Mapping of the QTL (quantitative trait locus) conferring partial resistance to leaf blast in rice cultivar Chubu 32

The rice cultivar Chubu 32 possesses a high level of partial resistance to leaf blast. The number and chromosomal location of genes conferring this resistance were detected by restriction fragment length polymorphism (RFLP) linkage mapping and quantitative trait locus (QTL) analysis. For the mapping, 149 F₃ lines derived from the cross between rice cultivar Norin 29, with a low level of partial resistance, and Chubu 32 were used, and their partial resistance to leaf blast was assessed in upland nurseries. A linkage map covering six chromosomes and consisting of 36 RFLP markers was constructed. In the map, only one significant QTL (LOD>2.0) for partial resistance was detected on chromosome 11. This QTL explained 45.6% of the phenotypic variation. The segregation ratio of the F3 lines was 3:1 for partial resistance to susceptibility. These results suggest that the partial resistance in Chubu 32 is controlled by a major gene. Received: 15 March 2001 / Accepted: 13 August 2001     

Molecular mapping of genes conferring aluminum tolerance in rice (Oryza sativa L.)

Crop productivity on acid soil is restricted by multiple abiotic stress factors. Aluminum (Al) tolerance seems to be a key to productivity on soil with a pH below 5.0, but other factors such as Mn toxicity and the deficiency of P, Ca and Mg also play a role. The development of Al-tolerant genotypes of rice is an urgent necessity for improving crop productivity in developing countries. Inhibition of root growth is a primary and early symptom of Al toxicity. The present study was conducted to identify genetic factors controlling the aluminum tolerance of rice. Several parameters related to Al tolerance, most importantly the relative root growth under Al stress versus non-stress conditions, were scored in 188 F₃ selfed families from a cross between an Al-tolerant Vietnamese local variety, Chiembau, and an Al-susceptible improved variety, Omon269–65. The two varieties are both Oryza sativa ssp. indica, but showed a relatively high level of DNA polymorphism, permitting the assembly of an RFLP map consisting of 164 loci spanning 1,715.8 cM, and covering most of the rice genome. A total of nine different genomic regions on eight chromosomes have been implicated in the genetic control of root and shoot growth under aluminum stress. By far the greatest effects on aluminum tolerance were associated with the region near WG110 on chromosome 1. This region does not seem to correspond to most of the genes that have been mapped for aluminum tolerance in other species, nor do they correspond closely to one another. Most results, both from physiological studies and from molecular mapping studies, tend to suggest that aluminum tolerance is a complex multi-genic trait. The identification of DNA markers (such as WG110) that are diagnostic for aluminum tolerance in particular gene pools provides an important starting point for transferring and pyramiding genes that may contribute to the sustainable improvement of crop productivity in aluminum-rich soils. The isolation of genes responsible for aluminum tolerance is likely to be necessary to gain a comprehensive understanding of this complex trait. Received: 29 March 2000 / Accepted: 16 August 2000     

Molecular-marker-facilitated studies of morphological traits in maize. II: Determination of QTLs for grain yield and yield components

Genetic factors controlling quantitative inheritance of grain yield and its components have not previously been investigated by using replicated lines of an elite maize (Zea mays L.) population. The present study was conducted to identify quantitative trait loci (QTLs) associated with grain yield and grain-yield components by using restriction fragment length polymorphism (RFLP) markers. A population of 150 random F₂₃ lines was derived from the single cross of inbreds Mo17 and H99, which are considered to belong to the Lancaster heterotic group. Trait values were measured in a replicated trial near Ames, Iowa, in 1989. QTLs were located on a linkage map constructed with one morphological and 103 RFLP loci. QTLs were found for grain yield and all yield components. Partial dominance to overdominance was the primary mode of gene action. Only one QTL, accounting for 35% of the phenotypic variation, was identified for grain yield. Two to six QTLs were identified for the other traits. Several regions with pleiotropic or linked effects on several of the yield components were detected.     

