marker-assisted selection in wheat - ictsd

Chapter 14 – Marker-assisted selection in Eucalyptus 257Figure 1Basic breeding scheme used in Eucalyptus breeding involving recurrent selection cycles fromwhich elite parent trees are derived for the establishment of seed orchards, as well as individualtrees to be tested and later recommended as clonesNative forest standsSelection of best trees ,possibly unrelatedProvenance trialsPROGENY TRIALSRECOMBINATIONMating of selected trees andgeneration of progeniesSELECTIONPhenotypic evaluation formain target traitsSELECTED POPULATIONVegetative material or seeds collectedClonal tests of selected treesEstablishment of seedorchardsFinal selection and operationalclone recommendationImproved seeds forcommercial forestsbreeds (Potts, 2004). For species that areeasily propagated vegetatively, such as E.grandis, E. urophylla and several of theirhybrids, clonally propagated breeding populationshave enhanced gains by allowingthe capture of additive and non-additivegenetic effects (Figure 1).Clonal forestry of EucalyptusAfter more than 25 years following theintroduction of clonal forestry of Eucalyptus(Campinhos, 1980; Brandão, Campinhosand Ikemori, 1984), this forest productionsystem is now perfectly integrated into thestrategies and plans of advanced generationbreeding programmes. Clonal propagationand hybrid breeding have constituted anextremely powerful combination of toolsfor the rapid improvement of the qualityof wood and wood products. While thefirst hybrid clones were selected based onlarge-scale screening of high-yielding spontaneoushybrids resistant to diseases (such asthe eucalypt canker), today clones are beingderived increasingly from deliberate interspecifichybrid production strategies (Figure2). Eucalypt hybrids, involving two or morespecies deployed as clones, currently makeup a significant proportion of eucalypt plantationforestry, particularly in the tropicsand subtropics. In a recent survey of clonalforestry in Brazil, for example, consideringall the large and medium-sized companies,the area planted with clones corresponded