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Application of Multistage Selection Indices to Crop Improvement

Dep. of Crop Science

J. C. Burns

USDA-ARS and Dep. of Crop Science and Animal Science, North Carolina State Univ., Box 7620, Raleigh, NC 27695-7620

^* Corresponding author.

Index selection to improve agronomic crop traits has generally been restricted to one-stage indices. Multistage selection has been confined to tree and animal breeding. This study was undertaken to compare predicted one-stage index genetic gains with two- and threestage gains when attempting to improve switchgrass (Panicum virgatum L.) forage quality and yield. These indices were compared within the context of two selection methods (mass and modified earto- row selection) and four levels of replicates (4, 6, 8, and 12). total of 33 switchgrass haif-sib families were evaluated for initial growth dry weight, in vitro dry matter disappearance (IVDMD), and N concentration, and for IVDMD of regrowth sampled in July (IVDMD1) and again in August (IVDMD2). One-stage index lection consisted of selecting all five traits simultaneously. In twostage selection, initial growth traits were selected in the first stage and regrowth traits were selected in the second stage. In three-stage selection, the first, second, and third stage traits were initial growth traits, regrowth IVDMD1, and regrowth IVDMD2, respectively. Predicted genetic gains of two- and three-stage indices were generally higher than one-stage index gains over the range of replicates and over the two selection methods. This indicates that breeding program costs could be reduced by decreasing the number of individuals evaluated following the first stage of selection. More consideration by breeders should be given to multistage selection as an alternative to one-stage index selection.

Key Words: Panicum virgatum L. • Switchgrass • Mass selection • Modified ear-to-row selection • Forage quality • Forage yield

Received for publication January 26, 1987.