SEARCH · PubMed Health

Results for “Introgression”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 397 records · Page 22Linked to original sources

PubMed1991

The evolutionary history of Drosophila buzzatii. XXI. Cumulative action of multiple sterility factors on spermatogenesis in hybrids of D. buzzatii and D. koepferae.

The genetic basis of sterility in male hybrids of Drosophila buzzatii and D. koepferae has been investigated by assessment of the effects on spermatogenesis of substituting separate chromosome segments of the recipient species with the homologous material from the donor species, either in heterozygous (autosomes) or hemizygous (X chromosome) condition, after successive backcrossing of hybrid females to either parental species. Introgressed segments were identified by the characteristic asynapsis of the polytene chromosomes in their heterospecific regions. Except for one case, the introgression of chromosome segments either from autosome 3, 4, or 5 brings about sterility only when the introgressed segment exceeds a minimum size (threshold size). Segments of equal size frequently produce similar abnormalities, whose severity increases with the size of the introgressed segment. Apparently, throughout these autosomes of D. buzzatii and D. koepferae there are many non-allelic, minor sterility genes, whose individual segregation cannot be recognized phenotypically, and which act cumulatively on the same characteristics of spermatogenesis, each contributing a small effect to the phenotype. Accordingly, these genes should be considered as polygenes, and the type of sterility they bring about should be properly designated polygenic sterility.

Animals↗

PubMed2001

Frequent cytoplasmic exchanges between oak species that are not closely related: Quercus suber and Q. ilex in Morocco.

Chloroplast (cp) and mitochondrial (mt) DNA variation were studied in 97 populations of cork oak (Quercus suber) in Morocco; in 31 of these populations, holm oak (Quercus ilex), a clearly distinct species, also occurred and was compared with Q. suber. Three cpDNA and one mtDNA primer pairs were used in the survey, each in combination with one restriction enzyme. Six haplotypes belonging to two very divergent lineages were detected; one lineage predominates in each species, and is probably ancestral, as inferred from comparisons with other oak species. In the mixed-species populations, cytoplasmic genomes were frequently shared across species, as indicated by an introgression ratio of 0.63. This index is a new measure of the propensity of species to share locally genetic markers, varying from zero (complete differentiation) to one (no differentiation). By contrast, more closely related deciduous oak species (Q. robur, Q. petraea and Q. pubescens) have introgression ratios varying from 0.82 to 0.97. The introgression events appear to have been more frequent in the direction Q. ilex (female) x Q. suber (male), a finding which seems attributable to the flowering phenology of these two species. This asymmetry may have favoured immigration of Q. suber beyond its main range, in regions already colonized by Q. ilex. There, rare hybridization and further introgression through long distance pollen flow have established populations that are morphologically indistinguishable from Q. suber but that have cytoplasmic genomes originating from the local Q. ilex populations.

DNA, Chloroplast↗

PubMed2000

Origin and evolution of invasive naturalized material of Rhododendron ponticum L. in the British isles.

Information concerning the area of origin, genetic diversity and possible acquisition of germplasm through hybridization is fundamental to understanding the evolution, ecology and possible control measures for an introduced invasive plant species. Rhododendron ponticum is extensively naturalized in the British Isles, but it is not known whether native material in Turkey, Spain or Portugal gave rise to the naturalized material, or to what extent introgression has affected this material. Chloroplast (cp) and nuclear ribosomal DNA (rDNA) restriction fragment length polymorphisms (RFLPs) were sought which could distinguish between native material of R. ponticum, and between 15 other Rhododendron species including R. ponticum's closest relatives. Thereafter, a total of 260 naturalized accessions of R. ponticum from throughout the British Isles was examined with respect to informative polymorphisms. It was found that 89% of these accessions possessed a cpDNA haplotype that occurred in native material of R. ponticum derived almost entirely from Spain, while 10% of accessions had a haplotype unique to Portuguese material. These results therefore indicated an Iberian origin for British material. rDNA or cpDNA evidence of introgression from R. catawbiense was found in 27 British accessions of R. ponticum, and such accessions were significantly more abundant in Britain's coldest region, eastern Scotland, than elsewhere. This could indicate that introgression from R. catawbiense confers improved cold tolerance. Introgression from R. maximum and an unidentified species was also detected.

