marker-assisted selection in wheat - ictsd

254Marker-assisted selection – Current status and future perspectives in crops, livestock, forestry and fisheucalypt breeding practice and the moleculartools available or in development.To set the stage for a realistic appraisal ofMAS for Eucalyptus, a brief introductionis presented of the main features of moderneucalypt breeding and clonal forestry inorder to provide a better understandingof the challenges and opportunities thatlie ahead for cost-efficient molecularbreeding. Following this section, some currentlow technological input applicationsof molecular markers in support of operationalbreeding are presented, such as thequantification of genetic diversity and relationships,the analysis of mating patternsand paternity in seed orchards and fingerprintingfor quality assurance and qualitycontrol of clonal propagation. Within theframework of MAS for trait advancement,after reviewing the status of QTL mappingin Eucalyptus, the challenges and somerealistic prospects for the application ofMAS to improve relevant traits are outlined.Finally, with the expected availabilityof a draft of the whole Eucalyptus genomewithin the next years, a succinct summaryis presented on the prospects of advancinggenomic approaches for gene identificationand subsequent application of MAS.Eucalyptus breeding and plantationforestryEucalyptus domesticationEucalypts spread rapidly around the worldfollowing their discovery by Europeansin the late eighteenth century (Eldridgeet al., 1993). They were introduced intocountries such as Brazil, Chile, France,India, Portugal and South Africa in thefirst quarter of the 1800s (Doughty, 2000)and rapidly adopted in forest plantationsas their fast growth and good adaptabilitybecame known. During the nineteenthand twentieth centuries, large quantitiesof seeds were collected and distributeddirectly from Australia through a numberof seed collection expeditions carried outboth by government organizations andprivate forestry companies throughout theworld.Eucalyptus species have a mixed matingsystem, but are predominantly outcrossersand animal pollinated. High levels of outcrossingare maintained by protandry andvarious incomplete pre- and post-zygoticbarriers to self-fertilization including strongselection against the products of inbreeding(Pryor, 1976). Although the major eucalyptsubgenera do not hybridize in nature,hybridization among species within thesame subgenus has been detected, oftenmaking separation of species difficult (Pryorand Johnson, 1971). Hybridization becomesmore frequent in exotic conditions outsidethe natural species range. In fact, this propertyhas been widely exploited by eucalyptbreeders who take advantage of the naturallyoccurring genetic variation for growthand wood properties among species (deAssis, 2000). Several artificial hybrid combinationshave been produced, althoughhybrid inviability tends to increase withincreasing taxonomic distance between theparents (Griffin, Burgess and Wolf, 1988;Potts and Dungey, 2004).In several countries the continued plantationfrom local seed sources gave riseto landraces adapted to the specific environmentof the country (Eldridge et al.,1993). Seed collections from such localexotic plantings of multiple species becamecommon and where plantings occurred, F 1hybrids were derived (Potts and Dungey,2004). While several of these F 1 hybrids performedwell, especially when deployed asclones, seed collection from hybrid standsoften resulted in plantations that performedpoorly in subsequent generations and were