Genetic Changes Associated with Different Methods of Recurrent Selection in Five Maize Populations: II. Indirectly Selected Traits

Abstract

Recurrent selection in a population can result in changes in traits other than those used directly as selection criteria. Such changes usually are not easily predicted or understood because they do not occur in a consistent manner. This study was conducted to compare changes in indirectly sdected traits (plant height, ear height, tassel branch number, and days to anthesis and silking) in five maize (Zea mays L.) populations (CGSynA, CGSynB, CGG, CGN, and CGW) that were selected for performance indices based on grain yield, grain moisture, and standability. Four selection methods were compared: modified ear‐to‐row (ME) in CGSynA, CGSynB, CGG, and CGN; half‐sib family (HS) in all five populations; selfed progeny (S) in five populations; and reciprocal recurrent selection (RRS) in CGSynA and CGW. Generally, response to indirect selection depended on (i) the selection method used, (ii) the initial mean value of a trait the original population, and (ii) correlations between indirectly and directly selected traits. The combination of these factors seems to determine whether an indirectly selected trait will increase, decrease, or remain constant in advanced cycles of selection. No general trend for response to indirect selection was observed for ear height, plant height, or tassel branch number. Days to anthesis and silking were mainly reduced. This uniform response of days to tlowering was partly due to non‐documented selection against later flowering plants in initial cycles of selection. Genetic drift generally acted in the opposite direction from response to selection, and I‐IS resulted in the least genetic drift. Generally, it seems that the indirectly selected traits changed in the way that would most efficiently contribute to the desirable changes of the directly selected traits.