified for characterizing each progeny. Supported by flow cytometry these markers were applied to infer mode of reproduction, genomic constitution and ploidy level. Microsatellites allele composition identical to the maternal parent was revealed in 1668 of 3032 seedlings indicating seed formation through apomixis. Complete genetic recombination was found in 398 seedlings. The remaining hybrids displayed a higher ploidy than that of the parental plants which was consistent with the fertilization of unreduced egg cells. Thus, for each cross-combination, microsatellite loci were identified which enabled a reliable prediction of the ploidy level. They can now be applied in routine screening to distinguish sexual from apomictic progeny.     

Selection for verticillium wilt resistance in potato breeding populations derived from four cross types

Verticillium wilt (VW) is one of the important yield-limiting diseases for potato production. To develop resistant clones, the potential for early generation selection was studied using three basic selection methods, individual, family, and within family selection, for two clonal generations. A total of 152 clones were derived from four cross types (2x × 2x, 2x × 4x, 4x × 2x and 4x × 4x). Clones were evaluated for maturity, symptom expression, yield and stem colonization in replicated trials. Heritability and selection response for the traits were estimated for each selection method. Direct selection in the second clonal generation and individual selection showed more gain than that from other methods. Both 2x × 2x and 4x × 2x families were higher yielding and had lower stem colonization scores than 2x × 4x and 4x × 4x crosses. Therefore, 2x × 2x or 4x × 2x crosses between carefully chosen parents with high yield and VW resistance may produce offspring with superior performance.     

Development of an ISSR-derived PCR marker linked to nematode resistance (Ha2) in spring barley

Cereal cyst nematodes ( Heterodera avenae Woll.) are economically damaging barley parasites in most cereal growing areas of the world and the development of resistant cultivars is the best measure against the pathogen. An ISSR (inter-simple sequence repeat) marker identified as closely linked with the H. avenae race 1 and 2 resistance gene ( Ha2 ) has been converted into a codominant sequence characterized amplified region marker ( Ha2S18 ) and mapped in barley 'SW Buddy' × 'SW Cecilia' DH population at 4.3 cM from the Ha2 locus on the long arm of chromosome 2H. The potential usefulness of Ha2S18 in large scale marker assisted selection schemes has been evaluated in a broad genetic background and is an important complement to the bioassay and to other linked DNA-markers for this trait.     

Quantitative trait loci analysis for resistance against Turnip mosaic virus based on a doubled-haploid population in Chinese cabbage

Turnip mosaic virus (TuMV) as the major virus infecting Brassica crops, often cause severe yield and quality losses in Chinese cabbage production in China. In this study, quantitative trait loci (QTL) analysis for TuMV resistance was conducted with a population of 100 doubled-haploid lines derived from the F₁ between 91-112 (resistant) and T12-19 (susceptible) through microspore culture. A total of 376 molecular markers including 235 amplified fragment length polymorphisms, 129 random amplified polymorphic DNAs, 10 simple sequence repeats, one SCAR and one morphological marker were employed to construct a linkage map with 10 linkage groups covering 809.1 cM with an average distance of 2.2 cM between loci. Resistance was assessed by artificial inoculation at the seedling stage and at the adult stage in field conditions, respectively. Four QTLs controlling TuMV resistance were identified with JoinMap QTL 4.0 and interval mapping method. Two QTLs ( Tu1 , Tu2 ) were associated with resistance at the seedling stage, each accounting for 58.2% and 14.7% of the phenotypic variation, respectively. Two QTLs ( Tu3 , Tu4 ) were found corresponding to the disease resistance at the adult plant stage, explaining 48.5% and 32.0% of the phenotypic variation, respectively. Marker-assisted selection for these major QTLs involved in TuMV resistance could be useful in Chinese-cabbage breeding programmes.     

不同环境条件下西瓜果实可溶性固形物含量的QTL分析

利用西瓜栽培品种97103和野生品种PI296341-FR为亲本构建了由117个稳定株系组成的F2S8代重组自交系永久群体。利用RAPD、SSR、AFLP和SCAR等203个标记,构建了该RIL群体的高密度分子遗传连锁图谱,覆盖基因组总长度1383.8cM,平均图距6.8cM。在新疆和北京2个地点的3个年份对果实可溶性固形物含量进行QTL比较分析。累计检测到18个QTL,分布在第1、2、3、5、14、15和19连锁群上。其中3种环境中能重复检出的QTL2个,贡献率为14.2%￣22.9%。两种环境中能重复检出的QTL6个,其贡献率为12.4%￣20.3%。仅能在单一环境下检测到的QTL10个,其贡献率为14.4%￣22.6%。根据不同环境条件下的QTL比较分析结果,认为第1连锁群上的qSSC-1a和qSSC-1b可能是控制可溶性固形物含量性状表达的主效QTL位点,这2个QTL位点的峰值分别落在标记N02_800a和Z03_250a上,这对西瓜可溶性固形物含量的标记辅助选择是非常有利的。     

Molecular mapping of black rot resistance locus Xca1bo on chromosome 3 in Indian cauliflower (Brassica oleracea var. botrytis L.)

