Alternative recurrent selection strategies using doubled haploid lines in hybrid maize breeding

Recurrent testcross selection based on doubled haploid lines can be highly effective in hybrid maize (Zea mays L.) breeding. As a consequence, however, the genetic variance of the breeding population is reduced more rapidly. To limit the reduction of variance, a minimum effective population size (N-e) has to be ensured. However, maintaining sufficient N-e restricts the achievable selection intensity, in particular when crosses are made every year to start a new selection program such that the hybrid breeding population representing one heterotic group is divided into multiple, timely staggered subpopulations. Intercrossing lines from different subpopulations, defined herein as interlinking, allows the breeder to alleviate this restriction. In this study, the formula for predicting the genetic gain from selection is extended to account for interlinking of subpopulations. The optimum allocation of test resources was determined for two interlinking strategies and a control mating scheme (without interlinking) under one-, two-, and three-stage testcross selection. Our results show that optimum interlinking of staggered subpopulations provides faster breeding progress than advancing non-interlinked subpopulations separately. Moreover, the manner in which subpopulations are interlinked and the proportion of intercrossed lines from different subpopulations is fundamental in the design of efficient recurrent selection plans.