Adaptation, Physiological↗

PubMed2003

Hybridization and Rorippa austriaca (Brassicaceae) invasion in Germany.

Introgressive hybridization between the invasive Rorippa austriaca and the native R. sylvestris in Germany has been studied using chloroplast DNA (trnL intron) and amplified fragment length polymorphism. Three hybrid zones between the invasive and native species were located in the Ruhr Valley (Mülheim) and at the River Main near Würzburg (Randersacker, Winterhausen). In each hybrid zone hybridization was indicated by additivity of region-specific amplified fragment length polymorphism markers proving independent hybridization events. The hybrids were either morphologically intermediate (R. x armoracioides) or were close to R. sylvestris. The trnL intron of R. austriaca is characterized by a species-specific deletion. This diagnostic chloroplast marker of R. austriaca was detected in three individuals of R. sylvestris providing evidence for introgression of the invasive chloroplast into the native species. Bidirectional introgression of R. austriaca markers into R. sylvestris and of R. sylvestris markers into R. austriaca was detected in the amplified fragment length polymorphism analysis. Some of the invasive R. austriaca populations showed high within-population variation. A possible association among introgression, within-population variation and invasion success is discussed. The morphologically intermediate hybrid R. x armoracioides is currently spreading in northern Germany. It forms large populations without its parent species R. austriaca and R. sylvestris. It is concluded that hybridization between invasive R. austriaca and native R. sylvestris may lead to the evolution of a new invasive species R. x armoracioides.

Cluster Analysis↗

PubMed2003

Evidence for bimodal hybrid zones between two species of char (Pisces: Salvelinus) in northwestern North America.

Dolly Varden (Salvelinus malma, Pisces: Salmonidae) and bull trout (Salvelinus confluentus) have widely overlapping, but largely parapatric ranges in watersheds in northwestern North America from Washington State to northern British Columbia. Genetic analysis of natural populations using diagnostic molecular markers revealed widespread local sympatry and hybridization with hybrids comprising 0-25% of the local samples. In a detailed analysis of hybridization using four nuclear DNA markers and mitochondrial DNA within the Thutade Lake watershed, northcentral British Columbia, hybrid genotypes constituted up to 9% of the population of juvenile char. There were significant deviations from Hardy-Weinberg, gametic, and cytonuclear equilibria, and local samples showed bimodal frequency distributions of genotypes. Pure parental and inferred backcross genotypes were most common, and F1 and F(n) hybrids were comparatively rare. Interspecific hybridization was asymmetrical, with most F1 hybrids (five of six) bearing S. confluentus mtDNA. The introgression of nuclear and mitochondrial alleles was asymmetrical, with S. confluentus mtDNA and Growth Hormone 2 introgressing into S. malma significantly more than either introgression of the three other nuclear loci, or introgression of S. malma alleles into S. confluentus. Substantial prezygotic isolation between the species likely depends on the large body size difference between them in sympatry: S. malma have small bodies and a stream resident life history (12-21 cm adult fork length at maturity), while S. confluentus are larger and adfluvial, i.e., they migrate to Thutade Lake where they grow to maturity before returning to tributary streams to spawn (40-90 cm at maturity). These traits may limit interspecific pairings because of size assortative pairing and size-dependent reproductive habitat use.

Animals↗

PubMed1994

Floral and ecological isolation between Aquilegia formosa and Aquilegia pubescens.