RFLP mapping of QTLs conferring salt tolerance during the vegetative stage in tomato

 Quantitative trait loci (QTLs) contributing to salt tolerance during the vegetative stage in tomato were investigated using an interspecific backcross between a salt-sensitive Lycopersicon esculentum breeding line (NC84173, maternal and recurrent parent) and a salt-tolerant Lycopersicon pimpinellifolium accession (LA722). One hundred and nineteen BC₁ individuals were genotyped for 151 RFLP markers and a linkage map was constructed. The parental lines and 119 BC₁S₁ families (self-pollinated progeny of the BC₁ individuals) were evaluated for salt tolerance in aerated saline-solution cultures with the salt concentration gradually raised to 700 mM NaCl+70 mM CaCl₂ (equivalent to an electrical conductivity of approximately 64 dS/m and a water potential of approximately −35.2 bars). The two parental lines were distinctly different in salt tolerance: 80% of the LA722 plants versus 25% of the NC84173 plants survived for at least 2 weeks after the final salt concentration was reached. The BC₁S₁ population exhibited a continuous variation, typical of quantitative traits, with the survival rate of the BC₁S₁ families ranging from 9% to 94% with a mean of 51%. Two QTL mapping techniques, interval mapping (using MAPMAKER/QTL) and single-marker analysis (using QGENE), were used to identify QTLs. The results of both methods were similar and five QTLs were identified on chromosomes 1 (two QTLs), 3, 5 and 9. Each QTL accounted for between 5.7% and 17.7%, with the combined effects (of all five QTLs) exceeding 46%, of the total phenotypic variation. All QTLs had the positive QTL alleles from the salt-tolerant parent. Across QTLs, the effects were mainly additive in nature. Digenic epistatic interactions were evident among several QTL-linked and QTL-unlinked markers. The overall results indicate that tomato salt tolerance during the vegetative stage could be improved by marker-assisted selection using interspecific variation. Received: 4 January 1999 / Accepted: 4 January 1999     

Development of diagnostic PCR markers closely linked to the tomato powdery mildew resistance gene Ol-1 on chromosome 6 of tomato

Lycopersicon hirsutum G1.1560 is a wild accession of tomato that shows resistance to Oidium lycopersicum, a frequently occurring tomato powdery mildew. This resistance is largely controlled by an incompletely dominant gene Ol-1 near the Aps-1 locus in the vicinity of the resistance genes Mi and Cf-2/Cf-5. Using a new F₂ population (n=150) segregating for resistance, we mapped the Ol-1 gene more accurately to a location between the RFLP markers TG153 and TG164. Furthermore, in saturating the Ol-1 region with more molecular markers using bulked segregant analysis, we were able to identify five RAPDs associated with the resistance. These RAPDs were then sequenced and converted into SCAR markers: SCAB01 and SCAF10 were L. hirsutum-specific; SCAE16, SCAG11 and SCAK16 were L. esculentum-specific. By linkage analysis a dense integrated map comprising RFLP and SCAR markers near Ol-1 was obtained. This will facilitate a map-based cloning approach for Ol-1 and marker-assisted selection for powdery mildew resistance in tomato breeding. Received: 21 June 1999 / Accepted: 1 December 1999     

Mapping the genome of rapeseed (Brassica napus L.). I. Construction of an RFLP linkage map and localization of QTLs for seed glucosinolate content

