marker-assisted selection in wheat - ictsd

234Marker-assisted selection – Current status and future perspectives in crops, livestock, forestry and fishscanning and in some cases computer tomography[CT] scanning), disease (mainlyresistance to internal parasites) and reproduction.The national evaluation systemin Australia (“Lambplan”) now has about120 000 new animals from about 450 flocksrecorded each year for terminal sire breedsand maternal breeds (A. Ball, personal communication).Performance recording takesplace only at the stud level, which in a senseis a dispersed nucleus, and a large proportionof the genetic basis of the commercial populationstems from these recorded flocks.The proportion of pedigree recorded individualsis high at the stud level, allowingbest linear unbiased prediction (BLUP) ofEBV. In New Zealand, a similar programmeexists (“Sheep Improvement Limited”[SIL]), in which pedigree and performancerecords are registered with genetic serviceproviders and the information “retailed”back to the breeders. SIL enters more than250 000 new animals per year from some750 recorded flocks, all pedigree recorded,and has a database of more than 5 millionanimal records. Across-flock EBVs areestimated for a proportion of these. In theUnited Kingdom, about 50 000 breedingewes and their lamb records are recordedevery year from 37 different breeds, andindices have been developed for terminalsand maternal (“hill”) breeds (Conington etal., 2004). Across-flock genetic evaluationprogrammes for meat sheep breeds existalso on smaller scales in France, Norwayand South Africa.Most breeding programmes for meatsheep focus on weight traits, and ultrasoundscanning is commonly used for fatand muscle traits. Reproduction traits arerecorded as numbers of lambs born andweaned. Selection for resistance to internalparasites can be based on faecal worm eggcounts (WECs) associated with naturalchallenge in the field, e.g. in Australia andNew Zealand, and this has been shown tobe reasonably heritable in Merino sheep(e.g. Khusro et al., 2004). EBVs for WECare produced for an increasing number offlocks in Australia and New Zealand.The traits that would most obviouslybenefit from MAS in meat sheep wouldbe traits related to carcass and carcassquality, reproduction and disease resistance.Ultrasound measurements are currentlyused to predict carcass fat and muscling.However, genetic correlations with traitsmeasured on carcass are only moderate(Safari, Fogarty and Gilmour, 2005) andspecific meat quality attributes such astenderness and colour might not be wellcaptured by current measurement. Carcasstraits are prime targets for MAS as theycannot be measured on breeding animalsand progeny or sib testing would be neededas an alternative. Reproduction traits aswell as maternal behaviour and ewe survivalare also good MAS targets as they aresex limited and are only expressed after thefirst round of reproduction. Disease resistancetraits are generally hard to measureunder uniform conditions and would alsogreatly benefit from MAS.Wool sheepBreeding for and recording of wool traits islimited to a few countries. The largest acrossflockscheme is found in Australia (mainlyfor the Merino breed), and smaller geneticevaluation schemes are run in New Zealand,South Africa and South America (Merinoand Corriedale). In Australia, the proportionof breeders participating in formalrecording and genetic evaluation is smallerfor wool than for meat sheep. However, theMerino industry is very large, constitutingthe vast majority of the Australian flockthat consists of about 100 million sheep. By