Habitat preference and pollination syndrome have been suggested as major factors in reproductive isolation among plant species. The columbine genus Aquilegia contains species that have been used as classic examples of reproductive isolation due to ecological and floral factors. In this analysis Aquilegia formosa, Aquilegia pubescens, and natural hybrid populations between these two species were assayed for genetic and morphological variation. Clinal variation was evident for three "random amplified polymorphic DNA" loci and five morphological characters along a transect extending from a lower altitude A. formosa population, through an intermediate hybrid population, to a higher altitude A. pubescens population. Similar clinal variation was also discovered for a transect that included A. formosa-like, hybrid, and A. pubescens-like populations at a single elevation. The change in the frequency of both sets of markers was closely associated with change in habitat. The molecular markers indicate the presence of bidirectional introgression between these two species. In contrast, there was apparently selection against introgression of four of the five alternate floral characters. Selection against the incorporation of floral characters from one species into the other species was suggested by the introgression of the DNA markers with little or no introgression of the four floral characters. These findings suggest the importance of adaptations associated with both pollination syndromes and habitat preference on species integrity.

Adaptation, Biological↗

PubMed1993

An autosomal factor from Drosophila arizonae restores normal spermatogenesis in Drosophila mojavensis males carrying the D. arizonae Y chromosome.

Males of Drosophila mojavensis whose Y chromosome is replaced by the Y chromosome of the sibling species Drosophila arizonae are sterile. It is shown that genetic material from the fourth chromosome of D. arizonae is necessary and sufficient, in single dose, to restore fertility in these males. In introgression and mapping experiments this material segregates as a single Mendelian factor (sperm motility factor, SMF). Light and electron microscopy studies of spermatogenesis in D. mojavensis males whose Y chromosome is replaced by introgression with the Y chromosome of D. arizonae (these males are symbolized as mojYa) revealed postmeiotic abnormalities all of which are restored when the SMF of D. arizonae is co-introgressed (these males are symbolized as mojYaSMFa). The number of mature sperm per bundle in mojYaSMFa is slightly less than in pure D. mojavensis and is even smaller in males whose fertility is rescued by introgression of the entire fourth chromosome of D. arizonae. These observations establish an interspecific incompatibility between the Y chromosome and an autosomal factor (or more than one tightly linked factors) that can be useful for the study of the evolution of male hybrid sterility in Drosophila and the genetic control of spermatogenesis.

Animals↗

PubMed1996

Inversion monophyly in African anopheline malaria vectors.

The African Anopheles gambiae complex of six sibling species has many polymorphic and fixed paracentric inversions detectable in polytene chromosomes. These have been used to infer phylogenetic relationships as classically done with Drosophila. Two species, A. gambiae and A. merus, were thought to be sister taxa based on a shared X inversion designated Xag. Recent DNA data have conflicted with this phylogenetic inference as they have supported a sister taxa relationship of A. gambiae and A. arabiensis. A possible explanation is that the Xag is not monophyletic. Here we present data from a gene (soluble guanylate cyclase) within the Xag that strongly supports the monophyly of the Xag. We conjecture that introgression may be occurring between the widely sympatric species A. gambiae and A. arabiensis and that the previous DNA phylogenies have been detecting the introgression. Evidently, introgression is not uniform across the genome, and species-specific regions, like the X-chromosome inversions, do not introgress probably due to selective elimination in hybrids and backcrosses.

Animals↗

PubMed1998

Candidate quantitative trait loci and naturally occurring phenotypic variation for bristle number in Drosophila melanogaster: the Delta-Hairless gene region.

