QTL identification for early blight resistance (Alternaria solani) in a Solanum lycopersicum × S. arcanum cross

Alternaria solani (Ellis and Martin) Sorauer, the causal agent of early blight (EB) disease, infects aerial parts of tomato at both seedling and adult plant stages. Resistant cultivars would facilitate a sustainable EB management. EB resistance is a quantitatively expressed character, a fact that has hampered effective breeding. In order to identify and estimate the effect of genes conditioning resistance to EB, a quantitative trait loci (QTL) mapping study was performed in F2 and F3 populations derived from the cross between the susceptible Solanum lycopersicum (syn. Lycopersicon esculentum) cv. ‘Solentos’ and the resistant Solanum arcanum (syn. Lycopersicon peruvianum) LA2157 and genotyped with AFLP, microsatellite and SNP markers. Two evaluation criteria of resistance were used: measurements of EB lesion growth on the F2 plants in glasshouse tests and visual ratings of EB severity on foliage of the F3 lines in a field test. A total of six QTL regions were mapped on chromosomes 1, 2, 5–7, and 9 with LOD scores ranging from 3.4 to 17.5. Three EB QTL also confer resistance to stem lesions in the field, which has not been reported before. All QTL displayed significant additive gene action; in some cases a dominance effect was found. Additive × additive epistatic interactions were detected between one pair of QTL. For two QTL, the susceptible parent contributed resistance alleles to both EB and stem lesion resistance. Three of the QTL showed an effect in all tests despite methodological and environmental differences.     

Development of somatic hybrids Solanum × michoacanum Bitter. (Rydb.) (+) S. tuberosum L. and autofused 4x S. × michoacanum plants as potential sources of late blight resistance for potato breeding

Key message

Phytophthora infestans resistant somatic hybrids of S. × michoacanum (+) S. tuberosum and autofused 4 x S. × michoacanum were obtained. Our material is promising to introgress resistance from S. × michoacanum into cultivated potato background.

Abstract

Solanum × michoacanum (Bitter.) Rydb. (mch) is a wild diploid (2n = 2x = 24) potato species derived from spontaneous cross of S. bulbocastanum and S. pinnatisectum. This hybrid is a 1 EBN (endosperm balance number) species and can cross effectively only with other 1 EBN species. Plants of mch are resistant to Phytophthora infestans (Mont) de Bary. To introgress late blight resistance genes from mch into S. tuberosum (tbr), genepool somatic hybridization between mch and susceptible diploid potato clones (2n = 2x = 24) or potato cultivar Rywal (2n = 4x = 48) was performed. In total 18,775 calli were obtained from postfusion products from which 1,482 formed shoots. The Simple Sequence Repeat (SSR), Cleaved Amplified Polymorphic Sequences (CAPS) and Random Amplified Polymorphic DNA (RAPD) analyses confirmed hybrid nature of 228 plants and 116 autofused 4x mch. After evaluation of morphological features, flowering, pollen stainability, tuberization and ploidy level, 118 somatic hybrids and 116 autofused 4x mch were tested for late blight resistance using the detached leaf assay. After two seasons of testing three somatic hybrids and 109 4x mch were resistant. Resistant forms have adequate pollen stainability for use in crossing programme and are a promising material useful for introgression resistance from mch into the cultivated potato background.     

A resistance gene against potato late blight originating from Solanum × michoacanum maps to potato chromosome VII

Solanum ×  michoacanum (Bitter.) Rydb. is a diploid, 1 EBN (Endosperm Balance Number) nothospecies, a relative of potato originating from the area of Morelia in Michoacán State of Mexico that is believed to be a natural hybrid of S. bulbocastanum × S. pinnatisectum. Both parental species and S. michoacanum have been described as sources of resistance to Phytophthora infestans (Mont.) de Bary. The gene for resistance to potato late blight, Rpi-mch1, originating from S. michoacanum was mapped to the chromosome VII of the potato genome. It confers high level of resistance since the plants possessing it showed only small necrotic lesions or no symptoms of the P. infestans infection and we could ascribe over 80% of variance observed in the late blight resistance test of the mapping population to the effect of the closest marker. Its localization on chromosome VII may correspond to the localization of the Rpi1 gene from S. pinnatisectum. When mapping Rpi-mch1, one of the first genetic maps made of 798 Diversity Array Technology (DArT) markers of a plant species from the Solanum genus and the first map of S. michoacanum, a 1EBN potato species was constructed. Particular chromosomes were identified using 48 sequence-specific PCR markers, originating mostly from the Tomato-EXPEN 2000 linkage map (SGN), but also from other sources. Recently, the first DArT linkage map of 2 EBN species Solanum phureja has been published and it shares 197 DArT markers with map obtained in this study, 88% of which are in the concordant positions.     

