marker-assisted selection in wheat

Chapter 14 – Marker-assisted selection in Eucalyptus 253IntroductionPlanted Eucalyptus forests occupy globallymore than 18 million hectares and havebecome the most widely planted hardwoodforest tree in the world (FAO, 2001).Eucalyptus tree species used in productionforestry are long-lived, evergreen speciesbelonging to the angiosperm familyMyrtaceae (Ladiges, Udovicic and Nelson,2003). They are native to Australia andadjacent islands where they occur naturallyfrom sea level to the alpine tree line, fromhigh rainfall to semi-arid zones, and fromthe tropics to latitudes as high as 43° south(Eldridge et al., 1993; Ladiges, Udovicicand Nelson, 2003). Fast growth rates and awide range of adaptability have contributedto the great interest that Eucalyptus speciesreceive in many countries outside theirnative range. Besides the fast growth thatallows for shorter rotations, many speciesdisplay wood properties that make themvery suitable for fuel and charcoal production,pulp and paper manufacture as well assawn wood. While E. globulus is the premierspecies for temperate zone plantationsin Australia, Chile, Portugal and Spain, elitehybrid clones involving E. grandis and E.urophylla are used extensively by the pulpand paper industry in tropical regions orBrazil, China, the Democratic Republic ofthe Congo and South Africa because oftheir wood quality, rapid growth, cankerdisease resistance and high volumetricyield.Planted Eucalyptus stands supply ina rational and efficient way, high-qualitywoody raw material that would otherwisecome from native tropical forests. In thedecades to come, the expansion of these“fibre farms” will likely be limited by thegrowth of crop plantations and by publicopinion pressure. Increased productivityof forests and refinements in the qualityof wood products by selective breedingwill become of increasing strategic importanceto the forest industry. Moleculartools based on the direct identificationof useful variation at the DNA level areexpected to provide new opportunities forthe genetic manipulation of growth, formand especially wood properties of plantedtrees by marker-assisted selection (MAS)approaches.Almost fifteen years have passed sincethe first experiments in molecular breedingof forest trees. The development of linkagemaps and quantitative trait loci (QTL)information in trees was greatly acceleratedby the advent of more accessible DNAmarker techniques, new concepts in linkagemapping and novel strategies for advancedgeneration tree breeding. From the outset,many expectations were generated for fastand accurate methods for early markerbasedselection in trees. Significant progresshas been made and the knowledge gatheredled to some short-term opportunitiesfor the incorporation of genomic analysisin tree genetics and breeding. However, italso became clear that several challengesremained before more refined and higherimpact applications could be implemented.In this chapter, an overview is presentedon the status of MAS in species ofEucalyptus. The term MAS is used in latusensu, i.e. encompassing the several moleculartechniques and approaches that offerpotential to contribute to eucalypt breeding.Some recent reviews have detailed severalaspects of Eucalyptus genome researchincluding gene discovery, candidate genemapping, functional genomics and physicalmapping (Moran et al., 2002; Grattapaglia,2004; Poke et al., 2005; Shepherd and Jones,2005; Myburg et al., 2006). The focusof this chapter is a more applied one,attempting to link the realities of current