Delta (Dl) and Hairless (H) are two chromosome 3 candidate neurogenic loci that might contribute to naturally occurring quantitative variation for sensory bristle number. To evaluate this hypothesis, we assessed quantitative genetic variation in abdominal and sternopleural bristle numbers among homozygous isogenic third chromosomes sampled from nature and substituted into the Samarkand (Sam) inbred chromosome 1 and 2 background; among homozygous lines in which the wild-derived Dl-H gene region was introgressed into the Sam chromosome 3 background; and among Dl-H region introgression lines as heterozygotes against the Sam wild-type strain and derivatives of Sam into which mutant Dl and H alleles had been introgressed. Variation among the Dl-H region introgression lines accounted for 36% (8.3%) of the total chromosome 3 among line variance in abdominal (sternopleural) bristle number and for 53% of the chromosome 3 sex x line variance in abdominal bristle number. Naturally occurring alleles in the Dl-H region failed to complement a Dl mutant allele for female abdominal bristle number and sternopleural bristle number in both sexes, and an H mutant allele for both bristle traits in males and females. These results are consistent with the hypothesis that naturally occurring alleles at Dl and H contribute to quantitative genetic variation in sensory bristle number.

Analysis of Variance↗

PubMed1999

Hybrid zones and the genetic architecture of a barrier to gene flow between two sunflower species.

Genetic analyses of reproductive barriers represent one of the few methods by which theories of speciation can be tested. However, genetic study is often restricted to model organisms that have short generation times and are easily propagated in the laboratory. Replicate hybrid zones with a diversity of recombinant genotypes of varying age offer increased resolution for genetic mapping experiments and expand the pool of organisms amenable to genetic study. Using 88 markers distributed across 17 chromosomes, we analyze the introgression of chromosomal segments of Helianthus petiolaris into H. annuus in three natural hybrid zones. Introgression was significantly reduced relative to neutral expectations for 26 chromosomal segments, suggesting that each segment contains one or more factors that contribute to isolation. Pollen sterility is significantly associated with 16 of these 26 segments, providing a straightforward explanation of why this subset of blocks is disadvantageous in hybrids. In addition, comparison of rates of introgression across colinear vs. rearranged chromosomes indicates that close to 50% of the barrier to introgression is due to chromosomal rearrangements. These results demonstrate the utility of hybrid zones for identifying factors contributing to isolation and verify the prediction of increased resolution relative to controlled crosses.

Alleles↗

PubMed2001

Evolutionary implications of divergent clines in an avian (Manacus: Aves) hybrid zone.

A previous study of the hybrid zone in western Panama between white-collared (Manacus candei) and golden-collared manakins (M. vitellinus) documented the unidirectional introgression of vitellinus male secondary sexual traits across the zone. Here, we examine the hybrid zone in greater genetic and morphological detail. Statistical comparisons of clines are performed using maximum-likelihood and nonparametric bootstrap methods. Our results demonstrate that an array of six molecular and two morphometric markers agree in cline position and width. Clines for male collar and belly color are similar in width to the first eight clines, but are shifted in position by at least five cline widths. The result is that birds in intervening populations are genetically and morphometrically very like parental candei, but males have the plumage color of parental vitellinus. Neither neutral diffusion nor nonlinearity of color scales appear to be viable explanations for the large cline shifts. Genetic dominance of vitellinus plumage traits is another potential explanation that will require breeding experiments to test. Sexual selection remains a plausible explanation for the observed introgression of vitellinus color traits in these highly dimorphic, polygynous, lek-mating birds. Two other clines, including a nondiagnostic isozyme locus, are similar in position to the main cluster of clines, but are broader in width. Thus, introgression at some loci is greater than that detected with diagnostic markers. Assuming that narrow clines are maintained by selection, variation in cline width indicates that selection is not uniform throughout the genome and that diagnostic markers are under more intense selective pressure. The traditional focus on diagnostic markers in studies of hybrid zones may therefore lead to underestimates of average introgression. This effect may be more pronounced in organisms with low levels of genetic divergence between hybridizing taxa.

Animals↗

PubMed2002

Hybrid bridges to gene flow: a case study in milkweeds (Asclepias).