QTL mapping of foliar glycoalkaloid aglycones in Solanum tuberosum×S. berthaultii potato progenies: quantitative variation and plant secondary metabolism

 Glycoalkaloids are quantitatively inherited in Solanum, and in high concentrations they can be toxic to humans. The increased use of wild potato germplasm to improve the pest resistance, yield, and quality characteristics of cultivated potato may elevate or introduce new, more toxic glycoalkaloids into the cultivated gene pool. Therefore, it is important to increase our understanding of their inheritance, accumulation, and biosynthesis. Glycoalkaloids have two basic constituents – a glycosidic grouping and a steroid alkaloid skeleton. Steroid alkaloids are classified as solanidanes and spirosolanes, of which solanidine and solasodine are, respectively, representatives. RFLP-mapped, diploid, reciprocal backcross potato progenies involving the parents S. tuberosum and S. berthaultii, which produce solanidine and solasodine, respectively, were analyzed for segregation of the glycoalkaloids solanine, chaconine, solasodine and solamargine to identify quantitative trait loci (QTLs) for the production of the aglycones solanidine and solasodine. The F₁ clone M200-30 exhibited low to nondetectable levels of solasodine and solanidine, suggesting that expression was controlled by recessive genes. In a backcross to berthaultii (BCB) and backcross to tuberosum (BCT), several QTLs for the accumulation of solasodine and solanidine were identified. Three QTLs explaining approximately 20% of the variation in solasodine were identified in BCB on chromosomes 4, 6, and 12. Similarly, three QTLs were identified in BCT on chromosomes 4, 8 and 11, but these accounted for only 10% of the variation observed in solasodine accumulation. Two QTLs for solanidine were identified in BCT on chromosomes 1 and 4. The QTL located on chromosome 1 was highly significant, accounting for 17% and 22% of the variation in solanidine accumulation in 1994 and 1995, respectively. This same QTL was also detected in BCB. The QTLs detected in this study probably represent structural and/or regulatory genes controlling the accumulation of solasodine and solanidine. Results are discussed in the context of steroid alkaloid accumulation and biosynthesis. Received: 27 August 1997 / Accepted: 16 March 1998     

Can the QTL for late blight resistance on potato chromosome 5 be attributed to foliage maturity type?

We investigated the association between late blight resistance and foliage maturity type in potato by means of molecular markers. Two QTLs were detected for foliage resistance against Phytophthora infestans (on chromosomes 3 and 5) and one for foliage maturity type (on chromosome 5). The QTL for resistance to late blight and the QTL for foliage maturity type on chromosome 5 appeared to be mapped on indistinguishable positions. We were interested whether this genetic linkage was due to closely linked but different genes, or due to one (or more) gene(s) with pleiotropic effects. We therefore developed an approach to detect QTLs, in which resistance to late blight was adjusted for foliage maturity type. This analysis revealed the same two QTLs for resistance against P. infestans, but the effect of the locus on chromosome 5 was reduced to only half the original effect. This is a strong indication that the two indistinguishable QTLs for foliage maturity type and for late blight resistance on chromosome 5 may actually be one gene with a pleiotropic effect on both traits. However, there was still a significant effect on resistance against P. infestans on the locus on chromosome 5 after adjusting for foliage maturity type. Therefore we cannot rule out the presence of two closely linked QTLs on chromosome 5: one with a pleiotropic effect on both late blight resistance and foliage maturity type, and another with merely an effect on resistance. In addition, the two QTLs for resistance to late blight showed an important epistatic interaction, suggesting that QTLs for resistance affect each other's expression.     