A linkage map of the rapeseed genome comprising 204 RFLP markers, 2 RAPD markers, and 1 phenotypic marker was constructed using a F₁ derived doubled haploid population obtained from a cross between the winter rapeseed varieties Mansholt's Hamburger Raps and Samourai. The mapped markers were distributed on 19 linkage groups covering 1441 cM. About 43% of these markers proved to be of dominant nature; 36% of the mapped marker loci were duplicated, and conserved linkage arrangements indicated duplicated regions in the rapeseed genome. Deviation from Mendelian segregation ratios was observed for 27.8% of the markers. Most of these markers were clustered in 7 large blocks on 7 linkage groups, indicating an equal number of effective factors responsible for the skewed segregations. Using cDNA probes for the genes of acyl-carrier-protein (ACP) and -ketoacyl-ACP-synthase I (KASI) we were able to map three and two loci, respectively, for these genes. The linkage map was used to localize QTLs for seed glucosinolate content by interval mapping. Four QTLs could be mapped on four linkage groups, giving a minimum number of factors involved in the genetic control of this trait. The estimated effects of the mapped QTLs explain about 74% of the difference between both parental lines and about 61.7 % of the phenotypic variance observed in the doubled haploid mapping population.     

RAPD and RFLP markers tightly linked to the locus controlling carnation (Dianthus caryophyllus) flower type

 Flower doubleness as a breeding characteristic is of major importance in carnation (Dianthus caryophyllus), one of the major cut-flowers sold worldwide, since flower architecture is of the utmost value in ornamentals. Based on the number of petals per flower, carnations are grouped into “single”, “semi-double” and “double” flower types. The first have five petals and are easily distinguishable, but of no economic value to the carnation industry. Flowers of standard and spray varieties, which constitute the largest market share, are usually of the double and semi-double type, respectively. These flower types are not easily distinguishable due to phenotypic overlaps caused by environmental conditions. To study the inheritance of this trait, several progeny segregating for flower type were prepared. Based on the number of single-flower type fullsibs among the offspring, we found that this phenotype is expressed only in plants homozygous for the recessive allele and that a dominant mutation in this allele causes an increase in petal number. Using random decamer primers, we identified a random amplified polymorphic DNA (RAPD) marker which is tightly linked to this recessive allele. The RAPD marker was cloned and used to generate a restriction fragment length polymorphic (RFLP) marker. This RFLP marker could discriminate with 100% accuracy between the semi-double and double- flower phenotypes in carnations of both Mediterranean and American groups. The advantages of RFLP over RAPD markers and their applicability to markerassisted selection in carnation are discussed. Received: 11 August 1997 / Accepted: 22 August 1997     

利用最大似然法进行水稻产量性状基因的分子作图

本研究根据对估计标记－数量性状基因座位（ＱＴＬ）之间重组率的两种分析方法（矩量法和最大似然法）、两种方差模型（ＱＴＬ基因型之间的方差同质和异质模型）的分析,揭示了ＬＯＤ值在标记－ＱＴＬ连锁检测上所得结果的相关性高于重组率估计值的相关性。采用最大似然法和异质方差模型,估计了水稻产量构成有关的ＱＴＬ与分布于１１对染色体上的５１个限制性片段长度多态性（ＲＦＬＰ）标记之间的重组率,并对似然比（以ＬＯＤ值表示）进行Ｘ￣２检验,发现７个存在显著连锁关系的标记－性状组合,其平均重组率为１０．０％。这些标记分布于第１、５、６、８和１１等５对染色体上,涉及７个ＲＦＬＰ标记和３个产量构成性状,即每穗颖花数（ＲＧ５７３、ＲＺ６１７、ＲＧ１０３）、单株穗数（ＲＧ６４Ｂ）和每穗实粒数（ＲＧ１０１、ＲＧ２４４、ＲＧ６５３）。     

Mapping of two genes for resistance to clubroot (Plasmodiophora brassicae) in a population of doubled haploid lines of Brassica oleracea by means of RFLP and AFLP markers

