|Barnes, Donald - RETIRED ARS EMPLOYEE|
|Henjum, Keith - UNIVERSITY OF MINNESOTA|
Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 18, 1999
Publication Date: May 1, 2000
Citation: Lamb, J.F., Samac, D.A., Barnes, D.K., Henjum, K.I. 2000. Increased herbage yield in alfalfa associated with selection for fibrous and lateral roots. Crop Science. 40:693-699. Interpretive Summary: A major goal of most plant breeding programs is to increase yield. In alfalfa, most forage yield increases have been credited to improved disease and pest resistance. Increased forage yield in alfalfa may result from increasing water and nutrient uptake by making changes in root growth patterns. Several researchers have reported that some alfalfa varieties with very branched root patterns tended to have greater forage yield. To further understand this association between forage yield and root growth pattern, we successfully created unique experimental alfalfa populations that are either taprooted (carrot-like) or very branched with lots of small fibrous roots within a single genetic source of alfalfa. We created taproot vs. branched-root pairs of populations in four different genetic sources of alfalfa. In all four alfalfa genetic sources the branched-root populations had significantly greater forage yield (7 to 16 %) compared to the taprooted populations. Our results present a new strategy for plant breeders to use for producing new higher-yielding alfalfa varieties.
Technical Abstract: A positive association between root morphology and herbage yield in alfalfa has been reported by several researchers. To further investigate this association we created populations that differ in root morphology within four unrelated experimental germplasm sources. Two germplasm sources were selected for few vs. many lateral roots and two sources underwent selection nfor few vs. many fibrous roots followed by selection for few vs. many lateral roots. After two cycles of divergent selection for root morphology, selected and unselected populations from all germplasm sources were evaluated for herbage yield, root traits, fall dormancy response, and resistance to disease. Herbage yield and root morphology traits were evaluated using a randomized complete block design with a split plot arrangement of treatments with eight replicates. Fertilizer rates (0 and 200 kg N ha-1) as whole plots and alfalfa populations subplots were established twice at each of two locations in May 1994. One experiment at each location was designated for the establishment year study. The other experiment at each location was designated for the first production year study. All entries were evaluated for fall dormancy response in 1994 and disease resistance in 1995 using standard protocols. Populations selected for more fibrous and/or lateral roots had greater herbage yield than populations selected for no or few fibrous and/or lateral roots in all four germplasm sources. No differences in root size or weight, dormancy, or disease resistance were identified between fibrous and/or branch-rooted vs. taprooted populations. Selection for fibrous and/or lateral roots within these germplasm sources increased herbage yield in alfalfa in the tested environments.