Development of allele-specific PCR and RT–PCR assays for clustered resistance genes using a potato late blight resistance transgene as a model

Members of the NBS-LRR gene family impart resistance to a wide variety of pathogens and are often found clustered within a plant genome. This clustering of homologous sequences can complicate PCR-based characterizations, especially the study of transgenes. We have developed allele-specific PCR and RT–PCR assays for the potato late blight resistance gene RB. Our assay utilizes two approaches toward primer design, allowing discrimination between the RB transgene and both the endogenous RB gene and numerous RB homeologs. First, a reverse primer was designed to take advantage of an indel present in the RB transgene but absent in rb susceptibility alleles, enhancing specificity for the transgene, though not fully discriminating against RB homeologs. Second, a forward primer was designed according to the principles of mismatch amplification mutation assay (MAMA) PCR, targeting SNPs introduced during the cloning of RB. Together, the indel reverse primer and the MAMA forward primer provide an assay that is highly specific for the RB transgene, being capable of distinguishing the transgene from all RB endogenous gene copies and from all RB paralogs in a diverse collection of wild and cultivated potato genotypes. These primers have been successfully multiplexed with primers of an internal control. The multiplexed assay is useful for both PCR and RT–PCR applications. Double MAMA-PCR, in which both PCR primers target separate transgene-specific SNPs, was also tested and shown to be equally specific for the RB transgene. We propose extending the use of MAMA for the characterization of resistance transgenes. Electronic supplementary material The online version of this article () contains supplementary material, which is available to authorized users.     

QTL mapping of fire blight resistance in Malus ×robusta 5 after inoculation with different strains of Erwinia amylovora

Fire blight caused by Erwinia amylovora is one of the most disastrous diseases in apple production. Whereas most apple cultivars are susceptible to fire blight, several wild apple species accessions like Malus ×robusta 5 (Mr5) bear significant resistance. The resistance of Mr5 is mainly inherited by a major quantitative trait locus (QTL) on linkage group 3. QTL mapping was performed after inoculation of the population 04208 (Idared × Mr5) using strains differing in their virulence to Mr5. The QTL mapping approach demonstrated that the major QTL on linkage group 3 could be confirmed after inoculation with strains non-virulent to Mr5. In contrast, the major QTL disappeared after inoculation with strains virulent to Mr5. Only after inoculation with the resistance breaking strain Ea 3049 was a minor QTL with a LOD >3 found on linkage group 3. Additionally, several minor QTLs were detected on linkage groups 5, 7, 11 and 14 of Mr5 after inoculation with virulent strains able to overcome the major resistance QTL of Mr5. Their usefulness for further breeding activities will be discussed. The strain-specific results obtained in the present study provide further evidence for the existence of gene-for-gene relationships in the host–pathogen system Mr5–E. amylovora. Of the newly discovered minor QTLs, the one detected on LG7 contributes significantly to fire blight resistance in the presence of the major QTL, independently of the strain used.     

Expression of the gene encoding Δ12 acyl-lipid desaturase from Synechocystis sp. PCC 6803 improves potato plant resistance to late blight infection

Transgenic (DesA-LicBM3) potato (Solanum tuberosum L., cv. Desnitsa) plants expressing gene encoding Δ12 acyl-lipid desaturase from Synechosystis sp. PCC 6803 were obtained. A significant increase in the relative content of polyunsaturated (linoleic and linolenic) fatty acids in transformants as compared with original genotype was demonstrated. The improved resistance of transgenic plants to late blight causal agent (Phytophthora infestans) as compared with original cultivar was observed.     

Mapping QTL associated with resistance to Fusarium head blight in the Nanda2419 × Wangshuibai population. II: Type I resistance

Fusarium head blight (FHB) is a serious disease in wheat and barley affecting both yield and quality. To identify genes for resistance to infection, the RIL population derived from ‘Nanda2419’ × ‘Wangshuibai’ and the parents were evaluated for percentage of infected spikes (PIS) in four different environments. Using a 2,960 cM marker framework map constructed for this population, ten chromosome regions were detected for their association with type I resistance through interval mapping with Mapmaker/QTL, among which QTLs mapped in the intervals of Xwmc349~Xgwm149 on chromosome 4B, of Xwmc96~Xgwm304 on chromosome 5A and of Xgwm408~Xbarc140 on chromosome 5B were revealed in at least three environments and have Wangshuibai as the source of resistance alleles. Qfhi.nau-4B and Qfhi.nau-5A had larger effects and explained up to 17.5 and 27.0% of the phenotypic variance, respectively. To detect epistasis QTLs, two-locus interactions were examined by whole genome scan. Interactions of five locus pairs were found to have significant effects on type I resistance with the LOD score ranging 3.8–6.5 and four of them conferred resistance in parental phase. The one with the most significant effect was Xcfd42~Xgwm469 (6D)/Xwmc390-2~Xbd04 (2A) pair. No QTL × E interaction was detected for PIS. It was found that flowering time did not have significant effects on PIS in this population. Our studies indicated that Wangshuibai is useful for breeding for both type I and type II scab resistance and the markers associated with the QTLs could be used in marker-assisted selection and isolation of scab-resistance QTLs. F. Lin and S.L. Xue equally contributed to this article     

