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Divergent Selection for In Vitro Dry Matter Digestibility in Switchgrass¹

The purposes of this study were to determine if phenotypic selection for in vitro dry matter digestibility (IVDMD) could be used to improve the IVDMD for switchgrass (Panicum virgatum L.) and to obtain heritability estimates of IVDMD in switchgrass. In 1973 a selection nursery of over 2,200 plants was established with transplanted seedlings of two similar Nebraska experimental strains. In 1974 about 800 plants that appeared to be agronomically superior were sampled for IVDMD. Single-plant selectlons for high and low IVDMD were made in each of the nursery rows. In 1976, ramets from 25 of the high-IVDMD selections and from 25 of the low-IVDMD selections were transplanted to establish isolated high- and low- IVDMD polycross (PC) nurseries. Seed harvested from these nurseries in 1977 and from the same openpollinated (OP) clones in the selection nursery in 1976 was used in 1978 to establish a replicated seeded sward nursery in which the following strains were compared: high IVDMD PC, high IVDMD OP, ‘Pathfinder,’ low IVDMD OP, and low IVDMD PC. Forage yields and IVDMD were measured in 1978 and 1979. Over the 2 years the strains averaged 51.5, 50.0, 49.4, 48.3, and 48.1% IVDMD, respectively. The high IVDMD PC strain was significantly higher in IVDMD than the other strains in both years. Realized heritabilities for high and low IVDMD were 0.59 and 0.55, respectively. Strains did not differ significantly for forage yield in either year; thus, the gain in IVDMD by breeding was achieved without any yield loss.

Key Words: Panicum virgatum (L.) • IVDMDP • Phenotypic selection

² Research agronomist, AR-SEA/USDA; George Holmes Professor of agronomy Univ. of Nebraska; and supervisory research geneticist, ARSEA/USDA, Lincoln, NE 68583.

Received for publication May 16, 1980.