Black rot is the most devastating disease of cauliflower worldwide causing severe damage to crop. The identification of markers linked to loci that control resistance can facilitate selection of plants for breeding programmes. In the present investigation, F₂ population derived from a cross between ‘Pusa Himjyoti’, a susceptible genotype, and ‘BR‐161’, a resistant genotype, was phenotyped by artificial inoculation using Xcc race 1. Segregation analysis of F₂ progeny indicated that a single dominant locus governed resistance to Xcc race 1 in ‘BR‐161’. Bulk segregant analysis in resistant and susceptible bulks of F₂ progeny revealed seven differentiating polymorphic markers (three RAPD, two ISSR and two SSR) of 102 markers screened. Subsequently, these markers were used to genotype the entire F₂ population, and a genetic linkage map covering 74.7 cM distance was developed. The major locus Xca1bo was mapped in 1.6‐cM interval flanked by the markers RAPD 04₈₃₃ and ISSR 11₆₃₅. The Xca1bo locus was located on chromosome 3. The linked markers will be useful for marker‐assisted resistance breeding in cauliflower.     

Identification of PCR-based markers linked to the powdery-mildew-resistance gene Pl1 from Malus robusta in cultivated apple

The availability of molecular markers linked to mildew resistance genes would enhance the efficiency of apple-breeding programmes. This investigation focuses on the identification of random amplified polymorphic DNA (RAPD) markers linked to the Pl₁ gene for mildew resistance, which has introgressed from Malus robusta into cultivated apples. The RAPD marker technique was combined with a modified ‘bulked seg-regant analysis’ mapping strategy. About 850 random decamer primers used as single primers or in combinations were tested by PCR analysis on the basis of resistant and susceptible DNA pools. Selected primers producing RAPD fragments were applied in an additional selection step to M. robusta and genotypes representing intermediate breeding stages of the breeding population 93/9, for which a 1:1 segregation could be observed for the resistance trait. Seven RAPD markers, all representing introgressed DNA sequences from M. robusta, were identified and arranged with the Pl₁ locus in a common linkage group. The two most tightly-linked RAPD markers, OPAT20₄₅₀ and OPD2₁₀₀₀ were mapped with a genetic distance of 4.5 and 5 cM, respectively, from the Pl₁ gene. Both markers are suitable for marker-assisted selection in apple breeding. The polymorphic DNA fragment OPAT20₄₅₀ was cloned and sequenced, and longer primers for the generation of a sequence-characterized amplified region (SCAR) marker have been constructed; this marker was easier to score than the original RAPD marker.     

Molecular mapping of QTLs for non-parasitic leaf spot resistance and comparison of half-sib DH populations in spring barley

Quantitative trait loci (QTLs) for resistance against non-parasitic leaf spots (NPLS) were first characterized in a spring barley double haploid population derived from the cross IPZ 24727/Barke (Behn et al., 2004). The aim of the present study was to identify QTLs for NPLS resistance in the half-sibling DH population IPZ 24727/Krona and to compare them with the QTLs of the population IPZ 24727/Barke. An anther culture-derived doubled haploid population of 536 DH lines was developed from the cross IPZ 24727 (resistant)/Krona (susceptible). Field trials were performed over two years in two replications, scoring NPLS and agronomic traits that might interact with NPLS. A molecular linkage map of 1035 cM was constructed based on AFLPs, SSRs and the mlo marker. QTL analyses for NPLS identified three QTLs that accounted for 30% of the phenotypic variation. For comparison of the QTLs from each DH population, a consensus map was generated comprising 277 markers with a length of 1199 cM. In both populations, the QTLs for NPLS mapped to chromosomes 1H, 4H and 7H. A common QTL with a great effect in both populations and over all environments was localized at the mlo locus on chromosome 4H, indicating that the mlo powdery mildew resistance locus has a considerable effect on NPLS susceptibility. The steps necessary to validate the QTLs and to improve the NPLS resistance by breeding were discussed.     

The first genetic linkage map of crape myrtle (Lagerstroemia) based on amplification fragment length polymorphisms and simple sequence repeats markers

Lagerstroemia (crape myrtle) are famous ornamental plants with large pyramidal racemes, long flower duration and diverse colours. Genetic maps provide an important genomic resource of basic and applied significance. A genetic linkage map was developed by genotyping 192 F₁ progeny from a cross between L. caudata (female) and L. indica (‘Xiang Xue Yun’) (male) with a combination of amplification fragment length polymorphisms (AFLP) and simple sequence repeats (SSR) markers in a double pseudo‐testcross mapping strategy. A total of 330 polymorphic loci consisting of 284 AFLPs and 46 SSRs showing Mendelian segregation were generated from 383 AFLP primer combinations and 150 SSR primers. The data were analysed using JoinMap 4.0 (evaluation version) to construct the linkage map. The map consisted of 20 linkage groups of 173 loci (160 AFLPs and 13 SSRs) covering 1162.1 cM with a mean distance of 10.69 cM between adjacent markers. The 20 linkage groups contained 2–49 loci and ranged in length from 7.38 to 163.57 cM. This map will serve as a framework for mapping QTLs and provide reference information for future molecular breeding work.     

