Submitted to: Central Alfalfa Improvement Conference
Publication Type: Abstract Only
Publication Acceptance Date: July 17, 1997
Publication Date: N/A
Technical Abstract: Methods utilizing 15N isotopes to estimate nitrate-N uptake in N2-fixing legumes are too expensive to use in plant breeding selection programs. Preliminary greenhouse studies demonstrated that Br uptake reflected nitrate-N uptake in alfalfa (Medicago sativa L.) herbage. Individual plant analysis showed variation in Br and nitrate-N uptake among plants within populations. To determine if plant age influences plant selection for nutrient uptake, selection was carried out in both an establishment (E) and first production (P) year stand. In July 1994, herbage was removed and irrigations of CaBr2 were initiated. Herbage was harvested on an individual plant basis and Br concentration and total N percentage of the herbage was determined. From these studies four populations were created that were high in total N content and either high or low in Br concentration for both the production and establishment year sources (HBrN-P, HBrN-E, LBrN-P, LBrN-E). .In 1995, selected and unselected populations were established and managed as previously described. In 1995 and 1996 herbage was removed and irrigations of CaBr2 and Ca(15NO3) were initiated. Three plants per plot were analyzed for total N percentage, 15N concentration, and Br concentrations. Bromide and nitrate-N uptake were positively correlated (r2 = 0.67 to 0.91) in both years of evaluation at both locations. The population selected for high Br in the production year stand (HBrN-P) ranked higher than the other populations for nitrate-N uptake in both the establishment and production year evaluations. HBrN-P was greater than its unselected parent population for nitrate-N uptake (p=0.11) when evaluated in the production year. A second cycle of selection for nitrate-N uptake using Br uptake as the selection criterion in alfalfa has been initiated.