Molecular dissection of interspecific variation between Gossypium hirsutum and Gossypium barbadense (cotton) by a backcross-self approach: I. Fiber elongation

The current study is the first installment of an effort to explore the secondary gene pool for the enhancement of Upland cotton (Gossypium hirsutum L.) germplasm. We developed advanced-generation backcross populations by first crossing G. hirsutum cv. Tamcot 2111 and G. barbadense cv. Pima S6, then independently backcrossing F₁ plants to the G. hirsutum parent for three cycles. Genome-wide mapping revealed introgressed alleles at an average of 7.3% of loci in each BC₃F₁ plant, collectively representing G. barbadense introgression over about 70% of the genome. Twenty-four BC₃F₁ plants were selfed to generate 24 BC₃F₂ families of 22–172 plants per family (totaling 2,976 plants), which were field-tested for fiber elongation and genetically mapped. One-way analysis of variance detected 22 non-overlapping quantitative trail loci (QTLs) distributed over 15 different chromosomes. The percentage of variance explained by individual loci ranged from 8% to 28%. Although the G. barbadense parent has lower fiber elongation than the G. hirsutum parent, the G. barbadense allele contributed to increased fiber elongation at 64% of the QTLs. Two-way analysis of variance detected significant (P<0.001) among-family genotype effects and genotype×family interactions in two and eight regions, respectively, suggesting that the phenotypic effects of some introgressed chromosomal segments are dependent upon the presence/absence of other chromosomal segments.Electronic Supplementary Material Supplementary material is available for this article at     

Fine mapping of trypanosomiasis resistance loci in murine advanced intercross lines

We have previously reported the results of genome-wide searches in two murine F₂ populations for QTLs that influence survival following Trypanosoma congolense infection. Three loci, Tir1, Tir2, and Tir3, were identified and mapped to mouse Chromosomes (Chrs) 17, 5, and 1 respectively, with confidence intervals (CIs) in the range 10–40 cM. The size of these CIs is to a large degree the consequence of limited numbers of recombination events in small chromosomal regions in F₂ populations. A number of population designs have been proposed to increase recombination levels in crosses, one of which is the advanced intercross line (AIL). Here we report fine mapping of Tir1, Tir2, and Tir3 in G6 populations of two independent murine AILs created by crossing the C57BL/6J strain with the A/J and BALB/cJ strains, respectively. Data were analyzed by two methods that gave equally informative and similar results. The three QTLs were confirmed in the A/J × C57BL/6J AIL and in the combined data set, but Tir2 was apparently lost from the BALB/cJ × C57BL/6J AIL. The reduction in CIs for the Tir loci ranged from 2.5 to more than ten-fold in G6 populations by comparison with CIs obtained previously in the equivalent F₂ generations. Mapping in the AILs also resolved the Tir3 locus into three trypanosomiasis resistance QTLs, revealing a degree of complexity not evident in extensive studies at the F₂ level. Received: 16 December 1999 / Accepted: 24 March 2000     

Extensive heterozygosity at three enzyme loci in hybrid sunfish populations

Hybrid populations of sunfishes were produced in two different ponds, and the frequencies of allelic isozyme phenotypes were determined for three enzyme systems—malate dehydrogenase (NAD), esterases, and tetrazolium oxidase—in order to estimate the extent of heterozygosity at four different genetic loci. Interspecific F₁ hybrid fry (red-ear male × bluegill female) were produced in vitro. These fry were stocked in ponds at the free-swimming stage. When 1 year old, the F₁ hybrids produced a large F₂ hybrid population. Successful hybrid reproduction occurred each year thereafter. In one pond, a 1-year-old F₂ population exhibited all three isozyme phenotypes (red-ear, F₁, bluegill) at most loci in the approximate ratio of the 1:2:1 expected. In a second pond, 5-year-old individuals of the F₂ generation were morphologically like the F₁ and were all heterozygous for the enzyme loci studied. This unusual degree of heterozygosity in the older F₂ population appeared to be the result of differential survival of mature heterozygous individuals and not the result of early embryonic lethality. The increased heterozygosity at these unlinked loci was assumed to reflect the condition at other genetic loci in the F₂ hybrids. Several possible mechanisms are advanced to explain this apparent heterosis.This research was supported by NSF grant GB-16425 (G.S.W.) and by funds from the Illinois Natural History Survey (W.F.C.).     