Genetic mapping of QTL for resistance to Fusarium head blight spread (type 2 resistance) in a Triticum dicoccoides × Triticum durum backcross-derived population

Improvement of resistance to Fusarium head blight (FHB) is a continuous challenge for durum wheat breeders, particularly due to the limited genetic variation within this crop species. We accordingly generated a backcross-derived mapping population using the type 2 FHB resistant Triticum dicoccoides line Mt. Gerizim #36 as donor and the modern Austrian T. durum cultivar Helidur as recipient; 103 BC₁F_6:7 lines were phenotyped for type 2 FHB resistance using single-spikelet inoculations and genotyped with 421 DNA markers (SSR and AFLP). QTL mapping revealed two highly significant QTL, mapping to chromosomes 3A and 6B, respectively. For both QTL the T. dicoccoides allele improved type 2 FHB resistance. Recombinant lines with both favorable alleles fixed conferred high resistance to FHB similar to that observed in the T. dicoccoides parent. The results appear directly applicable for durum wheat resistance breeding.     

Identification of agronomically important QTL in tetraploid potato cultivars using a marker–trait association analysis

Key message

Nineteen tuber quality traits in potato were phenotyped in 205 cultivars and 299 breeder clones. Association analysis using 3364 AFLP loci and 653 SSR-alleles identified QTL for these traits.

Abstract

Two association mapping panels were analysed for marker–trait associations to identify quantitative trait loci (QTL). The first panel comprised 205 historical and contemporary tetraploid potato cultivars that were phenotyped in field trials at two locations with two replicates (the academic panel). The second panel consisted of 299 potato cultivars and included recent breeds obtained from five Dutch potato breeding companies and reference cultivars (the industrial panel). Phenotypic data for the second panel were collected during subsequent clonal selection generations at the individual breeding companies. QTL were identified for 19 agro-morphological and quality traits. Two association mapping models were used: a baseline model without, and a more advanced model with correction for population structure and genetic relatedness. Correction for population structure and genetic relatedness was performed with a kinship matrix estimated from marker information. The detected QTL partly not only confirmed previous studies, e.g. for tuber shape and frying colour, but also new QTL were found like for after baking darkening and enzymatic browning. Pleiotropic effects could be discerned for several QTL.     

Advanced backcross QTL analysis of a Lycopersicon esculentum ×Lycopersicon parviflorum cross

Lycopersicon parviflorum is a sexually compatible, wild tomato species which has been largely unutilized in tomato breeding. The Advanced Backcross QTL (AB-QTL) strategy was used to explore this genome for QTLs affecting traits of agronomic importance in an interspecific cross between a tomato elite processing inbred, Lycopersicon esculentum E6203, and the wild species L. parviflorum (LA2133). A total of 170 BC2 plants were genotyped by means of 133 genetic markers (131 RFLPs; one PCR-based marker, I-2, and one morphological marker, u, uniform ripening). Approximately 170 BC3 families were grown in replicated field trials, in California, Spain and Israel, and were scored for 30 horticultural traits. Significant putative QTLs were identified for all traits, for a total of 199 QTLs, ranging from 1 to 19 QTLs detected for each trait. For 19 (70%) traits (excluding traits for which effects of either direction are not necessarily favourable or unfavourable) at least one QTL was identified for which the L. parviflorum allele was associated with an agronomically favourable effect, despite the overall inferior phenotype of the wild species. Received: 14 September 1999 / Accepted: 7 October 1999     

QTL mapping of stripe,leaf and stem rust resistance genes in a Kariega × Avocet S doubled haploid wheat population

Adult plant resistance to stripe (yellow) rust in the wheat cultivar Kariega has previously been ascribed to a major quantitative trait locus (QTL) on each of chromosomes 2B and 7D, along with a number of minor QTL. We have extended both the size of the cv. Kariega × cv. Avocet S mapping population, and the marker coverage within it, by assembling a set of Diversity Array Technology (DArT) markers. This has allowed for the analysis of the genetic basis of the adult plant and seedling resistances to stripe, leaf and stem rust present in the two mapping population parents. The stripe rust reactions of the segregating material were assessed in both field (three scoring dates) and greenhouse experiments. The chromosome 2B QTL became more important than the Lr34/Yr18 complex on chromosome 7D as the plants aged. As the infection progressed, the two QTL explained an increasing proportion of the variance for percentage leaf area infected. The cv. Kariega allele at the minor chromosome 4A QTL had a consistent effect on the severity of stripe rust infection and the overall plant reaction at the earlier scoring dates, but lost importance as the disease progressed. Several rust resistances were detected using an improved greenhouse-based test.     