A genetic map covering 615 cM in 12 linkage groups was assembled based on 92 RFLP and AFLP markers segregating in a population of 107 doubled haploid lines (DH lines) of Brassica oleracea. The DH-line population was obtained through microspore culture from the of two homozygous parents: DH-line Bi derived from the cabbage landrace Bindsachsener, and DH-line Gr from broccoli cv ‘Greenia’. Sixty-five percent of the loci, and in some cases complete linkage groups, displayed distorted segregation ratios, a frequency much higher than that observed in populations of the same species. DH-line Bi was resistant to clubroot, which is caused by a Dutch field isolate of Plasmodiophora brassicae. Resistance in the DH-line population was determined in two ways: by assigning symptom grades to each plant, and by measuring the fresh weights of the healthy and affected parts of the root system of each plant. Using a multiple QTL mapping approach to analyze the fresh weight data, we found two loci for clubroot resistance; these were designated pb-3 and pb-4. The additive effects of these loci were responsible for 68% of the difference between the parents and for 60% of the genetic variance among DH-line means. Also, indications for the presence of two additional, minor QTLs were found. Analysis of symptom grades revealed the two QTLs pb-3 and pb-4, as well as one of the two minor QTLs indicated by analysis of the fresh weight data. Received: 29 April 1996 / Accepted: 10 May 1996     

An interspecific (Capsicum annuum ×C. chinese) F2 linkage map in pepper using RFLP and AFLP markers

We have constructed a molecular linkage map of pepper (Capsicum spp.) in an interspecific F₂ population of 107 plants with 150 RFLP and 430 AFLP markers. The resulting linkage map consists of 11 large (206–60.3 cM) and 5 small (32.6–10.3 cM) linkage groups covering 1,320 cM with an average map distance between framework markers of 7.5 cM. Most (80%) of the RFLP markers were pepper-derived clones, and these markers were evenly distributed across the genome. By using 30 primer combinations, we were able to generate 444 AFLP markers in the F₂ population. The majority of the AFLP markers clustered in each linkage group, although PstI/MseI markers were more evenly distributed than EcoRI/MseI markers within the linkage groups. Genes for the biosynthesis of carotenoids and capsaicinoids were mapped on our linkage map. This map will provide the basis of studying secondary metabolites in pepper. Received: 20 October 1999 / Accepted: 3 July 2000     

Integrated map of AFLP, SSLP and RFLP markers using a recombinant inbred population of rice (Oryza sativa L.)

 A molecular map of rice consisting of 231 amplified fragment length polymorphisms (AFLPs), 212 restriction fragment length polymorphisms (RFLPs), 86 simple-sequence length polymorphisms (SSLPs), five isozyme loci, and two morphological mutant loci [phenol staining of grain (Ph), semi-dwarf habit (sd-1)] has been constructed using an F₁₁ recombinant inbred (RI) population. The mapping population consisted of 164 RI lines and was developed via single-seed descent from an intercross between the genetically divergent parents Milyang 23 (M) (tongil type) and Gihobyeo (G) ( japonica type). A subset of previously mapped RFLP and SSLP markers were used to construct the map framework. The AFLP markers were derived from ten EcoRI(+2) and MseI(+3) primer combinations. All marker types were well distributed throughout the 12 chromosomes. The integrated map covered 1814 cM, with an average interval size of 3.4 cM. The MG map is a cornerstone of the Korean Rice Genome Research Program (KRGRP) and is being continuously refined through the addition of partially sequenced cDNA markers derived from an immature-seed cDNA library developed in Korea, and microsatellite markers developed at Cornell. The population is also being used for quantitative trait locus (QTL) analysis and as the basis for marker-assisted variety development. Received: 24 June 1997 / Accepted: 25 November 1997     

Restriction fragment length polymorphism analysis of loci associated with disease resistance genes and developmental traits in Pisum sativum L.

