ABSTRACT
This chapter reviews the basic strategy behind the original development of selection indices and some of the modifications that have been developed subsequently. In most crop improvement programs, there is a need to improve more than one trait at a time. Recognition that improvement of one trait may cause improvement or deterioration in associated traits serves to emphasize the need for simultaneous consideration of all traits which are important in a crop species. The use of a selection index in plant breeding was originally proposed by Smith, who acknowledged critical input from Fisher. Subsequently, methods of developing selection indices were modified, subjected to critical evaluation, and compared to other methods of multiple-trait selection. The optimum selection index for improving a specified linear function of genotypic values is a linear function of phenotypic values in which the weights attached to each phenotypic value are chosen to maximize the correlation between genotypic worth and the selection index.