Mapping QTLs conferring early blight (Alternaria solani) resistance in a Lycopersicon esculentum×L. hirsutum cross by selective genotyping

Most commercial cultivars of tomato, Lycopersicon esculentum Mill., are susceptible to early blight (EB), a devastating fungal (Alternaria solani Sorauer) disease of tomato in the U.S. and elsewhere in the world. Currently, sanitation, long crop rotation, and routine application of fungicides are the most common disease control measures. Although no source of genetic resistance is known within the cultivated species of tomato, resistant resources have been identified within related wild species. The purpose of this study was to identify and validate quantitative trait loci (QTLs) conferring EB resistance in an accession (PI126445) of the tomato wild species L. hirsutum Humb. and Bonpl. by using a selective genotyping approach. A total of 820 BC₁ plants of a cross between an EB susceptible tomato breeding line (NC84173; maternal and recurrent parent) and PI126445 were grown in a greenhouse. During late seedling stage, plants were inoculated with mixed isolates of A. solani and subsequently evaluated for EB symptoms. The most resistant (75 plants = 9.1%) and most susceptible (80 = 9.8%) plants were selected and subsequently transplanted into a field where natural infestation of EB was severe. Plants were grown to maturity and evaluated for final disease severity. From among the 75 resistant plants, 46 (5.6% of the total) that exhibited the highest resistance, and from among the 80 susceptible plants, 30 (3.7% of the total) that exhibited the highest susceptibility, were selected. The 76 selected plants, representing the two extreme tails of the response distribution, were genotyped for 145 restriction fragment length polymorphism (RFLP) markers and 34 resistance gene analogs (RGAs). A genetic linkage map, spanning approximately 1298 cM of the 12 tomato chromosomes with an average marker distance of 7.3 cM, was constructed. A trait-based marker analysis (TBA), which measures differences in marker allele frequencies between extreme tails of a population, detected seven QTLs for EB resistance, one on each of chromosomes 3, 4, 5, 6, 8, 10 and 11. Of these, all but the QTL on chromosome 3 were contributed from the resistant wild parent, PI126445. The standardized effects of the QTLs ranged from 0.45 to 0.81 phenotypic standard deviations. Four of the seven QTLs were previously identified in a study where different populations and mapping strategy were used. The high level of correspondence between the two studies indicated the reliability of the detected QTLs and their potential use for marker-assisted breeding for EB resistance. The location of several RGAs coincided with locations of EB QTLs or known tomato resistance genes (R genes), suggesting that these RGAs could be associated with disease resistance. Furthermore, similar to that for many R gene families, several RGA loci were identified in clusters, suggesting their potential evolutionary relationship with R genes.     

Mapping of QTL for Fusarium head blight resistance and morphological and developmental traits in three backcross populations derived from Triticum dicoccum?×?Triticum durum

Breeding for resistance to Fusarium head blight (FHB) in durum wheat continues to be hindered by the lack of effective resistance sources. Only limited information is available on resistance QTL for FHB in tetraploid wheat. In this study, resistance to FHB of a Triticum dicoccum line in the background of three Austrian T. durum cultivars was genetically characterized. Three populations of BC₁F₄-derived RILs were developed from crosses between the resistant donor line T. dicoccum-161 and the Austrian T. durum recipient varieties DS-131621, Floradur and Helidur. About 130 BC₁F₄-derived lines per population were evaluated for FHB response using artificial spray inoculation in four field experiments during two seasons. Lines were genetically fingerprinted using SSR and AFLP markers. Genomic regions on chromosomes 3B, 4B, 6A, 6B and 7B were significantly associated with FHB severity. FHB resistance QTL on 6B and 7B were identified in two populations and a resistance QTL on 4B appeared in three populations. The alleles that enhanced FHB resistance were derived from the T. dicoccum parent, except for the QTL on chromosome 3B. All QTL except the QTL on 6A mapped to genomic regions where QTL for FHB have previously been reported in hexaploid wheat. QTL on 3B and 6B coincided with Fhb1 and Fhb2, respectively. This implies that tetraploid and hexaploid wheat share common genomic regions associated with FHB resistance. QTL for FHB resistance on 4B co-located with a major QTL for plant height and mapped at the position of the Rht-B1 gene, while QTL on 7B overlapped with QTL for flowering time.     

