Gain from two cycles of divergent selection for root morphology in alfalfa

Alfalfa (Medicago sativa L.) has been identified for use in phytoremediatio n. Phytoremediation is defined as the use of green plants to remove or cont ain environmental contaminants. Alteration of root morphology would increas e the degradative efficiency of alfalfa for phytoremediation. Root morpholo gy traits in alfalfa are heritable, but are strongly influenced by dormancy and geographic origin. Our objective was to create alfalfa source germplas ms that differ in root morphology within the same genetic background. Four experimental alfalfa germplasms differing in dormancy and genetic origin we re evaluated after two cycles of divergent selection for root morphology tr aits. Two sources were selected for few vs. many lateral roots and the othe r two sources were selected for few vs. many fibrous roots followed by one subsequent cycle of selection for few vs. many lateral roots. These diverge nt 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 a nd from the second experiment at the end of the first production gear. All plants were evaluated for number of lateral roots, fibrous root mass, tapro ot diameter, plant count per plot, and plot root weight. Two cycles of dive rgent selection for root morphology traits in all four source germplasms pr oduced alfalfa populations that differed in root morphology. Realized herit abilities 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 var ied among the four source germplasms and indicated that the choice of paren t germplasm will be a factor for success in producing alfalfa populations t hat differ in root morphology within a single genetic source.