INHERITANCE OF ROOT TRAITS IN ALFALFA

Root growth patterns influence nutrient uptake, productivity, and pers istence in alfalfa (Medicago sativa L.). Inheritance of traits affecti ng root growth patterns in alfalfa are not wed understood. Objectives of this research were to determine the affects of plant spacing and ge ographic location on root traits in alfalfa, to determine the inherita nce of seven root morphological traits of alfalfa, and to evaluate the association between root traits, fall dormancy, and seedling year her bage yield. Progenies of diallels and design II matings were planted d uring May 1991 at two locations in 30-cm rows with 2.5 cm between plan ts within the row. Plants were evaluated for seedling year herbage yie ld and fall dormancy. During October 1991, they were dug and evaluated for taproot diameter (TD), lateral root number (LRN), lateral root di ameter (LRD), lateral root position (LRP), fibrous root mass (FRM), pe rcentage of determinate taproots (PDT), and determinate taproot positi on (DTP). Border effects were determined by evaluating single plants f rom the ends of the plots separately from plants in the middle of the plots. Extra space on plot borders affected root morphology, but few p rogeny x border interactions were found. Location affected root morpho logy, and a few location x cross interactions were observed for TD and LRP. Additive genetic effects were important in controlling inheritan ce for TD, LRN, LRD, LRP, and FRM. These traits had moderate (45) to h igh (87) heritabilities. No genetic variances were detected for PDT or DTP. Taproot diameter was the root trait most highly correlated with fall dormancy (0.46-0.50) and seedling year herbage yield (0.61-0.75). Selection for LRN, LRD, and FRM at one location with uniform plant sp acing should be successful, Multiple location selection programs may b e more appropriate for TD and LRP.