Natural hybridization occurs throughout areas of sympatry for the North American milkweeds Asclepias exaltata and A. syriaca (Asclepiadaceae), even though the formation of F1 hybrid seed is a rare event. For introgressive hybridization to proceed, F1 and advanced hybrids must be released from reproductive barriers and successfully mate with one or both parental species. I investigated the mating system of natural hybrids between A. exaltata and A. syriaca in three populations in Shenandoah National Park, Virginia. Allozyme data and a maximum-likelihood procedure were used to estimate the frequency of six genotypic classes (parentals, F1, F2, and backcrosses) of the hybridizing populations, the pollinia received by hybrid plants, and the paternal parents of seeds produced by hybrids. F1 hybrids, backcross A. syriaca, and parental A. syriaca individuals were common in three hybrid populations. Even though self-pollinations and interhybrid pollinations were common, F2 seed production and the occurrence of F2 individuals were rare in hybrid populations. Hybrid plants received more pollen from A. syriaca than A. exaltata, which resulted in the production of more backcross-A. syriaca seed than backcross-A. exaltata seed. Asclepias exaltata was rare in the hybrid populations, but A. exaltata pollinia were received by hybrids and this species sired between 15% and 36% of the seeds produced on hybrids. The potential for introgression with A. exaltata populations is lower because this species is unsuccessful as the maternal parent in interspecific and backcross hand-pollinations. The asymetry of hybridization with A. syriaca as the maternal parent is further supported by the incorporation of maternally inherited chloroplast DNA markers in hybrids. Hybrid milkweeds frequently backcross with both parental species and may be released from the reproductive barriers that limit the formation of F1 hybrids in natural populations. The direction of interspecific gene flow and introgression in milkweeds is influenced by the reproductive biology of hybrids, the constituency of the surrounding population, and failure of some crosses to produce seeds. Finally, introgressive hybridization remains an important evolutionary force even when the initial formation of F1 hybrids in natural populations is rare.

Alleles↗

PubMed2003

Cryptic repeated genomic recombination during speciation in Gossypium gossypioides.

The Mexican cotton Gossypium gossypioides is a perplexing entity, with conflicting morphological, cytogenetic, and molecular evidence of its phylogenetic affinity to other American cottons. We reevaluated the evolutionary history of this enigmatic species using 16.4 kb of DNA sequence. Phylogenetic analyses show that chloroplast DNA (7.3 kb), nuclear ribosomal internal transcribed spacers (ITS; 0.69 kb), and unique nuclear genes (8.4 kb) yield conflicting resolutions for G. gossypioides. Eight low-copy nuclear genes provide a nearly unanimous resolution of G. gossypioides as the basalmost American diploid cotton, whereas cpDNA sequences resolve G. gossypioides deeply nested within the American diploid clade sister to Peruvian G. raimondii, and ITS places G. gossypioides in an African (rather than an American) clade. These data, in conjunction with previous evidence from the repetitive fraction of the genome, implicate a complex history for G. gossypioides possibly involving temporally separated introgression events from genetically divergent cottons that are presently restricted to different hemispheres. Based on repetitive nuclear DNA, it appears that G. gossypioides experienced nuclear introgression from an African species shortly after divergence from the remainder of the American assemblage. More recently, hybridization with a Mexican species may have resulted in cpDNA introgression, and possibly a second round of cryptic nuclear introgression. Gossypium gossypioides provides a striking example of the previously unsuspected chimeric nature of some plant genomes and the resulting phylogenetic complexity produced by multiple historical reticulation events.

Africa↗

PubMed1996

Detection and pattern of interspecific hybridization between Gliricida sepium and G. maculata in Meso-America revealed by PCR-based assays.