Mapping,genetic effects,and epistatic interaction of two bacterial canker resistance QTLs from<Emphasis Type="Italic"> Lycopersicon hirsutum</Emphasis>

Two quantitative trait loci (QTL) from Lycopersicon hirsutum, Rcm 2.0 and Rcm 5.1, control resistance to Clavibacter michiganensis subsp. michiganensis (Cmm). To precisely map both loci, we applied interval mapping techniques to 1,056 individuals in three populations exhibiting F₂ segregation. Based on a 1-LOD confidence interval, Rcm 2.0 mapped to a 14.9-cM interval on chromosome 2 and accounted for 25.7–34.0% of the phenotypic variation in disease severity. Rcm 5.1 mapped to a 4.3-cM interval on chromosome 5 and accounted for 25.8–27.9% of the phenotypic variation. Progeny testing of recombinant plants narrowed the QTL location for Rcm 2.0 to a 4.4-cM interval between TG537-TG091 and to a 2.2-cM interval between CT202-TG358 for Rcm 5.1. A population of 750 individuals exhibiting F₂ segregation was used to detect epistasis between both loci using ANOVA and orthogonal contrasts (P=0.027), suggesting that resistance was determined by additive gene action and an additive-by-additive epistatic interaction. A partial diallel mating design was used to confirm epistasis, advance superior genotypes, randomize genetic backgrounds, and create recombination opportunities. This crossing scheme created a more balanced population (n=112) containing the nine F₂ genotypic classes. Parents in the diallel were selected from the previous population based on resistance, genotype at the Rcm 2.0 and Rcm 5.1 loci, and horticultural traits. A replicated trial using the diallel population confirmed additive-by-additive epistasis (P<0.0001). These results validate the gene action, intra -locus interaction, and map position of two loci controlling resistance to Cmm.Communicated by G. Wenzel     

Energy transfer in polynucleotide homopolymers and copolymers

Using the fluorophore Tb³⁺ as a reporter, the effect of thallium (Tl⁺¹) on the transfer of energy in polyribonucleotides and polydeoxynucleotides at room temperature has been studied. In p(G), p(G, I), and pd(G)₆ thallium greatly increases the transfer of uv energy absorbed by the bases to Tb³⁺. In DNA, p(G, U), p(G, A), p(A, U), p(X), p(A), p(U), p(I), pd(G, A)₆, and pd(G, T)₅ thallium has little or no effect. Thallium increases intersystem crossing to the triplet states only in p(G), p(G, I), and pd(G)₆, and the triplets overlap the excited singlet state in Tb³⁺. In those G- and X-containing polymers showing little thallium effect, the evidence suggests that intersystem crossing is comparatively high to begin with. These polymers, including DNA, appear to transfer absorbed energy to triplet states efficiently at room temperature.     

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.     

Chromosomal location of genes conditioning low amylose content of endosperm starches in rice,Oryza sativa L.

Summary Eight dull mutants that lower the amylose content of rice endosperm as well as waxy mutant and a cultivar with common grains were crossed in a diallele manner. The amylose content of F₁ and F₂ seeds was determined on the basis of single grain analysis. It was concluded that the low amylose content of dull mutants is under monogenic recessive control. Alleles for low amylose content are located at five loci designated as du-1, du-2, du-3, du-4 and du-5. These loci are independent of wx locus located on chromosome 6. The five du loci have an additive effect in lowering the amylose content. Two loci, du-1 and du-4, were found to be located on chromosomes 7 and 4, respectively.     

Mapping quantitative trait loci (QTLs) for resistance to Gibberella zeae infection in maize

The basic prerequisite for an efficient breeding program to improve levels of resistance to pathogens in plants is the identification of genes controlling the resistance character. If the response to pathogens is under the control of a multilocus system, the utilization of molecular markers becomes essential. Stalk and ear rot caused by Gibberella zeae is a widespread disease of corn: resistance to G. zeae is quantitatively inherited. Our experimental approach to understanding the genetic basis of resistance to Gibberella is to estimate the genetic linkage between available molecular markers and the character, measured as the amount of diseased tissue 40 days after inoculation of a suspension of Fusarium graminearum, the conidial form of G. zeae, into the first stalk internode. Sensitive and resistant parental inbreds were crossed to obtain F₁ and F₂ populations: the analysis of the segregation of 95 RFLP (restriction fragment length polymorphism) clones and 10 RAPD (random amplified polymorphic DNA) markers was performed on a population of 150 F₂ individuals. Analysis of resistance was performed on the F₃ families obtained by selfing the F₂ plants. Quantitative trait loci (QTL) detection was based either on analysis of regression coefficients between family mean value and allele values in the F₂ population, or by means of interval mapping, using MAPMAKER-QTL. A linkage map of maize was obtained, in which four to five genomic regions are shown to carry factors involved in the resistance to G. zeae.     

