MULTISTAGE SELECTION INDEXES FOR MAXIMUM GENETIC GAIN AND ECONOMIC-EFFICIENCY IN RED-CLOVER

Selection index updating, a method of multistage selection, allows bre eders to determine the optimal truncation point of each stage so that the aggregate genetic gain (Delta H) or the gain to cost ratio (Delta H/C) is maximum. In this study, we demonstrated the use of selection i ndex updating on selection of red clover (Trifolium pratense L.). We d etermined the optimal selection schemes that optimized the balance bet ween cost saving and lowered genetic gain in multistage selection. A t otal of 78 red clover half-sib families were evaluated for petiole len gth (PL), seedling viper (Vig) measured at the seedling stage, and can opy height and individual plant dry weight recorded on initial growth (CH1 and DW1) and regrowth (CH2 and DW2). Alternative selection scheme s with different number of stages, traits, and proportions selected at various stages were examined to maximize either Delta H or Delta H/C. Single stage index selection had a greater predicted genetic gain tha n multistage selection, but it was also associated with higher costs. Early culling at the seedling stage resulted in significant cost savin gs 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 e fficient selection programs consisted of PL, Vig, DW1, and DW2. Inclus ion of CH1 and CH2 into the selection indices did not contribute to th e increase of the total genetic gain, nor to the increase of the ratio .