Evaluation of three recurrent selection methods in two short-season maize (Zea mays L.) synthetics
Numerous studies of response to selection have been made in maize (' Zea mays' L.) populations. However, determining the relative effectiveness of the various selection methods is difficult because the studies have involved different selection methods, populations, selection protocols, traits, number of cycles of selection, etc. Ideally, comparison of selection methods would involve selection for the same traits by using different methods in common base populations. These data are lacking in maize and, therefore, more empirical information is needed to enable breeders to make the best choice among the several methods of recurrent selection available for the improvement of maize populations. In this study, the effects of three recurrent selection methods were examined in two short-season synthetics: Canada Guelph Stiff Stalk (CGSS) and Canada Guelph Lancaster (CGL). The primary traits selected were performance index, its two components: grain yield and grain moisture, and reduced stalk lodging. The first objective was to evaluate the genetic changes associated with selfed progeny recurrent selection (S), half-sib reciprocal recurrent selection (RRS) using an inbred tester, and the combination of both (COM). The second objective was to evaluate the relative effectiveness of each selection method through observed and realized response to selection in populations ' per se', the interpopulation cross, and their effectiveness in the production of superior inbred lines. Smith's (1983) genetic model was used to separate genetic changes due to selection from those due to genetic drift effects. None of the three methods of recurrent selection proved to be best under all circumstances. Selfed progeny selection achieved the highest response to selection for most of the directly selected traits in CGSS, while COM was the best selection procedure for CGL. Genetic changes associated with selection and realized responses to selection were distinct for each selection method within each population, and depended to a large extent on the genetic structure of the base population. Genetic drift effects hindered response to selection, thus realized response to selection adjusted for random drift effects was a better indicator than observed response of the relative effectiveness of selection procedures in the improvement of the populations 'per se ' and their crosses.