Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/12/2004
Publication Date: 1/4/2005
Citation: Diaby, M., Casler, M.D. 2005. Rapd marker variation among divergent selections for neutral detergent fiber concentration in four smooth bromegrass populations. Crop Science. 45:24-35. Interpretive Summary: Dietary fiber is an important factor controlling intake of ruminants. Lower fiber concentration results in increased intake potential of a forage crop. Breeding for reduced fiber has been successful, but is highly labor intensive and time consuming. Molecular markers linked to genes controlling fiber would be useful to simplify and increase effiency of the selection process. We identified several RAPD markers that showed strong and significant changes in response to divergent selection for fiber in smooth bromegrass. Some of these markers should be useful in reducing the costs and time required to select for decreased fiber in smooth bromegrass.
Technical Abstract: Voluntary intake is generally considered to be the single most important factor limiting animal performance on high-forage diets. Neutral detergent fiber (NDF) is the laboratory variable most closely associated with voluntary intake potential. However, selection for low NDF generally leads to reduced forage yield. The objectives of this study were to estimate the correlation between forage yield and intake and to determine heterotic responses for both traits. Seven clones of smooth bromegrass (Bromus inermis Leyss.) were crossed in a diallel and four of the clones were selfed to create S1 families. The seven parent clones showed considerable diversity, as measured by 329 random amplified polymorphic DNA markers, mostly related to their pedigrees. The phenotypic correlation between forage yield and NDF decreased across generations, from 0.86 for parents, to 0.63 for GCA effects, and to 0.49 for the 21 cross means. The genotypic correlation between forage yield and NDF was reduced from 0.99 for parents to 0.71 for the 21 crosses. Forage yield heterosis effects averaged 14% with a range of -4 to 39%, with 15 of 21 values significantly different from zero. Mid-parent heterosis effects for NDF averaged -0.5% with a range of -3.1 to 2.6%, with seven of 21 values significantly different from zero. Mid-parent heterosis effects for forage yield and NDF had a moderate correlation of 0.44. The change in correlations across generations suggested that a part of the genetic correlation between forage yield and NDF is regulated by linkage. The general lack of heterosis for NDF indicated that losses in forage yield associated with selection for low NDF can be restored by heterosis for forage yield, following hybridization between complementary low-NDF populations. Recurrent selection for NDF to improve intake potential of smooth bromegrass must be conducted in multiple populations.