Predicted and Realized Gains from Selection for In Vitro Dry Matter Digestibility and Forage Yield in Switchgrass
Improved forage yield and quality, which can lead to more efficient livestock production, are important goals in switchgrass (Panicum virgatum L.) breeding. Objectives of this study were to determine the effectiveness of multiple cycles of recurrent restricted phenotypic selection (RRPS) in improving forage yield in switchgrass and in improving in vitro dry matter digestibility (IVDMD), and to compare predicted and realized gains from selection. Six switchgrass populations were developed by selecting a base population for one cycle of low and three cycles of high IVDMD and two cycles for high yield. Half-sib progenies of parents selected from the base population for high and low IVDMD were used to estimate heritability for IVDMD by parent-progeny regression. Realized gains from selection were determined in a seeded sward trial that included the base and six selected populations. Estimated and realized heritabilities for IVDMD were 0.40 and 0.31, respectively. Predicted gains and (in parenthesis) realized gains from selection for IVDMD in grams per kilogram per cycle were −21 (−15) for the Low IVDMD Cycle 1, 16 (15) for High IVDMD Cycle 1 (‘Trailblazer’), 14 (4) for the High IVDMDCycle 2, and 19 (18) for the High IVDMD Cycle 3 populations. There was a low but positive genetic correlation between forage yield and IVDMD of 0.10. Forage yield was not improved by RRPS, probably because of lack of genetic variability for forage yield in the base population. It is concluded that RRPS is effective for improving IVDMD in switchgrass, but was not effective in improving forage yield in the populations evaluated, and that predicted gains exceeded realized gains from selection for IVDMD due to limited selection for traits other than IVDMD.
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