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Howick, South Africa

Swain T.-L.,Institute for Commercial Forestry Research | Louw A.K.,Sappi Forests Research
Silvae Genetica

The sub-tropical species, Eucalyptus longirostrata (formerly E. punctata var longirostrata) and Corymbia henryi were investigated as alternative species for growth on the Zululand coastal plain in South Africa. Provenance/progeny trials were established in 2001 at two sites, namely, Nyalazi and Kwambonambi. The seed material purchased from the Commonwealth Scientific and Industrial Research Organization in Australia in 2000 included six provenances of E. longirostrata and five provenances of C. henryi. Six-year diameter at breast height measurements were completed in 2007. Individual narrow-sense heritability coefficients for diameter growth varied from 0.30 to 0.58 for both species, with heritabilities being higher at the drier Nyalazi site. Heritabilities and breeding values were calculated prior to making selections in field. A total of 143 selections were made in the E. longirostrata trials, and 113 in the C. henryi trials during 2008. Predicted gains for the next generation range from 2.8 cm (20%) to 6.1 cm (61%) increase in diameter for E. longirostrata, and 3.4 cm (23%) to 5.4 cm (49%) increase for C. henryi, depending on site and selection scenario. Provenance differences were evident in E. longirostrata at both sites; however, there were no significant differences between the C. henryi provenances of Australian origin. The top families of both species performed better than the hybrid controls at the Nyalazi site, indicating that both E. longirostrata and C. henryi are viable alternative species for successful growth on the drier sites of the Zululand coastal plain. Source

Kullan A.R.K.,University of Pretoria | van Dyk M.M.,University of Pretoria | Jones N.,Sappi Forests Research | Kanzler A.,Sappi Forests Research | And 2 more authors.
Tree Genetics and Genomes

Traits that differentiate cross-fertile plant species can be dissected by genetic linkage analysis in interspecific hybrids. Such studies have been greatly facilitated in Eucalyptus tree species by the recent development of Diversity Arrays Technology (DArT) markers. DArT is an affordable, high-throughput marker technology for the construction of high-density genetic linkage maps. Eucalyptus grandis and Eucalyptus urophylla are commonly used to produce fast-growing, disease tolerant hybrids for clonal eucalypt plantations in tropical and subtropical regions. We analysed 7,680 DArT markers in an F2 pseudo-backcross mapping pedigree based on an F1 hybrid clone of E. grandis and E. urophylla. A total of 2,440 markers (31. 7%) were polymorphic and could be placed in linkage maps of the F1 hybrid and two pure-species backcross parents. An integrated genetic linkage map was constructed for the pedigree resulting in 11 linkage groups (n = 11) with 2,290 high-confidence (LOD ≥ 3. 0) markers and a total map length of 1,107. 6 cM. DNA sequence analysis of the mapped DArT marker fragments revealed that 43% were located in protein coding regions and 90% could be placed in the recently completed draft genome assembly of E. grandis. Together with the anchored genomic sequence information, this linkage map will allow detailed genetic dissection of quantitative traits and hybrid fitness characters segregating in the F2 progeny and will facilitate the development of markers for molecular breeding in Eucalyptus. © 2011 The Author(s). Source

Kullan A.R.K.,University of Pretoria | van Dyk M.M.,University of Pretoria | Hefer C.A.,University of Pretoria | Jones N.,Sappi Forests Research | And 2 more authors.
BMC Genetics

Background: F1 hybrid clones of Eucalyptus grandis and E. urophylla are widely grown for pulp and paper production in tropical and subtropical regions. Volume growth and wood quality are priority objectives in Eucalyptus tree improvement. The molecular basis of quantitative variation and trait expression in eucalypt hybrids, however, remains largely unknown. The recent availability of a draft genome sequence (http://www.phytozome.net) and genome-wide genotyping platforms, combined with high levels of genetic variation and high linkage disequilibrium in hybrid crosses, greatly facilitate the detection of quantitative trait loci (QTLs) as well as underlying candidate genes for growth and wood property traits. In this study, we used Diversity Arrays Technology markers to assess the genetic architecture of volume growth (diameter at breast height, DBH) and wood basic density in four-year-old progeny of an interspecific backcross pedigree of E. grandis and E. urophylla. In addition, we used Illumina RNA-Seq expression profiling in the E. urophylla backcross family to identify cis- and trans-acting polymorphisms (eQTLs) affecting transcript abundance of genes underlying QTLs for wood basic density.Results: A total of five QTLs for DBH and 12 for wood basic density were identified in the two backcross families. Individual QTLs for DBH and wood basic density explained 3.1 to 12.2% of phenotypic variation. Candidate genes underlying QTLs for wood basic density on linkage groups 8 and 9 were found to share trans-acting eQTLs located on linkage groups 4 and 10, which in turn coincided with QTLs for wood basic density suggesting that these QTLs represent segregating components of an underlying transcriptional network.Conclusion: This is the first demonstration of the use of next-generation expression profiling to quantify transcript abundance in a segregating tree population and identify candidate genes potentially affecting wood property variation. The QTLs identified in this study provide a resource for identifying candidate genes and developing molecular markers for marker-assisted breeding of volume growth and wood basic density. Our results suggest that integrated analysis of transcript and trait variation in eucalypt hybrids can be used to dissect the molecular basis of quantitative variation in wood property traits. © 2012 Kullan et al.; licensee BioMed Central Ltd. Source

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