An F₂ population of pea (Pisum sativum L.) consisting of 174 plants was analysed by restriction fragment length polymorphism (RFLP) and random amplified polymorphic DNA (RAPD) techniques. Ascochyta pisi race C resistance, plant height, flowering earliness and number of nodes were measured in order to map the genes responsible for their variation. We have constructed a partial linkage map including 3 morphological character genes, 4 disease resistance genes, 56 RFLP loci, 4 microsatellite loci and 2 RAPD loci. Molecular markers linked to each resistance gene were found: Fusarium wilt (6 cM from Fw), powdery mildew (11 cM from er) and pea common Mosaic virus (15 cM from mo). QTLs (quantitative traits loci) for Ascochyta pisi race C resistance were mapped, with most of the variation explained by only three chromosomal regions. The QTL with the largest effect, on chromosome 4, was also mapped using a qualitative, Mendelian approach. Another QTL displayed a transgressive segregation, i.e. the parental line that was susceptible to Ascochyta blight had a resistance allele at this QTL. Analysis of correlations between developmental traits in terms of QTL effects and positions suggested a common genetic control of the number of nodes and earliness, and a loose relationship between these traits and height.     

Molecular characterization of the SCAR markers tightly linked to the Tm-2 locus of the genus Lycopersicon

The Tm-2 gene and its alleles conferring tomato mosaic virus resistance in tomato originate from Lycopersicon peruvianum, a wild relative of tomato. DNA fragments of several RAPD markers tightly linked with the Tm-2 locus in tomato were successfully cloned and sequenced. Subsequently, the 24-mer oligonucleotide primer pairs of the SCAR markers corresponding to the RAPD markers were designed based on the 5’-endmost sequences. A fragment of the same size as that of a SCAR marker was amplified in the ToMV-susceptible tomato line with no Tm-2, but the digests of the PCR fragments by AccI exhibited polymorphism in fragment length between the two lines. We chose three SCAR markers and three RAPD markers tightly linked with the Tm-2 locus, and examined whether the same-sized fragments corresponding to these markers were also present in three other lines carrying Tm-2a or one of the other Tm-2 alleles. The fragments corresponding to the three SCAR markers were present in all of the three lines, but the other markers (three RAPDs ) were absent in one or two lines, suggesting that the three SCAR markers are closer to Tm-2 than the other markers. Comparison of the nucleotide sequences of these fragments revealed that they are all homologous to the corresponding SCAR markers. Received: 8 November 1999 / Accepted: 15 November 1999     

Comparison of the genetic diversity of common wild rice (Oryza rufipogon Griff.) and cultivated rice (O. sativa L.) using RFLP markers

Forty fourth single-copy RFLP markers were used to evaluate the genetic diversity of 122 accessions of common wild rice (CWR, Oryza rufipogon Griff.) and 75 entries of cultivated rice (Oryza sativa L. ) from more than ten Asian countries. A comparison of the parameters showing genetic diversity, including the percentage of polymorphic loci (P), the average number of alleles per locus (A), the number of genotypes (Ng), the average heterozygosity (Ho) and the average genetic multiplicity (Hs) of CWR and indica and japonica subspecies of cultivated rice from different countries and regions, indicated that CWR from China possesses the highest genetic diversity, followed by CWR from South Asia and Southeast Asia. The genetic diversity of CWR from India is the second highest. Although the average gene diversity (Hs)of the South Asian CWR is higher than that of the Southeast Asian CWR, its percentage of polymorphic loci (P), number of alleles (Na) and number of genotypes (Ng) are all smaller. It was also found that the genetic diversity of cultivated rice is obviously lower than that of CWR. At the 44 loci investigated, the number of polymorphic loci of cultivated rice is only 3/4 that of CWR, while the number of alleles, 60%, and the number of genotypes is about 1/2 that of CWR. Of the two subspecies studied, the genetic diversity of indica is higher than that of japonica. The average heterozygosity of the Chinese CWR is the highest among all the entries studied. The average heterozygosity of CWR is about two-times that of cultivated rice. It is suggested that during the course of evolution from wild rice to cultivated rice, many alleles were lost through natural and human selection, leading to the lower heterozygosity and genetic diversity of the cultivated rice. Received: 19 May 1999 / Accepted: 26 April 2000     

Assignment of DNA markers to Nicotiana sylvestris chromosomes using monosomic alien addition lines