Gliricidia sepium provides a variety of products important for rural communities in tropical countries. Native populations in Meso-America currently form an important source of seed for distribution to farmers, but concerns centre on mechanisms which may lead to their genetic erosion, including anthropogenic dispersal and subsequent introgression from the related species, G. maculata. Populations of Gliricidia were examined genetically using approaches based on the polymerase chain reaction to test for interspecific hybridization and introgression between G. sepium and G. maculata. Analysis involved 13 RAPD and two RFLP-PCR markers which were identified to have species-diagnostic distributions. Data from both approaches corresponded and indicated three locations where multilocus genotypes were consistent with an hybrid origin. Data at one of these sites was consistent with introgression following hybridization. The hybrid origin of populations was supported by the intermediate geographical location of these sites to 'pure' populations of each species. Analysis of maternally inherited organellar DNA, which involved the detection of SSCPs in mitochondrial DNA amplification products, allowed further delineation of genetic structure among Gliricidia populations. Mitochondrial data indicated a high degree of organelle differentiation between sampled locations and identified G. sepium- and G. maculata-diagnostic haplotypes. This data supported the interpretation of genetic structure based on RAPDs and RFLP-PCR. In addition, cytonuclear analysis allowed the directionality of gene transfer during the formation of hybrid populations to be described. Despite evidence for the occurrence of interspecific hybridization and introgression in Gliricidia, important resource populations of G. sepium on the Pacific coast appear to have retained their genetic integrity. Implications in terms of the conservation and utilization of genetic resources within the genus are discussed.

Base Sequence↗

PubMed2004

Testing the utility of internally transcribed spacer sequences in coral phylogenetics.

Reef-building corals often possess high levels of intraindividual and intraspecific ribosomal DNA (rDNA) variation that is largely polyphyletic between closely related species. Polyphyletic rDNA phylogenies coupled with high intraindividual rDNA variation have been taken as evidence of introgressive hybridization in corals. Interpreting the data is problematic because the rDNA cluster evolves in a complex fashion and polyphyletic lineages can be generated by a variety of processes--such as incomplete lineage sorting and slow concerted evolution--in addition to hybridization. Using the genetically characterized Caribbean Acropora hybridization system, we evaluate how well rDNA data perform in revealing patterns of recent introgressive hybridization in contrast to genetic data from four single-copy loci. While the rDNA data are broadly consistent with the unidirectional introgression seen in other loci, we show that the phylogenetic signature of recent introgressive hybridization is obscured in the Caribbean Acropora by ancient shared rDNA lineages that predate the divergence of the species.

Analysis of Variance↗

PubMed2003

Fine mapping of quantitative trait loci for improved fruit characteristics from Lycopersicon chmielewskii chromosome 1.

The near-isogenic line (NIL) TA1150 contains a 56-cM introgression from Lycopersicon chmielewskii chromosome 1 and has several interesting phenotypic characteristics including fruit with orange color, high levels of soluble solids, thick pericarp, small stem scars, and good firmness. A set of overlapping recombinant lines (subNILs) was developed and field tested to fine map the quantitative trait loci (QTL) controlling these traits. The results indicated that the solids, pericarp thickness, and firmness QTL are distinct from the color locus. Several of the QTL mapped in this study, including the soluble-solids QTL, probably correspond to QTL mapped in other wild species of tomato. However, analysis of a set of TA523 subNILs containing complementary introgressions from Lycopesicon hirsutum chromosome 1 suggests that this wild species may contain a different locus for improved soluble solids. Thus, it might be possible to combine the L. chmielewskii and L. hirsutum alleles for these loci in a single line with the potential for extremely highly soluble solids. The TA1150 subNIL TA1688 contains the smallest introgression of the solids locus (approximately 19 cM), as well as the pericarp thickness and firmness QTL, with a yield that was equivalent to two of the three control lines. Isolation of recombinant subNILs from TA1688 should break the linkage between orange color and high solids and provide a small introgressed segment for marker-assisted breeding and genetic improvement of processing tomato.

Alleles↗

PubMed2003

Congenic strains confirm the presence of salt-sensitivity QTLs on chromosome 1 in the Sabra rat model of hypertension.

