Comparative genetic linkage maps of Eucalyptus grandis , Eucalyptus globulus and their F 1 hybrid based on a double pseudo-backcross mapping approach (original) (raw)
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Genetics, 1994
We have used a "two-way pseudo-testcross" mapping strategy in combination with the random amplified polymorphic DNA (RAPD) assay to construct two moderate density genetic linkage maps for species of Eucalyptus. In the cross between two heterozygous individuals many single-dose RAPD markers will be heterozygous in one parent, null in the other and therefore segregate 1:1 in their F1 progeny following a testcross configuration. Meiosis and gametic segregation in each individual can be directly and efficiently analyzed using RAPD markers. We screened 305 primers of arbitrary sequence, and selected 151 to amplify a total of 558 markers. These markers were grouped at LOD 5.0, theta = 0.25, resulting in the maternal Eucalyptus grandis map having a total of 240 markers into 14 linkage groups (1552 cM) and the paternal Eucalyptus urophylla map with 251 markers in 11 linkage groups (1101 cM) (n = 11 in Eucalyptus). Framework maps ordered with a likelihood support > or = 1000:1 w...
Genetics, 2004
The genetic architecture of hybrid fitness characters can provide valuable insights into the nature and evolution of postzygotic reproductive barriers in diverged species. We determined the genome-wide distribution of barriers to introgression in an F 1 hybrid of two Eucalyptus tree species, Eucalyptus grandis (W. Hill ex Maiden.) and E. globulus (Labill.). Two interspecific backcross families (N ϭ 186) were used to construct comparative, single-tree, genetic linkage maps of an F 1 hybrid individual and two backcross parents. A total of 1354 testcross AFLP marker loci were evaluated in the three parental maps and a substantial proportion (27.7% average) exhibited transmission ratio distortion (␣ ϭ 0.05). The distorted markers were located in distinct regions of the parental maps and marker alleles within each region were all biased toward either of the two parental species. We used a Bayesian approach to estimate the position and effect of transmission ratio distorting loci (TRDLs) in the distorted regions of each parental linkage map. The relative viability of TRDL alleles ranged from 0.20 to 0.72. Contrary to expectation, heterospecific (donor) alleles of TRDLs were favored as often as recurrent alleles in both backcrosses, suggesting that positive and negative heterospecific interactions affect introgression rates in this wide interspecific pedigree. several hybrid populations ; Burke South Africa.
A genetic linkage map for Eucalyptus globulus with candidate loci for wood, fibre, and floral traits
TAG Theoretical and Applied Genetics, 2002
A genetic linkage map containing potential candidate loci for wood, fibre and floral traits has been constructed for Eucalyptus globulus (Labill.) based on the segregation of 249 codominant loci in an outbred F 1 population of 148 individuals. The map contains 204 RFLP loci, including 31 cambium-specific expressed sequence tags (ESTs) and 14 known function genes, and 40 microsatellite and five isozyme loci. Independent male and female maps were constructed, and the 98 loci (39%) that segregated in both parents were used to combine the parental maps into an integrated map. The 249 loci mapped to 11 major linkage groups (n=11 in eucalypts) and a 12th small linkage group containing three loci that segregated in the male parent only. Total map distance is 1375 cM with an average interval of 6 cM. Forty one of the mapped loci identify known proteins (five isozymes) or sequences with known function (14 genes and 22 ESTs). The mapped genes include enzymes involved in lignin and cell-wall polysaccharide biosynthesis, and floral-development genes. This map will be used to locate quantitative trait loci for wood, fibre, and other traits in Eucalyptus.