 A sesquidiploid hybrid (PPS, 2n=32) between Nicotiana plumbaginifolia (PP, 2n=20) and N. sylvestris (SS, 2n=24) was backcrossed to N. plumbaginifolia to produce monosomic alien addition lines. A total of 89 2n=21 plants, each containing two sets of N. plumbaginifolia chromosomes and a single N. sylvestris chromosome, were obtained in the BC₁ and BC₂ generations. These plants were classified into 12 groups based on morphological characteristics. The N. sylvestris chromosomes in these plants were identified by RFLP and karyotype analyses. Among the 84 probes tested, 20 could not detect N. sylvestris-specific DNA bands, and the remaining 64 were assigned to 9 normal and 6 aberrant synteny groups. The 9 normal synteny groups corresponded to chromosomes 2, 4, 5, 6, 7, 8, 9, 10 and 12, respectively. Four aberrant synteny groups were the result of chromosome translocations, and 2 were deletions. Received: 10 April 1996 / Accepted: 5 July 1996     

Mapping of one major gene and of QTLs involved in resistance to clubroot in Brassica napus

Clubroot, caused by Plasmodiophora brassicae, is a damaging disease of Brassica napus. Genetic control and mapping of loci involved in high and partial quantitative resistance expressed against two single spore isolates (Pb137–522 and K92–16) were studied in the F₁ and DH progenies of the cross Darmor-bzh (resistant) x Yudal (susceptible). The high level of resistance expressed by Darmor-bzh to isolate Pb137–522 was found to be mainly due to a major gene, which we have named Pb-Bn1, located on linkage group (LG) DY4. Partial quantitative resistance showed by Darmor-bzh to the K92–16 isolate arose from the association of at least two additive QTLs detected on LGs DY4 and DY15; the QTL on DY4, explaining 19% of the variance, was mapped at the same position as the major gene Pb-Bn1. Epistatic interactions between nine regions with or without additive effects were detected. The total phenotypic variation accounted for by additive and epistatic QTLs ranged from 62% to 81% depending on the isolate. For one isolate, the relative effect due to additivity was similar to that due to epistasis. Received: 10 November 1999 / Accepted:18 February 2000     

RFLP mapping of QTLs conferring salt tolerance during germination in an interspecific cross of tomato

 Most cultivars of tomato (Lycopersicon esculentum) are sensitive to salinity during seed germination and at later stages. Genetic resources for salt tolerance have been identified within the related wild species of tomato. The purpose of the present study was to identify quantitative trait loci (QTLs) for salt tolerance during germination in an inbred backcross (BC₁S₁) population of an interspecific cross between a salt-sensitive tomato breeding line (NC84173, maternal and recurrent parent) and a salt-tolerant Lycopersicon pimpinellifolium accession (LA722). Onehundred and nineteen BC₁ individuals were genotyped for 151 restriction fragment length polymorphism (RFLP) markers and a genetic linkage map was constructed. The parental lines and 119 BC₁S₁ families (self-pollinated progeny of 119 BC₁ individuals) were evaluated for germination at an intermediate salt-stress level (150 mM NaCl+15 mM CaCl₂, water potential approximately −850 kPa). Germination was scored visually as radicle protrusion at 8-h intervals for 28 consecutive days. Germination response was analyzed by survival analysis and the time to 25, 50, and 75% germination was determined. In addition, a germination index (GI) was calculated as the weighted mean of the time from imbibition to germination for each family/line. Interval mapping, single-marker analysis and distributional extreme analysis, were used to identify QTLs and the results of all three mapping methods were generally similar. Seven chromosomal locations with significant effects on salt tolerance were identified. The L. pimpinellifolium accession had favorable QTL alleles at six locations. The percentage of phenotypic variation explained (PVE) by individual QTLs ranged from 6.5 to 15.6%. Multilocus analysis indicated that the cumulative action of all significant QTLs accounted for 44.5% of the total phenotypic variance. A total of 12 pairwise epistatic interactions were identified, including four between QTL-linked and QTL-unlinked regions and eight between QTL-unlinked regions. Transgressive phenotypes were observed in the direction of salt sensitivity. The graphical genotyping indicated a high correspondence between the phenotypes of the extreme families and their QTL genotypes. The results indicate that tomato salt tolerance during germination can be improved by marker-assisted selection using interspecific variation. Received: 29 January 1998 / Accepted: 4 June 1998     