Advanced backcross QTL analysis of a hard winter wheat × synthetic wheat population

Advanced backcross quantitative trait locus (AB-QTL) analysis was used to identify QTLs for yield and yield components in a backcross population developed from a cross between hard red winter wheat (Triticum aestivum L.) variety Karl 92 and the synthetic wheat line TA 4152-4. Phenotypic data were collected for agronomic traits including heading date, plant height, kernels per spike, kernel weight, tiller number, biomass, harvest index, test weight, grain yield, protein content, and kernel hardness on 190 BC₂F_2:4 lines grown in three replications in two Kansas environments. Severity of wheat soilborne mosaic virus (WSBMV) reaction was evaluated at one location. The population was genotyped using 151 microsatellite markers. Of the ten putative QTLs identified, seven were located on homoeologous group 2 and group 3 chromosomes. The favorable allele was contributed by cultivated parent Karl 92 at seven QTLs including a major one for WSBMV resistance, and by the synthetic parent at three QTLs: for grain hardness, kernels per spike, and tiller number. Mention of trade names or commercial products in this publication is solely for the purpose of providing specific information and does not imply recommendation or endorsement by the U.S. Department of Agriculture.     

Epistatic fire blight resistance QTL alleles in the apple cultivar ‘Enterprise’ and selection X-6398 discovered and characterized through pedigree-informed analysis

Most cultivated apple cultivars are highly susceptible to fire blight, caused by Erwinia amylovora. However, differences in resistance levels are observed among cultivars and could be used in breeding. In this paper, we investigated the genetic basis of fire blight resistance of the cultivar ‘Enterprise’ and the advanced breeding selection X-6398. Genotyped pedigrees were used for validating and curating historic pedigree records. Various quantitative trait locus (QTL) discovery approaches were applied on the full-sib families ‘Gala’ × ‘Enterprise’ (GaEn) and X-6398 × X-6683 (IW) with the software FlexQTL? and MapQTL®. The paternal lineage of ‘Enterprise’ was reconstructed and showed to include ‘Cox’s Orange Pippin’. The QTLs found varied with the software used. Using FlexQTL?, two were found on linkage groups (LGs) 7 and 13, favourable alleles inherited by Enterprise from ‘Cox’s Orange Pippin’ and ‘Golden Delicious’, respectively. The former was identical to the previously named FB_F7 allele from ‘Fiesta’, while the latter is new and has been named FB_13GD. X-6398 had a QTL at the same position as FB_F7. Its favourable allele was new, originating from the unknown grandfather of X-4598, and was named FB_7X-6398. Using MapQTL® on GaEn, FB_F7 was also identified. Performing the same analysis on the subset of offspring that carried the favourable allele of FB_F7, two putative QTLs on LG8 and on top of LG13 were identified, which showed interactions with FB_F7. Implication of the findings for breeding for fire blight-resistant apples is discussed. Single nucleotide polymorphism data on Enterprise and its ancestors are provided.     

Characterization of a V κ family in Mus musculus castaneus: sequence analysis

To examine genetic variation at immunoglobulin (Ig) multigene loci over short spans of evolutionary time, we have compared members of an Ig kappa chain variable (V ) region family from several mouse species. In this study, seven unique Igk-V24 family members have been isolated from Mus m. castaneus and characterized by nucleotide sequence determination for comparison to their counterparts in Mus m domesticus (BALB/c), and Mus pahari, representing 1–2 million years of evolution in the former case and 5–8 million years in the latter. Parsimony, together with evolutionary distances calculated for various paris of Igk-V24 family coding regions, relate all family members to a common progenitor existing roughly 24 million years ago (Mya). A significant portion of the M. m. castaneus family consists of pseudogene segments in various degrees of progressive degeneration. The substitution patterns and divergence rates for all gene segments are characteristic of their respective subsets, especially in the areas flanking the coding regions. Complex and variable patterns of diversity are seen in potentially expressed coding regions, which appear to reflect quite different selective pressures on various subregions within the V protein domain. These results indicate that evolutionary pressures are operating at the level of family subsets, their individual members, and subregions within similar molecules.The nucleotide sequence data presented in this report have been submitted to the GenBank nucleotide sequence database and assigned the accession numbers (Igk-CaV24) M80407; (Igk-CaV24A) M80408; (Igk-CaV24B.1) M80409; (Igk-CaV24B.2) M80410; (Igk-CaV24D.1) M80411; (Igk-CaV24D.2) M80412; and (Igk-CaV24D.3) M20892.