Mapping Fusarium wilt race 1 resistance genes in cotton by inheritance,QTL and sequencing composition

Knowledge of the inheritance of disease resistance and genomic regions housing resistance (R) genes is essential to prevent expanding pathogen threats such as Fusarium wilt [Fusarium oxysporum f.sp. vasinfectum (FOV) Atk. Sny & Hans] in cotton (Gossypium spp.). We conducted a comprehensive study combining conventional inheritance, genetic and quantitative trait loci (QTL) mapping, QTL marker-sequence composition, and genome sequencing to examine the distribution, structure and organization of disease R genes to race 1 of FOV in the cotton genome. Molecular markers were applied to F₂ and recombinant inbred line (RIL) interspecific mapping populations from the crosses Pima-S7 (G. barbadense L.) × ‘Acala NemX’ (G. hirsutum L.) and Upland TM-1 (G. hirsutum) × Pima 3-79 (G. barbadense), respectively. Three greenhouse tests and one field test were used to obtain sequential estimates of severity index (DSI) of leaves, and vascular stem and root staining (VRS). A single resistance gene model was observed for the F₂ population based on inheritance of phenotypes. However, additional inheritance analyses and QTL mapping indicated gene interactions and inheritance from nine cotton chromosomes, with major QTLs detected on five chromosomes [Fov1-C06, Fov1-C08, (Fov1-C11 ₁ and Fov1-C11 ₂₎ , Fov1-C16 and Fov1-C19 loci], explaining 8–31% of the DSI or VRS variation. The Fov1-C16 QTL locus identified in the F₂ and in the RIL populations had a significant role in conferring FOV race 1 resistance in different cotton backgrounds. Identified molecular markers may have important potential for breeding effective FOV race 1 resistance into elite cultivars by marker-assisted selection. Reconciliation between genetic and physical mapping of gene annotations from marker-DNA and new DNA sequences of BAC clones tagged with the resistance-associated QTLs revealed defenses genes induced upon pathogen infection and gene regions rich in disease-response elements, respectively. These offer candidate gene targets for Fusarium wilt resistance response in cotton and other host plants.     

Isolate-specific and broad-spectrum QTLs are involved in the control of clubroot in<Emphasis Type="Italic"> Brassica oleracea</Emphasis>

Clubroot, caused by Plasmodiophora brassicae, is one of the most damaging diseases of vegetable Brassica crops in the world. In this study, genetic control and mapping of loci implied in quantitative resistance against five isolates of P. brassicae were studied in the F₁ and F_2/3 progenies of the cross C10 (resistant kale)×HDEM (susceptible broccoli). A genetic map was constructed using RFLP, random and specific PCR-based markers. The 199 loci were assembled into nine linkage groups covering 1,226.3 cM. The F₃ families were assessed for resistance under controlled conditions with four single-spore isolates and one field isolate. A total of nine genomic regions were detected for clubroot resistance. Depending on the isolate, two to five QTLs were identified. The total phenotypic variation accounted for by QTLs ranged from 70% to 88% depending on the isolate. One of the QTLs (Pb-Bo1) was detected in all isolates and explained 20.7–80.7% of the phenotypic variation. Pb-Bo1 had a major effect on three isolates but this effect was weaker for the last two. Five QTLs with minor effect were identified in only one isolate. To construct clubroot resistant varieties, the existence of both broad-spectrum and isolate-specific QTLs should be taken into account for the choice of genomic regions to use in a marker-assisted selection strategy.Communicated by C. Möllers     

Inheritance of annual habit in celery: cosegregation with isozyme and anthocyanin markers

Summary Vernalization response was determined in an annual and two biennial celery strains, Apium graveolens L. and their F₂ hybrids. Although the annual strain did not require vernalization to bolt, plants exposed to 10°C for 7 days bolted 2 weeks earlier than non-treated plants. Inheritance studies based on F₂ and backcross segregations demonstrate that annual habit in celery is partially dominant over biennial and determined by a single gene designated Hb. Cosegregation studies of this trait with nine isozyme loci and a gene determining petiole anthocyanin pigmentation disclosed the following linkage relationships: Adh-1-Sdh-1-Mdh-1, and Got-1-Mdh-2-Hb-A. The recombination frequency observed for Hb and Mdh-2 was too large to use the latter as a useful marker for annual habit.     