Molecular mapping of a major gene conferring resistance to maize mosaic virus

 The objective of this study was to determine the genetic basis of resistance to maize mosaic virus (MMV). Molecular markers were used to map resistance loci to MMV in a set of 91 maize (Zea mays L.) recombinant inbred lines (RILs), derived from the cross between Hi31 (a B68 conversion resistant to MMV) and Kil4 (a Thai inbred susceptible to MMV). The RILs were evaluated for MMV resistance in disease nurseries in Hawaii in the winter of 1993 and the summer of 1994. Twenty-eight highly susceptible RILs were chosen for gene mapping using the pooled-sampling approach. Initial evidence from the pooled DNA indicated that restriction fragment length polymorphism (RFLP) probes on chromosome 3 near the centromere were biased to the susceptible parent allele. Analysis of 91 RILs at 103 RFLP loci confirmed the presence of a major MMV resistance gene on chromosome 3. The resistant allele at this locus, previously named Mv1, is present in the resistant parent Hi31 and traces back to the Argentine parent used in conferring common rust resistance to B68. We conclude that resistance to MMV in B68 and Caribbean flints involves a major gene mv1 on chromosome 3 located between RFLP markers umc102 and php20508. Received: 12 June 1996 / Accepted: 5 July 1996     

RFLP mapping of the genes controlling hybrid breakdown in rice (Oryza sativa L.)

 Complementary recessive genes hwd1 and hwd2 controlling hybrid breakdown (weakness of F₂ and later generations) were mapped in rice using RFLP markers. These genes produce a plant that is shorter and has fewer tillers than normal plants when the two loci have only one or no dominant allele at both loci. A cultivar with two dominant alleles at the hwd1 locus and a cultivar with two dominant alleles at the hwd2 locus were crossed with a double recessive tester line. Linkage analysis was carried out for each gene independently in two F₂ populations derived from these crosses. hwd1 was mapped on the distal region of rice genetic linkage map for chromosome 10, flanked by RFLP markers C701 and R2309 at a distance of 0.9 centiMorgans (cM) and 0.6 cM, respectively. hwd2 was mapped in the central region of rice genetic linkage map for chromosome 7, tightly linked with 4 RFLP markers without detectable recombination. The usefulness of RFLP mapping and map information for the genes controlling reproductive barriers are discussed in the context of breeding using diverse rice germplasm, especially gene introduction by marker-aided selection.     

RFLP analysis of soybean seed protein and oil content

Summary The objectives of this study were to present an expanded soybean RFLP map and to identify quantitative trait loci (QTL) in soybean [Glycine max (L.) Merr.] for seed protein and oil content. The study population was formed from a cross between a G. max experimental line (A81-356022) and a G. soja Sieb. and Zucc. plant introduction (PI 468916). A total of 252 markers was mapped in the population, forming 31 linkage groups. Protein and oil content were measured on seed harvested from a replicated trial of 60 F₂-derived lines in the F₃ generation (F₂₃ lines). Each F₂₃ line was genotyped with 243 RFLP, five isozyme, one storage protein, and three morphological markers. Significant (P<0.01) associations were found between the segregation of markers and seed protein and oil content. Segregation of individual markers explained up to 43% of the total variation for specific traits. All G. max alleles at significant loci for oil content were associated with greater oil content than G. soja alleles. All G. soja alleles at significant loci for protein content were associated with greater protein content than G. max alleles.