Gain from Two Cycles of Divergent Selection for Root Morphology in Alfalfa

Alfalfa (Medicago sativa L.) has been identified for use in phytoremediation. Phytoremediation is defined as the use of green plants to remove or contain environmental contaminants. Alteration of root morphology would increase the degradative efficiency of alfalfa for phytoremediation. Root morphology traits in alfalfa are heritable, but are strongly influenced by dormancy and geographic origin. Our objective was to create alfalfa source germplasms that differ in root morphology within the same genetic background. Four experimental alfalfa germplasms differing in dormancy and genetic origin were evaluated after two cycles of divergent selection for root morphology traits. Two sources were selected for few vs. many lateral roots and the other two sources were selected for few vs. many fibrous roots followed by one subsequent cycle of selection for few vs. many lateral roots. These divergent populations were evaluated using two fertilizer rates (0 and 200 kg N ha−1) and were established twice at each of two locations. Plants from one experiment at each location were dug at the end of the establishment year and from the second experiment at the end of the first production year. All plants were evaluated for number of lateral roots, fibrous root mass, taproot diameter, plant count per plot, and plot root weight. Two cycles of divergent selection for root morphology traits in all four source germplasms produced alfalfa populations that differed in root morphology. Realized heritabilities from all germplasm sources ranged from 21 to 48% for fibrous root mass and from 11 to 43% for lateral root number. Response to selection varied among the four source germplasms and indicated that the choice of parent germplasm will be a factor for success in producing alfalfa populations that differ in root morphology within a single genetic source. Joint contribution of the USDA-ARS, Plant Sci. Res. Unit, and Minn. Agric. Exp. Stn. Paper no. 981130075 of the MAES scientific journal series.