Genetic Structure of the Volga–Ural and Central Asian Populations Inferred from the Data on Alu Polymorphism

NineAlu loci (Ya5NBC5, Ya5NBC27, Ya5NBC148, Ya5NBC182, YA5NBC361, ACE, ApoA1, PV92, TPA25) were analyzed in six ethnic populations (Trans-Ural Bashkirs, Tatars-Mishars, Mordovians-Moksha, Mountain Maris, Udmurts, and Komi-Permyaks) of the Volga–Ural region and in three Central Asian populations (Uzbeks, Kazakhs, and Uigurs). All Alu insertions analyzed appeared to be polymorphic in all populations examined. The frequency of insertion varied from 0.110 in Mountain Maris at the Ya5NBC5 locus to 0.914 in Tatars at the ApoA1 locus. The data on the allele frequency distribution at nine loci point to the existence of substantial genetic diversity in the populations examined. The value of the observed heterozygosity averaged over nine Alu insertions varied from 0.326 in Mountain Maris to 0.445 in Kazakhs and Uigurs. The level of the interpopulation genetic differences for the Volga–Ural population (F _st = 0.061) was higher than for the populations of Central Asia (F _st = 0.024), Europe (F _st = 0.02), and Southeastern Asia (F _st = 0.018). The populations examined were highly differentiated both in respect of linguistic characteristics and the geographical position. The data obtained confirmed the effectiveness of the marker system used for the assessment of genetic differentiation and the relationships between the ethnic groups.     

A transgressive segregation factor (RKN2) in Gossypium barbadense for nematode resistance clusters with gene rkn1 in G. hirsutum

Host plant resistance is an important strategy for managing root-knot nematode (Meloidogyne incognita) in cotton (Gossypium L.). Here we report evidence for enhanced resistance in interspecific crosses resulting from transgressive segregation of clustered gene loci. Recently, a major gene, rkn1, on chromosome 11 for resistance to M. incognita in cv. Acala NemX was identified using an intraspecific G. hirsutum cross with susceptible cv. Acala SJ-2. Using interspecific crosses of Acala NemX × susceptible G. barbadense cv. Pima S-7, F₁, F₂, F_2:3, backcross, and testcross Acala NemX × F₁ (Pima S-7 × SJ-2), parental entries and populations were inoculated in greenhouse tests with M. incognita. Genetic analyses based on nematode-induced root galling and nematode egg production on roots, and molecular marker analysis of the segregating interspecific populations revealed that gene rkn1 interacted with a gene (designated as RKN2) in susceptible Pima S-7 to produce a highly resistant phenotype. RKN2 did not confer resistance in Pima S-7, but when combined with rkn1 (genotype Aa or aa), high levels of resistance were produced in the F₁ and segregating F₂, F₃, and BC₁F₁ populations. One SSR marker MUCS088 was identified tightly linked to RKN2 within 4.4 cM in a NemX × F₁ (Pima S-7 × SJ-2) testcross population. Using mapped SSR markers and interspecific segregating populations, MUCS088 linked to the transgressive gene from the susceptible parent and was located in the vicinity of rkn1 on chromosome 11. Diverse genome analyses among A and D genome diploid and tetraploid cottons revealed that marker MUCS088 (165 and 167 bp) is derived from G. arboreum, A₂ diploid genome. These results demonstrated that a highly susceptible parent contributed to nematode resistance via transgressive segregation. Derived highly resistant lines can be used as improved resistance sources in cotton breeding, and MUCS088 can be used to monitor RKN2 introgression in diverse populations. The close genomic location of the transgressive resistance determinants provides an important model system for studying transgressive segregation and epistasis in plants.     

