marker-assisted selection in wheat - ictsd

Chapter 19 – Technical, economic and policy considerations on marker-assisted selection in crops 393intuitively know: namely, the costs andbenefits of MAS projects are likely to varydepending on the crop being improved, thebreeding objective being pursued, the skillof the breeder, the capacity of the researchorganization, the location of the workbeing carried out, the cost of key inputs,and many other factors.Economic trade-offsWhile caution is required when extrapolatingfrom the results of a case study,general conclusions regarding the costeffectivenessof molecular markers in cropgenetic improvement work can be drawnbased on the findings of the CIMMYTstudy and a number of other studies carriedout elsewhere. Broadly speaking, two typesof benefits associated with MAS can be distinguished:cost savings and time savings.Cost savingsFor certain applications, MAS methods cansubstitute directly for conventional selectionmethods, and for these applications the relativecost-effectiveness of the two methodscan easily be determined by comparing thescreening cost per sample. Generally, as thecost of phenotypic screening rises, markersare more likely to represent a cost-effectivealternative. For applications in whichphenotypic screening is easy and cheap(e.g. visual scoring of plant colour), MASwill not offer any obvious advantages interms of cost. However, for applicationsin which phenotypic screening is difficultor expensive (e.g. assessing root damagecaused by nematodes or for a disease that isnot present in the field site), MAS will oftenbe preferable.Time savingsCost is an important factor affecting thechoice of breeding technology, but it is notthe only one. Plant breeders worry aboutcontrolling costs, but they also worry aboutgetting products out quickly. Therefore, itis not sufficient to consider potential costsavings alone. The time requirements ofalternative breeding strategies must also betaken into account, because even when MAScosts more than conventional selection (asit does in some, although not all, cases),breeders who use it may be able to generatea desired output quicker. Acceleratedrelease of improved varieties can translateinto large benefits, especially for the privateseed industry, so time is an important considerationin addition to cost.For breeding applications in which MASoffers cost and time savings, the advantagesof MAS compared with conventionalbreeding are clear. More problematic, however,are the many applications in whichMAS methods cost more to implementthan conventional selection methods butalso reduce the time needed to accomplisha breeding objective. This commonlyhappens, for example, with inbred lineconversion schemes based on backcrossingprocedures. In such schemes, MAS methodscan often be used to derive convertedinbred lines containing one or more incorporatedgenes in much less time than wouldbe possible using conventional selectionmethods alone.In applications that involve a tradeoffbetween time and money, under whatcircumstances is the higher cost of MASrelative to conventional breeding justified?The choice of the plant breedingmethod can be viewed as an investmentdecision and evaluated using conventionalinvestment criteria (Sanders and Lynam,1982). Using data from the CIMMYT casestudy, Morris et al. (2003) explored therelationship between time and money asit relates to crop improvement research