Phenotypic Recurrent Selection Methodology for Reducing Fiber Concentration in Smooth Bromegrass
Neutral detergent fiber (NDF) concentration, a laboratory predictor of voluntary feed intake by livestock, has become a popular selection criterion in forage breeding programs. The objective of this study was to make empirical comparisons among six phenotypic recurrent selection methods for reducing NDF concentration in smooth bromegrass (Bromus inermis Leyss.). There were three basic selection methods: vNB2 = vegetative harvest, NIRS (near-infrared reflectance spectroscopy) evaluation of NDF, and bi-parental selection; hNU2 = heading growth stage harvest, NIRS, and uni-parental selection; and hWU2 = heading growth stage, wet-laboratory analysis of NDF, and uni-parental selection. Each method was repeated in a replicated polycross nursery of selected individuals (vNP3, hNP3, and hWP3). The vNB2 selection method resulted in the greatest gain for the vegetative growth stage, averaging a 4.0 g kg−1 yr−1 (1.0% yr−1) reduction in NDF concentration. Polycrossing did not improve upon this method, but improved the other two selection methods by an average of 241% because of control of male gametes. The hWP3 selection method resulted in the greatest gain for the heading growth stage, averaging 3.4 g kg−1 yr−1 (0.6% yr−1). Realized gains for the vegetative growth stage selection methods were greater than predicted, likely because of extremely low sampling variation, resulting from uniform selection units. For maximum response, long-term selection for a target growth stage should be conducted at that growth stage. The use of NIRS was highly effective at the vegetative growth stage, but less effective at the heading growth stage.
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