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.

Of the four 2iP derivatives applied to cut carnations 2iP, IPA and IPAMP delayed the rate of flower senescence but did not delay longevity . 2iP9G was the least effective . ['H]2iP was rapidly transported to all flower components . The receptacular tissue apparently plays a major role in the distribution of the applied cytokinin to the rest of the flower parts . Over and above possible interconversion between 2iP, IPA and IPAMP the applied [' H]2iP was also converted to 2iP9G, Ade, Ado, tZ and DHZ . The presence of Ade indicates the involvement of cytokinin oxidase-type enzymes while the presence of tZ and DHZ indicates a degree of hydroxylation . These latter steps may contribute to the efficiency of 2iP in the system .

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SYNOPSISCurrent strategies for deployment of improved material from the tree breeding programmes of two South Mrican forestry companies are reviewed for all commercial species, including both hardwoods and softwoods. How high site variability and propagation constraints restrict this are examined and illustrated with examples. The multiplication techniques are viewed not just as a means of amplifying improved material, but also from a plant quality perspective and the effect this can have on the establishment of the crop. Lastly, two important questions are posed. Is enough known about the sexual reproduction of the commercial species in South Mrican forestry? What developments in vegetative propagation techniques are necessary to allow the exploitation of the gains being offered from advanced generation breeding in the tree improvement programmes within the two companies?

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