ROOT MORPHOLOGY OF ALFALFA PLANT INTRODUCTIONS AND CULTIVARS

Alfalfa (Medicago spp.) root morphology has a critical role in plant p ersistence and productivity traits. The objectives of this research we re to evaluate root morphological traits for 1067 plant introductions (PIs) from diverse geographic origins and from 110 North American cult ivars. All entries were grown in 2-m rows at the University of Minneso ta Agricultural Experiment Station at Rosemount, MN. Plants from both studies were evaluated during autumn of the establishment year for tap root diameter (TD), lateral root number (LRN), lateral root diameter ( LRD), lateral root position (LRP), and fibrous root mass (FRM). Variab ility was observed among PIs and North American cultivars for all trai ts. The range for all traits were greater in the PIs than in the culti vars. Discriminant analysis using root morphological traits to generat e canonical functions separated PIs assigned to germplasm groups from different geographic origins. Among the PIs, TD and LRD were positivel y correlated and LRN, LRP, and FRM were negatively correlated with fal l dormancy. Discriminant analysis using root traits to generate canoni cal functions separated the very fall dormant from the non-dormant cla sses. Semi-dormant classes for cultivars released before 1980 had some overlap, but some individual classes could be distinguished by root t raits. Semi-dormant classes for cultivars released after 1979 could no t be separated. Fall dormancy was negatively correlated with LRN, LRD, LRP, and FRM for cultivars released before 1980, but FRM was the only root trait correlated with fall dormancy for cultivars released after 1979. Our results suggest that recent plant breeding strategies for s emi-dormant alfalfa has influenced the relationship between fall dorma ncy and root morphology. Variation observed for root morphological tra its among all alfalfa entries evaluated indicated that selection for s pecific root modifications could be effective.