Multistage selection indices for maximum genetic gain and economic efficiency in red clover

Selection index updating, a method of multistage selection, allows breeders to determine the optimal truncation point of each stage so that the aggregate genetic gain (▵H) or the gain to cost ratio (▵H/C) is maximum. In this study, we demonstrated the use of selection index updating on selection of red clover (Trifolium pratense L.). We determined the optimal selection schemes that optimized the balance between cost saving and lowered genetic gain in multistage selection. A total of 78 red clover half-sib families were evaluated for petiole length (PL), seedling vigor (Vig) measured at the seedling stage, and canopy height and individual plant dry weight recorded on initial growth (CH1 and DW1) and regrowth (CH2 and DW2). Alternative selection schemes with different number of stages, traits, and proportions selected at various stages were examined to maximize either ▵H or ▵H/C. Single stage index selection had a greater predicted genetic gain than multistage selection, but it was also associated with higher costs. Early culling at the seedling stage resulted in significant cost savings and increased gain to cost ratio. The ratio was 9.857 or more with early culling and 3.062 or less without seedling selection. The most efficient selection programs consisted of PL, Vig, DW1, and DW2. Inclusion of CH1 and CH2 into the selection indices did not contribute to the increase of the total genetic gain, nor to the increase of the ratio. This revised version was published online in July 2006 with corrections to the Cover Date.