We previously detected by linkage analysis in segregating populations derived from crosses between the Sabra hypertension-prone rat (SBH/y) and the hypertension-resistant strain (SBN/y) two QTLs for salt susceptibility on chromosome 1, with sex specificity: in males SS1a and SS1b, and in females SS1b only. To provide support for a functional role of these QTLs in relation to hypertension, we constructed congenic strains by replacing most of or selected segments from chromosome 1 from SBN/y with the homologous chromosomal regions of SBH/y, or reciprocally from SBH/y with segments of SBN/y, leaving the other chromosomes unperturbed. Genetic screening with over 150 microsatellite markers confirmed the homozygosity of the targeted genomic inserts and of the remainder of the genomic background. The phenotype of the congenic strains was tested by salt loading with DOCA-salt over a 4-wk period and measuring blood pressure by tail-cuff (in all animals) or radiotelemetry (in select groups) at baseline and during salt loading. In the congenic strains in which a chromosomal segment incorporating QTL SS1a from SBN/y was introgressed onto the genomic background of SBH/y, the blood pressure response to salt loading, as measured by tail-cuff, was decreased by 16 mmHg in both males and females compared with the parental SBH/y; replacing the QTL SS1b reduced the blood pressure response by 30 and 21 mmHg, respectively. In the congenic strains in which both SS1a and SS1b were introgressed from SBN/y onto the genomic background of SBH/y, the reduction in blood pressure was 34 mmHg in males and 38 mmHg in females; these latter results were confirmed by radiotelemetry. When either one or both QTLs together were introgressed from SBH/y onto the SBN/y genomic background, tail-cuff measurements failed to detect an increase in blood pressure above baseline; telemetric measurements in the congenic strains introgressing both QTLs together, however, detected a significant rise in blood pressure after 3 and 4 wk of salt loading. Neither the origin of the Y chromosome nor the sex of the parental strain had any significant impact on the magnitude of the blood pressure response to salt loading. We conclude that the congenic rat strains that we constructed for the chromosome 1 QTLs provide functional evidence for the role of gene systems within QTLs SS1a and SS1b in the blood pressure response to salt loading. The unexpected finding was that QTL SS1a contributes to the hypertensive response also in females. The data indicate the lack of a Y chromosomal effect or of parental imprinting.

Animals↗

PubMed2026

The curious case of sporadic nematode susceptibility in "Tifguard" peanut (Arachis hypogaea): seed mixture or genetic instability?

The Runner-type peanut (Arachis hypogaea L.) cultivar "Tifguard" carries an introgressed chromosomal segment on chromosome A09 from A. cardenasii that confers resistance to root-knot nematode (RKN). Despite this, a proportion of "Tifguard" plants show RKN symptoms, which could plausibly be attributed to seed mixture or outcrossing. However, recent work has shown that cultivated peanut exhibits surprisingly frequent large-scale chromosomal instability (1% to 5%); suggesting that resistance loss could arise from spontaneous structural genomic change. To test these possibilities, we grew foundation seed in an RKN-infested field and collected symptomatic and asymptomatic plants. Lineages derived by single-seed descent were genotyped using the Axiom Arachis 48K SNP array v2 and whole-genome sequencing. Symptomatic lineages lacked the A. cardenasii introgression on chromosome A09 and instead carried the complete endogenous A. hypogaea A09 region at the expected dosage. There was no evidence of large-scale homoeologous exchange, deletion, or other genomic instability affecting this chromosome. Most susceptible plants were closely related to resistant "Tifguard" but lacked the A09 introgression, with a smaller proportion assignable to known nematode-susceptible cultivars, implicating seed mixture with a possible contribution from cross-pollination rather than genomic instability. Because resistance depends on a single major-effect segment, rare events have disproportionate phenotypic impact, placing high demands on genetic purity. For important traits conferred by major loci, marker-based testing across seed-increase stages could verify trait retention directly, and is increasingly practical as marker costs decline.

Arachis↗