Conservation Genetics, 2009
Human activities can promote increased hybridization in the genus Eucalyptus with potentially detrimental consequences for the persistence of rare species. However, many hybrid combinations have not been investigated with combined use of genetic markers and morphology. We assessed the efficiency of the STRUC-TURE program and morphological intermediacy for identifying hybrids between the uncommon tree, Eucalyptus aggregata, which putatively hybridizes with the common congeners, E. rubida and E. viminalis in south-eastern Australia. We sampled 1,005 seedlings across 27 populations, all seedlings were genotyped at 6 allozyme loci and scored for 22 stem and leaf characters. Both marker sets confirmed that E. aggregata is hybridizing with both E. rubida and E. viminalis. Allozymes revealed hybrids from E. aggregata trees in 88% of populations and hybrids comprised 7.3% of all seedlings. Both genetics and morphology indicated that *50% were likely to be F 1 hybrids, and both simulations and morphological characteristics indicated that the remainder were mostly backcrosses. Morphological analysis correctly distinguished 71% of F 1 hybrids from parentals and was least accurate when dealing with potential backcrosses (50% success). Hence, techniques using genetic data (no prior information) and the assessment of appropriate admixture thresholds through simulations provided the most accurate estimates of hybrid frequency. In this study, potential introgression and the high frequency of hybrids in small populations (*30%), suggests that hybridization should be considered in the management and conservation of E. aggregata.
Tree Genetics & Genomes, 2022
The evolutionary trajectory of a population both influences and is influenced by characteristics of its genome. A disjunct population, for example is likely to exhibit genomic features distinct from those of continuous populations, reflecting its specific evolutionary history and influencing future recombination outcomes. We examined genetic diversity, population differentiation and linkage disequilibrium (LD) across the highly disjunct native range of the Australian forest tree Eucalyptus globulus, using 203,337 SNPs genotyped in 136 trees spanning seven races. We found support for four broad genetic groups, with moderate F ST , high allelic diversity and genome-wide LD decaying to an r 2 of 0.2 within 4 kb on average. These results are broadly similar to those reported previously in Eucalyptus species and support the 'ring' model of migration proposed for E. globulus. However, two of the races (Otways and Southeastern Tasmania) exhibited a much slower decay of LD with physical distance than the others and were also the most differentiated and least diverse, which may reflect the effects of selective sweeps and/or genetic bottlenecks experienced in their evolutionary history. We also show that F ST and rates of LD vary within and between chromosomes across all races, suggestive of recombination outcomes influenced by genomic features, hybridization or selection. The results obtained from studying this species serve to illustrate the genomic effects of population disjunction and further contribute to the characterisation of genomes of woody genera.
BMC plant biology, 2006
Eucalypts are the most widely planted hardwood trees in the world occupying globally more than 18 million hectares as an important source of carbon neutral renewable energy and raw material for pulp, paper and solid wood. Quantitative Trait Loci (QTLs) in Eucalyptus have been localized on pedigree-specific RAPD or AFLP maps seriously limiting the value of such QTL mapping efforts for molecular breeding. The availability of a genus-wide genetic map with transferable microsatellite markers has become a must for the effective advancement of genomic undertakings. This report describes the development of a novel set of 230 EMBRA microsatellites, the construction of the first comprehensive microsatellite-based consensus linkage map for Eucalyptus and the consolidation of existing linkage information for other microsatellites and candidate genes mapped in other species of the genus. The consensus map covers approximately 90% of the recombining genome of Eucalyptus, involves 234 mapped EMBR...
Tree Physiology, 2005
Eucalyptus is the most economically important hardwood plantation tree cultivated in tropical and subtropical countries. Inter-simple sequence repeat (ISSR) markers were used to evaluate genetic relationships within and between individuals of six Eucalyptus species. A total of 583 loci (265 to 1535 bp) were amplified from 149 individuals belonging to the six Eucalyptus species using seven ISSR primers (two to three nucleotide repeats anchored with one or two nucleotides at the 3′ or 5′ region). The ISSR fragments indicated significant polymorphism and genetic diversity among the individuals. Cluster analysis and principal component analysis revealed the occurrence of wide genetic diversity among populations of E. tereticornis Sm., E. camaldulensis Dehnh. and E. urophylla S.T. Blake and narrow genetic diversity among populations of E. citriodora Hook. and E. grandis W. Hill ex Maiden. Genetic diversity was high in E. tereticornis Sm. (47.27%) and low in E. citriodora (18.64%). Maximum Nei's genetic identity (0.897) was observed between E. camaldulensis and E. tereticornis species, whereas maximum genetic diversity (0.286) was found between individuals of E. citriodora and E. grandis.