Linkage map construction and mapping QTL for cotton fibre quality using SRAP, SSR and RAPD

Tetraploid cotton is one of the most extensively cultivated species. Two tetraploid species, Gossypium hirsutum L. and G. barbadense L., dominate the world's cotton production. To better understand the genetic basis of cotton fibre traits for the improvement of fibre quality, a genetic linkage map of tetraploid cotton was constructed using sequence‐related amplified polymorphisms (SRAPs), simple sequence repeats (SSRs) and random amplified polymorphic DNAs (RAPDs). A total of 238 SRAP primer combinations, 368 SSR primer pairs and 600 RAPD primers were used to screen polymorphisms between G. hirsutum cv. Handan208 and G. barbadense cv. Pima90 which revealed 749 polymorphic loci in total (205 SSRs, 107 RAPDs and 437 SRAPs). Sixty‐nine F₂ progeny from the interspecific cross of ‘Handan208’בPima90’ were genotyped with the 749 polymorphic markers. A total of 566 loci were assembled into 41 linkage groups with at least three loci in each group. Twenty‐eight linkage groups were assigned to corresponding chromosomes by SSR markers with known chromosome locations. The map covered 5141.8 cM with a mean interlocus space of 9.08 cM. A × test for significance of deviations from the expected ratio (1: 2: 1 or 3: 1) identified 135 loci (18.0%) with skewed segregation, most of which had an excess of maternal parental alleles. In total, 13 QTL associated with fibre traits were detected, among which two QTL were for fibre strength, four for fibre length and seven for micronaire value. These QTL were on nine linkage groups explaining 16.18‐28.92% of the trait variation. Six QTL were located in the A subgenome, six QTL in the D subgenome and one QTL in an unassigned linkage group. There were three QTL for micronaire value clustered on LG1, which would be very useful for improving this trait by molecular marker‐assisted selection.     

DAF marker tightly linked to a major locus for Ascochyta blight resistance in chickpea (Cicer arietinum L.)

Resistance of chickpea against the disease caused by the ascomycete Ascochyta rabiei is encoded by two or three quantitative trait loci, QTL1, QTL2 and QTL3. A total of 94 recombinant inbred lines developed from a wide cross between a resistant chickpea line and a susceptible accession of Cicer reticulatum, a close relative of cultivated chickpea, was used to identify markers closely linked to QTL1 by DNA amplification fingerprinting in combination with bulked segregant analysis. Of 312 random 10mer oligonucleotides, 3 produced five polymorphic bands between the parents and bulks. Two of them were transferred to the population on which the recent genetic map of chickpea is based, and mapped to linkage group 4. These markers, OPS06-1 and OPS03-1, were linked at LOD-scores above 5 to markers UBC733B and UBC181A flanking the major ascochyta resistance locus. OPS06-1 mapped at the peak of the QTL between markers UBC733B (distance 4.1 cM) and UBC181A (distance 9.6 cM), while OPS03-1 mapped 25.1 cM away from marker UBC733B on the other flank of the resistance locus. STMS markers localised on this linkage group were transferred to the population segregating for ascochyta resistance. Three of these markers were closely linked to QTL1. Twelve of 14 STMS markers could be used in both populations. The order of STMS markers was essentially similar in both populations, with differences in map distances between them. The availability of flanking STMS markers for the major resistance locus QTL1 will help to elucidate the complex resistance against different Ascochyta pathotypes in future. This revised version was published online in August 2006 with corrections to the Cover Date.     

Detection of RAPD markers linked to the everbearing gene in Japanese cultivated strawberry

To identify markers for the everbearing gene in strawberries, 199 F₁ progeny plants were produced from a cross between ‘Ever Berry’ (a Japanese everbearing strawberry) and ‘Toyonoka’ (a Japanese Junebearing strawberry) as the experimental population. The results of flowering tests produced 97 everbears and 102 Junebears. The chi‐square test gave a goodness of fit for the expected ratio of 1 : 1 for everbears to Junebears, suggesting the inheritance of the everbearing trait is controlled by a monogenic dominant gene. RAPD analyses on this trait were carried out using ‘Ever Berry’ and ‘Toyonoka’. Seventy‐one primers, which produced 89 polymorphic fragments between the two parents, were identified from a total of 175 primers. Five markers relating to the everbearing trait were selected from 26 of the 199 progeny plants. The remaining 173 seedlings were analysed with these five markers and a linkage map was constructed using all of the 199 F₁ progeny plants. The length of this linkage group is 39.7 cM. The closest markers found, OPE07‐1 and OPB05‐1, are respectively mapped at 11.8 and 15.8 cM on each side of the everbearing gene.