marker-assisted selection in wheat - ictsd

286Marker-assisted selection – Current status and future perspectives in crops, livestock, forestry and fishsmaller regions of intact DNA over manygenerations. Candidate genes targeted inthese studies can be identified by genemapping, expressed sequence tag (EST)sequencing, gene expression profiling orfunctional studies (transgenics). If variationcan be found in the sequence of these genesin different phenotypes, it allows MAS tobe used for within- and between-familyselection in forest trees.The application of biotechnology intree improvement research is currentlytaking different paths in developed anddeveloping countries due to contrastingregulatory approval processes for geneticallymodified plants and differences inpublic acceptance of genetically modifiedorganisms (GMOs). There is considerableresistance in developed countries towardstransgenic trees, which has more to do withtheir possible effects on other plants andon the environment than with concernsabout transgenic wood (Sedjo, 2004).Long-term field trials are needed to ensurethe stability of any genetic modificationand the absence of negative impacts ongrowth and resistance to environmentalstresses before they can be incorporatedinto industrial plantations (Strauss et al.,1998; Strauss et al., 2004). Regulationcosts, possible trade restrictions, lack ofpublic acceptance of transgenics and lackof support by major forestry certificationgroups such as the Forest StewardshipCouncil (FSC) are currently barriers to thedevelopment of transgenics (Sedjo, 2004).Consequently, trials of transgenic trees indeveloped countries remain in the researchphase, mostly conducted with young treesgrown under glasshouse conditions (seeWalter and Killerby, 2004 for review). Dueto these problems, some research has shiftedtowards alternative methods of investigatinggene function and incorporating desirablegenes into breeding populations, mainlythrough association mapping.Recent MAS research in forest trees hasbeen greatly assisted by advances in ourunderstanding of tree genomes. The completesequencing of plant genomes such asArabidopsis (Arabidopsis Genome Initiative,2000) and rice (Yu et al., 2002) is improvingour understanding of the number of genesinvolved (25 000–55 000) in the developmentof different organs and the functionof the genes.The Populus genome was the first treegenome to be sequenced with 58 036predicted genes (www.jgi.doe.gov/poplar)and efforts are under way to sequencethe Eucalyptus genome (www.ieugc.up.ac.za), a genus of particular importance incountries with developing economies inAsia and South America. To date, partialcoverage of the E. camaldulensis genome(600 Mb) has been completed by randomshotgun sequencing, through collaborationbetween Oji Paper and the Kasuza DNAResearch Institute in Chiba, Japan (S. PotterEnsis, personal communication). A draftsequence, based on four-fold coverage ofthe genome is expected to be availableby mid-2007 (Poke et al., 2005). Thelarge genome size of conifers is currentlya barrier to whole genome sequencing;however, comprehensive EST sequencingis likely to yield most genes expressed intarget tissues.Genomic resources and tools are nowbeing established for important foresttree species. Rapidly growing numbersof ESTs are publicly available in a rangeof species including Eucalyptus grandis,Pinus radiata, P. taeda, Picea abies, Populustrichocarpa, P. tremula x tremuloides andCryptomeria japonica (see Krutovskii andNeale, 2001 and Strabala, 2004 for reviews)and Avicennia marina (Mehta et al., 2005).