Molecular dissection of interspecific variation between Gossypium hirsutum and G. barbadense (cotton) by a backcross-self approach: II. Fiber fineness

A backcross-self population from a cross between Gossypium hirsutum and G. barbadense was used to dissect the molecular basis of genetic variation governing two parameters reflecting lint fiber fineness and to compare the precision of these two measurements. By applying a detailed restriction fragment length polymorphism (RFLP) map to 3,662 BC₃F₂ plants from 24 independently derived BC₃ families, we were able to detect 32 and nine quantitative trait loci (QTLs) for fiber fineness and micronaire (MIC), respectively. The discovery of larger numbers of QTLs in this study than previously found in other studies based on F₂ populations grown in favorable environments reflects the ability of the backcross-self design to resolve smaller QTL effects. Although the two measurements differed dramatically in the number of QTLs detected, seven of the nine MIC QTLs were also associated with fiber fineness. This supports other data in suggesting that fiber fineness more accurately reflects the underlying physical properties of cotton fibers and, consequently, is a preferable trait for selection. Negative transgression, with the majority of BC₃F₂ families showing average phenotypes that were poorer than that of the inferior parent, suggests that many of the new gene combinations formed by interspecific hybridization are maladaptive and may contribute to the lack of progress in utilizing G. barbadense in conventional breeding programs to improve upland cotton.Electronic Supplementary Material Supplementary material is available for this article at     

Chromosomal localization of four isozyme loci by trisomic analysis in rice (Oryza sativa L.)

Summary Four genes coding for isozymes in rice (Oryza sativa L.), were located to respective chromosmes through trisomic analysis. Twelve primary trisomics in IR36 background were crossed with 2 lines having contrasting alleles at four loci. For each gene, all 12 disomic and trisomic F₁ hybrids were screened for allele dosage effects. Either F₂ or BC1 populations of all cross combinations were assessed for gene segregtion. Evidence from both sources indicated the following locations: Pgi-1 on chromosome 4, Sdh-1 on chromosome 6, Est-8 on chromosome 7 and Adh-1 on chromosome 11. The location of Sdh-1 was further confirmed through the production of triallelic heterozygotes with trisomic 6.     

High resolution mapping of chromosomal regions controlling resistance to gastrointestinal nematode infections in an advanced intercross line of mice

Fine mapping of quantitative trait loci (QTL) associated with resistance to the gastrointestinal parasite Heligmosomoides polygyrus was achieved on F₆/F₇ offspring (1076 mice) from resistant (SWR) and susceptible (CBA) mouse strains by selective genotyping (top and bottom 20% selected on total worm count in week 6). Fecal egg counts were recorded at weeks 2, 4, and 6, and the average was also analyzed. Blood packed cell volume in weeks 3 and 6 and five immunological traits (mucosal mast cell protease 1, granuloma score, IgG1 against adult worm, IgG1, and IgE to L4 antigen) were also recorded. On Chromosome 1 single-trait analyses identified a QTL with effects on eight traits located at about 24 cM on the F₂ mouse genome database (MGD) linkage map, with a 95% confidence interval (CI) of 20-32 cM established from a multitrait analysis. On Chromosome 17 a QTL with effects on nine traits was located at about 18 cM on the MGD map (CI 17.9-18.4 cM). Strong candidate genes for the QTL position on Chromosome 1 include genes known to be involved in regulating immune responses and on Chromosome 17 genes within the MHC, notably the Class II molecules and tumor necrosis factor.     

Mapping of QTLs involved in nematode resistance, tuber yield and root development in Solanum sp.

A backcross population, derived from the cross (S. tuberosumxS. spegazzinii)xS. tuberosum was used to map QTLs involved in nematode resistance, tuber yield and root development. Complete linkage maps were available for the interspecific hybrid parent as well as the S. tuberosum parent, and interval mapping for all traits was performed for both. Additionally, the intra- and inter-locus interactions of the QTLs were examined. The Gro1.2 locus, involved in resistance to G. rostochiensis pathotype Ro1, that was previously mapped in the S. tuberosumxS. spegazzinii F₁ population, was located more precisely on chromosome 10. A new resistance locus, Gro1.4, also conferring resistance to G. rostochiensis pathotype Ro1, was found on chromosome 3. Different alleles of this locus originating from both parents contributed to the resistant phenotype, indicating multiallelism at this locus. No interlocus interactions were observed between these two resistance loci. For resistance to G. pallida no QTLs were detected. One minor QTL involved in tuber yield was located on chromosome 4. Two QTLs involved in root development and having large effects were mapped on chromosomes 2 and 6 and an epistatic interaction was found between these two loci.     