THE GENETICS OF HYBRIDISATION IN THE TEMPERATE EUCALYPTUS
The use of hybrid eucalypts in commercial forestry has generally resulted from opportunistic crossing events with superior individuals being vegetatively propagated in large numbers. To develop strategies to breed hybrids, it is important to understand the barriers to hybridisation in the genus and as well as the genetic behavior of hybrid populations. Using F 1 hybrid populations of E. gunnii × globulus, E. nitens × globulus and outcrossed parental controls we demonstrate, firstly, the importance of environment on hybrid performance and secondly, that high levels of F 1 and advanced generation hybrid inviability can occur at an early age, even in crosses between closely related species. Inviable F 1 hybrids are a sensitive indicator of genomic incompatibility and add a cost to hybrid selection and production. However, surviving F 1 's may be vigorous and of interest to breeders. F 1 hybrid populations do not appear to conform to classical quantitative genetic models for growth with inflated estimates of additive genetic variance and poor predictability of hybrid performance. Nevertheless, this does not appear to be so for other more highly heritable traits. Advanced generation hybridisation is one means of overcoming the constraints and costs of poor clonal propagation and F 1 hybrid seed production, but hybrid breakdown may substantially reduce genetic gains.
Detection and mapping of a lethal locus in a eucalyptus hybrid population
Pesquisa Agropecuária Brasileira, 2011
The objective of this work was to verify the existence of a lethal locus in a eucalyptus hybrid population, and to quantify the segregation distortion in the linkage group 3 of the Eucalyptus genome. A E. grandis x E. urophylla hybrid population, which segregates for rust resistance, was genotyped with 19 microsatellite markers belonging to linkage group 3 of the Eucalyptus genome. To quantify the segregation distortion, maximum likelihood (ML) models, specific to outbreeding populations, were used. These models consider the observed marker genotypes and the lethal locus viability as parameters. The ML solutions were obtained using the expectation-maximization algorithm. A lethal locus in the linkage group 3 was verified and mapped, with high confidence, between the microssatellites EMBRA 189 e EMBRA 122. This lethal locus causes an intense gametic selection from the male side. Its map position is 25 cM from the locus which controls the rust resistance in this population.
Annals of Botany, 2001
Eucalyptus acmenoides Schauer (white mahogany) and E. cloeziana F. Muell (Gympie messmate) are largely allopatric but have several sympatric populations across their range in eastern Queensland, Australia. In this study, veri®cation of interspeci®c hybridization at the site of one such sympatric population was carried out using morphological and molecular (nuclear and cytoplasmic) characters. Capsule morphology was intermediate in hybrids, particularly with respect to the number of valves per capsule. Hybridization was found to occur in both directions with maternal inheritance of a taxon-speci®c polymorphism in the inverted repeat of the J LA region of the chloroplast genome. However, E. acmenoides acted as the maternal parent in all but one hybrid individual, possibly due to protandry of owering. High levels of polymorphism in microsatellite loci existed between E. acmenoides and E. cloeziana in the hybrid zone. Formation of hybrids was most likely limited to F 1 mating and was restricted in both numbers and dispersal within the hybrid zone. Current taxonomy places E. cloeziana and E. acmenoides into dierent subgenera, Idiogenes and Monocalyptus respectively. This is signi®cant as it is the only example of natural hybridization between subgenera within the Eucalyptus genus, suggesting that the taxonomic classi®cation of E. acmenoides and E. cloeziana should be investigated further.