marker-assisted selection in wheat - ictsd

Chapter 14 – Marker-assisted selection in Eucalyptus 259that the actual “pulp factory” is the tree.Particularly in vertically integrated pulpproduction systems, as highly productiveclonal forests with over 40 m 3 /ha/yr becamethe standard (Binkley and Stape, 2004), thefocus shifted quickly from volume growthto wood quality with the objective of improvingpulp yield per hectare by reducingwood specific consumption (WSC), i.e. theamount of wood in cubic metres necessaryto produce one tonne of pulp. Trees thatyield more cellulose generate savings all theway from tree harvesting, transportation,chipping and pulping while mitigating theneed for an accelerated expansion of theforest land base.Clonal forestry of E. grandis xE. urophylla selected clones in the 1980swas able to reduce WSC from 4.9 to4.0 m 3 /tonne of pulp (Ikemori, Penchel andBertolucci, 1994). However, it is now wellknown by breeders that E. globulus has thebest combination of wood properties forpulp and paper among the commerciallyplanted Eucalyptus species, resulting in ahigh pulp yield requiring approximately25 percent less wood to produce the sametonne of cellulose. While only 3.0 m 3 ofE. globulus wood are required per tonneof pulp, 4 m 3 are needed from selected E.grandis. E. globulus has a very adequatewood density in the range of 550 kg/m 3 ,the longest fibre length and the largest contentof holocellulose and pentosans of anyother intensively planted species (Sanchez,2002). E. globulus, however, is much moredemanding on soil fertility, is not adaptedto tropical temperatures, is slower growingand more difficult to propagate clonallythan E. grandis. In the last ten years, basedon the very successful pioneering experiencesin Brazil led by Teotônio de Assis,several breeding programmes in tropicalcountries have started an intensive effortto introgress superior E. globulus pulptraits into the tropical and subtropical highyielding genetic backgrounds of E. grandisand E. urophylla. Given the very highgenetic diversity that segregates in suchcrosses together with the technical possibilityof practising intensive within-familyselection and clonal propagation, this efforthas resulted in the development of exceptionaltrees that combine superior growthand adaptability to tropical conditions,higher pulp yielding wood and easy propagationusing minicutting/hydroponicstechnology (de Assis, 2000, 2001; Figure 3).A new wave of clonal forestry is thereforestarting that will most likely result inanother significant jump in the quality ofEucalyptus forests.It is therefore in the context of a highlyspecialized industrially-oriented breedingprogramme that fully exploits the powerof hybrid breeding and clonal forestry thatone needs to discuss the prospects of MASin Eucalyptus. Understanding the fundamentaldifferences between E. grandis andE. globulus at the molecular level to exploitbetter the natural allelic variation that existsin the genus has been the starting point.Marker-assisted managementof genetic variation in breedingpopulationsThe use of genome information for thepractice of directional selection of superiorgenotypes still represents a challenge thatdepends on further and more refined experimentalwork (see below). Nevertheless,molecular markers can be used immediatelyto solve several questions related to themanagement and identification of geneticvariation in breeding and production populations.These applications can be usefulessentially to any breeding programmeindependently of its stage of develop-