Theoretical study of the intermolecular potential energy and second virial coefficient in the mixtures of CH4 and Kr gases: a comparison with experimental data

The intermolecular potential energy surface (IPS) in the mixtures of CH₄–Kr gases from ab initio calculations has been explored. The ab initio calculation was performed at the second-order Møller–Plesset perturbation theory (MP₂), with the 6-311+G(2df,2pd) basis set, for three relative orientations of two CH₄–Kr molecules as a function of CH₄–Kr separation distance. In this work, the IPS, U(r), of the CH₄–Kr complex has been investigated, where the vertex (V), edge (E) and face (F) of CH₄ approaches to Kr have been considered. Then, adjustable parameters of the Lennard-Jones and Buckingham potential energy function are fitted to the ab initio MP2/6-311+G(2df,2pd) interaction energies for three different orientations. Assuming a given set of parameters, we theoretically obtained second virial coefficients for the CH₄–Kr system, and compared with the experimental data at different temperatures. Trivial differences can be observed between the experimental and computational results.     

Genetics and molecular mapping of a male fertility restoration locus (Rfg1) in rye (Secale cereale L.)

 A gene determining the restoration of cytoplasmic genic male sterility (CMS) caused by the Gülzow (G)-type cytoplasm was mapped by analyzing an F₂ and F₃ population comprising 140 and 133 individual plants, respectively. The target gene, designated Rfg1, was mapped on chromosome 4RL distally to three RFLP (Xpsr119, Xpsr167, Xpsr899) and four RAPD (XP01, XAP05, XR11, XS10) loci. Xpsr167 and Xpsr899 are known to be located on the segment of chromosome 4RL which was ancestrally translocated and is homoeologous to the distal end of other Triticeae 6S chromosomes. It is suggested that Rfg1 may be allelic to the gene determining the restoration of rye CMS caused by the Pampa (P) cytoplasm (chromosome 4RL) and to Rfc4 that on rye addition lines of chromosome 4RL restores male fertility of hexaploid wheat with T. timopheevi cytoplasm. Homoeoallelism to two loci for cytoplasmic-male-sterility restoration on chromosomes 6AS and 6BS in hexaploid wheat is also suggested. Received: 1 December 1997 / Accepted: 10 February 1998     

Genetic control of aluminium tolerance in rye (Secale cereale L.)

 Aluminium (Al) tolerance in roots of two cultivars (“Ailés” and “JNK”) and two inbred lines (“Riodeva” and “Pool”) of rye was studied using intact roots immersed in a nutrient solution at a controlled pH and temperature. Both the cultivars and the inbred lines analysed showed high Al tolerance, this character being under multigenic control. The inbred line “Riodeva” was sensitive (non-telerant) at a concentration of 150 μM, whereas the “Ailes” cultivar showed the highest level of Al tolerance at this concentration. The segregation of aluminium-tolerance genes and several isozyme loci in different F₁s, F₂s and backcrosses between plants of “Ailés” and “Riodeva” were also studied. The segregation ratios obtained for aluminium tolerance in the F₂s analysed were 3 : 1 and 15 : 1 (tolerant : non-tolerant) while in backcrosses they were 1 : 1 and 3 : 1. These results indicated that Al tolerance is controlled by, at least, two major dominant and independent loci in rye (Alt1 and Alt3). Linkage analyses carried out between Al-tolerance genes and several isozyme loci revealed that the Alt1 locus was linked to the aconitase-1 (Aco1), nicotinamide adenine dinucleotide dehydrogenase-2 (Ndh2), esterase-6 (Est6) and esterase-8 (Est8) loci, located on chromosome arm 6RL. The order obtained was Alt1-Aco1-Ndh2-Est6-Est8. The Alt3 locus was not linked to the Lap1, Aco1 and Ndh2 loci, located on chromosome arms, 6RS, 6RL and 6RL respectively. Therefore, the Alt3 locus is probably on a different chromosome. Received: 18 March 1997 / Accepted: 21 March 1997