Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 12, 2013
Publication Date: July 1, 2013
Citation: Casler, M.D. 2013. Partial decomposition of the genetic correlation between forage yield and fiber using semi-hybrids. Crop Science. 53:1403–1411. Interpretive Summary: Efforts to improve the forage quality of bromegrass by breeding for reduced fiber content have been plagued by consistent reductions in forage yield. In an effort to solve this problem, bromegrass hybrids were created in an attempt to generate hybrid vigor (improved performance) for forage yield. A total of 48 hybrids were created, one third of these being low-fiber lines of bromegrass. Four of the 16 low-fiber hybrids had significant hybrid vigor for forage yield, as indicated by hybrid yield superior to the average of the parents. Two of these hybrids experienced no change in fiber content. These results indicate that the previously strong relationship between yield and fiber can be partially broken by the use of hybrids. It is possible to decrease fiber content without sacrificing forage yield through the use of hybrids. These results will be of value to other forage breeders who seek to improve forage quality.
Technical Abstract: Voluntary intake potential of a forage crop is generally considered to be the most important feed characteristic regulating animal performance. Efforts to develop forage crops with reduced bulk volume, measured by neutral detergent fiber (NDF) concentration, are associated with reduced plant fitness, prompting a need to modify breeding objectives and methods. The objective of this study was to determine if semi-hybrids between complementary low-NDF populations could be used to restore all or a portion of the forage yield lost to drift during selection for low NDF in smooth bromegrass (Bromus inermis Leyss). A total of 48 semi-hybrids of smooth bromegrass were created by pair-crossing within four base (original) populations, four high-NDF populations, and four low-NDF populations. There was a progressive decline in genetic variation and with increased NDF concentration. Mid-parent heterosis was positive and significant for four of six semi-hybrids at the low-NDF level. Two of these semi-hybrids also had positive and significant heterosis for NDF, reflecting the typical positive genetic correlation between the two traits. However, two of these semi-hybrids had no heterotic effect for NDF, resulting in partial decay of the genetic correlation due to a combination of linkage and drift acting on alleles that independently control these two traits. Because about one third of this genetic correlation is malleable by manipulation of linkage and drift, there is potential to produce low-NDF smooth bromegrass populations without sacrificing forage yield potential.